Chemistry for CSEC [Second Edition] 9781408525036

Table of contents :
Front Cover
Title Page
Copyright
Contents
Introduction
Section A
A1 States of Matter
A1.1 The particulate nature of matter
A1.2 Evidence for the particulate theory of matter
A1.3 The three states of matter
Key Concepts
Practice Exam-Style Questions
A2 Mixtures and their separation
A2.1 Elements, compounds and mixtures
A2.2 Solutions, suspensions and colloids
A2.3 Solubility
A2.4 Separating mixtures
A2.5 Extraction of sucrose from sugar cane
Key Concepts
Practice Exam-Style Questions
A3 Atomic Structure
A3.1 The structure of atoms
A3.2 The electronic configuration of an atom
A3.3 Isotopes and radioactivity
Key Concepts
Practice Exam-Style Questions
A4 The periodic table and periodicity
A4.1 Arrangement of elements in the periodic table
A4.2 Trends in Group II of the periodic table
A4.3 Trends in Group VII of the periodic table
A4.4 Trends in Period 3 of the periodic table
Key Concepts
Practice Exam-Style Questions
A5 Strucutre and Bonding
A5.1 Chemical bonding
A5.2 Formation of ionic bonds
A5.3 Writing chemical formulae of ionic compounds
A5.4 Formation of covalent and metallic bonds
A5.5 Structure and properties of solids
Key Concepts
Practice Exam-Style Questions
A6 Chemical equations and reactions
A6.1 Writing and balancing chemical equations
A6.2 Types of chemical reactions
Key Concepts
Practice Exam-Style Questions
A7 The mole concept
A7.1 The mole and mass
A7.2 The mole and gas volumes
A7.3 The mole and concentration of solutions
A7.4 The mole and chemical formulae
A7.5 The mole and chemical reactions
Key Concepts
Practice Exam-Style Questions
A8 Acids, bases and salts
A8.1 Properties and reactions of acids
A8.2 Properties and reactions of bases
A8.3 Strength of acids and alkalis
A8.4 Salts
A8.5 Neutralisation reactions
A8.6 Volumetric analysis
Key Concepts
Practice Exam-Style Questions
A9 Oxidation-reduction reactions
A9.1 Oxidation and reduction- and introduction
A9.2 Oxidation numbers
A9.3 Oxidising and reducing agents
Key Concepts
Practice Exam-Style Questions
A10 Electrochemistry
A10.1 The electrochemical series
A10.2 Electrical conduction
A10.3 Electrolysis
A10.4 Quantitative electrolysis
A10.5 Industrial applications of electrolysis
Key Concepts
Practice Exam-Style Questions
A11 Rates of Reaction
A11.1 Measuring rates of reaction
A11.2 Factors affecting rates of reaction
Key Concepts
Practice Exam-Style Questions
A12 Energetics
A12.1 Energy changes during reactions
A12.2 Calculating energy changes
Key Concepts
Practice Exam-Style Questions
Section B
B13 Introduction to organic chemistry
B13.1 Organic compounds
B13.2 Homologous series
Key Concepts
Practice Exam-Style Questions
B14 Hydrocarbons - alkanes and alkenes
B14.1 Sources and extraction of hydrocarbonds
B14.2 Alkanes
B14.3 Alkenes
Key Concepts
Practice Exam-Style Questions
B15 Alcohols, alkanoic acids and esters
B15.1 Alcohols
B15.2 Alkanoic acids
B15.3 Esters
Key Concepts
Practice Exam-Style Questions
B16 Polymers
B16.1 Addition polymers
B16.2 Condensation polymers
Key Concepts
Practice Exam-Style Questions
Section C
C17 Characteristics of metals
C17.1 Physical properties of metals
C17.2 Chemical properties and reactions of metals
C17.3 Reactions of metal compounds
Key Concepts
Practice Exam-Style Questions
C18 Reactivity, extraction and uses of metals
C18.1 The reactivity of metals
C18.2 The extraction of metals
C18.3 Uses of metals and their alloys
Key Concepts
Practice Exam-Style Questions
C19 Metals in living systems and the environment
C19.1 The corrosion of metals
C19.2 The impact of metals on living systems and the environment
Key Concepts
Practice Exam-Style Questions
C20 Non-metals
C20.1 Physical properties of non-metals
C20.2 Chemical properties and reactions of non-metals
C20.3 Laboratory preparation and uses of gases.
C20.4 The uses of non-metals
C20.5 Harmful effects of non-metals and their componds
C20.6 Green Chemistry
Key Concepts
Practice Exam-Style Questions
C21 Water
C21.1 The unique properties of water
C21.2 The treatment of water for domestic purposes
Key Concepts
Practice Exam-Style Questions
C22 Qualitative Analysis
C22.1 Identification of cations
C22.2 Identification of anions
C22.3 Identification of gases
Key Concepts
Practice Exam-Style Questions
Periodic Table
Index
Back Cover

Citation preview

Chemistry for

®

CSEC

Anne

Elizabeth

Tindale

Ritchie

Dianne

Sarah

Luttig

Chapman

Jennifer

Anna

Murray

Bowman

s s er P ytisrevinU dr o f x O

I N C LU D E S

fo

Edition

CD

t r aP

2nd

Chemistry for

®

CSEC

Anne

2nd

Tindale

Edition Elizabeth

Ritchie

Dianne

Sarah

Chapman

Jennifer

Anna

1

Luttig

Murray

Bowman

3 Great

Clarendon

Oxford

It

University

furthers

and

Oxford

©

Anne

The

First

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in

means,

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Data

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sent

part

of

prior

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in

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reproduction

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mark

of

countries

Sarah

Chapman

2014

2014

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by

any

of

rights

the

2014

be

reproduced,

form

or

Oxford

licence

outside

Department,

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may

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scholarship,

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2014

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permission

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Acknowledgements

Cover

photograph:

Illustrations:

Page

make-up:

Thanks

are

due

development

Photo

8.2.1,

18.3.1,

4.4.2;

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3.3.3.

Contents

Introduction

A5.5

1

Str ucture

Key

Section

A1

A

Principles

States

of

of

chemistry

2

matter

Practice

The

A1.2

Evidence

proper ties

of

solids

par ticulate

nature

of

matter

86

exam-style

questions

for

Chemical

t he

equations

and

reactions

matter

Writing

and

balancing

chemical

The

t hree

states

Key

concepts

of

matter

Types

of

exam-style

questions

A2.1

and

their

Elements,

separation

compounds

A2.2

Solutions,

A2.3

Solubility

96

concepts

99

questions

The

mole

concept

101

and

mixtures

colloids

A7.1

The

mole

and

mass

A7.2

The

mole

and

gas

101

A7.3

The

mole

and

concentration

16 volumes

106

19 of

22 solutions

A2.4

Separating

mixtures

A2.5

Extraction

of

sugar

Key

sucrose

A7.4

The

mole

and

chemical

formulae

1 1 1

A7.5

The

mole

and

chemical

reactions

1 13

Key

concepts

from

cane

30

exam-style

questions

structure

The

str ucture

A3.2

The

electronic

A3.3

of

atoms

Key

configuration

Acids,

bases

The

periodic

A4.1

A4.2

and

table

radioactivity

reactions

of

acids

121

A8.2

Proper ties

and

reactions

of

bases

128

A8.3

Strengt h

A8.4

Salts

A8.5

Neutralisation

A8.6

Volumetric

questions

and

of

periodicity

elements

in

A4.4

Trends

Group

46

46

II

of

t he

in

Group

VII

of

A9

Period

55

3

of

t he

Structure

Formation

A5.3

Writing

ionic

A5.4

questions

bonding

A5.2

bonding

of

ionic

chemical

bonds

formulae

compounds

Formation

metallic

of

questions

154

and

reactions

reduction

156

–

an

Oxidation

Oxidising

Key

156

numbers

and

159

reducing

agents

concepts

Practice

164

170

exam-style

questions

171

62

exam-style

Chemical

Oxidation

A9.3

periodic

concepts

A5.1

152

exam-style

A9.2

60

and

148

introduction

A10

A5

145

analysis

Oxidation–reduction

A9.1

t he

table

in

Practice

132

135

reactions

concepts

Practice

periodic

table

Key

alkalis

t he

table

in

periodic

and

45

51

Trends

acids

40

table

A4.3

of

44

Arrangement

Trends

121

and

37

exam-style

periodic

salts

Proper ties

Key

A4

and

A8.1

of

concepts

Practice

120

34

atom

Isotopes

questions

34

A3.1

an

exam-style

33

A8 Atomic

1 19

32 Practice

A3

108

25

concepts

Practice

100

16

and

suspensions

exam-style

15

A7 Mixtures

reactions

14 Practice

A2

chemical

9 Key

Practice

89

4 A6.2

A1.3

89

par ticulate equations

of

88

2 A6.1

t heor y

80

2 A6

A1.1

and

concepts

covalent

bonds

Electrochemistry

173

64

A10.1

The

65

A10.2

Electrical

65

A10.3

Electrolysis

69

A10.4

Quantitative

A10.5

Industrial

of

72

and

76

electrochemical

series

conduction

173

176

179

electrolysis

applications

188

of

electrolysis

191

Key

195

concepts

Practice

exam-style

questions

197

iii

Contents

A11

Rates

of

reaction

A11.1

Measuring

A11.2

Factors

Key

198

rates

of

affecting

reaction

rates

of

reaction

concepts

Practice

exam-style

questions

C18

Reactivity,

198

metals

202

C18.1

The

reactivity

209

C18.2

The

extraction

210

C18.3

Uses

Energetics

212

A12.1

Energy

A12.2

Calculating

Key

changes

during

energy

reactions

changes

concepts

Practice

questions

of

B

Organic

chemistry

Introduction

to

organic

B13.1

Organic

B13.2

Homologous

217

C19

chemistry

B14.1

Sources

–

Alkanes:

alkanes

C

questions

and

extraction

Metals

224

B14.3

Alkenes:

C

Key

alkenes

in

living

systems

Alcohols,

corrosion

of

The

impact

metals

H

and

alkanoic

Alkanoic

Esters:

C20.2

Chemical

proper ties

questions

acids

C

H

and

esters

OH

2n

acids:



239

of

uses

C20.5

Harmful

and

of

C

H

COOH

2n



Key

253

non-metals

of

324

non-metals

compounds

326

chemistr y

330

concepts

334

exam-style

questions

336

255

Water

338

C21.1

The

unique

proper ties

C21.2

The

treatment

of

water

338

260

of

water

for

pur poses

342

269

questions

concepts

345

271

exam-style

questions

346

Qualitative

analysis

polymers

concepts

C22.1

Identification

of

cations

questions

chemistry

of

C17.1

Physical

C17.2

Chemical

C22.2

Identification

of

anions

351

C22.3

Identification

of

gases

354

281 concepts

Reactions

of

of

metals

283

compounds

concepts

Practice

282

and

metals

metal

exam-style

356

questions

358

periodic

table

360

282

of

proper ties

exam-style

282

metals

proper ties

reactions

347

275

279

exam-style

Inorganic

347

272

The

iv

uses

1

polymers

Condensation

Key

318

and

263

exam-style

Characteristics

C17.3

non-metals

preparation

effects

t heir

Green

Practice

C17

of

321

The

Key

–

316

and

272

Practice

C

non-metals

gases

C20.4

C20.6

C22

Section

of

255

concepts

Addition

Key

315

1

Polymers

B16.2

questions

proper ties

Laborator y

Practice

B16.1

31 1

313

316

Physical

Key

B16

environment

exam-style

C20.1

C20.3

251

RCOOR

Practice

living

concepts

domestic Key

309

on

Non-metals

246

n

B15.3

t he

metals

2n

n

B15.2

of

2

exam-style

Alcohols:

the

237

C21 B15.1

and

The

Practice

B15

308

309

Practice

239



concepts

Practice

questions

C19.2

226

242

2n

n

307

C19.1

of

H

n

302

236

hydrocarbons

B14.2

299

alloys

230

exam-style

and

t heir

226

series

concepts

Hydrocarbons

metals

and

exam-style

reactions

B14

of

294

226

compounds

Practice

metals

environment

C20

Key

of

concepts

Practice

Key

B13

of

metals

systems Section

uses

212

223

exam-style

and

294

Key

A12

extraction

288

291

questions

293

Index

361

Introduction

To

the

Chemistr y

you

student

for

achieve

experienced

for

you

The

to

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Chemistr y

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divided

Chemistry,

into

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B,

t hree

sections;

Organic

Section

Chemistry,

A,

and

Section C, Inorganic Chemistry. Chapters 1–12 of t his book cover

topics

in

Section

Chapters

17–22

A,

Chapters

cover

topics

13–16

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The

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Chemistr y

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t he

activities

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assessment.

1

Section

A

States

of

matter

A1

Chemistry

is

the

study

of

the

structure

and

behaviour

of

Objectives

By

the

be

able

end

of

this

topic

you

matter.

will

Everything

has

●

give

a

●

give

the

denition

four

of

main

matter

ideas

both

beings

of

us

is

made

of

matter.

Matter

explain

theory

why

particulate

of

and

of

and

volume.

animals

are

all

Air,

water,

matter.

sand,

Matter

human

exists

in

states.

The

three

main

states

of

matter

are

solid,

matter

scientists

theory

mass

the

various particulate

●

around

to:

nd

the

liquid

and

gas.

matter

useful

identify

●

the

three

main

states

the

relationship

of

A1.1

The

particulate

nature

of

matter

matter

explain

●

Matter between

temperature

and

the

As motion

of

far

bac k

idea

a

t hat

piece

half

Exam

is

important

definitions

Chemistry.

provided

boxes

of

that

key

These

for

you

you

know

terms

in

the

the

‘Key

in

how

for

par ticles.

called

example,

many

cuts

a

will

t hought

He

Democr itus

piece

you

t hat

of

have

it

asked

gold,

to

ended

t his

developed

in

make

at

question:

half

and

before

some

t hen

you

point,

‘f

t he

cut

can

t he

you

cut

cut

it

it

smallest

in

no

and

t hat

building

t hese

bloc k s

of

smallest

matter.

bits

of

Today

matter,

scientists

or

particles ,

have

added

would

to

be

bits

t he

Democr itus’

of

matter.

book.

particulate

particulate

t heor y

is

theory

theory

ver y

of

useful

of

matter

because

matter

states

it

t hat

helps

all

us

matter

to

is

explain

made

bot h

of

par ticles.

t he

physical

fact proper ties of matter and also t he differences between t he t hree states of matter.

We Matter

is

anything

occupies

that

has

will

Key

that

looking

at

t he

t hree

states

of

matter

in

detail

in

Unit

A1.3.

space.

par ticulate

matter

is

t heor y

●

all

made

●

t he

●

t here

are

spaces

●

t here

are

forces

par ticles

are

of

of

in

matter

has

four

main

ideas:

par ticles

constant,

random

motion

fact

particulate

states

be

mass

The

The

philosopher

of

fact’

This

!

Greek

idea and now descr ibe matter and its proper ties using t he par ticulate t heor y

are

The

and

a

Democr itus

matter,

basic

the

used

definitions

throughout

Key

matter,

again,

The

!

BC

consisted

tip

of

It

460

matter

of

fur t her?’

✔

as

particles.

all

theory

matter

is

of

between

t he

par ticles

matter

made

up

of

attraction

between

t he

par ticles.

of

particles.

matter

of



The

is

made

par ticles

par ticles

Figure

constant

1.1.1

par ticulate

The

particulate

t heor y

of

are

theory

matter

in

there

motion

of

can

are

between

spaces

par ticles

matter

be

used

to

explain

many

physical

phenomena t hat we obser ve in our ever yday lives. Examples of some of t hese

are

2

given

on

t he

next

page.

t

explains:

States

of

The

●

and

How

is

it

can

Why

●

e.g.

e.g.

be

t he

States

density

rise

in

liquid

freezer

can

smelt

at

t he

get

of

of

cause

forms

gas

harder

between

it

vibrate

in

in

t he

e.g.

why

matter

pebbles

change

into

a

solid,

e.g.

when

water

side

of

you

a

room,

t he

e.g.

when

chicken

is

fr ying,

kitchen.

wit h

an

increase

in

temperature,

drive.

become

crisper

when

soaked

in

water,

liquids,

e.g.

cer tain

in

insects

can

‘walk’

on

water.



Figure

1.1.2

Pebbles

sink

in

water

matter

common

in

to

increases

as

vegetables

tension

t hese

Par ticles

gases,

of

potatoes.

of

most

and

nature

ice.

Matter can exist in various forms or

t he

liquids

t hroughout

ot her

a

solids,

particulate

water.

can

it

move

pressure

cer tain

raw

a

a

tyres

Surface

●

in

smell

car

Why

●

a

in

bubbles

cooling

placed

Why

●

The

difference

sink

●

matter

states

t he

t heir

liquid

are

lies

solid

xed

state

t he

solid,

in

t he

state

have

energy

have

position

states. The t hree states of matter t hat are

liquid

t he

and

medium

and

and

least

t hey

amount

are

amounts

gaseous

states.

arrangement

packed

of

of

of

t hey

difference

par ticles.

energy,

closely

energy,

The

t he

t hey

toget her.

move

simply

Par ticles

about

slowly

and t hey have small spaces between t hem. Par ticles in t he gaseous state have

t he

greatest

spaces

The

energy

par ticles

in

its

t he

faster

of

hanging

a

t hey

will

can

is

g reater

t his

directly

This

substance

The

move

study

change

temperature.

substance.

t hey

energy,

You

par ticles

matter

temperature

t he

of

t hem.

of

and

changing

t he

amount

between

one

change

of

and

detail

to

t he

physical

state

t he

kinetic

rapidly

greater

related

from

increases

t he

about

in

energy

t hey

Unit

to

of

par ticles

large

of

anot her

because

energ y

t he

have

1.3.

temperature

state

occurs

kinetic

in

t he

by

increasing

t he

par ticles

possess,

t he

move.

state

by

changing

temperature

is

a

physical

change.

A

physical

change occurs when t he form of t he substance is changed wit hout changing

its

chemical

t he

same

gaseous

composition,

chemical

state,

i.e.

Summary

1

State

2

If

a

the

of

the

water

the

3

Explain

4

What

are

5

What

is

water

in

water

t he

as

a

liquid

solid,

i.e.

state

and

ice,

as

has

exactly

water

in

t he



Figure

three

vapour.

of

main

ideas

potassium

purple

particulate

evidence

example,

as

1.1.3

states

The

of

drinks

illustrate

the

matter

questions

three

crystal

water,

for

par ticles

colour

theory

of

the

particulate

manganate( VII )

spreads

of

is

theory

dropped

throughout

matter

does

this

the

of

matter.

into

water.

a

beaker

What

observation

of

features

provide

for?

why

scientists

the

the

three

nd

states

relationship

the

of

particulate

theory

of

matter

useful.

matter?

between

temperature

and

the

movement

of

particles?

3

Evidence

for

the

particulate

theory

of

matter

A1.2

Objectives

By

the

be

able

end

of

States

this

topic

you

Evidence

for

the

particulate

theory

of

of

matter

matter

will

n t he previous unit we mentioned t hat scientists nd t he par ticulate t heor y

to:

of matter ver y useful because it allows t hem to explain t he physical proper ties

explain

●

evidence

which

of

supports

the

particulate

matter.

suppor t

of

and

the

processes

same

ideas.

time

There

t hough,

are

simple

scientists

practical

have

to

provide

activities

evidence

involving

to

d iffusion

diffusion

and

describe

experiments

osmosis

which

we

can

perform

to

provide

evidence

for

t he

existence

of

and

●

t he

t heir

matter

explain

●

At

theory

movement

of

par ticles.

osmosis

which

Diffusion demonstrate

diffusion

and

osmosis

explain

●

sugar

and

We

the

to

uses

control

preserve

of

salt

and

garden

food

have

into

pests

items.

a

all

freshener.

t he

smell

t hrough

of

had

baker y,

All

matter

air

are

Key

Diffusion

particles

t hese

to

is

in

concentration

!

cosmetic

of

seems

t he

experience

a

smells

travel

as

a

one

of

being

or

are

of

t he

air.

of

and

a

smell,

into

at

a

This

d iffusion.

motion

lower

aware

climbing

produced

t hrough

result

constant

to

of

shop

a

point

move

t hat

in

process

Diffusion

will

whet her

car

t he

of

shop

t he

occurs

from

a

it

is

walking

contains

or

smell

air

but

travelling

because

region

an

car,

par ticles

of

higher

concentration.

fact

is

the

from

movement

an

area

concentration

to

concentration

until

an

of

area

they

of

higher

of

Investigating

lower

are

the

particulate

theory

of

matter

evenly

Your

teacher

may

use

this

activity

to

assess:

distributed.

●

observation,

recording

●

analysis

interpretation.

Y ou

will

be

potassium

and

supplied

with

and

a

manganate( VII)

reporting

straw,

a

beaker

containing

distilled

water

and

a

crystal.

Method

1

Place

the

bottom

2

Drop

the

moving

3

Very

straw

of

the

vertically

crystal

the

in

the

beaker

of

water

until

it

touches

the

beaker.

of

potassium

manganate( VII)

into

the

straw

without

straw.

carefully

remove

the

straw

trying

to

disturb

the

water

as

little

as

possible.

4

✔

Exam

tip

the

5 It

is

very

important

questions

in

distinguish

and

to

must

your

or

while

what

you

If

the

If

what

examinations

are

are

you

colour

immediately

begins

to

spread

throughout

Leave

the

beaker

to

has

and

spread

observe

conclusion

can

throughout

after

you

draw

all

a

the

few

days.

water

in

Note

the

that

beaker.

the

purple

What

about:

asked

then

is

a

the

spaces

b

the

movement

between

the

water

particles

you

of

the

potassium

manganate( VII)

particles?

and

used

being

asked

conclude

then

purple

would

experiment

you

would

experiment,

you

the

water.

colour

observations

you

how

answering

observations,

describe

performed.

when

between

conclusions.

give

see

tests

Observe

to

state

from

must

the

The

potassium

illustrated

in

manganate(VII)

Figures

1.2.1

and

cr ystal

1.2.2

are

t he

bot h

water

composed

in

of

t he

experiment

minute

particles.

give

The par ticles in t he cr ystal are packed closely toget her and t hose in t he water

what

you

can

deduce

from

the

have observations.

A

deduction

is

ver y

minute by

using

data

from

the

small

spaces

between

t hem.

When

t he

cr ystal

is

in

t he

water,

t he

made

cr ystal

par ticles

slowly

separate

from

each

ot her

and

diffuse

into

t he

experiment

spaces between t he water par ticles. This continues until all t he par ticles have to

arrive

at

a

conclusion.

separated

4

from

t he

cr ystal

and

have

diffused

between

t he

water

par ticles.

States

of

matter

Evidence

for

the

particulate

theory

of

matter

straw

beaker

of

water

the

potassium

water

purple

becomes

colour

a

throughout

manganate(VII)

crystal



The

cr ystal

solution

Figure

1.2.1

Potassium

crystal

being

placed

gradually

where

diffusion

is

in

t he

t he

manganate(v II)



and

colour

an

solvent.

aqueous

Figure

solution

1.2.3

is

illustrates

water

particles

random

spaces

with

moving

crystal

small

from

between

a

while

the

throughout

i.e.

process

particles

each

diffuse

purple

the

water

a

of

other

into

the

the

separate

and

spaces

water

particles

particles

packed

manganate(VII)

After

formed,

t he

between

crystal

potassium

1.2.2

spreads

experiment.

water

at

Figure

water

d issolves

water

occurring

in

closely

together

crystal

before

dissolving

after

dissolving



Investigating

Your

teacher

diffusion

may

use

in

this

observation,

recording

●

analysis

interpretation.

Y our

and

teacher

will

perform

and

the

1.2.3

Explanation

of

diffusion

gases

activity

●

Figure

to

assess:

reporting

following

experiment:

Method

1

Place

2

Soak

a

Seal

4

Allow

5

Use

During

them

the

time

your

t he

for

called

t he

as

off

of

the

of

the

a

at

gas

to

air

The

what

in

of

the

t he

and

1.2.4

and

glass

stands.

ammonia

solution

and

concentrated

hydrochloric

acid

and

tube.

t he

tube

to

vapours

during

and

ammonia

react

retort

stoppers.

happened

gas

ammonium

glass

chloride

Figures

The

two

concentrated

hydrogen

gas.

in

between

rubber

ammonia

collide

in

end

with

and

chlor ide

t he

wool

explain

called

length

each

illustrated

t hey

chlor ide .

in

tube

ammonia

t hrough

meet,

ammonium

1 m

cotton

glass

hydrogen

diffuse

par ticles

glass

pieces

experiment

gives

par ticles

least

observations

off

gas

at

simultaneously

ends

solution

a

tube

separate

place

3

glass

the

1.2.5,

diffuse.

and

t he

a

each

white

forms

a

any

changes.

ammonia

acid

hydrogen

towards

Observe

experiment.

hydrochloric

form

chloride

to

ot her.

solid

ring

gives

chloride

When

known

inside

t he

tube.

5

Evidence

for

the

particulate

cotton

theory

wool

in

wool

matter

soaked

hydrochloric

cotton

of

in

acid

a

chemical

involved,

(g)

equation

NH

The

glass

Figure

1.2.4

chloride

(g)

a

gas

gas

Ammonia

diffuse

and

(g)

and

and

(s)

a

(s)

indicate

t he

state

of

t he

chemicals

solid:

each

wool

soaked

hydrochloric

cotton

wool

other

in

acid

faster

This

of

soaked ●

chloride

NH

t he

forms

because

chloride

experiment

ammonium

chloride

l(s) 4

acid

t hrough

chloride

Hl(g)

ammonium

hydrogen

hydrogen

towards

hydrogen





hydrochloric

tube

cotton

t he

par ticles.

air

t han

Therefore,

t he

provides

closer

t he

to

ammonia

t he

hydrogen

following

t he

cotton

par ticles

are

ammonia

chloride

wool

soaked

lighter

par ticles

t han

move

in

t he

much

par ticles.

evidence

for

t he

par ticulate

t heor y

matter:

Par ticles

are

par ticles

must

able

to

move

–

t he

ammonia

and

hydrogen

chloride

ammonia

●

There

are

between

t hem white



where

indicating

3

in

matter

ammonia

ammonia



of

We can represent t he reaction between t he ammonia and hydrogen chloride

as

soaked

States

Figure

1.2.5

ring

to

have

spaces

t he

air,

move

moved

between

par ticles

ammonia

between

towards

and

each

each

–

ot her

t here

hydrogen

to

must

form

have

chloride

t he

been

white

ring.

spaces

par ticles

to

allow

ot her.

forms

After

a

while

a

white

ring

Osmosis forms

inside

the

glass

tube

Osmosis

water

region

!

Key

is

wit h

of

water

solution

the

from

movement

a

region

molecules,

or

a

case

of

t hrough

lot

differentially

substances is

molecules

special

of

water

a

diffusion,

which

d ifferenti ally

molecules

to

a

involves

permeable

region

wit h

t he

movement

membrane

fewer

water

of

from

a

molecules.

fact A

Osmosis

a

molecules

pure

e.g.

water,

of

with

a

to

pass

t hrough

membrane

but

not

is

a

ot hers.

membrane

You

may

also

t hat

nd

allows

t he

some

membrane

water

a

lot

being

called

membrane

dilute

a

to

permeable

a

semi-permeable

t hat

surrounds

or

selectively

biological

cells

is

permeable

membrane.

differentially

The

cell

permeable.

region

A differentially permeable membrane contains minute pores. Water molecules with

fewer

water

molecules,

e.g.

a

are concentrated

solution,

through

able

ot her differentially

permeable

to

pass

t hrough

t hese

pores.

However,

t he

par ticles

of

many

a

substances,

which

may

be

dissolved

in

t he

water,

are

unable

to

pass

membrane.

t hrough.

When

concentrations,

t he

water

t he

more

two

are

separated

molecules

dilute

molecules,

solutions,

will

do

by

diffuse

solution

however,

e.g.

to

not

t he

sucrose

a

differentially

t hrough

more

move

solutions,

t he

t hey

have

permeable

pores

in

concentrated

because

which

are

t he

membrane,

membrane

solution.

unable

different

to

The

pass

from

sucrose

t hrough

t he pores in t he membrane. The volume of t he more dilute solution decreases

and

t he

volume

of

t he

more

differentially

concentrated

permeable

solution

increases.

membrane

sucrose

cannot

molecule

pass

through

the

differentially

permeable

membrane

water

molecule

diffuses

the

through

differentially

permeable

membrane

dilute

sucrose

concentrated

solution



Figure

1.2.6

Theoretical

explanation net

of

6

osmosis

sucrose

solution

movement

water

of

molecules

States

of

matter

Evidence

Investigating

Your

teacher

may

●

manipulation

●

analysis

Y ou

will

lled

be

with

osmosis

and

use

and

in

this

green

activity

for

the

particulate

theory

of

matter

paw-paw

to

assess:

measurement

interpretation.

supplied

distilled

with

water

a

piece

and

of

one

green

beaker

paw-paw

lled

with

(the

experiment

concentrated

may

sodium

be

done

chloride

with

potato

or

yam),

one

beaker

solution.

Method

1

Cut

2

Measure

3

Place

4

Allow

5

Remove

6

Measure

7

Explain

the

piece

and

three

containing

the

distilled

8

the

Explain

chloride

in

to

length

into

remain

from

record

the

in

solution

of

which

strips

the

for

Feel

placed

equal

containing

chloride

each

of

length.

strip.

solutions

beakers.

the

distilled

water

and

place

the

other

three

strips

into

the

beaker

solution.

one

hour.

strips

and

take

note

of

the

texture

of

each

strip.

strip.

in

water

distilled

water

molecules

become

move,

from

more

the

rigid

and

paw-paw

have

into

increased

the

distilled

in

length

water

or

from

the

paw-paw).

strips

(consider

or

each

sodium

the

six

beaker

strips

paw-paw

length

into

of

the

length

paw-paw

into

the

in

the

the

direction

water

why

the

concentrated

the

the

paw-paw

strips

strips

and

decrease

the

strips

why

green

record

of

the

(consider

of

from

the

the

placed

in

direction

sodium

concentrated

in

which

chloride

the

solution

sodium

water

into

chloride

molecules

the

solution

move,

become

from

the

oppy

and

paw-paw

softer

into

the

and

sodium

paw-paw).

distilled

water concentrated

beaker

sodium

chloride paw-paw



solution

Figure

1.2.7

Paw-paw

strips

in

strips

distilled

sodium

concentrated

distilled

paw-paw

increase



Figure

the

1.2.8

After

concentrated

a

chloride

water

strips

in

while

sodium

the

strips

in

water

solution

increase

decrease

in

in

t he

length

in

size

and

those

in

length

Did

experiment

illustrated

in

Figures

1.2.7

and

1.2.8,

t he

of

t he

paw-paw

cells

act

as

differentially

permeable

can

pass

t hrough

t he

cell

membranes,

eit her

into

or

out

of

t he

If

Distilled water has a higher water content (or lower sodium chloride

water.

concentration) than the paw-paw cells, therefore water moves

water

into the cells

takes

out

The

paw-paw

cells

have

a

higher

water

content

t han

t he

of

chloride

solution,

t herefore

water

moves

out

of

t he

cells

resulting

in

t he

paw-paw

strip

becoming

in

the

does

same

in

the

way

in

paw-

you

sweat

a

This

lowers

the

in

your

place

your

blood

and

lot

and

starts

cells.

you

For

lose

amount

of

osmosis

to

this

pull

water

reason

shor ter

and

important

to

drink

lots

of

it

is

water

by on

osmosis,

it

concentrated very

sodium

as

cells:

by osmosis, resulting in the paw-paw strip becoming longer and more rigid.

●

works

cells

paw.

●

know?

membranes. your

Water

you

cell Osmosis

membranes

solution

sodium

? During

chloride

concentrated

strips

decrease

chloride

and

solution

paw-paw

size

water

a

hot

day

or

when

you

exercise.

sof ter.

7

Evidence

for

the

particulate

theory

of

matter

States

Practical

We

use

garden

t he

pests

and

many

t han

of

snails,

to

snails

being

of

moist

our

to

and

chloride

dissolves.

is

in

food

various

ways.

These

include

controlling

items.

herbivores,

The

ot her

by

die.

skin

water

We

using

Figure

1.2.9

sodium

serious

of

t hese

This

garden

pests

means

evaporating

make

use

sodium

Snails

deliquescent,

When

are

animals.

prevent

and

gardens



Sodium

osmosis

plants.

most

dehydrate

in

of

pests

precious

skin

matter

osmosis

preser ving

garden

t hemselves

t hem

and

our

t he

of

principles

Controlling

Slugs

uses

of

of

are

serious

which

chloride

is

lot

sprinkled

more

to

ravage

permeable

need

bodies

control

to

keep

causing

slugs

and

salt).

garden

t hat

which

t hey

t heir

facts

(table

means

a

t hat

from

t hese

chloride

is

pests

pests

it

absorbs

on

slugs

water

and

readily

snails,

it

absorbs some of t he moisture surrounding t heir bodies and dissolves forming

a

concentrated

solution.

This

causes

water

inside

t heir

bodies

to

move

out

and into t he solution by osmosis. f t he slugs and snails lose more water t han

t heir

bodies

Preserving

can

food

ot h

sodium

sh,

fr uits

cr ystallised

t he

●

same

tolerate,

to

and

sugar

vegetables.

fr uits,

way

die

from

dehydration.

items

chloride

and

t hey

guava

We

jelly

preser ve

are

used

are

and

all

glacé

to

preser ve

familiar

cherries.

food

wit h

ot h

items,

salt

salt

sh,

and

e.g.

meat,

salt

pork,

sugar

work

in

foods:

They withdraw water from the cells of the food items by osmosis. This

makes the water unavailable for the chemical reactions in cells which cause

decay. Without these reactions occurring, the food items do not decay.

●

They

also

decay,

wit hdraw

e.g.

growing

bacteria

and

water

and

causing

from

fungi.

t he

food

t he

This

microorganisms

prevents

items

to

(a)



8

t hese

t hat

bring

organisms

about

from

decay.

(b)

Figure

1.2.10

(a)

Salt

sh

and

(b)

crystallised

fruits

are

examples

of

preserved

food

items

States

of

matter

The

Summary

1

For

each

of

particulate

a

If

a

b

If

the

experiments

theory

the

bottles

of

2

State

of

3

Why

4

When

30

do

a

we

5.0 cm

Explain

its

of

how

to

control

to

preserve

The

You

have

and

gas.

raw

potato

was

in

a

a

is

the

into

a

of

the

evidence:

beaker

of

concentrated

to

each

other,

a

white

between

chip

to

case

was

have

of

osmosis

of

placed

to

diffusion.

diffusion?

in

water

increased

matter

and

to

and

left

5.5 cm.

explain

for

Use

your

this.

used:

garden

sh.

three

states

already

t hree

t hat

st ates

proper ties.

of

of

matter

matter

Objectives

matter

exists

have

in

t hree

st ates:

noticeable

solid,

differences

liquid

in

By

the

be

able

Physic al

properties

are

c haracter istics

t hat

end

of

or

measured

wit hout

c hanging

t he

c hemical

Shape,

volume,

density,

compressibility,

composition

solubility,

and

explain

of

boiling

physical

point

are

proper ties

all

of

examples

t he

t hree

of

physical

st ates

can

be

will

the

difference

the

three

states

of

a in

terms

of

energy

and

particles,

and

melting

proper ties.

explained

of

The forces

different

you

be

arrangement

point

topic

t heir

can

matter

subst ance.

this

to:

between

obser ved

matter

water.

and

next

feature(s)

provides

dropped

solution

special

theory

chloride

the

●

physical

of

bottles.

found

particulate

is

placed

differences

is

state

experiment

throughout

and

two

osmosis

long

below,

the

ammonia

the

and

length

slugs

lear nt

The

that

sodium

b

spreads

opened

between

the

a

A1.3

are

which

manganate(v II)

colour

acid

say

minutes,

described

for

potassium

similarities

knowledge

5

matter

concentrated

forms

any

of

purple

hydrochloric

cloud

states

questions

crystal

water,

three

by

of

attraction

between

t he particles

par ticulate

t heor y

of

matter. ●

Table

and

1.3.1

t he

summarises

arrangement

t he

of

physical

par ticles

in

proper ties

t he

t hree

of

t he

t hree

states

of

matter

account

for

properties

states.

matter

in

the

of

terms

arrangement

We

can

use

t he

arrangement

of

par ticles

in

t he

t hree

states

of

matter

t he

physical

proper ties

of

t he

different

three

of

of

states

of

energy

and

particles,

and

to forces

explain

physical

the

of

attraction

between

states: particles

●

Solids

have

a

xed

shape

because

t heir

par ticles

are

arranged

in

a

regular ●

way

and

t hey

are

unable

to

move

out

of

t heir

xed

explain

state

●

Solids

t heir

any

have

a

xed

par ticles

closer

are

volume

packed

and

ver y

are

ver y

closely

difcult

toget her

to

the

changes

compress

and

cannot

be

pushed

in

terms

arrangement

because

●

understand

of

ow

●

Liquids

can

because

t heir

par ticles

are

able

to

move

past

each

energy

and

particles

boiling,

condensation,

Liquids

of

melting,

evaporation,

toget her.

●

of

positions.

freezing

and

ot her.

sublimation

be

compressed

slightly

because

t heir

par ticles

have

small ●

spaces

between

t hem

enabling

t hem

to

be

pushed

closer

understand

heating

●

Gases

t heir

take

t he

par ticles

attraction

shape

move

between

and

volume

freely

t hem,

and

of

t he

rapidly.

t herefore

container

They

t hey

have

spread

t hey

only

out

to

and

interpret

toget her.

are

in

weak

ll

cooling

curves.

because

forces

any

and

of

available

space.

●

Gases

are

between

easy

to

t hem,

compress

t herefore

because

t hey

can

t heir

be

par ticles

pushed

have

closer

large

spaces

toget her.

9

The

three

states

of

matter

States



T able

1.3.1

The

properties

Property

Shape

of

the

three

states

Solid

and

volume

of

Solids

have

and

a

a

fixed

Gas

Liquids

fixed

a

volume.

fixed

they

do

not

shape,

have

volume.

a

the

container

of

and

always

Gases

fixed

definite

shape

occupy

have

but

Liquids

the

is

the

part

that

the

A

take

gas

will

space

of

is

they

is,

horizontal.

of

Most

solids

have

a

high

density.

Compressibility

Solids

to

The

density

usually

are

very

difficult

compress.

density

of

Liquids

can

is

of

the

The

particles

particles

packed

together,

regular

Forces

of

between

attraction

the

The

particles

in.

volume

volume

in

a

strong

and

attraction

have

between

of

the

and

movement

are

very

of

Arrangement

in

small

kinetic

particles

fixed

not

those

Particles

particles

a

solid

have

amounts

energy.

vibrate

position.

a

gas

the

of

shape

the

entire

in.

a

low

are

easy

to

pressure

particles

and

of

the

spaces

as

attraction

strong

Particles

in

a

kinetic

The

as

large

weak

attraction

the

spaces

them.

particles

very

are

arranged

have

between

particles

between

have

forces

of

between

them.

solid.

liquid

have

Particles

energy

particles

particles

about

The

small

a

The

are

them.

of

than

their

of

it

shape

compress.

randomly

particles

more

The

in

Gases

very

arranged

forces

between

them.

Energy

have

The

of

The

is

have

the

density.

be

particles

between

forces

Gases

up

container

solids.

when

randomly

usually

is

the

it

a

volume.

take

therefore,

and

have

or

applied.

The

pattern.

particles

very

are

closely

liquids

than

compressed

slightly

Arrangement

of

lower

not

the

placed

and

surface

do

shape

container

Density

matter

matter

Liquid

shape

of

in

a

large

solid.

energy.

move

move

slowly.

in

a

gas

amounts

The

about

of

have

kinetic

particles

freely

and

rapidly.

of

particles

Changing

Did

?

you

Matter

A SCUBA

fact

to

divers

that

compress.

SCUBA

2250

T o

of

use

very

of

average

tank

holds

this,

milk

think

cartons

be

of

consequently

sized

order

about

we

of

can

change

changed

state

is,

from

one

t herefore,

state

air.

a

need

changes

change

change

to

changing

milk

hold

to

a

remove

its

of

water

heat

are

t he

into

chemical

state

in

kinetic

ice

we

of

diving

milk,

tank

therefore,

holds

the

a

anot her

by

energy.

to

a

by

change

in

is

a

Figure

of

put

hanging

composition

summarised

energy

need

heating

in

or

cooling.

temperature

t he

t he

t he

par ticles.

water

state

physical

of

For

and

into

a

example,

t he

freezer,

substance

change.

The

in

i.e.

wit hout

different

1.3.1.

one add

litre

to

caused

the

easy

compressed

understand

Most

are

An

diving

litres

carton.

make

gases

state

know?

heat

SCUBA

same

volume evaporates/

of

air

as

2250

empty

milk

cartons!

melts

boils

LIQUID

SOLID

freezes

GAS

condenses

sublimates

sublimates



Figure

of

1.3.1

Summary

of

the

changes

remove

state

We

will

changes

10

now

in

look

state

in

in

more

Figure

detail

1.3.1.

at

heat

each

of

t he

processes

t hat

cause

t he

States

of

matter

The

three

states

of

matter

Melting

When

more

a

solid

is

heated,

vigorously.

t he

par ticles

Eventually

t he

gain

kinetic

par ticles

are

energy

able

to

and

begin

overcome

to

vibrate

t he

Key

!

strong Melting

forces

of

attraction

between

t hem

and

t hey

move

more

freely

and

fact

point

is

the

constant

fur t her temperature

at

which

a

solid

apar t forming a liquid, i.e. t he solid melts. The temperature remains constant changes

into

a

liquid.

while t he solid is melting because all t he heat energy being supplied is used to

overcome

t he

temperature

forces

is

of

known

attraction

as

t he

between

melting

t he

solid

par ticles.

This

constant

point

Evaporation

When

Some

a

liquid

of

t he

is

heated,

par ticles

t he

near

par ticles

t he

gain

surface

of

kinetic

t he

energy

liquid

and

have

move

enough

faster.

Did

?

When

energy

to

overcome

t he

forces

of

attraction

between

t hem

and

are

able

t he

liquid

par ticles

and

t hat

become

leave

t he

a

vapour.

liquid

These

take

lots

par ticles

of

energy

are

wit h

said

to

t hem,

of

t he

sweat

and

the

evaporates

water

from

in

our

evaporate.

leading

to

it

takes

energy

with

it

causing

cooler.

If

we

a our

cooling

we

sweat

skin,

The

know?

to

the

leave

you

kinetic

bodies

to

feel

put

liquid. alcohol

even

on

faster

our

skin,

than

it

evaporates

water

because

Boiling it

When

a

where

it

kinetic

star ts

t he

t he

is

to

energy

wit hin

while

liquid

boil.

and

liquid

liquid

overcome

heated

t he

temperature

is

At

at

boiling

of

known

temperature

t his

star ted

and

forces

is

its

point

to

move

its

because

t he

liquid

fast

surface.

attraction

as

t he

t he

eventually

heat

between

boiling

par ticles

enough

The

reaches

to

have

change

temperature

energy

t he

being

liquid

a

cer tain

gained

into

a

enough

gas

remains

supplied

point

has

a

water.

even

lower

This

differs

from

evaporation

in

oiling

place

●

occurs

at

any

oiling

place

a

specic

our

skin

when

we

than

feel

sweat.

bot h

is

par ticles.This

used

to

constant

Key

!

fact

point

two

point

temperature

ways.

temperature,

whereas

evaporation

can

is

at

into

a

the

constant

which

a

liquid

gas.

take

temperature.

takes

only

at

than

point

constant

changes ●

makes

colder

Boiling

oiling

boiling

at

place

t he

t hroughout

surface

of

t he

t he

liquid,

whereas

evaporation

takes

✔

liquid.

If

Exam

you

are

tip

asked

to

give

a

difference

Condensation

between

When

t he

temperature

of

a

gas

is

lowered,

t he

par ticles

lose

kinetic

two

things,

it

is

essential

energy that

you

describe

the

specific

and begin to move more slowly. The forces of attraction between t he par ticles property

become

liquid,

stronger

i.e.

t he

causing

liquid

t he

par ticles

to

move

closer

toget her

forming

a

condenses.

of

‘whereas’

describe

each,

to

link

just

using

the

the

two.

word

Do

not

one.

Freezing

When t he temperature of a liquid is lowered, t he par ticles lose kinetic energy

and begin to move more slowly. The forces of attraction between t he par ticles

become

stronger

causing

t he

par ticles

to

move

even

closer

toget her

!

Key

forming Freezing

a

solid,

i.e.

t he

liquid

freezes.

The

temperature

at

which

t his

occurs

fact

is

point

temperature

t he

freezing

freezing

point,

e.g.

at

the

which

constant

a

liquid

point changes

The

is

called

point

water

of

has

a

a

pure

substance

melting

point

has

and

a

t he

same

freezing

value

point

of

as

t he

into

a

solid.

melting

0 °.

Sublimation

When

t he

forces

of

attraction

between

t he

par ticles

in

a

solid

are

weak,

t he

addition of a small amount of heat can cause t he solid to change directly into

a gas, wit hout passing t hrough t he liquid state. f t he gas is t hen cooled it will

change

directly

solid

a

to

gas

or

back

a

gas

to

to

t he

a

solid.

solid

it

When

is

said

a

to

substance

changes

directly

from

a

sublime

11

The

three

states

of

matter

States

Examples

dioxide

balls

or

sublime



Figure

1.3.2

Solid

air

fresheners

of

substances

(known

as

‘dr y

camphor

balls

releasing

t heir

which

ice’),

are

undergo

sublimation

ammonium

made

of

fragrances

chloride

and

napht halene.

into

t he

are

of

iodine,

carbon

napht halene.

Solid

air

matter

Mot h

fresheners

also

air.

sublime

(a)

cotton

wool

Observing

est

sublimation

in

iodine

tube

Your

may

observation,

●

iodine

teacher

use

this

recording

activity

and

to

assess:

reporting.

crystals

iodine

vapour

Y ou

will

cotton

be

supplied

wool

and

a

with

pair

a

of

test

tube,

a

small

iodine

crystal,

a

piece

of

tongs.

Method

1

Place

the

2

iodine

mouth

Hold

the Bunsen

the

the

tube

of

the

test

in

crystal

test

tube

the

into

the

test

tube

and

place

the

cotton

wool

into

tube.

with

ame

tongs

of

a

at

a

Bunsen

45°

angle

burner

and

until

all

heat

the

the

bottom

iodine

of

crystal

has

burner

sublimed.

(b)

iodine

crystals

3

Observe

4

Remove

5

Observe

During

heated,

the

it

what

the

happens

tube

what

from

the

happens

experiment

sublimes

and

as

the

iodine

ame

as

the

tube

illustrated

forms

and

in

purple

is

heated.

let

is

it

cool.

cooling.

Figure

iodine

1.3.3,

vapour

as

the

which

iodine

diffuses

cr ystal

up

the

is

test

tube. The top of the tube is much cooler and when the vapour reaches the top,



Figure

1.3.3

heated

and

Iodine

(b)

sublimes

when

cooled

(a)

when

it

sublimes

back

Heating

f

t he

on

a

The

state

graph

water

and

a

solid,

forming

cooling

temperature

changes

is

to

cur ve

a

against

shown

increases.

in

shows

of

a

pure

liquid

time,

Figure

t hat

However,

temperature

12

to

a

ring

of

iodine

cr ystals

around

the

inside

of the tube.

remains

curves

solid

and

a

is

t hen

heating

measured

to

a

gas,

curve

is

at

inter vals

and

t he

as

it

is

heated

temperature

obtained.

The

is

heating

and

plotted

cur ve

for

1.3.4.

as

t he

heating

graph

constant

occurs,

has

for

a

t he

two

temperature

horizontal

period

of

time

of

t he

sections

even

substance

where

t hough

t he

heating

States

of

matter

continues.

state

is

water

These

where

melting

is

of

t he

0 °.

temperature

t he

happen

melting

point

t his

The

occurs

has

t here

and

substance

The

remains

substance

when

second

e.g.

t he

at

for

t he

a

change

of

temperature

until

change

constant

boiled,

is

all

of

t he

state

is

t his

where

point

is

The

remains

substance

boiling

water

state.

of

has

change

constant

melted,

boiling

t he

rst

occurs

substance

at

states

of

matter

of

t he

e.g.

and

three

for

t he

until

all

100 °.

140

)C°(

120 gas

and

liquid boiling

100

point

erutarepme T

80

60 liquid

40

20 solid

and

liquid melting

0

20

solid

point

(ice)

40

Time



Figure

1.3.4

The

as

heating

heat

is

curve

added

for

water

f t he temperature of a gas is measured at inter vals as it is cooled and changes

state to a liquid and t hen to a solid, and t he temperature is plotted on a graph

against

shown

time,

in

a

cooling

Figure

curve

is

obtained.

The

cooling

cur ve

for

water

is

1.3.5.

140 gas

(steam)

)C°(

120 gas

and

liquid boiling

100

point

erutarepme T

80

liquid

60

40

20

melting

0

point

solid 20

40

Time



Like

Figure

heating

1.3.5

cur ves,

The

as

heat

cooling

cooling

is

removed

curve

cur ves

for

have

water

two

horizontal

sections.

The

rst

is

where t he state changes from gas to liquid and t he second is where it changes

from

liquid

to

solid.

Summary

1

Complete

what

is

the

of

Name

state

Gas

Solid

3

4

below.

The

rst

row

is

completed

as

an

example

of

given

to

change

Energy

state

change

Melting

added

or

removed

to

state

Added

gas

liquid

to

to

What

liquid

to

to

Liquid

2

of

to

Liquid

table

required.

Change

Solid

questions

solid

gas

are

a

Explain

b

Give

Explain

the

main

what

three

what

differences

occurs

examples

a

heating

during

of

between

and

boiling?

sublimation.

solids

curve

evaporation

which

undergo

sublimation.

shows.

13

The

three

states

of

matter

States

Key

matter

concepts

●

Matter

●

The

is

dened

proper ties

matter,

which

matter

states

made

–

t he

–

t here

are

spaces

–

t here

are

forces

par ticles

Matter

●

The

exists

are

in

difference

energy

of

t he

energy

anyt hing

matter

all

The

is

as

of

–

●

●

of

constant,

mass

states:

between

random

t he

attraction

t hree

has

explained

and

by

occupies

t he

space.

particulate

theory

of

par ticles

between

of

t hat

be

t hat:

of

in

can

t he

motion

par ticles

between

solid,

t hree

t he

liquid

states

par ticles.

and

is

due

gas

to

t he

arrangement

and

par ticles.

of

t he

par ticles

is

directly

related

to

t he

temperature

of

t he

par ticles.

●

Diffusion

t heor y

●

of

Diffusion

and

osmosis

provide

evidence

to

suppor t

t he

par ticulate

matter.

is

t he

concentration

movement

to

an

area

of

of

par ticles

lower

from

an

area

concentration

of

until

higher

t hey

are

evenly

distributed.

●

Osmosis

lot

of

wit h

is

t he

water

fewer

water

differentially

●

The

●

The

and

energy

account

of

t he

water

a

molecules,

e.g.

are

food

can

change

from

solid

●

Matter

can

change

from

gas

●

The

names

given

are

to

t he

melting,

of

to

from

or

a

pure

region

water,

solution,

of

processes

to

wit h

to

a

a

region

t hrough

to

pests

chloride

solids,

t hree

wit h

and

a

liquids

and

gases

states.

wit h

t he

addition

solid

wit h

t he

removal

cause

boiling,

sodium

sugar.

gas

which

evaporation,

in

t he

liquid

liquid

garden

sodium

par ticles

to

to

control

wit h

proper ties

Matter

anot her

solution

concentrated

used

●

to

a

items

arrangement

physical

molecules

dilute

membrane.

osmosis

preser ve

and

for

of

e.g.

permeable

principles

chloride

movement

molecules,

t he

change

of

of

from

condensation,

heat.

heat.

one

state

freezing

and

sublimation.

●

Melting

point

●

wit h

weak

When

t he

changes

against

●

When

against

14

t he

of

from

a

time,

in

attraction

of

solid

heating

from

a

temperatures

known

as

t he

melting

respectively.

at

any

gas

state

t hrough

temperature

state

specic

occurs

change

temperature

state

t he

liquid

passing

forces

time,

changes

a

at

point,

temperature

and

leads

to

t he

liquid.

is

wit hout

occur

boiling

of

t he

Sublimation

versa,

●

of

boiling

t he

Evaporation

cooling

●

and

and

of

a

pure

is

liquid

is

t heir

substance

to

from

state.

gas,

a

t

solid

to

occurs

a

in

gas,

or

vice

compounds

molecules.

is

and

measured

t he

as

it

is

temperature

heated

is

and

plotted

obtained.

pure

liquid

curve

straight

between

liquid

curve

to

cooling

a

to

t he

substance

to

solid,

is

and

obtained.

measured

t he

as

it

is

temperature

cooled

is

and

plotted

States

of

matter

Practice

i)

Practice

exam-style

State

what

t he

level

funnel

Which

is

of

made





t he

of

following

provide(s)

evidence

t hat

af ter

t he

expect

30

sucrose

to

have

solution

happened

in

t he

minutes.

Explain

t he

reason

for

your

(4

iii)

Name

t he

process

occurring

in

t he

Diffusion

,

A

second

and





and

D



only



substance

t hrough

t he

X

as

liquid

it

t he

was

state

temperature

heated

to

t he

from

of

mark)

an

t he

gaseous

solid

state.

are

plotted

in

Figure

2.

Use

t he

Her

information

in

only

t he C

measured



results 

student

unknown

state and

marks)

apparatus.

(1

b

Decomposition

A

mark)

obser vations.

Osmosis



t histle

(1

matter

par ticles?



B

of

questions ii)

1

would

questions

questions to

Multiple-choice

you

exam-style

Figure

to

answer

t he

following

questions.

only

80

2

Par ticles

in

a

solid: 70

packed

B

are

capable

C

have

large

spaces

D

have

weak

forces

Liquids

A

t he

differ

closely

of

random

from

par ticles

toget her

in

between

of

t hem

attraction

gases

a

movement

in

liquid

between

t hem.

t hat:

can

move

more

freely

60

50

erutarepme T

are

)C°(

3

A

t han

40

30

20

10

t hose

in

a

gas 0

B

t he

par ticles

in

a

gas

are

closer

toget her

t han

t hose

in 10

a

liquid 20

C

t he

par ticles

t han

D

t he

t hose

in

in

par ticles

a

a

in

liquid

possess

more

kinetic

energy

0

t hem

a

gas

t han

have

t hose

weaker

in

a

The

forces

of

conversion

of

Figure

a

gas

to

a

2

liquid

is

described

during

Graph

12

14

showing

heating

16

18

20

22

24

26

(min)

the

against

temperature

of

substance

time

as: What

Over

state

what

is

X

in

at

68 °?

temperature

(1

range

does

X

exist

C

condensation

D

boiling.

iii)

From

take

Which

show

of

t he

following

lists

consist

of

substances

iv)

which

state?

t he

A

Aluminium

B

Ammonium

chloride,

chloride,

iodine,

C

Ammonium

chloride,

napht halene,

D

Aluminium

sulfate,

iodine,

carbon

carbon

dioxide,

it

Describe,

X

has

in

star ts

terms

what

to

melt,

completely

is

of

how

long

melted?

energy

and

happening

to

v)

monoxide.

Using

draw

iodine.

X

napht halene.

o

to

represent

a

par ticle

par ticles

as

t hey

of

n

order

to

a

investigate

student

set

t he

up

par ticulate

t he

nature

apparatus

of

shown

Extended

(2

1

below

and

lef t

it

for

30

response

glass

a

Describe

thistle

b

funnel

Water

t he

of

T WO

can

level

of

sucrose

15%

sucrose

y

for

solution

i) 35%

sucrose

differences

differentially

t hem

reference

EAH

of

steam

to

investigate

of

evidence

to

suppor t

the

a

matter.

solid,

between

of

t heir

and

to

t he

a

(4

liquid

t hese

t heir

and

t hree

par ticles,

par ticles,

t he

can

permeable

membrane

ii)

a

cr ystal

shape.

used

as

of

kinetic

a

gas.

states

forces

in

of

marks)

Explain

terms

attraction

energy.

explain

clearly

(6

t he

marks)

reason

following:

be

conver ted

to

liquid

water

by

solution

beaker

Apparatus

pieces

exist

reducing

particulate

its

of

temperature

potassium

chloride

(3

has

a

ver y

marks)

denite

(2

marks)

nature

Total of

marks

solution

c

1

15

question

t heor y

arrangement

between

original

Figure

in

marks)

minutes. par ticulate



X,

appear

15 °.

it

in 7

glass

as

marks)

question

matter,

Figure

of

X

substance

would

it

mark)

behaviour

(3

T WELE

at

does

substance

Total

a

t he

marks)

(1

melts.

dioxide.

carbon

(2

time

until

par ticles,

sublimation?

Structured

6

mark)

in

evaporation liquid

5

10

melting ii)

B

8

attraction

i)

A

6

liquid. X

4

4

Time



between

2

gas

15

marks

matter

15

A2

Mixtures

Elements,

and

compounds

their

and

separation

mixtures

form

a

part

of

our

Objectives

By

the

be

able

end

of

this

topic

you

everyday

will

foil

●

distinguish

between

substances

and

pure

we

explain

an

When

we

wrap

our

food

in

aluminium

our

the

difference

element,

a

are

food

using

we

are

an

element.

eating

a

When

we

compound.

place

When

salt

we

on

drink

a

mixtures

cold ●

lives.

to:

soda

we

are

drinking

a

mixture.

It

may

be

useful

to

between

compound

and

a

know

how

to

separate

some

of

these

mixtures

into

their

mixture

component ●

give

examples

compounds

●

explain

a

the

of

and

mixtures

difference

homogeneous

heterogeneous

parts.

An

example

of

this

is

the

purification

elements,

and

of

drinking

water.

between

a

mixture.

A2.1

Elements,

compounds

and

mixtures

Matter can be classied into two main groups: pure substances and mixtures.

Pure

substances

●

They

have

●

Their

●

The

a

xed,

proper ties

component

physical

Mixtures

●

They

●

Their

t he

following

constant

are

xed

par ts

of

characteristics.

composition.

and

a

general

constant.

pure

substance

cannot

be

separated

by

means.

have

have

a

t he

following

variable

proper ties

individual

●

have

are

general

characteristics.

composition.

variable

since

t heir

components

retain

t heir

own,

proper ties.

The component parts of mixtures can be separated by physical means.

Pure

substances

Mixtures

can

be

heterogeneous

breakdown

of

can

be

fur t her

fur t her

mixtures .

t hese

classied

classied

The

tree

into

into

elements

and

homogeneous

diagram

in

Figure

compounds.

mixtures

2.1.1

shows

and

t he

groups.

matter

pure

mixtures substances

elements



Pure

A

2.1.1

homogeneous

heterogeneous

mixtures

mixtures

Classication

of

matter

substances

pure

substance

following

16

Figure

compounds

xed

is

composed

of

only

one

type

of

material

proper ties:

●

a

shar ply

dened,

constant

melting

●

a

shar ply

dened,

constant

boiling

●

a

constant

density.

point

point

or

freezing

point

and

has

t he

Mixtures

and

their

separation

Elements,

compounds

and

mixtures

To determine if a substance is pure or not, its melting point or boiling point is

determined.

Any

impurities

in

a

pure

substance

will

usually

lower

its

melting

Did

? point

and

usually

cause

raise

it

t he

to

melt

boiling

over

point

a

of

wider

a

pure

temperature

substance

range.

and

mpurities

cause

it

to

boil

over

In

a

many

ice

wider

temperature

will

produce

only

one

(Unit

single

2.4)

spot

may

on

a

also

be

used.

f

a

chromatogram.

substance

f

it

is

not

is

pure

pure

it

is

it

t han

one

will

The

and

Your

●

may

observation,

Y our

boiling

points

of

pure

water

and

teacher

the

the

snow

the

the

(sodium

roads

dissolves

the

use

this

perform

activity

and

the

to

its

and

roads

in

chloride)

to

in

surface

the

freezing

melt

the

of

the

film

the

point

temperature

ice

starts

freezing

18 °C,

saturated

recording

will

on

about

sodium

solution

teacher

on

lowers

lower

the

salt

salt

water

below

chloride

on

ice,

spot.

this

Comparing

where

problem

rock

spread

ice.

of

more

a

range.

chromatography

produce

know?

countries

pose

winter,

Paper

you

will

to

the

melt.

point

the

sodium

of

to

ice

Salt

of

can

water

freezing

chloride

to

point

of

solution.

assess:

reporting.

following

demonstration.

Method

3

1

Place

2 cm

2

Place

an

open

Place

4

Half

a

distilled

inverted

end

3

of

facing

water

closed

in

end

a

test

tube.

capillary

tube

into

the

test

tube

with

the

downwards.

thermometer

in

the

tube.

3

ll

a

250 cm

assembly

is

5

Heat

the

ensure

of

in

beneath

the

the

oil

bubbles

indicates

bath

surface

beaker

that

beaker

is

emerges

that

the

so

of

over

even.

from

water

a

and

the

the

place

surface

Bunsen

test

of

burner,

heating

capillary

the

the

above

the

test

water

tube

in

the

test

tube

oil.

Continue

the

in

oil

that

level

gently

heating

with

tube.

tube

is

stirring

until

This

a

constantly

rapid

stream

to

stream

of

bubbles

boiling.

thermometer

6

Remove

last

7

the

bubble

Reheat

Record

the

heat

emerges

oil

the

source

bath

from

and

This

is

observe

the

the

reading

the

the

capillary

repeat

temperature

temperatures.

and

boiling

stream

tube,

cooling

after

of

record

process

each

point

of

trial

the

When

the closed

end

stirring

rod

more.

average

test

all

three

Repeat

the

procedure

using

a

sodium

chloride

water.

solution

tube

oil

in

place

9

conclusion

sodium

can

chloride

you

draw

about

the

boiling

points

of

pure



solution?

Figure

An

element

is

t he

simplest

form

of

matter.

t

cannot

be

broken

down

simpler

by

ordinar y

chemical

or

physical

means.

We

say

means’

to

exclude

nuclear

reactions.

The

smallest

t hat

has

t he

same

proper ties

as

t he

element

is

an

the

boiling

fact

cannot

is

be

a

pure

substance

broken

down

into

‘ordinar y

par ticle

simpler

atom.

substances

by

any

in ordinary

element

Determining

liquid

element

any

chemical

a

into

that

anyt hing

2.1.2

of

Key

!

Elements

an

solution

heat

water

point

An

or

chloride

water.

What

and

water

of sodium

the

tube

beaker

distilled

8

capillary

temperature.

twice

and

distilled

bubbles.

chemical

or

physical

Each means.

element

is

composed

of

only

one

kind

of

atom.

17

Elements,

compounds

and

mixtures

Mixtures

Examples

copper

of

elements

(Cu),

which

are

is

iron

(Fe),

composed

which

of

is

only

and

composed

copper

of

atoms

their

only

and

separation

iron

atoms,

oxygen

(O

), 2

which

is

composed

of

only

oxygen

atoms.

Compounds

Key

!

fact Compounds

are A

compound

is

a

pure

contains

types

of

element

together

or

and

properties

more

which

chemically

proportions

their

two

in

in

of

more

than

chemically,

one

t hey

are

kind

of

always

atom.

These

present

in

atoms

t he

by

mass

and

t hey

cannot

be

separated

by

physical

same

means.

A

different

are

bonded

a

compound

elements

fixed

such

have

composed

toget her

substance

propor tions that

are

combined

way

that

can

t hat

combined,

be

t he

e.g.

represented

compound

t he

chemical

by

is

chemical

a

made

up

formula

of

of

formula ,

and

water

t he

is

H

which

ratio

in

indicates

which

t hey

t he

have

O. 2

changed.

Examples

oxygen

of

in

compounds

a

ratio

of

are

2 : 1,

water,

sodium

which

chloride

is

composed

(NaCl),

of

which

sodium and chlorine in a ratio of 1 : 1 and met hane (CH

hydrogen

is

and

composed

of

), which is composed 4

of

carbon

and

hydrogen

in

a

ratio

of

1 : 4.

The proper ties of a compound are  xed and are different from t he proper ties

of

t he

individual

hydrogen

is

a

and

elements

oxygen

are

t hat

bot h

for m

gases

at

t he

room

compound.

temperature,

For

example,

however,

water

liquid.

Mixtures Key

!

fact

Mixtures

A

mixture

consists

substances

in

two

(elements

compounds)

together

of

more

and/or

physically

varying

or

means.

combined

are

combined,

will

be

Some

component

of

t he

investigating

of

two

t heir

physical

in

or

more

substances

components

Unit

met hods

2.4,

are

can

for

which

be

separating

ltration,

are

not

separated

chemically

by

mixtures,

evaporation,

physical

which

we

cr ystallisation,

proportions.

distillation,

Each

composed

t herefore

retains

its

fractional

distillation

and

chromatography.

n

a

mixture

t he

own

component par ts are not in a xed ratio and t hey retain t heir own, individual independent

properties

and

has

physical undergone

with

any

no

other

chemical

proper ties.

reaction

substance

in

the

Homogeneous

mixtures

mixture.

A

homogeneous

are

uniform

mixture

t hroughout

distinguished

from

each

is

one

t he

in

which

mixture.

ot her.

A

t he

The

solution

is

a

proper ties

and

component

composition

par ts

homogeneous

cannot

be

mixture.

Examples of homogeneous mixtures are air, salt dissolved in water and metal

alloys

such

as

brass,

Heterogeneous

a

mixture

which

can

be

t he

copper

and

zinc.

mixtures

A heterogeneous mixture

in

of

component

distinguished

is a non-uniform mixture, for example, a mixture

par ts

from

are

each

in

different

ot her,

states.

alt hough

not

The

component

always

wit h

t he

par ts

naked

(a)

eye.

Suspensions

Examples

muddy

The

can

Figure

in

Figure

distinguished

●

f

t here

is

●

f

t here

are

2.1.3

(a)

Gold

is

an

heterogeneous

mixtures

are

salt

mixtures.

and

sand,

mayonnaise,

and

only

2.1.4

by

one

show

looking

kind

of

at

how

t he

atom,

elements,

par ticles

t hen

it

is

compounds

t hat

an

make

up

and

t he

mixtures

substance.

an

element,

(b)

copper

sulfate

is

water

is

of

an

a

compound

example

of

a

or

more

kinds

of

atoms

element.

joined

toget her

in

t he

same

ratio,

and

(c)

it

is

a

compound.

an

●

example

two

example

t hen

of

18

heterogeneous

are

water.

diagrams

be

colloids

(c)

(b)



of

and

f

t here

is

a

combination

muddy

mixture.

t hen

it

is

a

mixture.

of

two

or

more

elements

and/or

compounds,

Mixtures

and

their

separation

Solutions,

suspensions

and

colloids

n Figure 2.1.4, elements are represented in diagrams D, E and H, compounds

are

represented

diagrams

atoms

A,

are

F

not

in

diagrams

and

.



is

arranged

a

B,

and

mixture

regularly

A

C

G

and

and

not

among

t he

B

a

mixtures

compound

green

Summary

1

Copper

is

2

What

is

a

3

What

are

4

What

is

A2.2

example,

described

blue

D

the

E

diagrams

shown



I

the

F

atoms

Figure

of

2.1.4

as

an

element.

What

does

this

tell

us

about

are

the

differences

difference

suspensions

bot h

Elements,

compounds

and

mixtures

copper?

water

is

a

between

between

a

a

pure

substance

homogeneous

suspensions

and

colloids

solution,

form

muddy

mixture

and

par t

water

of

is

a

and

mixture?

and

a

heterogeneous

colloids

our

Objectives

ever yday

suspension

mixture?

lives.

and

milk

For

By

the

be

able

end

of

this

topic

you

will

to:

and

●

fog

different

compound?

the

sea

t he

in

questions

Solutions,

Solutions,

because

C

H

represented

atoms.

In

G

are

explain

the

terms

solvent,

colloids.

solute

●

and

identify

solution

different

types

of

Solutions solutions

A

solution

is

known

is

as

a

homogeneous

t he

solvent

and

mixture.

t he

minor

The

major

component

component

is

known

of

as

a

solution

t he

solute.

Some solutions may contain more t han one solute, e.g. sea water. The solute

and

a

solvent

liquid,

salt

is

can

t he

t he

be

gases,

liquid

solute

is

and

liquids

always

water

is

or

solids.

t he

solvent,

t he

solvent.

When

e.g.

in

a

a

gas

or

a

solid

mixture

of

dissolves

salt

●

in

a

●

in

2.2.1

gives

examples

of

various

between

suspension

describe

some

water,

solution,

a

T able

2.2.1

Examples

of

different

types

Solvent

Example

Components

solid

liquid

sea

sodium

of

liquid

soda

solid

solid

brass

water

carbon

of

chloride

the

in

give

in

water

examples

dioxide

in

Key

liquid

white

gas

gas

air

rum

a

a

of

and

solutions,

colloids.

fact

water

solution

is

a

homogeneous

copper

mixture

liquid

of

and

solution

A zinc

the

properties

solutions.

! gas

solution,

solutions

Solute

water

a

colloid

colloid

types

of

of

a

suspension

suspensions



and

distinguishing

●

Table

distinguish

ethanol

in

water

components,

usually oxygen,

water

vapour,

consisting

argon

and

carbon

dioxide

in

a

one

of

of

two

or

which

more

is

liquid.

nitrogen

19

Solutions,

suspensions

and

colloids

Mixtures

A

saturated

at

a

solution

par ticular

study

is

one

t hat

temperature

saturated

solutions

in

in

contains

t he

more

as

much

presence

detail

in

of

and

solute

as

can

undissolved

Unit

their

separation

be

dissolved

solute.

You

will

2.3.

Suspensions

A

suspension

cont aining (a)

Figure

2.2.1

(a)

Soda

water

brass

are

examples

of

par ticles

mixture

whic h

can

Key

is

a

par ticles

The

be

eye.

f

in

a

lef t

are

undisturbed,

suspension

components

separated

Examples

of

Dust

air

which

minute,

but

by

of

eventually

a

suspension

ltration.

are

dispersed

in

in

suspensions

is

a

suspension

of

a

solid

visible,

in particles

naked

heterogeneous ●

in

t he

fact

suspension

mixture

to

solutions

settle.

A

heterogeneous

and

t he (b)

!

a

(b)

visible



is

minute

a

gas.

another 

substance,

usually

a

liquid.

Figure

2.2.2

Muddy

water

is

an

Powdered chalk in water is an example

●

example

of

a

suspension

of a suspension of a solid in a liquid.

Muddy

●

water

is

anot her

example

of

a

solid

suspended

in

a

liquid.

Colloids

A

colloid

is

inter mediate

The

par ticles

undisturbed

Key

!

A

colloid

one

is

in

a

The

those

larger

the

are

than

of

particles

usually

particles

a

are

a

of

a

Examples

you

●

Smoke

●

Fog

also

but

solution.



in

10

1

very

in

of

air

is

and

Do

out

the

standing

for

20

be

separate

mixture

a

Transmission

of

a

microscope,

colloid

are

t hat

are

suspension.

and

if

lef t

t hose

of

a

inter mediate

suspension.

a

colloid

of

a

solid

in

a

gas,

also

known

as

a

solid

aerosol.

as

sprays

liquid

in

air

are

colloids

of

a

liquid

dispersed

in

a

gas,

aerosols.

are

colloids

of

a

liquid

dispersed

in

a

liquid,

also

emulsions.

and

jelly

are

colloids

of

a

solid

dispersed

in

a

liquid,

also

known

comparison

is

of

given

t he

in

distinguishing

Table

proper ties

of

solutions,

suspensions

and

2.2.2.

T able

2.2.2

A

comparison

of

the

properties

of

solutions,

(less

than

one

nanometre

diameter)

than

are

visible

and

1000

that

to

of

a

the

solution

naked

nanometres

in

but

eye

they

(between

diameter)

heterogeneous

transparent

usually

and

suspensions

Suspension

greater

not

colloids

opaque,

large

to

enough

the

1000

naked

so

eye

that

they

(greater

nanometres

in

are

visible

than

diameter)

heterogeneous

some

are

translucent

opaque

no

no

yes

no

no

yes

filtration?

components

the

and

Colloid

small

generally

components

after

solution

mayonnaise

as

homogeneous

Appearance

by

a

aerosol

1

mixture

separated

proper ties

a

a

millimetre

Solution

size

the

wit h

of

gels.

colloids



Particle

Can

The

even

par ticles

t hose

millimetres

nanometres

Property

of

seen

and

colloids

known

Gelatine



T ype

settle.

cont aining

solution

know?

6

nanometre

of

and

Milk

●

A

1 000 000

not

be

a

liquid.

as

1

do

cannot

of

in

●

Did

t hey

t hose

known

?

colloid

mixture

t hose

smaller

suspension,

those

of

dispersed

substance,

dispersed

than

a

between

heterogeneous

which

substance

another

in

heterogeneous

size

fact between

mixture

a

in

has

been

while?

of

light

transmits

light

appearing

transparent

will

scatter

light

does

not

transmit

light;

it

is

opaque

Mixtures

and

their

Comparing

a

separation

the

Solutions,

properties

of

a

solution,

a

suspension

suspensions

and

colloids

and

colloid

Your

teacher

may

●

observation,

●

manipulation

Y ou

will

be

use

this

recording

and

supplied

activity

and

to

assess:

reporting

measurement.

with

two

beakers,

a

lter

funnel

held

in

a

retort

stand,

(a)

lter

and

paper,

distilled

water,

calcium

hydroxide

powder,

copper( II)

sulfate

gelatine.

Method

1

Half

2

Place

mix

3

ll

the

a

beaker

large

with

spatula

water.

full

of

calcium

hydroxide

powder

into

the

water

and

vigorously.

Hold

the

mixture

up

to

the

light

and

look

through

it.

Is

it

transparent

or

opaque? (b)

4

Place

the

lter

paper

in

the

lter

funnel

and

place

the

second

beaker

below 

it.

5

Filter

Leave

settle

half

the

the

mixture.

other

half

of

Could

the

you

separate

mixture

for

two

the

components

hours.

Does

the

by

ltering?

Figure

(b)

2.2.3

(a)

mayonnaise

Using

is

a

your

answers

solution,

Repeat

sure

of

colloids

mixture

a

from

3,

points

suspension

or

a

4

and

5,

decide

whether

the

colloid

the

that

experiment

you

stir

each

with

colloid.

of

the

the

copper( II)

mixtures

sulfate

until

there

and

is

gelatine,

Y ou

may

need

to

heat

the

gelatine

no

longer

particle

size

making

any

solid



Figure

of

remaining.

suspension

mixture

increasing

7

and

examples

out?

solution

6

Milk

are

2.2.4

particles

in

A

comparison

solutions,

of

the

colloids

size

and

gently. suspensions

8

Record

your

ndings

Summary

1

2

3

How

does

the

particle

a

solution

b

a

suspension

of

a

does

b

can

c

will

the

not

be

not

Classify

a

table.

questions

a

Which

in

compare

transmit

separated

settle

of

a

mayonnaise

b

chalk

c

fog

d

white

dust

in

with

compare

following

each

size

out

the

is

of:

that

with

true

of

a

that

of

a

suspension

of

a

colloid?

solution,

a

suspension

or

a

colloid?

light

by

ltration

after

standing?

following

as

a

solution,

a

suspension

or

a

colloid:

water

vinegar.

21

Solubility

Mixtures

A2.3

Objectives

By

the

be

able

end

of

this

topic

you

dene

explain

The

the

term

solubilit y

a

in

a

of

a

 xed

solute

mass

of

is

an

indication

solvent

at

a

of

how

par ticular

muc h

of

t he

temperature.

solute

For

can

example,

solubility

we what

separation

Solubility

dissolve

●

their

will

to:

●

and

can

 nd

t he

solubility

of

sodium

c hlor ide

in

water

by

deter mining

saturated 3

how solution

muc h

sodium

explain

the

effect

dissolve

in

of

10 cm

water

at

temperature

on

the

reac hes

solubility

of

more

more

solute

can

be

dissolved

in

t he

a

par ticular

solvent,

saturation

point

and

we

say

t he

solution

is

t he

saturated .

from

a

solute

is

added

to

t he

solvent,

t he

solute

will

remain

in

solid

f

for m

a

and substance

no

solubility

any describe

When

of

solution

●

can

is

temperature.

●

c hlor ide

will

be

mixed

wit h

t he

saturated

solution.

The

solubility

of

a

solute

in

solubility

water

is

usually

measured

as

t he

mass

of

solute

t hat

will

saturate

10 0 g

of

curve

water. perform

●

calculations

using

solubility

and

will

is

saturate

given

the

mass

100 g

of

of

solute

Key

solvent

at

a

speci c

solubility

at

a

a

solute

and

in

t he

a

solvent

is

determined

by

t he

str ucture

of

t he

temperature.

effect

of

temperature

on

solubility

For most solid solutes in water, solubility increases as temperature increases.

fact

means

which

solution

contains

can

be

as

undissolved

in

a

much

dissolved

temperature,

is

the

at

a

t hat

saturate

form

saturated

as

of

solvent,

temper ture

which

a

temperature.

will

A

has

that

This

!

combination

fact

The Solubility

solvent

temperature.

solute

Key

and

curve.

The

!

solute

a

given solubility

Eac h

is

a

as

will

not

saturated

since

t he

xed

less

of

temperature

mass

be

at

water.

saturated

one

t he

of

at

increases,

A

a

solution

higher

temperature

solute

can

is

dissolve

a

is

a

cr ystals

lower

mass

of

solute

saturated

temperature,

cooled,

at

greater

which

and

of

if

t he

a

at

one

solution

solute

will

temperature.

solution

You learnt earlier in t his unit t hat solubility in water is usually measured as

solute

t he mass of solute which will saturate 100 g of water. The unit for solubility

given

presence

of

is

solute.

g

n

per

100 g

water .

determining

However,

solubility

of

a

it

is

not

solute

in

practical

water

in

to

weigh

t he

100 g

laborator y,

of

water.

we

make

−3

use

of

t he

fact

t hat

pure

water

has

a

density

of

1 g cm

.

n

ot her

words,

3

1 cm

3

of

water

has

a

mass

of

1 g,

or

1 g

of

water

has

a

volume

of

1 cm

.

)retaw

3

This

70

means

t hat

100 g

of

water

has

a

volume

of

100 cm

,

and

it

is

easy

to

3

measure

g 001

60

100 cm

of

water

in

t he

laborator y.

50

When

we

plot

solubility

of

a

solute

against

temperature,

we

draw

a

graph

rep

40

known as a solubility curve . The solubility cur ve for potassium chlorate(V),

g(

30

ytilibuloS

KClO

,

is

shown

in

Figure

2.3.1.

3

20

Looking at t he solubility cur ve in Figure 2.3.1, you can see t hat t he solubility 10

of

potassium

chlorate(V)

increases

wit h

an

increase

in

temperature.

0

Solubility 0

10

20

30

40

50

60

T emperature



Figure

2.3.1

Graph

70

80

90

of

potassium

as

t his

can

be

used

to

obtain

various

useful

for

pieces

of

example:

the ●

solubility

such

100

information,

(°C)

showing

cur ves

The

solubility

of

a

solid

at

any

temperature

wit hin

t he

range

of

t he

chlorate( V)

graph. against

temperature

Example

✔

Exam

tip

What

Before

reading

any

graph

you

is

t he

Solubility ensure

scale

that

of

you

each

can

axis.

interpret

the

22

two

axes

will

The

not

of

KClO

of

potassium

chlorate(V)

at

78 °C?

scales

at

78 °C



35 g

per

100 g

water

3

the

of ●

the

solubility

must

necessarily

The

temperature

at

which

cr ystals

would

just

star t

to

form

if

an

be

unsaturated

solution

point

it

containing

same.

where

is

just

saturated.

a

xed

mass

of

solute

is

cooled

to

t he

Mixtures

and

their

separation

Solubility

Example

At

what

temperature

would

cr ystals

just

begin

to

form

if

an

unsaturated

solution of potassium chlorate(V) containing 20 g of potassium chlorate(V)

dissolved

in

100 g

Temperature

at

of

water

which

is

20 g

cooled

of

from

KClO

80 °C?

saturates

100 g

of

water



55 °C.

3

∴

●

temperature

The

mass

of

at

which

solute

temperature

is

t hat

cr ystals

would

just

begin

cr ystallise

to

out

form

of

a



55 °C

saturated

solution

if

its

decreased.

Example

What

mass

solution

is

of

decreased

At

potassium

containing

64 °C,

from

25 g

of

chlorate(V)

100 g

64 °C

to

KClO

of

water

would

when

cr ystallise

t he

out

temperature

of

of

a

saturated

t he

solution

22 °C?

saturates

100 g

of

water.

3

At

22 °C,

7 g

of

KClO

saturates

100 g

of

water.

3

∴

mass of KClO

cr ystallising out of a saturated solution containing 100 g 3

of

●

The

is

water

mass



of

25 g



solute

7 g

to



be

18 g

added

to

resaturate

a

solution

if

its

temperature

increased.

Example

What mass of potassium chlorate(V) must be added to resaturate a solution

containing

increased

At

32 °C,

250 g

from

10 g

of

water

32 °C

of

to

KClO

if

t he

temperature

of

t he

saturated

solution

is

82 °C?

saturates

100 g

of

water.

3

At

82 °C,

38 g

of

KClO

saturates

100 g

of

water.

3

∴

mass

of

KClO

to

be

added

to

resaturate

a

solution

containing

100 g

3

of

and

water

mass



of

38 g



KClO

10 g

to

be



28 g

added

to

resaturate

a

solution

containing

3

28

____

250 g

of

water





250 g



70 g

100

●

The

a

minimum

given

mass

of

water

required

to

dissolve

a

xed

mass

of

solute

at

temperature.

Example

What is t he minimum mass of water required to dissolve 40 g of potassium

chlorate(V)

At

74 °C,

at

32 g

74 °C?

of

KClO

saturates

100 g

of

water.

3

100

____

∴

40 g

of

KClO

saturate



40 g

of

water



125 g

of

water.

3

32

Minimum

mass

of

water

required



125 g

23

Solubility

Mixtures

Investigating

Your

teacher

may

●

observation,

●

manipulation

Y ou

will

be

supplied

water

the

bath),

a

a

use

this

recording

and

placed

with

effect

of

temperature

activity

and

to

on

and

their

separation

solubility

assess:

reporting

measurement.

in

groups

boiling

by

tube,

burette,

a

a

your

teacher

thermometer,

balance

and

and

a

each

beaker

potassium

group

with

will

be

water

(for

a

nitrate.

Method

Each

group

potassium

teacher

your

1

will

will

tell

results

Using

determine

nitrate,

you

with

the

the

varying

the

the

temperature

from

mass

6 g

that

to

at

16 g,

your

which

just

group

a

specic

saturates

is

to

use.

mass

10 g

Y ou

of

will

of

water.

then

Y our

share

class.

balance,

weigh

your

group’s

mass

of

potassium

nitrate.

3

2

Using

is

3

the

burette,

equivalent

Add

the

using

the

Carefully

all

the

nitrate

heat

T ake

6

Observe

the

the

boiling

the

easiest

7

Note

8

T o

it

9

to

the

see

that

and

Average

outlined

Mass

of

distilled

out

as

solution

at

water

just

the

you

at

the

water

in

the

boiling

tube

(this

to

the

boiling

carefully

to

tube

and,

dissolve

as

much

stir

the

it

stirring

it

constantly

until

and

as

and

it

of

stir

cools.

the

the

solution

Look

tube

as

for

that

gently.

signs

is

of

where

it

is

forming.

which

temperature

by

bath

bottom

the

is

temperature

board

bath,

dissolved.

water

temperature

the

two

in

of

crystals

your

weighed

the

has

especially

the

T emperature

stir

nitrate

the

you

solution

tube

note

your

on

of

possible.

temperature

ensure

again

as

solution

crystallisation,

10 cm

nitrate

thermometer,

potassium

5

place

10 g).

potassium

potassium

4

to

your

crystals

just

accurate,

at

which

readings

teacher

reheat

the

and

(the

start

to

the

crystals

record

table

is

it

form.

solution

just

in

start

the

given

and

to

cool

form.

table

below).

(°C)

KNO

saturating

10 g

of

water

(g)

6.0

8.0

10.0

12.0

14.0

16.0

3

Solubility

of

KNO

(g

per

100 g

water)

3

10

Once

and

all

water

11

the

at

each

the

On

sheet

of

1

Dene

2

What

effect

3

What

is

the

of

Record

graph

class

have

potassium

temperature,

temperature.

a

from

mass

each

Summary

24

results

calculate

paper,

i.e.

the

these

draw

been

nitrate

solubility

solubilities

a

solubility

recorded,

that

of

in

copy

dissolved

potassium

your

curve

in

the

table

100 g

nitrate

of

at

table.

for

potassium

nitrate.

questions

solubility.

the

does

unit

temperature

used

for

have

measuring

on

the

solubility

solubility?

of

solids

in

liquids?

Mixtures

and

A2.4

Since

their

separation

Separating

mixtures

mixtures

into

form

t heir

a

Separating

mixtures

par t

of

our

component

Objectives

ever yday

par ts

is

lives,

t he

impor tant.

separation

Examples

of

t hese

include

By

the

be

able

of

drinking

water

and

t he

making

of

lter

coffee.

f

you

end

of

on

a

deser t

island

wit hout

any

drinking

water,

your

topic

you

will

identify

suitable

techniques

to

were

separate

stuck

this

to:

t he

●

purication

mixtures

knowledge

the

components

the

types

of

of

mixtures

separating

mixtures

could

help

you

to

make

pure

water

from

sea

water.

●

Mixtures

physical

are

type

means.

component

e.g.

a

met hods

of

proper ties

The

par ts

par ticle

of

is

size,

matter

met hod

t he

by

boiling

by

point,

t hat

you

component

t he

which

determined

separation

of

where

components

a

t he

mixture

physical

solubility.

will

par ts

be

t hat

can

allows

be

be

2.4.1

of

into

t hese

wit h

mixtures

to

t he

be

by

its

each

met hod.



T able

2.4.1

simple

t he

distillation,

physical

and

separated

of

the

methods

used

to

separate

describe

the

in

method

Physical

properties

of

component

A

mixture

liquid.

of

The

a

solid

and

components

a

liquid

are

where

solid

based

does

on

not

their

dissolve

different

in

the

particle

and

A

by

ltration,

mixture

the

liquid

of

is

a

solid

lower

which

than

is

that

dissolved

of

the

in

solid.

a

liquid

The

where

methods

the

only

boiling

allow

point

for

the

solid.

The

components

are

separated

based

on

their

A

different

explain

the

liquid

of

is

collected.

a

solid

lower

The

which

than

is

that

dissolved

of

components

the

are

in

solid.

a

liquid

Both

separated

where

the

based

liquid

on

the

and

their

boiling

the

point

solid

different

terms

and

ltrate,

distillate

boiling

●

mixture

the

funnel

of

explain

the

miscible distillation

separating

collection

points.

Simple

a

fractional

chromatography

residue of

crystallisation,

distillation,

distillation,

●

crystallisation

processes

sizes.

and

Evaporation

funnel

parts

the

separated

fractional

separating

mixtures

simple

Filtration

crystallisation,

separating

evaporation,

Separation

mixtures

chromatography

involved

summary

a

of

ltration,

distillation,

mixtures A

by

evaporation,

●

by

describe

separated

par ts,

summarises

toget her

t he

separated

separated

properties

Table

studying,

can

difference

and

between

immiscible

of

can

liquids.

be

boiling

points.

Fractional

distillation

A

mixture

points,

of

i.e.

two

there

completely.

The

(or

is

more)

a

miscible

difference

components

in

are

liquids

volatility.

which

have

Miscible

separated

based

different

liquids

on

are

their

boiling

ones

different

that

mix

boiling

points.

Separating

funnel

A

mixture

of

Immiscible

separated

Chromatography

A

mixture

(or

based

of

components

and

two

liquids

more)

are

on

their

dissolved

are

attraction

to

immiscible

liquids

different

liquids

do

not

which

mix.

have

The

different

components

densities.

are

densities.

substances

separated

the

which

which

based

on

will

their

travel

through

different

a

material.

solubilities

in

a

The

solvent

material.

Filtration

Filtration

does

a

not

is used to separate a mixture of a solid and a liquid where t he solid

dissolve

suspension.

in

t he

Filtration

liquid,

makes

i.e.

it

use

is

of

used

lter

to

separate

paper

to

t he

components

separate

t he

solid

filter

paper

filter

funnel

of

from

t he liquid. The lter paper works like a sieve, keeping back t he solid par ticles.

The

solid

par ticles

are

too

big

to

pass

t hrough

t he

lter

paper,

whereas

t he

the

in

liquid

par ticles

are

small

enough

to

pass

the

The

par t

residue.

t he

of

t he

The

mixture

par t

of

t he

t hat

stays

mixture

behind

t hat

solid

the

remains

filter

paper

as

t hrough.

passes

in

t he

lter

t hrough

t he

paper

lter

is

called

paper

is

residue

t he

called

suppor t

ltrate

Filtration

is

one

of

t he

steps

used

in

t he

purication

of

drinking

water.

Most the

simple

water

purication

devices

t hat

you

might

use

in

your

homes

liquid

through:

ltration

as

t heir

solid

impurities

form

of

lter

main

from

paper

to

met hod

t he

water.

separate

of

A

purifying

coffee

t he

t he

machine

coffee

granules

water.

makes

from

They

use

t he

of

separate

a

lter

coffee.

in

filters

use

called

t he

it

the

is

filtrate

t he



Figure

2.4.1

Filtration

apparatus

25

Separating

mixtures

Mixtures

and

their

separation

Evaporation solvent

evaporates

quickly

Evaporation is used to separate a solution of a solid dissolved in a liquid, but it into

the

air

only allows the solid to be collected. During evaporation, the solution is boiled

allowing boiling

the

liquid

to

vaporise

into

the

air.

The

solute

is

left

behind

in

the

solution

container.

Evaporation

is

a

fairly

rapid process

and

if

all

the

liquid

evaporates,

the solid remaining lacks any cr ystalline str ucture . The method is not suitable

if

heat

the

solid

to

be

collected

is

decomposed

by

heat.

Evaporation

is

useful

to

obtain the sodium chloride from a sodium chloride solution.

Crystallisation

solute

is

left

Like evaporation, crystallisation is used to separate a solution of a solid dissolved behind

in 

Figure

2.4.2

a

liquid,

and

it

only

allows

the

solid

to

be

collected.

Unlike

evaporation,

the

Evaporation

solution is not boiled, it is left in a container at room temperature for the liquid

to vaporise into the air. Crystallisation is a slow process and the solid remaining

has solvent

a

distinct

water slowly

at

of

structure.

crystallisation

is

t

required.

is

used

Water

if

of

a

hydrated

solid

crystallisation

is

containing

water

that

is

room

incorporated

temperature

this filter

crystalline

evaporates

paper

impurities

to

in

Unit

within

8.4.

the

crystalline

Crystallisation

is

structure

useful

to

and

obtain

you

will

learn

hydrated

more

copper(II)

about

sulfate

prevent

entering

crystals (CuSO

.5H 4

O) from a copper(II) sulfate solution.

2

solution evaporating

basin

Simple

Simple

crystals

of

the

distillation

distillation

is

also

used

to

separate

a

solution

of

a

solid

dissolved

in

a

solute

liquid. t allows both the solid and the liquid to be collected. Simple distillation is are

left

behind

an appropriate method of separation only if the liquid has a lower boiling point 

Figure

2.4.3

Crystallisation

t han

key

The

●

t he

solid,

i.e.

components

met hod

The

by

mixture

vaporisation

●

The

vapour

condenser

down

●

The

t he

poured

of

Figure

2.4.4

Apparatus

for

which

is

t he

t he

heated

up

cools

and

t he

vapour

in

before

distillation

apparatus

distillation

if

distillation

condenses

and

of

when

an

solute

t he

a

used

distillation

in

and

condenser

into

becomes

apparatus

ask

t he

is

works

until

a

is

it

solid.

Liebig

as

One

of

follows:

boils

and

t he

most

is

ask

back

collected

solution

of

evaporating

t he

in

as

and

a

t he

t he

liquid

basin

and

to

as

it

passes

liquid.

The

lef t

t he

Liebig

passes

d istillate

distillation

has

into

liquid

ask

vaporised,

to

t he

cr ystallise

gradually

solution

to

obtain

can

required.

distillation thermometer

boiling

point

liquid

of

Liebig

condenser

distillation water

out

flask

anti-bumping

granules

assist

smooth

boiling

receiver cold

water

in

distillate

heat

26

be

cr ystals

simple

records

t he

condenser.

occurs.

rises

it

liquid

t he

concentration

increases



t he

of

Mixtures

The

t he

and

their

t hermometer

condenser.

t he

pure

f

liquid,

Distillation

t he

separation

solid

distilled

is

a

and

used

t hen

ver y

t he

water

is

t he

to

monitor

temperature

t he

distillate

useful

liquid

from

Separating

tap

is

met hod

af ter

water

t he

temperature

remains

of

at

t he

vapour

t he

boiling

entering

point

of

pure.

of

separation

separation.

and

constant

can

be

if

you

However,

used

to

it

need

is

obtain

to

also

pure

collect

used

water

to

bot h

make

from

✔

n

bot h

t hese

cases,

any

solution

remaining

in

t he

distillation

Exam

ask

is

very

since

it

is

not

important

to

draw

separation

Fractional

which

are

line

you

diagrams

are

of

the

required. apparatus

Fractional

that

is able

discarded

tip

sea It

water.

mixtures

used

in

the

different

processes.

distillation

distillation

miscible

is

and

used

have

to

separate

different

a

mixture

boiling

points

of

two

that

or

are

more

close

liquids

together.

Miscible liquids are liquids that are able to mix. The apparatus used in fractional

distillation is similar to that used in simple distillation. However, a fractionating

column

is attached between a round-bottomed ask and the Liebig condenser.

Fractional

distillation

can

be

used

to

separate

a

solution

of

ethanol

and

water

since the boiling point of ethanol is 78 °C and that of water is 100 °C.



The

fractionating

surface

by

area.

many

liquid

the

with

top

of

of

times

fractionating

the

on

column.

the

the

has

Vaporisation

condensation

place

column

lowest

column

a

the

Vapours

boiling

of

of

The

temperature

constant

the

each

the

point

and

2.4.5

a

Fractional

fractionating

distillation

column

thermometer.

takes

surface

first

using

followed

vapour

Figure

large

at

liquid

the

as

remains

boiling

it

distils

point

of

separately

reach

enter

water

the

out

condenser

Liebig

condenser

cold

water

distillation

in

flask

receiver.

A

fresh

anti-bumping

is

used

granules

each

receiver

to

catch

distillate

heat

?

Did

The

The

met hod

by

which

t he

apparatus

for

fractional

distillation

works

is

you

process

of

know?

fractional

as distillation

is

used

in

several

follows. industries

come ●

The

mixture

boils

and

vapours

of

bot h

liquids

enter

and

move

up

across.

●

As

the

mixture

increasingly

lower

the

of

in

point

consists

where

vapours

richer

boiling

column

into

column

moves

more

(ethanol),

only

condenser,

the

t hey

of

the

condense

up

volatile

until

more

condenses

the

the

is

vaporise

fractionating

component,

vapour

volatile

and

and

column,

i.e.

the

reaching

component.

collected

as

the

many

the

This

top

The

vapour

of

t he

less

volatile

liquid,

i.e.

t he

one

with

t he

(water),

condenses

in

t he

fractionating

column

and

separate

the

(Unit

15.1),

have

in

the

fermentation

of

the

vapour

higher

and

in

passes

industry

to

different

fractions

kerosene

Also

the

rum

ethanol

the

mixture

separate

petroleum

and

liquid

air

into

crude

such

diesel

can

(Unit

be

oxygen

as

oil

into

gasoline,

14.1).

fractionally

and

nitrogen

boiling

returns

to

which

have

various

uses

t he (Unit

round-bottomed

to

from

gases

point

used

the

distillate

wit h

is

becomes

distilled ●

It

might

times.

it

one

you

t he

industry

fractionating

that

20).

ask.

27

Separating

mixtures

Mixtures

●

When

almost

temperature

reaching

second

●

Once

of

t he

top

t he

to

of

container

t he

liquid,

all

begins

t he

and

liquid

Separating

is

volatile

showing

column

liquid

t hat

and

a

has

distilled

mixture

distilling

of

over.

their

over,

bot h

This

is

separation

t he

vapours

is

collected

in

a

discarded.

temperature

t hat

more

rise,

and

reaches

t hen

t he

boiling

distilled

into

a

point

t hird

of

t he

less

volatile

container.

funnel

A separating funnel is used to separate a mixture of liquids that are immiscible

and

have

different

densities.

Immiscible

liquids

are

liquids

which

are

unable

oil liquid

to mix. A separating funnel is a container that has a tap at the bottom, allowing

interface water

oil

one

liquid

reduce

water

to

the

are

be

drained

amount

two

of

liquids

off

before

liquids

that

lost

are

the

at

other.

the

t

is

usually

interface

immiscible

and

of

they

the

have

conical

two

in

shape

liquids.

different

Oil

to

and

densities.

f

a mixture of oil and water is placed in a separating funnel, the oil with a lower

density

The

●

met hod

The

r un

●

oats

tap

The

tap

by

is

into

of



Figure

2.4.6

separating

Separation

runs

●

The

t he

a

is

tap

you

Chromatography

is

their

use

it

work.

to

forensic

For

analyse

presence

of

from

example,

body

illegal

they

fluids

drugs,

to

for

the

to

explosives.

crime

scenes,

are

detect

If

the

colourless,

a

on

the

with

the

them

t he

liquid

wit h

again

(oil)

a

to

to

second

whic h

t hrough

a

wit h

t he

is

as

follows:

higher

density

(water)

to

interface

almost

reaches

it

and

t he

rst

second.

allow

r un

a

into

container

ver y

t he

are

small

amount

container

and

of

t he

t hen

liquid

closed.

wit h

The

discarded.

are

is

used

coloured

to

mater ial,

e.g.

or

separate

can

lter

be

a

mixture

paper.

coloured,

of

The

and

dissolved

substances

whic h

are

will

separated

on:

how

soluble

how

strongly

and,

residues

spots

that

locating

are

t hey

in

are

t he

solvent

attracted

to

used

t he

paper.

inks

and

food

colourings

are

mixtures

of

two

or

more

dyes,

which

can

at

separated

by

paper

chromatography.

by

which

from

form

agent

chromatogram.

colourless

t hey

analyse

The

met hod

paper

chromatography

works

is

as

follows:

is

A

drop

of

the

dye

mixture

is

placed

1

cm

from

the

bottom

of

a

rectangular

This

of

absorbent

paper,

e.g.

lter

paper.

The

paper

is

then

hung

in

a

spots,

containing

solvent

so

that

the

lower

edge

is

below

the

surface

of

coloured.

the

●

solvent

The

●

rates.

The

t hat

The

t he

●

dyes

paper

dyes

Once

is

t hat

t he

to

paper,

known

as

dr y.

each

a

above.

t he

paper

and

However,

most

least

t he

soluble

and

and

There

will

be

a

in

its

t he

a

t he

solvent

in

travel

and

t he

up

mixture,

t he

paper

least

attracted

to

most

attracted

to

at

distance.

and

distance.

movement

par t

dyes

dyes

solvent

least

pattern

representing

chromatogram

t he

fur t hest

t he

completed

dissolves

different

in

t he

soluble

slowest

has

one

is

fastest

t he

t he

solvent

it.

t he

t he

are

travel

allowed

t he

are

dye

up

wit h

travel

paper

the

moves

t hem

different

t he

●

and

solvent

carr ying

28

liquid

works

chromatography

beaker making

funnel

density.

below.

chromatog raphy

piece reacts

t he

●

●

sprayed

opened

●

be airports,

t he

higher

scientists

Many blood

as

a

separating

allow

replaced

has

used

based

in

to

which

know?

travel

by

t he

container

density

of

substances

extensively

is

is

contents

funnel

Paper

Did

which

closed

lower

Paper

?

water

out

funnel

using

the

opened

t he

container water

on

of

of

up

t he

different

t he

paper,

t he

coloured

mixture.

This

paper

dyes

on

pattern

is

Mixtures

and

their

separation

Separating

mixtures

Your

may

teacher

use

Separating

using

this

mixtures

chromatography

activity

to

assess: drop

of

dye

mixture,

●

observation,

●

manipulation

be

recording

and

Y ou

will

two

water-based

supplied

and

datum

measurement.

with

a

markers

piece

of

e.g.

ink

reporting

of

lter

different

paper,

colours

a

beaker,

and

food

a

capillary

line

solvent

tube,

colouring.

Method solvent

edge

1

Measure

the

length

your

depth

of

the

beaker

with

a

ruler.

The

depth

will

be

the

front

of

–

solvent

fastest

moving

of

lter

paper. different

dye

coloured

2

Cut

the

lter

paper

into

a

rectangular

strip,

4 cm

wide

and

the

length

as dyes slowest

measured

in

1

point

above.

datum

line

moving

dye

3

Draw

the

a

pencil

line

at

line

1 cm

across

intervals

the

strip

with

a

2 cm

pencil

up

from

the

bottom

and

mark

dot. 

Figure

2.4.7

Separation

using

paper

chromatography

4

Attach

the

5

Make

with

to

6

a

top

a

with

drop

enough

in

the

the

its

second

place

hung

of

with

dot

the

Place

is

the

beaker

strip

lower

one

of

the

marker

of

food

water

a

glass

just

the

the

on

second

colouring

the

rod

on

beaker

bottom

so

above

markers

on

into

beaker,

to

edge

the

rst

third

that

the

it

the

in

beaker.

Make

a

dot

capillary

tube

dot.

the

be

suspended

the

dot.

Use

pencil

will

be

of

pencil

dot.

when

strip

can

bottom

pencil

the

so

of

that

the

strip

of

lter

immersed

in

paper

the

? water,

but

the

coloured

dots

will

be

above

the

Did

Using

7

Hang

the

bottom

and

strip

of

the

spread

of

lter

paper

up

the

paper

and

lter

in

the

watch

paper

beaker

the

as

so

colours

the

water

that

in

the

rises

the

water

three

up

the

wets

dots

the

Compare

colours

9

If

the

in

separate

that

plants,

known

actually

paper.

any

of

Which

What

as

3

a

For

is

on

the

them

of

into

your

used

with

common

made

two

markers.

Did

they

contain

any

and

green

as

of

it

can

be

pigment

in

chlorophyll,

is

three

pigments,

different

orange,

yellow

green.

different

theirs

with

to

coloured

see

if

markers

different

from

coloured

you,

markers

had

yours.

questions

a

of

the

components

separation

main

separation

each

class

results

in

properties

deciding

2

the

your

colours

Summary

1

from

the

common?

members

compare

results

know?

chromatography

shown

coloured

8

you

water.

the

their

of

a

mixture

are

considered

when

technique?

difference

between

using

distillation

and

evaporation

method?

following

mixtures,

component

a

a

mixture

of

salt,

b

a

mixture

of

oil,

black

sugar

explain

how

you

would

separate

parts:

pepper

and

and

water

water.

29

Extraction

of

sucrose

from

sugar

cane

A2.5

Objectives

By

the

be

able

end

of

Mixtures

this

topic

you

Extraction

of

sucrose

from

and

sugar

their

separation

cane

will

Sugar

to:

cane

was

rst

introduced

to

t he

Caribbean

by

t he

Dutch

in

about

1625

and has been a ver y impor tant par t of its economy ever since. The production

●

describe

the

extraction

of

of sucrose from t he sugar cane plant is an industrial process t hat makes use of

sucrose

from

sugar

cane

several

●

draw

a

ow

diagram

the

steps

the

separation

sugar

which

are

of

separation

involved

sucrose

in

from

The

processes

The

sugar

and

cut

The

pieces

to

The

The

cane

clarier

t he

●

The

juice

takes

mud

●

The

or

juice,

and

of

sucrose

from

sugar

cane

are

as

way

or

2.5.2

Sugar

cane

in

is

transpor ted

revolving

in

taken

t he

This

to

knives

cr ushers

produces

t he

boiler

to

is

acidic

which

and

t he

factor y,

cleaned

shredder.

water

is

juice

furnace

contains

occurs.

The

neutralises

precipitate

moves

remove

claried

or

to

t he

water

into

t he

juice.

juice,

under

syr up

Figure

as

to

t he

cane

sprayed

and

where

out,

i.e.

impurities,

juice

any

t hey

is

acids

are

t he

The

which

heated

in

t he

cane

it

is

on

t hem

bre,

burnt

enters

and

juice

conver ted

is

about

it

boils

by

t he

85%

is

or

to

t he

calcium

and

into

causes

larger,

water,

pressures

successively

t he

juice

process.

35%

is

2.5.3

Andrew’s

Sugar

Factory

goes

to

into

The

t hat

lower

juice

Barbados

t he

a

as

factor y

elds.

series

d istillation

so

ltration

produces

of

occurs.

t he

juice

temperatures.

concentrated

water.

in

continuous

This

returned

lower

at

about

mud

vacuum

and

boiling

containing

where

where

successively

next

lter

impurities.

factor y

evaporators

evaporates

rotar y

insoluble

ower 

in

boilers.

which

to

caramelised

t hick

by

precipitation

t hen

are

one

t he

added

boilers

t he

har vested,

par ticles.

claried

four

from

Sugar

is

place

boilers

2.5.1

for

are

present.

bagasse

impurities

insoluble

30

separation

crushed

sugar

where

hydroxide

Figure

t he

pieces

t hen

t he

heat

stalks

small

are

dissolve

supply

●

cane

into

bagasse.



in

cane.

●

Figure

involved

follows:

●



techniques.

showing

from

but

t he

not

last

t hree

These

passes

n

t his

charred

boiler

is

a

Mixtures

and

their

separation

Extraction

●

The

t hick

place.

soon

t he

t he

t he

are

The

syr up

added

molasses.

sugar

basket.

speed.

●

The

tumbled

in

evaporated

as

is

for

in

of

is

of

molasses

are

and

t he

sugar

sugar

t hen

The

cr ystals.

separated

a

is

t he

by

perforated

revolves

sugar

As

and

massecuite.

contains

in

As

called

viscous

forms

cane

takes

sugar.

sugar,

and

t his

holes

centrifuge.

wit h

of

t hick

centrifuge

t hrough

t he

grains

formation

basket

from

crystallisation

massecuite

t he

sucrose

saturated

small

and

Each

in

out

dr um

t he

where

becomes

cr ystals

placed

forced

outer

it

t he

syr up

centrifuges.

are

unrened

of

molasses

is

until

exceeded,

nuclei

mixture

t he

cr ystalliser

remaining

t he

t he

t hrough

sugar

(1)

in

t he

point

and

molasses

behind

damp,

is

massecuite

collected

The

The

in

into

ser ve

t he

cr ystals

The

remain

to

form,

centrifugation

are

moves

saturation

cr ystals

called

●

Here

as

‘seed’,

syr up

of

at

high

basket

and

cr ystals

basket.

sugar

heated

cr ystals

are

collected

and

dried

by

being

air.

cane

shredder

(2)

crushers bagasse

(fibre)

(3)

clarifier

(4)

cane

filter

juice

heat

water

molasses seed

cr ystal

thick

syrup

(8)

collectors (6)

(5)

boiler

cr ystalliser

heat

raw

sugar (7)



Figure

2.5.4

Summary

1

Draw

a

Why

is

it

from

sugar

diagram

of

the

various

stages

in

the

extraction

of

sucrose

questions

simple

separation

2

Flow

centrifuge

of

ow

diagram

sucrose

important

to

from

use

a

of

the

sugar

steps

which

are

involved

in

the

cane.

series

of

boilers

in

the

extraction

of

sucrose

cane?

31

Extraction

of

sucrose

from

sugar

cane

Mixtures

Key

Matter

●

A

pure

can

be

Pure

●

An

par ts

substances

element

simpler

is

of

is

a

its

cannot

be

pure

in

of

proper ties

be

any

a

are

into

t hat

ordinar y

are

one

separated

substance

such

substances

only

classied

which

and

pure

substance

by

pure

element

propor tions

●

a

into

composed

can

substances

compound

types

is

composition,

component

●

classied

substance

constant

A

their

separation

concepts

●

●

and

t heir

t

constant

has

and

a

xed,

t he

means.

and

compounds

broken

or

contains

toget her

t hat

and

be

mixtures

material.

physical

cannot

t hat

of

elements

chemical

bonded

way

xed

by

and

type

down

physical

two

or

more

chemically

proper ties

in

have

into

any

means.

different

xed

changed.

A mixture consists of two or more substances combined together in varying

proportions. Each component retains its own independent properties

and has undergone no chemical reaction with any other substance in the

mixture. The components of mixtures can be separated by physical means.

●

Mixtures

can

be

heterogeneous

●

A

homogeneous

composition

cannot

●

A

classied

be

are

solution

are

mixture

is

a

A

heterogeneous

●

A

suspension

par ticles

A

are

colloid

is

substance

dispersed

t han

●

of

100 g

●

A

saturated

A

at

as

wit h

is

each

in

which

t he

t he

sample

proper ties

and

t he

and

components

ot her.

mixture

usually

is

a

consisting

a

liquid.

non-uniform

heterogeneous

in

anot her

are

in

of

The

two

or

more

par ticles

in

a

solution

mixture

which

substance,

mixture

anot her

smaller

mixture.

in

in

usually

which

substance,

t han

t hose

of

minute,

a

t he

a

visible,

liquid.

par ticles

usually

but

a

of

one

liquid.

The

suspension,

but

larger

solution.

measure

at

a

of

given

Possible

simple

given

also

is

a

t he

mass

of

solute

temperature.

curve

solution

temperature,

affects

temperature

The

which

will

saturate

unit

of

solubility

contains

as

much

is

a

g

per

is

a

t hat

in

solubility.

t he

The

presence

solubility

of

solute

as

undissolved

of

most

solids

The

met hod

separation

extraction

showing

of

by

t he

how

component

which

met hods

are

fractional

of

sucrose

cr ushing,

cr ystallisation

32

be

water

increases.

graph

proper ties

t he

distillation,

processes:

can

solute.

in

t he

solubility

of

a

solute

a

par ts

mixture

ltration,

distillation,

can

of

be

a

mixture

evaporation,

a

are

used

and

from

sugar

precipitation,

separating

centrifugation.

cane

involves

ltration,

to

separated.

cr ystallisation,

funnel

and

chromatography.

●

xed

temperature.

physical

determine

●

a

a

a

solubility

The

mixture

a

solution

Temperature

varies

●

is

mixture

from

which

dispersed

solvent

increases

●

of

and

water

dissolved

●

is

par ticles

Solubility

a

heterogeneous

are

t hose

mass

of

dispersed

a

mixtures

small.

●

●

homogeneous

t hroughout

homogeneous

one

extremely

is

uniform

distinguished

components,

into

mixtures

t he

vacuum

following

distillation,

Mixtures

and

their

separation

Practice

iv)

Practice

exam-style

At

1

Which

of

t he

temperature

and

Y

t he

v)

What

is

t he

The

following

components

vi)

What

mass

of

is

a

can

be

separated

A

mixture

contains

two

or

more

pure

Figure

2

The

Y

from

combined

shows

of

X

at

46 °C?

(1

mark)

(1

would

cr ystallise

out

of

a

mark)

saturated

100 g

62 °C

to

of

water

if

t his

24 °C?

solution

main

steps

(3

mixture

has

a

xed

component

melting

par ts

t he

in

t he

marks)

extraction

of

substances from

sugar

cane.

toget her. Step

D

of

containing

cooled

sucrose

A

solubility

means.

chemically

C

of

by

b

B

solubilities

correct?

mixture

is

physical

t he

same?

questions

solution

A

are

questions

questions X

Multiple-choice

what

exam-style

of

a

1

Step

2

Step

3

Step

4

point.

mixture

are

in

a

xed

ratio. Cutting

and Precipitation

2

3

The

solubility

of

a

solid

in

water

A

increases

as

temperature

increases

B

increases

as

temperature

decreases

C

remains

D

decreases

The

constant

as

following

as

temperature

temperature

are

all

crushing

usually:

increases

Step

increases

colloids

6

Step

5

except: Vacuum

A

Centrifugation

fog

distillation

B

air

C

milk

D

mayonnaise



Figure

from

4

The

process

of

fractional

distillation

depends

on

in

Flow

chart

showing

the

extraction

of

sucrose

cane

a

i) difference

2

sugar

Complete

t he

char t

by

labelling

t he

boxes

in

3 A

melting

B

densities

points

C

solubilities

D

boiling

of

t he

components

of

t he

of

t he

components

of

t he

and

5.

(2

marks)

mixture

ii)

Describe

t he

process

taking

place

in

step

2.

mixture

(2 of

t he

components

of

t he

mixture

in

points

of

t he

components

of

t he

Why

is

it

necessar y

best

sand

is

way

to

separate

sodium

chloride

solution

boilers

B

carefully

C

ltering

simple

pouring

t he

lower

pressures

in

step

off

t he

sodium

chloride

solution

Extended

response

Chemical

(1

15

substances

marks

question

can

t he

combine

components

of

in

which

various

can

be

ways

to

separated

form

by

means.

question

1

shows

t he

solubility

cur ves

for

two

a

What

do

you

b

Solutions,

understand

by

t he

term

‘mixture’?

ionic (2

solids,

mark)

distillation

various

Figure

4?

mixture

mixtures,

Structured

under

Total

evaporation

a

t he

and

7

6

have

by:

A

D

to

mixture

successively The

marks)

water

iii)

5

steps

t he:

X

and

following

Y.

Use

t his

information

to

answer

marks)

t he suspensions

and

colloids

are

examples

of

questions. mixtures.

mixtures

90

lef t

to

Explain

in

terms

stand

and

t he

of

differences

par ticle

size,

transmission

of

between

t hese

t hree

sedimentation

light.

(6

when

marks)

)retaw

Y

80

c

You

are

given

sodium

g 001

70

The

a

mixture

chloride,

solubilities

lead

of

of

t hree

chloride

t hese

t hree

solid

and

chlorides:

silver

chlorides

chloride.

in

water

are

60 X

rep

given

in

t he

table

below.

50

g(

Compound

40

Solubility

in

cold

Solubility

ytilibuloS

water

in

hot

water

30

sodium

chloride

soluble

soluble

insoluble

soluble

insoluble

insoluble

20

lead

chloride

10

silver

chloride

0

0

10

20

30

40

50

60

70

80

i) T emperature

Use

t he

devise 

Figure

1

Solubility

curves

for

ionic

information

substances

X

and

a

scheme

i)

Dene

t he

solubility

iii)

term

Temperature

Explain

of

‘solubility’.

has

t he

which

how

you

greatest

(2

effect

on

at

your

marks)

t he

compound?

arrived

to

ii)

Draw

a

pieces

(1

answer

to

in

separate

t he

t he

table

to

mixture

into

mark)

par ts.

labelled

of

scheme.

(5

diagram

apparatus

you

to

show

used

in

one

your

of

(2

marks)

t he

separation

(2

marks)

par t ii)

Total above.

its

Y

component

ii)

given

(°C)

15

marks

marks)

33

A3

Atomic

For

a

long

structure

time,

people

believed

that

all

matter

Objectives

By

the

be

able

end

of

this

topic

you

will

consisted

water.

give

●

the

atomic

symbols

of

the

structure

of

Scientists

relative

charge

of

an

dene

a

proton,

a

earth,

fire,

air

and

know

that

the

smallest

identifying

is

an

atom.

Atoms

are

the

basic

the

represent

now

scale

terms

and

matter

matter.

into

On

a

mixtures

macroscopic

and

pure

scale

we

substances;

we

going

to

investigate

matter

on

a

microscopic

by

looking

at

the

structure

of

the

atom.

atomic

mass

atoms

of

neutron

electron

number

●

elements:

and

are

●

basic

now

matter

blocks

classified

the

mass

and

of

building

an

atom

give

four

elements

describe

●

the

the

particle common

●

of

to:

number

by

A3.1

nuclear

The

structure

of

atoms

notation

Regardless interpret

●

nuclear

determine

the

number

particles

in

an

metals

of

atom

an

have

is

the

element

the

the

one

gram

of

gold

identifying

can

and

be

one

masses

is

kilogram,

will

broken

par ticle

classied

non-metals

smallest

that

same

can

one

exhibit

gram

t he

or

same

are

into

of

an

into

smaller

element

metals

given

in

and

Units

is

par ts,

an

it

non-metals.

4.4,

17 .1

and

represented

The

and

The

in

3.1.1

by

atomic

an

atomic

symbols

of

symbol,

some

of

which

t he

represents

commonest

Tables

and

3.1.2.

properties T able

3.1.1

The

atomic

symbols

of

the

common

metals

element.

Element

Atomic

Aluminium

Al

symbol

Element

Atomic

Lithium

Li

Barium

Ba

Magnesium

Mg

Beryllium

Be

Manganese

Mn

Calcium

Ca

Mercury

Hg

Chromium

Cr

Nickel

Ni

Cobalt

Co

Potassium

K

Copper

Cu

Silver

Ag

Gold

Au

Sodium

Na

Iron

Fe

T in

Sn

Lead

Pb

Zinc

Zn

T able

3.1.2

The

atomic

symbols

of

the

common

symbol

non-metals

Non-metals

is

Exam

essential

atomic

with

form

34

that

and

care,

your

letters

tip

you

symbols

elements

atom

still

of

a

For

be

gold.

proper ties

Each

of

that

making

capital

know

all

you

sure

and

the

Element

Atomic

Element

Atomic

Argon

Ar

symbol

Neon

Ne

Boron

B

Nitrogen

N

Bromine

Br

Oxygen

O

Carbon

C

Phosphorus

P

Chlorine

Cl

Silicon

Si

Fluorine

F

Sulfur

S

Helium

He

Hydrogen

H

the

common

write

that

them

you

common Iodine

I

Krypton

Kr

correctly.

one

of

element

atom

elements

still



It

will

20.1.

Metals

✔

one

proper ties.

atom.

component

exist

chemical

be

element.



as

have

t hese

fact can

An

if

smallest

Elements

Key

you

all

atom.

The

!

whet her

element,

of

example, subatomic

of

notation

par ticular to

symbol

are

of

t he

given

Atomic

We

structure

cannot

t hic kness

see

of

a

The

atoms

because

human

hair,

t hey

an

are

atom

is

incredibly

more

small.

t han

a

Compared

million

times

to

structure

of

atoms

t he

smaller.

Did

?

you

know?

7

The

average

t hat,

on

diameter

average,

However,

t here

an

are

of

an

atom

atom

is

25

par ticles

is

about

million

t hat

are

2.5



times

even

10

mm,

smaller

smaller

whic h

t han

t han

a

an

means

millimetre.

atom.

These

The

atomic

the

Latin

fundamental

par ticles

are

called

subatomic

particles

and

atoms

are

name

of

t hese

the

and

copper

Subatomic

Cu,

particles

is

are

of

of

some

derived

the

from

element.

of

the

Latin

name

For

for

iron

is

par ticles. ferrum

Atoms

are

made

example,

up

symbols

elements

made

up

of

t hree

subatomic

par ticles:

protons,

neutrons

is

lead

Pb,

the

symbol

cuprum

is

and

and

plumbum

silver

is

for

its

and

iron

is

Fe,

symbol

its

is

symbol

argentum,

and symbol

Ag.

electrons.

Protons

●

and

neutrons

are

found

in

t he

centre

of

an

atom

in

an

area electrons

known

as

t he

nucleus.

Protons

and

neutrons

are

collectively

known

the

nucleons.

Electrons

●

around

Nearly

are

t he

t he

found

nucleus

(sometimes

but

all

just

volume

of

t hat

involved

are

Mass

and

Protons

are

at

in

called

movement

an

t he

of

atom.

in

mass

quite

a

a

series

t he

an

atom

distance

of

shells).

t he

levels

Most

electrons

When

charge

of

is

from

t he

known

of

t he

t he

reactions

in

nucleus,

as

atom

around

chemical

concentrated

energ y

is

in

occur,

it

nucleus.

spinning

empty

space,

constitutes

is

t he

t he

electrons

reaction.

of

subatomic

particles

the

positively

charged

par ticles

and

electrons

are

negatively

nucleus

charged. contains

The

size

of

electron.

t he

charge

Neutrons

are

on

a

proton

electrically

is

equal

neutral

so

to

t he

have

size

no

of

t he

charge.

charge

In

an

on

atom,

an

and

an

of

atom

is

protons

is

always

electrically

t he

neutral

same

and

as

has

t he

no

number

of

electrons.

protons

neutrons

t he 

number

nucleus

shells

fact

nucleus

its

orbit

as

Figure

3.1.1

The

structure

of

an

atom

Therefore,

charge.

The mass of a proton is equal to t he mass of a neutron. The mass of a proton is

24

extremely

small,

Comparing

1836

The

times

mass

heavier

proper ties

Table



t he

only

1.67



10

g.

of

proton

to

t han

of

a

a

an

The

mass

t hat

of

of

an

an

electron

electron,

a

is

even

proton

smaller.

is

about

electron.

proton,

neutron

and

electron

are

summarised

in

3.1.3.

T able

3.1.3

Subatomic

The

properties

particle

of

a

Relative

Proton

proton,

a

neutron

charge

and

Relative

1

1

Neutron

0

1

Electron

1

an

electron

mass

1

_____

1836

Atomic

number

! The

is

number

unique

world

t hat

to

of

a

protons

in

par ticular

have

t he

same

an

atom

element,

is

known

i.e.

t here

atomic

number.

means

t hat

For

as

are

t he

no

atomic

two

example,

number

elements

t he

atomic

in

t he

number

hydrogen

The

20

atomic

is

1,

whic h

number

of

calcium

is

ever y

20,

hydrogen

t herefore,

atom

ever y

has

calcium

1

fact

Atomic

number

protons

in

of

of

Key

and

an

the

is

the

nucleus

number

of

one

of

atom

element.

proton.

atom

has

protons.

35

The

structure

of

atoms

Atomic

In

an

atom,

protons,

Mass

!

Key

t he

since

t he

number

number

of

of

electrons

electrons

is

equal

is

to

always

t he

equal

atomic

to

t he

structure

number

of

number.

number

fact The

number

of

protons

and

neutrons

in

an

atom

is

known

as

t he

mass

number. The mass number is not unique to a par ticular element, for example Mass

number

is

the

total

number

polonium of

protons

nucleus

of

and

neutrons

one

atom

of

in

an

and

astatine

bot h

have

a

mass

number

of

210.

the

element.

The number of neutrons can be calculated by subtracting t he atomic number

from

t he

mass

number

Nuclear

number,

of

i.e.

neutrons



mass

number



atomic

number

notation

We can represent an atom (or ion) of an element using the

nuclear notation:

A

X Z

where

This

X



atomic

notation

protons,

is

symbol,

ver y

neutrons

A

useful

and



mass

number

because

electrons

number

of

protons

●

The

number

of

neutrons

is

equal

to

A

●

The

number

of

electrons

is

equal

to

t he

Examples



T able

to

allows

us

Z

to



atomic

calculate

number.

t he

number

of

atom.

The

to

equal

it

an

●

equal

is

in

and

Z



Z

number

of

protons,

which

is

Z

are

3.1.4

given

The

Element

in

Table

number

Nuclear

of

3.1.4.

subatomic

particles

Number

of

Protons

(Z)

in

the

atoms

of

three

elements

notation

Neutrons

(A–Z)

Electrons

14

Nitrogen

N

7

7

7

AI

13

14

13

Cl

17

20

17

7

27

Aluminium 13

37

Chlorine 17

The

nuclear

elements

on

notations

page

Summary

1

Which

a

2

Dene

of

the

the

3

For

each

electrons

of

elements

in

the

36

B

and

5

is/are

be

found

responsible

b

mass

following

in

t he

periodic

table

volume

for

of

the:

the

atom?

number.

nuclear

notations,

give

the

number

neutrons.

11

a

can

terms:

number,

the

atom

atom

following

atomic

all

questions

particle(s)

mass

for

360.

40

23

b

Na 11

c

Ca

20

of

protons,

of

Atomic

structure

A3.2

The

Electrons

spin

energ y

The

electronic

around

shells.

Each

t he

configuration

nucleus

energy

shell

of

is

a

an

atom

xed

in

a

of

an

series

distance

of

from

atom

levels

and

t he

electrons

in

t he

same

shell

have

t he

t he

same

known

nucleus

amount

of

configuration

of

as

By

the

be

able

end

electrons

are

arranged

in

t he

energy

shells

in

a

specic

way.

t he

arrangement

of

electrons

in

an

atom,

known

as

t he

of

(or

str ucture),

using

anot her

scientic

this

topic

you

will

t he

give

We

the

maximum

allowed

number

in

the

of

rst

can

energy

shells

of

an

atom

electronic

work

●

conguration

atom

energy.

three

represent

an

to:

electrons

The

of

Objectives

●

atom

electronic

out

the

electronic

model.

conguration

electron

of

the

rst

20

elements

proton

represent

●

the

conguration

×

electronic

of

an

atom

in

writing

represent

●

the

conguration

energy

shells

shell

an

atom

by

a

diagram

explain

●

electronic

of

the

term

valence

electron. neutron

nucleus

×



In

t his

Figure

scientic

around

t he

3.2.1

Model

model,

nucleus,

but

t he

as

of

the

arrangement

energy

t his

is

shells

only

a

of

are

electrons

drawn

model,

t his

is

in

as

an

atom

concentric

not

how

t hey

circles

actually

Did

? look.

The

is

The

shell

shells

are

closest

number

2,

to

and

numbered

t he

so

according

nucleus

is

to

assigned

t heir

distance

number

1,

t he

from

next

t he

you

know?

nucleus.

fur t hest

away

on.

The

maximum

number

that

an

shell

energy

of

can

electrons

hold

is

2

Each

shell

can

hold

up

to

a

cer tain

maximum

number

of

electrons:

given

by

is

shell

3 ●

shell

number

1

can

hold

a

maximum

of

2

the

can,

the

shell

number

2

can

hold

a

maximum

of

8

therefore,

shell

8

number

3

may

be

considered

to

hold

a

maximum

of

of

32

filling

electrons.

shells

maximum

hold

more

numbers

conguration

of

an

electrons,

since

atom

you

wit h

but

will

more

it

not

t han

is

not

have

20

necessar y

to

work

to

out

know

t he

t heir

electron

have

3,

in

electrons.

2

The

by

negative

an

electrostatic

around

t he

energy

t hey

energy

t han

can

electrons

only

force

nucleus

possess.

t hose

occupy

a

are

constantly

of

and

attraction .

t heir

Electrons

in

t he

distance

in

shells

specic

being

shell

t he

if

The

t hey

have

t he

closest

from

to

electrons

from

shells

fur t her

attracted

t he

t he

t he

positive

maintain

nucleus

to

t he

required

t heir

because

nucleus

nucleus.

nucleus

In

fact,

spin

of

have

t he

chemical

in

an

proper ties

atom

of

of

t hat

an

element

element,

in

depend

par ticular,

on

t he

shell

t he

outermost

energy

where

Shell

actually

n

number

hold

electrons

next

2

a

and

shell

electrons

number

However,

4.

have

(up

maximum

3,

When

in

4

to

been

electrons

number

placed

after

these

placed

any

10)

8

are

Only

are

when

something

shell

electrons

number

number

a

number

placed

electrons

shell

hold

happens.

in

remaining

placed

in

shell

3.

less

electrons

energy.

t he

arrangement

number

of

Key

fact

of

electrostatic

force

of

electrons

attraction

in

18

can

been

the

An

electrons

of

electrons.

shell

! The

4

up

unusual

Fur t her

,

electrons number

●

number.

2n

electrons

maximum

●

formula

is

the

force

that

exists

shell. between

two

oppositely

charged

particles.

37

The

electronic

configuration

of

an

atom

Atomic

Shell

Key

!

by

an

electronic

atom

is

electrons

diagrams

fact The

The

structure

the

in

configuration

arrangement

the

energy

drawing

a

conguration

shell

diagram

or

of

in

an

atom

writing

of

an

using

element

can

numbers.

In

be

represented

order

to

draw

a

of

shell

of

shells

electronic

of

diagram

of

an

atom,

t he

following

steps

must

be

followed.

the

1)

Determine

t he

number

of

protons,

neutrons

and

electrons

in

t he

atom

atom.

2)

using

t he

Draw

a

atomic

small

neutrons

3)

Work

electrons,

up

4)

shell

circle

inside

out

t he

in

2,

Represent

number

for

t his

and

t he

order,

so

t he

nucleus

number

and

(Unit

write

t he

3.1).

number

of

protons

and

circle.

electronic

and

mass

i.e.

ll

conguration

up

shell

1

rst

by

and,

lling

when

up

t hat

t he

is

shells

full,

star t

wit h

to

ll

on.

electronic

conguration

by

drawing

concentric

circles

around t he nucleus. The number of circles you should draw is determined

by t he number of shells t hat you are going to ll or par tially ll. Use crosses

or

dots

as

a

to

pair.

contains

represent

Draw

5

or

t he

more

t he

electrons.

electrons

in

Draw

t he

t he

ot her

2

electrons

shells

as

in

pairs

shell

number

when

t he

1

shell

electrons.

Examples

12

1

The

str ucture

of

a

carbon

atom,

C. 6

×

××

A

carbon

6

6p

×

atom

has:

protons

× 6n

6

neutrons

6

electrons.

(12



6)

× 12



T able

3.2.1

Determining

the

electronic

conguration

of

a

carbon

atom

C

carbon,

6

Shell



Figure

of

a

3.2.2

carbon

Electronic

number

Maximum

number

of

electrons

Number

of

electrons

in

carbon

conguration

atom

1

2

2

2

8

4

The

t he

electronic

symbol

shell

of

conguration

t he

separated

element

by

of

a

carbon

followed

commas,

i.e.

C

by

atom

t he

can

be

number

written

of

by

electrons

writing

in

each

(2,4)

39

2

The

str ucture

of

a

potassium

atom,

K. 19

×

××

A

potassium

atom

has:

×× 19

20

20n

××

××

××

××

19p

19



protons

neutrons

(39



19)

electrons.

T able

3.2.2

Determining

the

electronic

conguration

of

a

potassium

atom

×× Shell

number

Maximum

number

of

electrons

Number

of

electrons

in

potassium

××

1

2

2

2

8

8

3

8

8

4

not

39

potassium,

K 19



Figure

of

a

3.2.3

Electronic

potassium

conguration

atom

The

38

electronic

necessary

conguration

1

of

a

potassium

atom

is

K

(2,8,8,1)

Atomic

structure

3

str ucture

The

Examples

given

in

of

t he

The

of

ot her

t he

configuration

congurations

diagrams

in

Figure

3.2.4

of

atoms

and

are

of

ot her

written

×

an

atom

Table

are

3.2.3.

××

8p

×

5p

0n

elements

in

Element

Electronic

hydrogen

H

(1)

boron

B

(2,3)

oxygen

O

6n

(2,6)

8n

sodium

Na

argon

Ar

calcium

Ca



T able

3.2.3

(2,8,1)

(2,8,8)

(2,8,8,2)

Written

congurations

×

1

of

electronic

the

atoms

shown

in

× Figure

11

H

configuration

××

×

1p

hydrogen,

of

atoms.

electronic

shell

electronic

boron,

16

B

oxygen,

O

5

1

3.2.4

8

×

×

××

××

××

××

20p

20n

××

××

××

××

××

××

××

××

22n

××

18p

××

××

12n

××

××

××

××

11p

××

✔

It

argon,

Na

Ar

important

that

shell

Ca

calcium,

diagrams

numbers



Figure

3.2.4

Shell

diagrams

showing

the

electronic

congurations

of

atoms

Valence

draw

of

1

to

20,

i.e.

atomic

hydrogen

in

the

periodic

to

table.

electrons

example,

The

can

atoms

elements

The electrons in t he outermost energy shell are known as

For

you

of

calcium

different

of

20

18

11

is

tip

40

40

23

sodium,

Exam

potassium

outer most

(2,8,8,1)

e le c t ro ns

are

has

t he

one

valence

on es

t h at

valence electrons .

electron.

are

involve d

in

c h emical

reactions, i.e. t he va le n ce e le ct ro n s. A dia g ram o f an a tom can b e drawn t h at

shows

only

t he

va le n c e

e le ct ro n s.

×

××

3.2.5

Diagrams

electrons

1

What

2

Represent

is

the

11p

12n

18p

20n

O

boron,

sodium,

oxygen,

maximum

a

number

electronic

shell

of

electrons

conguration

diagram

and

argon

atoms

the

of

allowed

each

of

in

Ar

showing

the

shell

the

b

elements

chlorine,

2?

atoms

20

c

Cl

neon,

17

in

number

following

35

Mg 12

of

and

argon,

writing:

24

each

sodium

Na

only

magnesium,

For

××

questions

the

both

of

3.2. 5.

××

oxygen,

Summary

3

Fig ure

××

B

valence

a

in

×

boron,

using

g ive n

××

8n

×

Figure

××

× 6n

a re

×

8p

×

5p



E xa mple s

question

2,

Ne. 10

give

the

number

of

valence

electrons.

39

Isotopes

and

radioactivity

Atomic

A3.3

Objectives

By

the

be

able

end

of

this

topic

you

Isotopes

and

structure

radioactivity

will

Isotopy to:

The dene

●

the

terms

isotope

atomic

number

is

unique

to

a

particular

element.

For

example,

all

atoms

and

of

magnesium

have

an

atomic

number

of

12,

i.e.

they

all

have

12

protons

and,

isotopy

therefore, ●

dene

●

explain

relative

atomic

12

electrons.

The

number

of

neutrons

in

atoms

of

the

same

element

mass

is not unique. For example, most magnesium atoms have 12 neutrons, however, what

is

meant

by

a

some radioactive

have

number describe

●

13

neutrons

and

others

have

1 4

neutrons.

Atoms

the

uses

of

protons

and

electrons

but

different

numbers

of

neutrons

same

called

isotopy

isotopes.

In

ot her

words,

numbers.

Key

the

are

of

isotopes. The occurence of these different isotopes is known as radioactive

!

with

isotope

fact ●

isotopes

Isotopes

have

t he

same

atomic

number

but

different

mass

have:

the same chemical properties and electrical properties because they have

the same number and arrangement of electrons, e.g. if the different isotopes

Isotopes

are

different

atoms

of

the

of magnesium react with oxygen, the chemical reaction would be the same same

element

that

have

the

same

●

number

but

of

protons

different

and

numbers

slightly

different

of

neutrons.

neutrons,

different

Most

Key

!

are

fact

of

the

the

is

the

same

same

electrons

occurrence

element

number

but

of

that

of

have

The

isotope

abund ance

t he

proper ties

different

because

isotopes

of

of

t he

different

magnesium

have

numbers

slightly

of

of

more

unstable

an

t he

t han

ones

element

one

decay

in

a

isotope,

into

sample

but

ot her

of

t he

not

all

isotopes.

element

of

The

is

t hese

isotopes

percentage

referred

to

as

of

t he

isotope.

have

protons

different

atoms

e.g.

masses.

elements

stable.

each

Isotopy

physical

electrons

of

and

numbers

Examples

of

1

Carbon

neutrons.

Carbon, atomic number 6, has

three naturally occurring isotopes, one with

a mass number of 12, one with a mass number of 13 and one with a mass

number of 1 4. There are two main methods of representing these isotopes:

●

Using

nuclear

C

By

14

C

6

●

notation:

13

12

C

6

6

name:

carbon-12

or

C-12

carbon-13

or

C-13

carbon-14

or

C-14.

Carbon-12 has 6 neutrons, carbon-13 has 7 neutrons and carbon-1 4, which

is unstable, has 8 neutrons. Carbon-12 is the most abundant carbon isotope.

In fact 98.89% of all naturally occurring carbon is the carbon-12 isotope.

Did

?

you

2

know?

Hydrogen

Hydrogen

The

is

deuterium

heavier

since

it

made

of

from

normal

heavy

used

than

has

an

normal

extra

hydrogen

This

nuclear

of

is

has

three

naturally

in

known

heavy

reactors

Water

place

as

water

to

is

slow

H

thus

the

fast-moving

enabling

a

isotopes.

hydrogen

1

down

occurring

hydrogen

neutron.

deuterium

water.

in

isotope

neutrons,

sustained

2

or

protium

H

1

3

or

deuterium

1

H

or

tritium

1

chain 

Figure

3.3.1

The

three

isotopes

of

hydrogen

reaction.

Hydrogen is the only element that has different names for its isotopes.

These are given in Figure 3.3.1. Protium, or normal hydrogen as it is usually

40

Atomic

structure

Isotopes

and

radioactivity

called, has a single proton in its nucleus. It is the most abundant hydrogen

isotope, making up 99.985% of all naturally occurring hydrogen.

3

Chlorine

35

Chlorine

has

two

naturally

occurring

Cl,

isotopes,

or

chlorine-35,

and

17

37

Cl,

or

chlorine-37 .

Approximately

75%

of

naturally

occurring

chlorine

17

is

t he

chlorine-35

Relative

Chemists

mass

of

smaller

system

ensure

in

To

t he

To

could

unit

t hat

a

t hese

ratio

t his

t he

units

mass

of

a

gram

t he

6

or

t he

atom.

is

t he

t hat

chlorine-37

carbon-12

of

isotope.

of

of

but

They

atoms.

t he

They

wit h,

mass

because

needed

but

of

a

t he

much

designed

t hey

each

had

atom

a

to

and

atoms.

t he

has

was

chose

number

unit

as

assigned

t he

as

a

basis

to

work

nature.

t hey

mass

new

was

one-twelf t h

chosen

in

mass,

a

t his

atom

atoms,

work

abundance

dened

carbon-12

of

to

isotope

and

carbon-12

Therefore,

mass

easier

of

clumsy.

representative

masses

stability

They

mass

ver y

t he

are

representative

A

t he

becomes

measure

are

because

neutrons.

amu.

1.00

to

actual

great

12,

25%

measure

it

numbers

numbers

as

its

be

to

small,

numbers

to

and

grams

so

us

and

mass

system

of

carbon-12

mass

a

t han

because

protons

is

gives

same

make

use

atom

t hat

carbon-12

of

atomic

an

design

from

isotope

mass

number

12,

i.e.

one-twelf t h

a

of

t he

of

mass

a

of

it

t he

12.00

carbon-12

for

has

6

mass

atomic

atom

has

Key

!

fact

amu. Relative

atomic

mass,

A

,

is

the

r

The

mass

of

carbon-12

Relative

an

atom

atom

atomic

was

of

an

t hen

mass

is

element

assigned

given

t he

compared

a

value

symbol

to

one-twelf t h

known

as

relative

t he

mass

atomic

of

a

mass .

average

mass

element

compared

the

A

mass

of

of

an

one

atom

to

atom

of

an

one-twelfth

of

carbon-12.

r

Relative atomic mass, t herefore, compares t he mass of an atom of an element

to

one-twelf t h

value,

When

relative

t he

mass

atomic

calculating

of

mass

t he

a

carbon-12

has

no

relative

atom.

Because

it

is

a

comparative

units

atomic

mass

of

an

element,

t he

of

each

isotope

is

taken

into

account.

For

example,

fact

relative A

abundance

Key

!

t he

radioactive

isotope

has

an

relative unstable

nucleus

which

decays

atomic mass of chlorine, which is 35.5, is t he average mass of t he two isotopes spontaneously

of

chlorine

gas,

and

according

approximately

25%

consists

to

75%

of

t he

t heir

of

relative

t he

abundance.

sample

chlorine-37

consists

of

In

a

t he

75

atomic

mass

of

chlorine



and

atomic

neutrons)

isotopes

not

real

a

when

whole

atom

of

mass

an

gives

atom

has.

calculating

number,

carbon

e.g.

has

a

rough

idea

However,

relative

t he

of

chlorine-35

isotope

form

by

to

emitting

a

more

stable

particles

and

radiation.

25

t he

because

atomic

relative

12.01 1

chlorine

____



(

35

)



37



)

35.5

100

number

we

mass,

atomic



(

100

Relative

of

isotope.

____

Relative

sample

are

t he

mass

of

of

nucleons

looking

relative

carbon

at

a

(protons

mixture

atomic

is

but

you

know?

of

mass

12.01 1,

Did

?

The

three

and

radiation

main

types

of

particles

is

no

nucleons.

isotopes

•

by

radioactive

are:

alpha

( )

consist

of

neutrons

Radioactivity

emitted

particles,

2

protons

and

have

which

and

a

2

charge

of

2

Some isotopes have unstable nuclei. These are known as rad ioactive isotopes . •

beta

( )

particles,

which

These isotopes undergo radioactive decay by spontaneously ejecting par ticles consist

and

radiation

from

t heir

nuclei.

Radioactive

isotopes

eject

t hese

become

different

more

stable

and

in

t he

process

t hey

may

produce

an

an

electron

atom

of

a

element.

•

charge

gamma

is

a

form

of

time

taken

for

half

of

t he

nuclei

in

a

sample

of

a

radioactive

isotope

( )

of

radiation,

high

radioactive

decay

is

known

as

t he

half-life

of

t he

which

energy

radiation

and

to has

undergo

have

1

electromagnetic

The

and

par ticles a

to

of

neither

mass

nor

a

charge.

isotope.

41

Isotopes

and

radioactivity

Uses

of

radioactive

Carbon-14

Carbon-14

up

to

d ating

living

mass.

is

of

sites.

5700

is

t he

When

It

determine

which

use

contain

in

ratio

a

of

t he

have

t he

age

of

been

fact

or

carbon-14

as

living

constantly

living

to

old,

makes

same

(animals)

a

animal

remains,

isotopes

plant

and

discovered

t hat

t he

in

places

half-life

of

such

as

radioactive

years.

present

organism

food

used

years

organisms

This

carbon-14

t he

is

60 000

archeological

All

structure

dating

about

carbon-14

Atomic

in

organism

in

body

molecules

dioxide

dies,

carbon-12

dioxide

organism’s

takes

carbon

and

carbon

it

in

in

t he

decays,

a

specic

ratio

atmosphere.

it

is

containing

replaced

carbon

in

As

by

t he

because

t he

form

(plants).

stops

taking

in

t hese

carbon

containing

molecules and t he carbon-14 is not replaced as it decays. The ratio of carbon-14

to

by

carbon-12,

comparing

expected



Figure

to

3.3.2

determine

Carbon-14

the

age

of

dating

some

is

used

fossils

of

t herefore,

t he

ratio

carbon-14

for

was

ratio

t hat

half

decreases.

of

carbon-14

organism

of

The

t he

if

age

to

it

a

specimen

carbon-12

was

expected

of

alive.

amount,

in

For

t he

can

be

specimen

example,

t hen

t he

determined

if

wit h

t he

specimen

t he

amount

would

be

5700 years old, if it was a quar ter of t he expected amount, t hen t he specimen

would

be

1 1 400

years

old.

Radiotherapy

Radiotherapy

tumours

are

sensitive

to

uses

radiation

composed

damage

of

by

to

cure

rapidly

or

control

dividing

radiation.

They

cancer.

cells

can

and

be

Cancerous

these

cells

controlled

are

or

growths

or

particularly

eliminated

by

irradiating the area containing the growth with external or internal radiation.

External

irradiation

radiation

Internal

gamma

a

tiny

from

beta

Figure

treat

3.3.3

Radiotherapy

cancerous

growths

is

used

can

involves

emitter,

protective

be

carried

radioactive

irradiation

or

cancerous 

a

into

capsule

tumour.

For

or

out

cobalt-60

eit her

t he

wire

injecting

target

(a

example,

by

directing

source

area,

a

radioactive

a

t he

placing

seed)

is

beam

a

isotope,

radiation

directly

used

to

of

cancerous

radioactive

or

iodine-131

at

at

treat

t he

gamma

growt h.

usually

source

site

t hyroid

of

a

in

t he

cancer

to

and radioactive seeds containing iridium-192, palladium-103 and iodine-125

are

used

to

treat

breast

and

prostate

cancer

and

brain

tumours.

Tracers

Radioactive

isotopes

are

used

as

tracers

in

the

medical

eld

as

a

diagnostic

tool. These tracers generally have a short half-life so they do not remain in the

body

for

ver y

bloodstream

long.

and

as

A

it

small

amount

moves

around

of

the

the

tracer

body

it

is

usually

emits

injected

gamma

rays

into

the

which

can

be obser ved using special equipment. This allows the physician to obser ve the

functioning of specic organs. Examples of medical tracers are:

●

Technetium-99

studies

of

skeleton,

●

most

is

used

organs

lungs,

Iodine-131

t hyroid

is

liver,

used

to

to

in

gall

produce

t he

body,

bladder

image

images

and

and

especially

and

carr y

carr y

t he

out

brain,

functional

hear t

muscle,

kidneys.

out

functional

studies

of

t he

gland.

Another example of the use of radioactive tracers is in determining the uptake of

atmospheric carbon dioxide by plants. Plants can be grown in an environment

containing radioactive carbon dioxide, i.e. carbon dioxide that has been made

by

42

replacing

the

carbon-12

atoms

in

the

molecules

with

carbon-1 4

atoms.

Atomic

structure

Isotopes

and

radioactivity

Using a Geiger counter (a machine that detects radiation) the parts of the plant

that absorb the radioactive carbon dioxide can be identied.

Energy

generation

Radioactive isotopes are used to generate electricity in nuclear power stations.

The

isotopes

they

undergo

smaller

an

it

splits

of

of

split

ones

two

that

ssion,

Nuclear

either

into

amount

are

nuclear

nuclei.

atom

also

used

power

i.e.

smaller

The

releasing

atoms

or

more

large

the

use

releases

neutrons

neutrons

and

amounts

nucleus

splits,

uranium-235

plutonium-239

and

released

ver y

when

stations

uranium-235

energy.

release

two

can

is

or

usually

by

a

free

neutrons

strike

This

energy

sets

when

into

two

plutonium-239.

str uck

three

then

energy.

or

of

other

up

a

If

neutron,

and

atoms,

chain

a

large

which

reaction

which releases enormous amounts of energy.

Did

?

you

know?

Ba 3

One

energy

235

type

of

atom

bomb

derives

U

neutrons Ba

Kr

its

destructive

force

from

nuclear

1

fission.

Only

two

atom

bombs

have

neutron Ba 235

235

energy

U

been

used

during

warfare,

both

by

U

Kr

the

USA

War

Kr

II.

towards

The

first,

the

a

end

of

uranium

World

fission

Ba

235

bomb,

U

code

named

‘Little

Boy’,

energy

was

Kr

city



Figure

3.3.4

The

chain

reaction

in

splitting

a

uranium

exploded

of

The

fission

t he

chain

reaction

is

controlled,

t he

energy

produced

can

be

used

electricity.

If

t he

chain

reaction

is

not

controlled,

it

results

Heart

A

explosion

as

occurs

in

an

atom

hear t.

It

connected

in

the

Man’,

was

in

plutonium

named

detonated

Japan

three

over

days

later.

bomb.

is

to

is

a

medical

implanted

t he

hear t

device

under

muscle

t hat

t he

by

is

skin

used

just

to

regulate

below

t he

t he

collar

beating

bone

of

and

is

early

1970s,

some

Did

?

you

pacemakers

were

developed

that

were

powered

by

is

to

thought

100

that

people

pacemakers

radioactive decay, it emits energy. In the pacemaker batter y, this energy is used

by

generate

an

electric

powered

current

by

which

chemical

delivers

batteries

about

have

a

0.2

milliwatt

lifespan

of

of

about

power.

10

only

living

that

plutonium-238

use

for

Pacemakers

know?

electrodes.

batteries containing plutonium-238. As the plutonium-238 undergoes natural

to

a

code

a

It

In

Japanese

August,

pacemakers

pacemaker

t he

such

second,

bomb,

Nagasaki

nuclear

6

to

‘Fat

generate

the

on

atom

1945.

If

over

Hiroshima

was

never

several

about

today

are

powered

batteries.

really

reasons,

50

have

Their

developed

one

of

the

years.

main

ones

being

the

reluctance

of

To replace the batteries, the pacemaker has to be surgically removed and then

people

replaced.

Since

the

half-life

of

plutonium-238

is

about

87

years,

to

have

by

plutonium-238

batteries

should

be

able

to

deliver

current

for

lifetime

Summary

1

Dene

a

2

the

without

having

to

be

the

sodium,

following

in

their

body

replaced.

terms:

b

similarities

Na-23

3

Explain

why

4

Explain

what

5

How

is

plutonium

life.

questions

isotope

Give

containing

a for

patient’s

device

pacemakers radioactive

powered

a

and

relative

a

and

differences

between

atomic

the

two

mass.

isotopes

of

Na-22.

atomic

radioactive

carbon-14

relative

used

in

mass

has

isotope

the

no

units.

is.

dating

of

fossil

samples?

43

Isotopes

and

radioactivity

Atomic

Key

●

concepts

Atoms

are

t he

identifying

●

Atoms

basic

par ticle

consist

par ticles:

●

structure

Protons

known

of

and

an

t hree

protons,

as

building

of

of

are

nucleus.

and

found

Protons

matter.

t hat

fundamental

neutrons

neutrons

t he

blocks

element

has

An

t he

par ticles,

atom

is

proper ties

known

as

t he

of

smallest

t he

element.

subatomic

electrons

in

the

and

centre

of

neutrons

t he

are

atom

in

an

collectively

area

known

as

nucleons

●

Electrons

levels

amount

●

Protons

of

The

an

found

size

as

at

quite

energ y

a

distance

shells.

from

Electrons

in

t he

t he

nucleus

same

in

shell

a

series

have

of

t he

same

energy.

are

neutrons

●

are

known

positively

have

of

no

t he

electron.

charged,

charge

In

an

electrons

are

negatively

charged

and

charge.

on

atom,

a

proton

t he

is

equal

number

of

to

t he

protons

size

of

equals

t he

t he

charge

on

number

of

electrons.

●

The

mass

of

a

proton

is

equal

to

t he

mass

of

a

neutron.

An

electron

has

a

1 ____

mass

of

t he

mass

of

a

proton

or

a

neutron.

1836

●

Protons

are

and

neutrons

responsible

●

The

number

●

The

total

mass

●

The

as

●

of

are

t he

protons

number

of

responsible

volume

in

an

protons

of

an

atom

and

for

t he

mass

of

an

atom.

Electrons

atom.

is

known

neutrons

as

in

t he

an

atomic

atom

is

number

known

as

t he

number

electrons

t he

Each

for

are

arranged

electronic

electron

in

t he

energy

shells

in

a

specic

way

known

conguration

shell

can

hold

up

to

a

cer tain

maximum

number

of

electrons.

●

Shells

●

The

closest

electronic

using

Electrons

●

The

Isotopes

number

They

of

is

same

nucleus

by

a

shell

outermost

proper ties

t he

are

have

Isotopy

t he

in

or

t he

chemical

electrons

●

in

t he

atoms

different

protons

t he

t he

ll

conguration

numbers

●

●

to

t he

of

an

atom

are

can

known

element

be

represented

in

writing

t he

of

valence

depend

same

but

number

atoms

protons

as

on

t he

electrons

arrangement

of

element.

of

electrons

atomic

occurrence

number

an

atoms

and

same

of

rst.

diagram.

shell

of

of

up

and

different

but

of

element

t he

have

numbers

different

same

electrons

t hat

but

mass

of

t he

same

neutrons.

numbers.

element

t hat

different

have

numbers

of

neutrons.

●

●

Isotopes

of

physical

proper ties.

The

an

relative

element

atomic

have

mass,

t he

A

,

is

same

a

chemical

number

t hat

proper ties

compares

but

t he

different

average

r

mass

●

of

Some

an

atom

isotopes

wit h

have

one-twelf t h

unstable

t he

nuclei.

mass

These

of

are

a

carbon-12

known

as

atom.

rad ioactive

isotopes

●

Radioactive

dating,

44

isotopes

have

radiot herapy,

many

tracers,

uses.

energy

Some

of

t hese

generation

are

and

carbon-14

pacemakers.

Atomic

structure

Practice

Structured

Practice

exam-style

1

If

t he

of

mass

atomic

in

t he

number

a

i)

of

an

of

t he

following

table

by

lling

in

t he

gaps.

atom

nucleus

question

Complete

questions

number

neutrons

questions

questions 6

Multiple-choice

exam-style

is

t he

59

and

atom

t he

is

Particle

number

32,

t hen

t he

Mass

Atomic

Number

Number

number

number

of

of

neutrons

electrons

is:

56

A

27

B

32

C

59

D

91

Fe

26

58

Fe

(7

ii)

A

sample

39

2

A

potassium

atom

is

written

as

of

56

K.

Which

of

of

t he

iron

was

found

to

contain

a

marks)

mixture

58

Fe

and

Fe

in

a

ratio

of

7

to

3.

Calculate

t he

19

following

statements

about

I

It

has

an

atomic

II

It

has

20

neutrons.

number

III

It

has

19

IV

The

A

I

B

II

C

I,

a

potassium

of

atom

are

relative

tr ue?

number

Students

were

information

protons

and

electrons

is

D

I,

IV

and

II

and

III

only

III

and

Which

of

iron.

asked

given

questions

in

t he

based

table

on

marks)

t he

below.

Atomic

Electron

number

configuration

A

25

—

2,8,2

B

17

8

—

only

IV

t he

of

Mass

only

The

3

sample

number

only

III

t he

39. Element

and

of

(2

b

of

mass

19.

electrons.

total

atomic

following

is

t he

electronic

conguration

following

statements

were

taken

from

one

of of

t he

student’s

exercise

books.

These

statements

19

uorine,

F? 9

are

A

INCORRECT.

In

each

case,

explain

why

t he

2,8,8,1 statement

B

2,8,1

C

2,8

D

2,7

is

incorrect

and

t hen

give

t he

correct

A

2

statement.

i)

INCORRECT

‘The

4

Isotopes

of

an

element

I

t he

same

atomic

II

t he

same

number

of

III

has

have:

number

of

but

different

electrons

but

mass

different

numbers

numbers

ii)

neutrons

t he

same

physical

proper ties

but

different

B

I

I

2

STATEMENT:

number

valence

–

Explain

–

Give

‘The

chemical

it

–

Explain

–

Give

t he

correct

element

is

because

statement

is

incorrect.

statement.

(3

conguration

has

a

why

mass

t he

of

number

statement

element

of

marks)

is

B

is

2,8,7

17 .’

incorrect.

only

and

II

t he

correct

statement

.

(3

C

II

D

I,

and

II

III

and

of

15

marks

only

III

Extended

Which

marks)

only

Total

5

it

STATEMENT:

electron

because

of

electrons.’

why

t he

INCORRECT

proper ties

A

atomic

t he

following

is

not

a

use

of

response

question

radioactive

7

a

The

following

nuclear

notations

refer

to

atoms

of

isotopes?

aluminium A

energy

B

carbon

C

chemot herapy

D

radiot herapy

and

uorine:

generation

19

27

Al

dating

and

F

13

9

Draw

shell

diagrams

aluminium

b

A

naturally

atom

occurring

21

X

15%

i)

ii)

element

str ucture

of

atom.

X

an

(4

consists

of

marks)

85%

X.

can

you

Determine

What

is

Explain

–

deduce

a

relative

element

atomic

mass

of

X.

radioactive

occurring

isotope?

marks)

naturally

(2

marks)

(2

marks)

how:

carbon-14

and

naturally

(2

t he

uranium-235

–

about

X?

occurring

c

t he

uorine

10

What

element

ii)

show

a

22

and

10

i)

to

and

animal

is

is

used

used

to

remains.

to

generate

determine

electricity

t he

age

of

(5

Total

plant

marks)

15

marks

45

The

A4

periodic

table

and

periodicity

Elements

are

arranged

in

the

periodic

table

in

increasing

Objectives

By

the

be

able

●

end

of

this

topic

you

will

order

of

atomic

number.

The

arrangement

of

the

to:

describe

the

historical

development

of

the

elements

in

wealth

information

of

specific

rows

and

about

columns

the

provides

properties

of

a

elements

periodic

in

the

same

group

and

in

the

same

period

of

the

table

●

explain

how

arranged

in

elements

the

periodic

are

●

identify

metals,

explain

in

the

is

non-metals

the

periodic

difference

and

an

●

give

and

the

elements

give

the

elements

explain

in

in

in

the

same

the

the

in

same

to

a

based

periodic

group

Ever yone

the

labs

of

the

periodic

predict

the

chemical

properties

of

on

its

location

in

the

table.

of

elements

in

the

table

a

familiar

one

on

wit h

t he

t he

wall.

period ic

The

table

periodic

of

table

elements

is

a

as

most

chemistr y

classication

of

all

t he

elements and it is incredibly impor tant to chemists. It shows t he symbol, full

period

down

is

have

of

group

name,

t he

mass

number

elements

and

t heir

into

and

atomic

columns

and

number

rows

of

based

each

on

element

t he

and

str ucture

of

it

organises

t heir

atoms

proper ties.

period.

arranged

and

in

in

t he

periodic

order

chemically

wit h

similar

of

table

show

increasing

similar

proper ties

to

each

recur

period icity.

atomic

ot her

number,

occur

per iodically

When

all

elements

at

regular

t hroughout

t he

t hat

elements

are

inter vals,

t he

are

physically

i.e.

t hose

series.

fact

Historical Periodicity

elements

of

of

properties

change

along

Key

ability

Arrangement

Elements

!

values

table

the

conguration

how

elements

and

main

between

conguration

similarities

electronic

●

the

periods

similarities

electronic

●

the

element

A4.1 groups

of

table

metalloids

●

One

modern

table periodic

table.

is

with

the

recurrence

similar

development

of

the

periodic

table

of

physical

and

Early in t he 19t h centur y, scientists star ted to tr y to classify elements based on

chemical

properties

at

regular

t he similarities between t hem. Four scientists made impor tant contributions intervals

in

the

periodic

table.

to

t he

development

Newlands,

Johann

In

Dmitri

of

t he

modern

Mendeleev

and

periodic

Henr y

table:

Johann

Döbereiner,

John

Moseley.

Döbereiner

1829,

Johann

Döbereiner

noted

that

certain

groups

of

three

elements

possessed similar chemical and physical properties, e.g. he found that lithium,

sodium

the

and

three

potassium

elements

in

were

a

all

group

soft,

were

reactive

metals.

arranged

in

He

order

also

of

observed

increasing

that

if

relative

atomic mass, then the relative atomic mass of the middle element was close to

the average of the other two elements. He called these groups



T able

4.1.1

Elements

and

Döbereiner’s

their

relative

triads

of

atomic

elements

masses

lithium

sodium

potassium

7.0

23.0

39.0

calcium

strontium

barium

40.0

88.0

137.0

chlorine

bromine

iodine

35.5

80.0

127.0

Average

23.0

88.5

81.25

46

triads

relative

atomic

mass

The

periodic

John

In

1865,

atomic

John

periodicity

mass

had

and

ever y

arranging

t he

sodium

similar

Newlands

t hat

recurred

Arrangement

of

elements

in

the

periodic

table

put

for ward

discovered

discovered

eighth

t he

t hat

element.

elements

was

Be

Figure

Dmitri

been

in

his

at

of

time

similar

For

Octaves.

in

order

element

and

of

and

arranged

order

wit h

atomic

lit hium

of

physical

star ting

relative

bot h

He

increasing

chemical

example,

increasing

eight h

L aw

t he

and

t he

56

relative

proper ties

lit hium

mass,

he

sodium

and

found

showed

proper ties.

Li



and

Newlands

elements

t hat

table

B

4.1.1

C

N

Newlands’

O

F

octaves

of

Na

Mg

Al

Si

P

S

Cl

elements

Mendeleev

In 1869, Dmitri Mendeleev published his ‘ Periodic Classication of Elements ’

in

which

he

elements

arranged

with

elements

similar

in

chemical

increasing

and

relative

physical

atomic

properties

mass

and

together

in

placed

vertical

columns. His table was widely accepted at the time for two reasons:

●

he

lef t

been

●

he

gaps

switched

families.

before

group

as

his

For

In

1914,

of

wit h

suggested

to

placed

and

better

127 ,

so

bromine,

by

elements

relative

classify

tellurium,

mass

was

able

t he

had

all

of

atomic

t hem

relative

t hat

to

predict

proper ties

Mendeleev

periodic

is

not

yet

into

atomic

iodine

which

fell

mass

chemical

mass

in

128,

t he

showed

same

similar

t he

of

credited

proper ties

gallium,

wit h

being

of

t he

which

t he

missing

was

creator

not

of

t he

table.

rearranged

instead

similar

of

t heir

chemical

periodic

periodic

atomic

in

non-met als .

t he

corresponding

table

number.

t he

elements

relative

in

atomic

proper ties

all

t he

table

masses.

fell

in

t he

In

based

t his

same

on

new

t heir

order,

groups.

table

consists

A

copy

of

of

103

t he

elements

periodic

arranged

table

can

in

be

order

found

of

on

360.

Elements

r uns

he

predicted

Moseley

modern

modern

Unit

order

atomic

chlorine

1875.

t he

Henr y

increasing

page

t he

elements

Mendeleev

he

numbers

elements

The

t he

Moseley

atomic

The

t hat

proper ties.

until

version

relative

uorine,

e.g.

discovered

ignored

example,

table,

elements,

Henry

seemed

adjacent

iodine,

chemical

Using

it

discovered

occasionally

and

rst

when

4.4.

t he

moder n

The

Looking

from

above

met als

excluding

and

per iodic

proper ties

at

t he

per iodic

aluminium

t he

hydrogen

of

(H),

are

t able

(Al)

non-met als.

t able

can

met als

in

Figure

stepping

All

met als

t he

and

be

and

divided

4.1.2,

down

elements

t he

into

non-met als

to

to

t he

solid

ast atine

t he

elements

to

met als

are

lef t

t he

line

(At)

of

and

given

in

whic h

divides

t he

r ight

line,

of

t he

47

Arrangement

of

elements

in

the

periodic

table

The

line,

including

border

t he

inter mediate

include

(Sb),

hydrogen,

line

are

known

between

boron

(B),

tellur ium

(Te)

are

as

t hose

silicon

and

non-met als.

met alloid s .

of

(Si),

met als

Some

The

and

ger manium

polonium

periodic

of

table

t he

proper ties

periodicity

elements

of

non-met als.

(Ge),

and

The

ar senic

whic h

met alloids

are

met alloids

(As),

antimony

(Po).

metals

0

non-metals

1 H I

II

III

Li

Be

Na

Mg

IV

V

VI

He

VII

2

3

transition

4

5

B

C

N

O

F

Ne

Al

Si

P

S

Cl

Ar

metals

K

Ca

Sc

Ti

V

Cr

Mn

Fe

Co

Ni

Cu

Zn

Ga

Ge

As

Se

Br

Kr

Rb

Sr

Y

Zr

Nb

Mo

Tc

Ru

Rh

Pd

Ag

Cd

In

Sn

Sb

T e

I

Xe

Cs

Ba

La

Hf

T a

W

Re

Os

Ir

Pt

Au

Hg

Tl

Pb

Bi

Po

At

Rn

6

metals

Elements

on

metalloids;

metallic

Figure

4.1.2

Metals

and

non-metals

in

the

periodic

The

Did

?

The

you

periodic

most

table

textbooks

found

consists

in

of

periodic

T o

date,

elements

have

discovered

Elements

up

californium,

exist

to

synthesised

nuclear

cases

in

number

rest

few

been

table

rows

are

is

called

ver tical

Eight

t he

of

last

proper ties

including

have

laboratories

very

have

some

divided

into

ver tical

columns

called

groups

and

periods

columns

t hese

are

of

elements.

numbered

There

using

are

Roman

18

groups

numerals

in

t he

from

periodic

group

being

Group

0.

Elements

in

t he

same

group

I

show

to

VII,

similar

synthesised.

accelerators.

only

element

or

and

the

and

characteristics.

actually

atomic

naturally,

non-metals

however,

wit h been

are

Groups

table. 118

line

some

103

Groups elements.

this

have

table

horizontal

know?

near

characteristics

non-metallic



or

they

In

98,

and,

because

of

t his,

some

groups

have

been

assigned

special

names:

been ●

Group

I

–

alkali

●

Group

II

●

Group

VII

●

Group

0

metals

or

–

alkaline

ear t h

metals

some

atoms

of

the

–

halogens

synthesised.

Between

–

noble

Groups

transition

gases.

II

and

elements

or

III

t here

transition

are

ten

groups

of

elements

called

t he

metals.

Periods

Did

?

you

know?

Periods are horizontal rows of elements numbered using Arabic numerals from

1

Naming

newly

discovered

to

7 .

Moving

along

a

period,

the

properties

of

the

elements

gradually

change

or

from metals on the left-hand side to non-metals on the right-hand side.

synthesised

by

the

Pure

elements

International

and

(IUPAC).

Applied

Many

are

is

controlled

Union

of

Chemistry

named

Electronic

configuration

and

the

periodic

table

after

Looking at t he electronic conguration of t he elements in t he periodic table, famous

scientists

or

places,

immediately e.g.

einsteinium

and

between

48

we

can

see

similar ities

between

californium.

elements

in

t he

same

period.

elements

in

t he

same

group

and

The

periodic

Figure

in

t he

4.1.3

table

and

periodicity

summarises

periodic

t he

Arrangement

electronic

conguration

of

t he

rst

20

of

elements

in

the

periodic

table

elements

table.



Figure

4.1.3

The

electronic

Groups

conguration I

II

III

IV

V

VI

VII

of

the

rst

20

elements

0

in

H

the

periodic

table

He

1

(1)

(2)

sdoireP

Li

Be

B

C

N

O

F

Ne

(2,1)

(2,2)

(2,3)

(2,4)

(2,5)

(2,6)

(2,7)

(2,8)

Na

Mg

Al

Si

P

S

Cl

Ar

(2,8,1)

(2,8,2)

(2,8,3)

(2,8,4)

(2,8,5)

(2,8,6)

(2,8,7)

(2,8,8)

K

Ca

(2,8,8,1)

(2,8,8,2)

2

3

4

Groups

The

similarities

group

●

all

are

as

elements

t heir

(Ca)

t he

are

all

all

shell

electronic

of

conguration

in

(Na)

(S)

has

Group

has

two

2,

any

i.e.

group

six

0

of

elements

a

t his

shell

again

it.

all

as

same

in

t he

neon

element

is

same

shell

one

is

more

calcium

for

example,

maximum

electrons

in

hold.

electron

(Li)

for

VI

t he

eight

can

in

valence

electrons

shell,

has

of

number,

Group

which

lit hium

and

valence

in

(Ne)

t his

has

example,

1

electrons

group

electron

number

hold,

of

number

(Mg)

two

t he

and

outermost

maximum

For

number

t he

have

same

electrons

shell

can

t he

each

above

t he

full

in

same

have

magnesium

t hey

is

valence

have

t he

t hey

(Be),

and

electrons

group,

t hree

have

shell,

electrons

once

directly

has

group

ber yllium

same

electrons

down

element

same

electron

valence

sulfur

number

Moving

sodium

t he

t he

of

(He)

number

t he

example,

in

elements

helium

t he

for

number

example,

●

in

outermost

electrons,

●

in

follows:

has

two

shell

t han

shells

and

shells.

Periods

The

similarities

period

●

all

are

as

elements

same

electrons

t he

calcium

Moving

in

of

(Ca)

and

and

all

conguration

period

any

t he

number

is

of

elements

in

t he

same

same

period,

the

t he

number

of

each

(P)

●

the

number

of

shells,

element

For

ve

of

an

i.e.

electrons

magnesium

t hey

all

t he

have

electrons

has

electron

one

example,

valence

for

and

more

silicon

in

t he

(Mg)

t heir

and

valence

can

t he

shells

shells

t hat

it

is

in

Period

valence

has

4.

electron

four

valence

electrons.

be

same

is

of

example,

(Si)

configuration

atom

is

number

number,

remembering

electrons

occupied

and

period

contain

it.

has

number,

valence

period

t he

electronic

period

●

as

t hat

before

conguration

t he

valence

(Na),

3

shells

directly

t heir

sodium

same

electron

t he

four

have

example,

in

phosphor us

electronic

number

for

occupied

has

Determining

The

electronic

same

are

shell

element

electrons

t he

electrons,

along

t he

t he

shell,

(Al)

number

contain

t han

in

electron

aluminium

●

in

follows:

of

determined

atoms

from

t he

group

t hat:

as

the

t he

same

group

as

the

number

period

number.

49

Arrangement

of

elements

in

the

periodic

table

The

For

Exam

✔

example,

periodic

tip

electrons

Correctly

representing

electronic

the

configuration

str ucture

of

if

a

elements

is

extremely

is

used

to

reactivity

of

in

determine

of

bonding

when

it

an

an

atom

atom

forms

a

will

the

be

know

type

can

involved

t hat

sesaercni

increases

s a

s e

F

s e s a e r c in

e r tu

e r tu a n

cillatem

ic ll ta e m

Fr

nature

increases

cillatem-non

erutan

e r c

erutan

sesaercni

nature

in

metallic

reactive

its

a

is

in

Group

phosphor us

electron

is

number

electronic

electronic

t hat

shells.

V

and

atom

Period

has

Therefore,

3

ve

t he

of

t he

valence

electronic

(2,8,5).

and

period

conguration

conguration

calcium

you

Unit

t he

3.2

are

be

(Fr)

is

the

most

in

learnt

arrangement

number

number

of

an

element

is

is

in

Group

of

II

a

known.

calcium

For

can

example,

and

Period

atom

4

of

is

if

t he

(2,8,8,2),

periodic

of

of

in

proper ties

in

t hat

trends

t he

summarised

down

a

a

t he

are

same

t he

be

you

you

table.

as

in

t he

t hey

way

t hat

elements

directly

group

table

chemical

electrons

such

of

periodic

electrons

valence

arranged

These

the

and

properties

atoms

have.

t here

in

a

of

t he

The

are

related

to

in

an

element,

trends

in

same

in

in

t he

group

electronic

t he

element

elements

par ticular

elements

of

or

depend

par ticular,

t he

periodic

physical

in

a

and

par ticular

congurations

period.

These

of

trends

follows.

●

Moving

●

Moving down a group, the non-metallic nature of the elements

●

Moving

along

a

period,

t he

metallic

●

Moving

along

a

period,

t he

non-metallic

group,

t he

metallic

nature

of

nature

t he

of

elements

t he

nature

increases

elements

of

t he

decreases

decreases

elements

increases

These

It

is

trends

are

impor tant

Their

Francium

if

t he

In

can

n

group

trends

elements

o

t he

General

period.

n

atom

t hat

compound.

chemical

a

occupied

phosphor us

determine

table

n

phosphor us

periodicity

the

and

t he

ic ll ta e m -

t hree

t hat

determine

and

atoms

on

non-metallic

can

table

important.

determined It

know

you

and

of

Alternatively, of

you

table,

periodic

atoms

all

shown

to

note

have

in

Figure

t hat

full

4.1.4.

elements

outer

in

electron

Group

shells

0

are

and,

chemically

because

of

unreactive.

t his,

t hey

have

a stable electronic conguration. Atoms of all ot her elements do not have full

metal

outer

electron

shells

and

are,

t herefore,

unstable.

In

order

to

become

stable,

t hey need to attain t he electronic conguration of a noble gas, i.e. a full outer Fluorine

reactive



Figure

4.1.4

(F)

is

the

most

non-metal

Trends

in

electron

the

shell.

They

can

do

t his

by

losing

or

gaining

valence

electrons.

periodic

The

willingness

of

an

atom

of

an

element

to

lose

or

gain

valence

electrons

is

table

a

strong

valence

shell

indication

electrons

when

t hey

of

its

and

metallic

or

non-metals

non-metallic

tend

to

gain

nature.

Metals

electrons

into

tend

t heir

to

lose

valence

react.

When atoms lose or gain valence electrons t hey form positively or negatively

Key

!

fact charged par ticles known as

which An

ion

is

an

electrically

atoms

or

formed

gains

when

gain

ions. They are said to have ionised. The ease wit h

valence

an

atom

how

reactive

t hey

electrons,

known

as

ease

of

ionisation ,

are.

loses

electrons.

In

●

general:

The

ease

group

wit h

and

t herefore,

along

●

The

a

a

increases

wit h

and

going

along

period.

will

units.

r ight

going

which

t herefore,

a

metal

from

atoms

to

lef t

down

lose

electrons

along

a

a

group

period.

and

increases

The

going

going

reactivity

from

right

down

of

to

a

metals,

lef t

period.

ease

group

which

going

metals,

You

50

or

charged

determines particle

lose

be

non-metal

from

lef t

increases

studying

t he

to

atoms

r ight

going

reasons

along

up

for

gain

a

a

electrons

period.

group

t his

in

and

more

increases

The

reactivity

going

detail

going

from

in

lef t

t he

of

to

next

up

non-

right

t hree

The

periodic

table

Summary

1

Name

three

What

a

3

is

the

Group

For

scientists

For

a

it

b

is

the

in

Give

How

A4.2

Group

in

in

of

ber yllium,

Trends

made

to

Period

I

the

of

3

the

of

metallic

along

a

contributions

elements

in

c

VII

periodic

table,

periodic

to

chemically

all

ver y

the

periodic

Group

state

but

give

the

similarities

table,

give

the

similarities

and

of

an

atom

of

potassium,

given

that

4.

and

is

nature

period

S

number

of

sulfur,

given

that

its

(2,8,6).

of

elements

change

when

moving

down

a

period?

in

Group

periodic

table

II

is

calcium,

of

the

periodic

composed

strontium,

of

t he

barium

table

following

and

Objectives

elements:

radium.

By

the

be

able

metals

which

display

ver y

similar

proper ties.

end

reactive

t hey

are

and

so

are

collectively

reactive,

t hey

are

known

never

as

found

alkaline

naturally

are

The

always

found

elements

in

in

nature

Group

II

combined

are

listed

wit h

in

ot her

Figure

t heir

symbols,

atomic

numbers

and

electron

this

topic

you

will

give

the

general

properties

of

are

II

elements

earth

in

give

the

chemical

properties

of

t heir

elements

4.2.1,

of

to:

These

They

II

elements

in

compare

the

reactivity

of

Group

toget her

II

wit h

table

and

●

compounds.

periodic

table?

Group

free

the

0

●

Because

of

the

Group

metals.

II

conguration.

arrangement

Period

number

magnesium,

are

Group

conguration.

the

conguration

the

following

Group

electronic

and

group

t he

II

important

●

elements

in

table.

electronic

electronic

the

and

Group

their

Trends

II

given

their

Group

does

group

in

in

electronic

6

who

periodic

b

elements

Give

the

name

elements

differences

5

of

II

differences

4

periodicity

questions

development

2

and

elements

with

oxygen,

water

arrangements.

and

●

beryllium

dilute

predict

unknown

Be

hydrochloric

the

properties

elements

in

acid

of

Group

II

4

based

(2,2)

●

on

explain

group

why

trends

elements

in

magnesium

Group

II

show

similar

chemical

Mg 12

properties (2,8,2)

●

calcium

explain

Group

Ca

going

20

why

II

the

reactivity

elements

down

the

of

increases

group.

(2,8,8,2)

strontium

Sr 38

(2,8,18,8,2)

barium

Ba 56

(2,8,18,18,8,2)

radium

Ra 88

(2,8,18,32,18,8,2)



Figure

4.2.1

Group

II

elements

and

their

electronic

congurations

51

Trends

in

Group

II

of

the

periodic

table

The

General

Group

II

They

are

fairly

●

They

are

shiny,

t hey

layer

A

Key

cation

frmed

elements

●

as

!

properties

react

on

t he

have

sof t

of

t he

Group

following

table

and

periodicity

elements

general

proper ties

in

common.

metals.

silver y-white

wit h

II

periodic

t he

surface

when

oxygen

of

t he

in

freshly

t he

air.

cut,

This

but

turn

reaction

dull

forms

ver y

a

quickly

dull

oxide

metal.

fact

is

a

when

positively

a

metal

charged

atom

●

They

●

Their

have

atoms

fairly

have

high

●

Their

atoms

lose

melting

points

and

boiling

points.

ion

two

valence

electrons.

loses

t heir

valence

electrons

readily

to

form

metal

cations

electrons. 2

wit h

a

Going

●

it

charge

down

becomes

Chemical

Group

II

of

t he

2,

e.g.

group,

easier

for

t he

have

They

react

wit h

oxygen

●

They

react

wit h

water

●

They

react

wit h

dilute

chlorides

The

ease

(see

with

hydrochloric

as

the

Unit

reactivity

is,

of

the

and

of

to

t he

lose

Group

form

form

and

the

metal.

metal

two

5.2).

radii)

valence

increase

and

electrons.

elements

acid

proper ties

(see

to

Unit

and

form

in

common.

8.2).

hydrogen

salts

known

gas.

as

metal

gas.

react

for

rank

Unit

(atomic

hydroxides

different

we

(see

oxides

hydrogen

If

t heir

II

basic

metals

Ba

atoms

chemical

hydrochloric

however,

2

Ca

following

to

to

8.4)

which

acid

of

t he

●

,

radii

atoms

reactivity

elements

Mg

t he

2

with

the

the

oxygen,

different

metals

water

metals

from

the

and

and

most

is

dilute

known

reactive

to

the least reactive, based on how fast or how vigorously they react, the reactivity

increases going

reactive

Comparing

Your

●

teacher

the

may

observation,

Y ou

will

dilute

be

reactivity

use

this

recording

supplied

hydrochloric

with

acid

of

magnesium

activity

and

test

and

and

to

down the group. Ber yllium, at the top of the group, is the

radium,

and

at

the

bottom

of

the

group,

is

the

most

least

reactive.

calcium

assess:

reporting.

tubes,

strips

distilled

of

freshly

cleaned

magnesium

two

tubes.

ribbon,

pieces

of

freshly

cleaned

calcium,

water.

Method

3

1

Pour

tube

2 cm

and

of

a

dilute

piece

of

hydrochloric

calcium

to

acid

the

into

each

second

of

tube.

test

Compare

the

Add

a

strength

piece

of

of

magnesium

effervescence

ribbon

occurring

in

to

the

the

rst

two

tubes.

3

2

Pour

a

Y ou

3

2 cm

piece

of

might

Based

on

consider

4

If

you

more

5

If

you

more

52

of

distilled

calcium

need

the

is

to

leave

or

less

barium

vigorous

or

the

to

each

of

for

vigorous

dilute

two

a

while

or

hydrochloric

than

with

than

with

tubes.

the

and

Add

observe

that

a

strength

you

piece

of

them

of

magnesium

effervescence

ribbon

occurring

in

to

the

the

rst

two

tube

and

tubes.

periodically.

observed

in

steps

1

and

2,

which

metal

would

you

calcium?

acid

and

distilled

water,

would

you

expect

the

effervescence

to

be

magnesium?

hydrochloric

vigorous

test

Compare

effervescence

magnesium

dilute

of

tube.

tubes

strength

to

less

into

second

reactive,

beryllium

vigorous

added

water

the

relative

more

added

to

acid

and

calcium?

distilled

water,

would

you

expect

the

effervescence

to

be

The

A

periodic

compar ison

wit h

oxygen,

Examples

are

of

given.

and

a

table

and

in

(aq)

of

t he

a

You

periodicity

t he

water

dilute

c hemical

indicates

an

of

magnesium,

hydroc hlor ic

equations

equations

have

Trends

reactivity

and

c hemical

Similar

bar ium.

solid

and

can

already

be

aqueous

t he

wr itten

come

equation.

for

In

across

t hese

solution,

acid

calcium

is

given

reactions

for

(g)

t he

and

equations,

i.e.

a

to

solution

II

of

the

periodic

table

4.2.1.

magnesium

wit h

indicate

(l)

Group

bar ium

Table

wit h

reactions

(s)

and

in

in

indicates

where

calcium

a

gas

a

and

liquid

water

is

t he

solvent.



T able

4.2.1

Reactions

Reaction

Oxygen

(or

air)

of

magnesium,

calcium

Magnesium

(Mg)

Reacts

to

slowly

exposure

flame,

to

air.

producing

barium

Calcium

form

If

and

a

coating

ignited,

white,

of

magnesium

magnesium

solid

burns

magnesium

oxide

with

a

(MgO)

on

blinding

Reacts

white

oxide.

oxygen

(CaO)



magnesium

O



(g)

of

on

Very

clean

producing

magnesium

form

calcium

a

Reacts

oxide

to

form

air.

burns

a

(Ba)

very

oxide

(BaO)

to

If

air.

readily

coating

of

on

to

barium

exposure

ignited,

a

brick

red

flame,

burns

with

an

barium

apple

green

2MgO(s)

2

producing

reacts

magnesium

to

calcium

exposure

ignited,

calcium

Water

Barium

oxide with

2Mg(s)

readily

coating

if magnesium

(Ca)

very

hydroxide

slowly

with

)

(Mg(OH)

cold

and

Reacts

water,

hydrogen

gas

(H

2

).

cold

white,

solid

flame,

oxide.

solid

vigorously

water,

with

producing

barium

Reacts

producing

with

very

cold

white,

oxide.

vigorously

water,

2

calcium

hydroxide

producing

barium

magnesium magnesium

water





hydrogen

(Ca(OH)

)

and

hydrogen

hydroxide

(Ba(OH)

2

)

and

2

hydroxide gas

(H

).

hydrogen

gas

(H

2

Mg(s)

Dilute

hydrochloric

acid

Reacts

O(l)

2H



Mg(OH)

2

vigorously

to

(aq)

produce

magnesium

chloride

H



2

).

2

(g)

2

(MgCl

)

and

Reacts

very

vigorously

to

Reacts

violently

to

2

hydrogen

gas

(H

).

produce

calcium

chloride

produce

barium

chloride

2

(CaCl

)

and

hydrogen

gas

(BaCl

2

hydrochloric magnesium





hydrogen

(H

).

(H

2

acid

Mg(s)

From

t he

trends

in

t he

reactivity

MgCl

(aq)

t he

Group

II

metals,

H



2

of

t han

vigorously

barium,

calcium,

but

and

less

t han

t he

magnesium,

reactivity

vigorous

t han

of

radium

gas

).

we

(g)

2

can

predict

t he

Did

? less

hydrogen

2

reactivity of ber yllium, strontium and radium. We would expect ber yllium to

react

and

chloride

2HCl(aq)



)

2

magnesium

to

strontium

react

to

even

be

more

more

you

know?

vigorously

vigorous

t han

Group

II

metals

fireworks

barium.

air

or

oxygen

flames.

brick

and

red

Group

e.g.

a

a

II

bright

metals

strontium

chloride

they

red

is

used

burn

to

light

produces

a

Compounds

may

also

carbonate

colour

produces

an

in

in

coloured

used

white

calcium

colour.

crimson

often

producing

Magnesium

produce

effect

are

because

and

be

of

used,

produces

barium

apple

green

colour.



Figure

4.2.2

Compounds

of

Group

II

elements

are

often

used

as

reworks

53

Trends

in

Group

II

of

the

periodic

table

The

An

explanation

of

the

trends

in

periodic

Group

table

and

periodicity

II

Elements in Group II all have ver y similar c hemical proper ties because t heir

atoms

all

have

ionise

by

losing

ions,

i.e.

Since

t hey

Group

t he

●

t he

t he

number

t he

t he

by

atomic

The

less

radii

easier

for

full

to

t he

t herefore,

get

of

combination

attracted

of

t he

of

atoms

atoms,

t herefore,

t he

to

positive

of

t he

extra

shell

Moving

As

lled

fur t her

a

react

now

electrons

to

full.

lose,

moving

down

t hey

c harged

t he

i.e.

g roup,

electron

away

shells,

from

t he

more

shielded

from

t he

positive

nucleus

factors

nucleus

t heir

down

t he

reactive

means

going

valence

t he

t he

t he

electrons.

valence

g roup

The

electrons

and

ease

of

it

are

becomes

ionisation,

g roup.

smallest,

Group

t hat

down

ionise

II

t he

element.

least

easily.

Radium

Ber yllium

atoms,

most

being

is,

t he

reactive Group

element.

The

electronic

Figure

str ucture

of

t he

 rst

t hree

elements

in

Group

II

is

given

4.2.3.

×

×

×

××

××

××

×

Ca

××

××

××

××

××

Mg

×

××

××

×

Be

××

××



Figure

4.2.3

Summary

1

What

2

a

is

the

Does

b

3

Give

Compare

diagrams

of

the

rst

three

elements

in

Group

II

questions

reactivity

down

the

Shell

collective

the

going

54

2,

down

result:

largest, ionise t he most easily. Radium is, t herefore, t he

II

is

however,

increases.

become

t hey

positively

shells.

two

lose

electron

increases.

when

for m

nucleus

become

going

being

least

to

and

number

shells

due

metals,

proper ties,

elements

electrons

t hese

outer

same

electron

positive

increases

Ber yllium

t he

electron

t he

t heir

t he

Being

electrons

c hemical

bigger

electrons

extra

t his,

have

valence

pull

electrons.

valence

similar

occupied

t he

valence

t he

doing

reactivity

t herefore,

●

ver y

of

attractive

In

two

elements

have

II

valence

t heir

c ations.

all

all

two

the

reason

the

name

of

the

for

the

elements

elements

in

in

Group

Group

II

group?

for

reactivity

your

of

answer

beryllium

to

a

and

above.

calcium.

II?

increase

or

decrease

in

The

periodic

A4.3

Group

table

and

Trends

VII

in

t he

periodicity

in

Trends

Group

periodic

table

VII

is

of

the

composed

periodic

of

t he

table

following

in

Group

VII

of

the

periodic

table

Objectives

elements:

By

the

be

able

end

of

this

topic

you

will

to:

uorine, chlorine, bromine, iodine and astatine. These elements are all non-

●

give

the

general

properties

of

metals. They display similar proper ties and are chemically ver y reactive. They

Group

are

collectively

known

as

t he

halogens.

The

elements

in

Group

VII

are

Figure

4.3.1,

toget her

wit h

t heir

symbols,

atomic

numbers

and

elements

listed

●

in

VII

give

the

chemical

properties

of

electron

Group

VII

elements

arrangements.

●

explain

Group

uorine

why

VII

chemical

F

elements

show

in

similar

properties

9

●

(2,7)

explain

why

elements

in

the

reactivity

Group

VII

of

the

increases

chlorine

going

up

the

group

Cl 17

●

describe

displacement

(2,8,7)

reactions

bromine

Group

Br 35

●

(2,8,18,7)

of

elements

in

VII

explain

the

term

oxidising

strength

●

predict

the

properties

of

iodine

unknown

elements

in

Group

VII

I 53

based

on

group

trends.

(2,8,18,18,7)

astatine

At 85

(2,8,18,32,18,7)



Figure

General

Group

VII

4.3.1

Group

properties

elements

●

They

are

●

They

exist

●

They

are

have

poisonous

as

VII

of

t he

elements

Group

following

and

their

VII

electronic

congurations

elements

general

proper ties

common.

elements.

non-polar,

diatomic

molecules,

e.g.

F

,

Cl

2

generally

in

soluble

in

non-polar

solvents

,

Br

2

and

and

I

2

2

slightly

soluble

in

water.

●

They

have

low

●

Their

●

Their atoms readily accept an electron into their valence shells to form non-

atoms

melting

have

points

seven

and

valence

boiling

points.

!

ion

●

They

share

an

electron

1, e.g. F

readily

fact

electrons. An

metal anions with a charge of

Key

with

, Cl

other

, Br

and I

non-metal

(see Unit 5.2).

atoms

(see

Unit

anion

is

formed

gains

a

negatively

when

a

charged

non-metal

atom

electrons.

5.4).

Group VII elements have different colours and states at room temperature, as

summarised



T able

4.3.1

in

Table

Some

4.3.1.

physical

at

room

properties

of

temperature

the

rst

four

Element

State

fluorine

gas

pale

chlorine

gas

yellow

bromine

liquid

red-brown

elements

solid

Group

VII

Colour

yellow

green

–

temperature

iodine

in

grey-black

heated

–

the

liquid

forming

the

forming

solid

a

evaporates

an

orange

sublimes

purple

readily

at

room

vapour

readily

when

vapour

55

Trends

in

Group

VII

of

the

periodic

table

The

Chemical

Group

VII

reactivity

elements

react

of

Group

wit h

most

VII

metals

periodic

table

and

periodicity

elements

to

form

ionic

compounds

(Unit

5.2) and t hey react wit h most ot her non-metals to form covalent compounds

(Unit

5.4).

Examples

1

2

Chlorine

reacts

Sodium



2Na(s)



Chlorine

reacts

Hydrogen

H

reactivity

Fluorine,

bottom

An

at

of

t he

Cl

of

to

form

sodium

sodium

(g)

chloride.

chloride

2NaCl(s)

2

wit h

t he

top

hydrogen

gas

to

chlorine

Cl



t he

sodium

chlorine



(g) 2

The

wit h

form

hydrogen

hydrogen

(g)

chloride

gas.

chloride

2HCl(g)

2

Group

of

group,

explanation

t he

is

t he

of

VII

elements

group,

least

the

is

t he

increases

most

going

reactive

and

up

t he

group.

astatine,

at

t he

reactive.

trends

in

Group

VII

Elements in Group VII all have ver y similar chemical proper ties because t heir

atoms

all

have

seven

valence

electrons.

Being

non-metals,

when

t hey

react

t hey ionise by gaining one valence electron and t hey form negatively charged

ions,

Since

all

i.e.

all

have

t he

anions.

t he

●

reactivity

t he

electron

of

of

pull

valence

t he

inner

have

t he

elements

atoms

get

t herefore,

of

t he

of

outer

same

electron

number

proper ties.

increases.

As

smaller

t he

positive

of

is

electrons

However,

Moving

a

shell

up

now

to

gain,

moving

t he

full.

group,

i.e.

up

t he

1,

t hey

Group

VII

number

of

result:

due

to

valence

t he

decrease

electrons

in

become

number

closer

of

to

lled

t he

nucleus

become

electron

combination

t heir

decreases.

electrons

full

t his,

chemical

shells

t he

t he

The

t he

shells,

attractive

●

similar

electron

radii

doing

elements

ver y

occupied

In

less

shielded

from

t he

positive

nucleus

by

shells.

t hese

two

factors

means

t hat

t he

valence

electrons

are

more attracted to t he positive nucleus going up t he group, as are any electrons

being gained by t he atoms. It becomes easier for t he atoms to gain an electron

Key

!

fact into t heir valence shell going up t he group. The ease of ionisation, t herefore,

Electronegativity

of

how

strongly

an

is

a

measure

atom

increases

going

up

Fluorine

atoms,

t he

group.

attracts

being

t he

smallest,

ionise

t he

most

easily.

Fluorine

is,

electrons.

t herefore,

t he

Group

F

Cl

t he

largest,

VII

most

ionise

least

Group

easily.

VII

element.

Astatine

is,

Astatine

t herefore,

atoms,

t he

least

being

reactive

element.

The

tendency

The

electronegativity

Fluorine

reactive

t he

is

for

t he

atoms

of

most

to

attract

t he

electrons

atoms,

is

t herefore,

electronegative

known

as

increases

element

and

electronegativity .

going

up

astatine

Group

is

t he

VII.

least

electronegative.

The 

Figure

two

56

4.3.2

elements

Shell

in

diagrams

Group

VII

of

the

electronic

rst

Figure

4.3.2.

str ucture

of

t he

rst

two

elements

in

Group

VII

is

given

in

The

periodic

The

melting

explained

t he

t he

The

are

and

atoms,

lowest.

points

relative

t he

t hat

Astatine,

which

t he

Trends

means

t he

t he

t he

Group

t he

as

The

and

atoms,

large

melting

elements

forces

point

boiling

has

t he

astatine

and

can

Fluorine,

intermolecular

point

t he

VII

molecules.

molecules.

largest

between

t hat

t he

of

known

melting

having

forces

of

size

smallest

molecules,

means

intermolecular

t he

boiling

at

has

small

which

strongest,

periodicity

looking

t hese

weakest,

and

points

by

smallest

between

are

table

of

largest

of

VII

of

the

periodic

table

be

having

are

t he

uorine

molecules.

molecules

boiling

Group

attraction

forces ,

point

also

in

point

are

of

t he

astatine

highest.

F

F

fluorine

(F

)

2

Cl

Cl

chlorine

(Cl

)

2

Br

Br

bromine

(Br

)

2

I

I

iodine

(I

)

2



Figure

4.3.3

Displacement

A

d isplacement

t he

place

of

Comparing

the

sizes

of

the

rst

four

halogen

molecules

reactions

reaction

anot her

occurs

element

in

a

when

an

element

compound.

A

in

more

its

free

reactive

state

takes

element

will

displace a less reactive element from a compound containing t he less reactive

element.

element

However,

from

a

a

less

reactive

element

will

not

displace

a

more

reactive

compound.

For example, if chlorine gas is bubbled into a solution of potassium bromide,

t he chlorine will displace t he bromine from t he potassium bromide forming

potassium

chloride

chlorine

Cl

(g) 2

However,

will

not

if

and

are

t he

all

and

potassium bromide



2KBr(aq)

bromine

determine

solution

of

a

colour.

from

a

t he



whet her

colour

a

of

t he

e.g.

different

is

a

is

iodide

Chlorine

brown

added

potassium

colourless,

and

is

chlorine

halogen

potassium

occurs

bromine:



displace

bromine

To

and

to

potassium

and

wit h

resulting

(KI)

are

halogen

a

chloride

reaction

a

solution

is

chloride

all

it

bromine

grey-black

is

(aq) 2

t he

occurred,

potassium

obser ved.

(KCl),

can

Br



solution,

has

or

colourless.

forms,

bromine

bromine

reaction

reaction

sodium



occurs:

no

displacement

potassium

to

no

chloride

mixed

chloride

2KCl(aq)

yellow-green,

solution

potassium

If

be

halide

potassium

a

identied

and

by

its

solutions

on

(KBr)

reaction

distinctive

iodine

depending

aqueous

solution

bromide

displacement

red-brown

precipitate

The

an

halide

will

t he

range

amount

produced.

57

Trends

in

Group

VII

of

the

periodic

table

The

Investigating

Your

teacher

may

observation,

●

Y ou

will

be

bromine,

displacement

use

this

recording

supplied

iodine,

with

activity

and

test

potassium

reactions

to

periodic

of

the

table

and

periodicity

halogens

assess:

reporting.

tubes

and

chloride,

aqueous

potassium

solutions

bromide

of

and

chlorine,

potassium

iodide.

Method

3

1

Pour

2 cm

3

of

potassium

potassium

iodide

solution

each

to

bromide

solution

tube

and

into

solution

another

shake.

into

test

a

test

tube.

tube

Carefully

Observe

any

colour

solution

into

a

and

2 cm

add

chlorine

changes.

3

2

Pour

2 cm

3

of

potassium

potassium

iodide

solution

each

to

chloride

solution

tube

and

into

another

shake.

test

test

tube.

tube

and

Carefully

Observe

any

colour

solution

into

a

2 cm

add

Pour

2 cm

bromine

potassium

potassium

bromide

solution

each

4

Record

5

Using

From

●

3

of

t he

to

your

your

results,

chlorine

and

in

a

the

and

another

test

Observe

elements

above

bromine

chloride

into

shake.

test

tube.

any

tube

and

Carefully

colour

2 cm

add

of

iodine

changes.

table.

place

activity

displaces

potassium

chloride

solution

tube

results

practical

Chlorine

of

changes.

3

3

of

we

can

from

in

see

increasing

order

of

reactivity.

t hat:

potassium

bromide

producing

bromine:



potassium bromide



2KBr(aq)

potassium

chloride

bromine



Br

(aq) 2

Cl

(aq) 2

2KCl(aq)



potassium

red-brown

bromide chlorine solution ●

Chlorine

displaces

iodine

from

potassium

iodide

producing

potassium

solution

chloride

and

chlorine



iodine:

potassium

iodide

potassium

chloride



iodine

I

(aq) 2

Cl

(aq)

2KI(aq)



2

2KCl(aq)

 brown

●

Bromine

bromide

solution

of

bromine

displaces

and

from

potassium

iodide

producing

potassium

iodine:

and

bromine potassium

iodine



potassium

iodide

potassium bromide



2KBr(aq)



iodine

chloride

I

(aq) 2

(aq)

Br 2



Figure

added

4.3.4

to

Chlorine

potassium

solution

bromide

2KI(aq)



brown

is

solution ●

No

displacement

reaction

occurs

between

bromine

and

potassium

chloride.

●

✔

Exam

No

From

If

a

question

displacement

reactions

occur

wit h

iodine.

tip

asks

you

to

t he

trends

in

t he

displacement

reactions

involving

chlorine,

bromine

describe

and iodine, we can predict t hat uorine, at t he top of Group VII, will displace a

chemical

reaction,

you

must

all t he ot her halogens from compounds containing t hem. However, astatine, provide

all

observations,

including

at any

colour

t he

t heir

58

bottom

of

Group

changes.

compounds.

VII,

will

not

displace

any

of

t he

ot her

halogens

from

The

periodic

table

and

Displacement

Displacement

oxidising

a

substance.

moving

of

how

The

up

increases

reactions

of

can

t he

easily

oxidising

t he

g roup

moving

Trends

reactions

strengt hs

measure

periodicity

up

be

one

oxidising

explained

Group

VII

of

t he

by

t he

takes

to

t he

Oxid ising

electrons

elements

ability

ionise

Group

VII

of

the

periodic

table

strength

consider ing

elements.

substance

strengt h

because

t he

and

in

in

by

from

Group

relative

strength

VII

gaining

is

anot her

increases

an

electron

g roup.

Key

!

An

fact

oxidising

the

oxidation

agent

of

brings

another

about

reactant

Comparing t he relative oxidising strengt hs of chlorine, bromine and iodine, by

we

see

t hat

chlorine

has

t he

strongest

oxidising

strengt h

and

iodine

has

causing

reactant

weakest.

We

say

t hat

chlorine

is

t he

strongest

oxid ising

agent

and

iodine

to

atom

lose

or

ion

electrons.

in

In

that

the

is process,

t he

an

t he

the

oxidising

agent

gains

weakest. electrons.

A

stronger

agent.

oxidising

This

is

why

agent

will

chlorine

accept

displaces

electrons

t he

from

bromide

a

ions

weaker

in

t he

oxidising

potassium

bromide. Each chlorine atom in a chlorine molecule accepts an electron from

a

bromide

(Cl

ion)

t hen

ion

and

pair

to

ion).

(Br

each

form

chlorine

a

As

a

bromide

bromine

result,

ion

each

forms

a

chlorine

bromine

(aq)



2

Chlorine

is

said

displacement

iodide.

Again,

You

bromide

chloride

ion

ion

from

bromine

will be a

Group

will

What

is

Group

2

chloride

bromine

ion

atoms

bromine

2Cl

have

a

oxid ised

bot h

lot

more

in

we

t he

can

(aq)

t he

chlorine

about

molecule



(aq) 2

potassium

and

bromine

oxidation

displacement

predict

Br

t hat

bromide.

oxidised

reactions

reactions

uorine,

at

in

In

t he

t he

Unit

involving

t he

top

of

ot her

potassium

9.

chlorine,

Group

VII,

oxidising agent t han chlorine and astatine, at t he bottom of

a

weaker

oxidising

agent

t han

iodine.

questions

similar

in

the

electronic

conguration

of

the

elements

in

VII?

a

Does

b

Give

the

going

What

4

List

5

a

What

b

Give

is

the

up

the

3

to

(aq)

trends

be

Summary

1

to

iodine,

stronger

VII,

2Br

learn

t he

and

Two

a



reactions,

will

atom.

forms

molecule:

 molecule

Cl

atom

reactivity

the

by

elements

would

a

for

the

in

you

potassium

the

elements

in

Group

VII

increase

or

decrease

group?

reason

meant

of

term

Group

for

answer

VII

if

in

above.

strength’?

order

an

a

to

‘oxidising

observe

iodide

reason

your

of

increasing

aqueous

solution

oxidising

of

strength.

chlorine

is

added

solution?

your

answer

to

a

above.

59

Trends

in

Period

3

of

the

periodic

table

The

A4.4

Objectives

By

the

be

able

end

of

this

topic

you

Trends

give

Period

the

properties

of

3

how

the

properties

elements

change

along

Period

explain

the

why

the

to

along

Period

Did

Silicon

is

abundant

oxygen,

the

is

a

in

making

the

on

up

It

is

which

are

from

silicon

a

Physical

Earth

of

led

found

The

following

elements:

sulfur,

chemical

proper ties

of

t hese

chlorine

elements

devices

4.4.1

Moving

from

lef t

to

right,

t he

metallic

change

nature

in

decreases

and

metals,

t he

t hose

non-metallic

to

or

t he

right

are

nature

increases.

non-metals

and

The

elements

silicon,

in

properties

of

metals

and

non-metals

have

t he

following

solid

at

room

physical

are

●

They

have

high

melting

●

They

have

high

densities.

●

They

are

good

●

They

are

shiny

●

They

are

malleable,

proper ties

temperature,

points

and

except

boiling

in

common.

mercur y,

which

is

a

liquid.

points.

Trends

conductors

of

heat

and

electricity.

in

appearance.

i.e.

t hey

i.e.

can

be

t hey

can

drawn

be

out

hammered

into

into

different

shapes,

and

wires.

its

●

They

are

sonorous,

chip

t hey

make

a

ringing

sound

when

hit.

have

t he

following

physical

proper ties

in

common.

●

its

They

are

bromine

usually

is

a

gases

at

room

temperature,

however,

some

are

solid

and

liquid.

debut

forms

●

They

have

low

melting

●

They

have

low

densities.

points

and

●

They

are

●

In

t he

solid

state

t hey

are

dull

●

In

t he

solid

state

t hey

are

brittle.

●

In

t he

solid

state

t hey

make

boiling

points.

the

computer

not

in

i.e.

silicon

electronic

made

would

number

its

invention

exist

Period

poor

conductors

of

heat

and

electricity.

today.

summar y

of

t he

trends

of

a

t he

in

appearance.

dull

sound

elements

in

when

hit.

Period

3

is

given

in

Table

4.4.1.

3

Na

Mg

Al

Si

P

S

Cl

Ar

I

II

III

IV

V

VI

VII

0

11

12

13

14

15

16

17

18

(2,8,1)

(2,8,2)

(2,8,3)

(2,8,4)

(2,8,5)

(2,8,6)

(2,8,7)

(2,8,8)

loses

loses

loses

shares

configuration

Loses/gains/shares

1e

2e

3e

4e

gains

3e

gains

2e

gains

1e

none

electrons

at

25 °C

Electrical

conductivity

solid

solid

solid

conductor

conductor

conductor

solid

semi-

solid

solid

insulator

insulator

gas

insulator

gas

insulator

conductor

60

Metal/non-metal

metal

Ease

increasing

of

ionisation

t he

metalloid.

They

computer

without

Electronic

State

of

after

calculators

modern

and

period.

the

to

of

first

silicon

number

Atomic

and

●

A

Group

t he

semiconductor,

has

chips

of

technology

T able

of

phosphor us,

most

28%

pocket

The

foundation



silicon,

from

moving

manufacture

which

1961.

such

composed

know?

second

computers.

using

is

3.

element

crust.

devices

to

physical

semi-metal

Non-metals chips

table

aluminium,

properties

change

non-metal

you

property

in

periodic

t he

are

ductile,

use

The

along

lef t

Metals

a

table

3

elements

metal

Earth’ s

t he

elements

t he

middle,

?

periodic

moving

to

of

the

of

t he

●

of

periodicity

non-metals

describe

the

in

magnesium,

argon.

moving

●

3

and

metals

and

and

Period

table

will

to:

sodium,

●

in

periodic

metal

ease

of

ionisation

metal

metalloid

non-metal

increasing

non-metal

ease

of

ionisation

non-metal

non-metal

The

periodic

table

and

periodicity

Trends

(a)



(b)

Figure

An

As

4.4.1

you

Metals

along

learnt

to

it.

t he

As

a

t he

t he

radii

positive

to

3.

ease

and

one

electrons

has

more

of

its

of

the

periodic

table

around

or

to

elements

t heir

volcano

vent

and

(c)

chlorine

gas

3

atoms

tend

a

lose

or

gain

valence

non-metallic

gain

electrons.

decreases

non-metallic

nature.

Moving

because

nature

t heir

increases

increases.

valence

moving

electron

sulfur

metallic

t he

and

(b)

which

t heir

3

(c)

Period

non-metals

nature

However,

in

wit h

of

decreases

3

sparklers,

trends

t he

gain

Period

in

Period

electrons

from

and

one

lef t

in

t he

to

more

same

right

electron

along

proton

t han

t he

t he

shell,

period,

element

result:

number

electrons

4.1,

metallic

ability

has

the

electrons

t he

in

burning

indication

electrons

number

causing

●

3,

element

before

Unit

lose

lose

element

of

strong

to

t heir

shell

each

in

a

Period

because

Each

is

tend

ability

●

Magnesium

explanation

electrons

i.e.

(a)

in

of

to

of

positive

attraction

get

t he

protons

between

in

t he

t he

nuclei

positive

of

t he

atoms

nucleus

and

gets

t he

greater,

valence

stronger

atoms

protons

in

get

t he

smaller

nucleus,

due

to

pulling

t he

increasing

t he

outer

number

electrons

of

closer

to

t he

nucleus.

The

combination

more

attracted

harder

gain

for

t he

Since

t he

is

t he

Aluminium

Figures

reactive.

ionisation

t he

protons

i.e.

17 .

Argon

has

a

is

t he

is

a

t heir

atoms

its

t he

ionise

stable

is

of

t hree

t he

by

and

electronic

t he

is

found

i.e.

it

two

and

easily

gaining

t he

is

least

t he

to

t he

contains

t he

of

t he

and

its

least

and

nucleus,

and

t he

has

t he

is

i.e.

t he

13

most

reactive.

t he

atoms

two

least

of

period.

nucleus.

ease

chlorine

t hree

and

is

in

easily

t he

its

to

ot her

3.

ionisation

t herefore,

sulfur

smallest

and

more

reactive.

of

increases

has

15

protons,

Chlorine

reactive.

right

eight

conguration,

is

electrons,

easily

most

most

t hem

In

Period

in

are

becomes

for

along

protons

protons

t he

and

largest

t he

of

It

period.

along

ease

1 1

easier

t he

decreases

has

more

ionises

phosphor us,

is

t he

electrons

period.

and

along

increases

electrons,

least

Chlorine

ionises

full,

has

valence

t he

electrons

aluminium

atoms

t he

along

moving

elements

Sodium

non-metals

easily

t he

t hat

going

valence

and

Phosphor us

means

shell

losing

and

ionises

non-metal

shell

t he

4.4.3).

nucleus.

most

by

smallest

and

period.

in

of

factors

nucleus

valence

ionise

largest

4.4.2

of

t he

electron

lose

magnesium

Phosphor us

ionises

to

t heir

Aluminium

Non-metal

along

atoms

sodium,

Sodium

(see

into

two

positive

electronegativity

metal

metals

t hese

t he

atoms

electrons

words,

of

to

it

of

chlorine.

electrons.

does

not

However,

Because

ionise

and

it

of

is

its

valence

t his,

argon

chemically

unreactive.

61

Trends

in

Period

3

of

the

periodic

table

The

Silicon

of

sodium

Na

12p

found

reacts

usually

ionise.

magnesium

M



Group

IV

and

non-metallic

by

electronic

13p

in

and

usually

The

11p

is

metallic

sharing

str ucture

a

electrons

of

14p

is

metalloid

proper ties.

t he

wit h

elements

15p

It

because

has

ot her

in

periodic

four

table

it

has

3

a

valence

non-metal

Period

and

is

combination

electrons

atoms.

given

periodicity

in

It

does

Figure

16p

17p

18p

silicon

phosphorus

sulfur

chlorine

argon

Al

Si

P

S

Cl

Ar

4.4.2

Electronic

conguration

of

the

elements

in

Period

not

4.4.2.

aluminium

Figure

and

3

0.20

)mn(

0.18

suidar

0.16

0.14

cimotA

0.12

0.10

0.08

Na

Mg

Al

Si

P

S

Cl

Ar

Element



Figure

Summary

1

Chlorine

of

2

the

4

5

62

Trends

in

the

atomic

and

magnesium

periodic

table.

One

are

is

both

a

one

is

the

metal?

b

Which

one

is

the

non-metal?

does

3

Which

b

Give

is

the

a

Which

b

Give

Which

the

metallic

change

a

is

the

of

the

from

more

more

in

for

for

Period

3

Give

elements

in

Period

and

the

which

one

is

a

reasons

THREE

are

found

3

or

answer

for

your

reasons

non-metallic

or

answer

has

the

a

for

your

nature

of

above.

chlorine?

to

a

above.

greatest

Period

3

answer.

magnesium?

to

in

non-metal.

right?

sulfur

your

and

THREE

sodium

your

reactive,

reason

element

to

reactive,

reason

Give

nature

left

elements

metal

Which

How

radii

questions

a

Period

3

4.4.3

metallic

nature?

answer.

elements

in

The

periodic

Key

table

Scientists

●

Dmitri

●

t he

star ted

Period icity

The

The

elements

All

periodic

All

●

The

in

This

two

●

Group

dilute

●

The

of

●

II

down

The

The

of

t he

The

of

the

periodic

table

in

t he

being

early

t he

19t h

creator

centur y.

of

t he

rst

version

elements

inter vals

periodic

wit h

in

t he

table

similar

physical

periodic

are

and

table.

arranged

in

order

of

II

ver tical

group

is

t he

period

is

of

columns

called

groups

and

periods

same

t he

have

of

an

in

have

same

same

have

all

as

t he

as

t he

t he

same

t he

element

similar

number

group

are

valence

of

occupied

electron

number.

determined

t he

of

number.

number

period

par ticular,

ver y

same

number

proper ties

of

by

t he

valence

because

electrons.

t hey

all

have

have

of

similar

reactions

wit h

oxygen,

water

and

acid.

Group

to

t he

lose

II

of

elements,

t heir

Group

II

valence

elements

t heir

atoms

being

metals,

depends

on

t he

ability

electrons.

increases

to

lose

going

t heir

down

valence

t he

group

electrons

increases

group.

Group

reactivity

VII

have

ver y

similar

proper ties

because

t hey

all

have

electrons.

of

Group

atoms

of

VII

to

Group

ability

of

elements,

gain

VII

t heir

an

being

electron

elements

atoms

to

non-metals,

into

t heir

increases

gain

an

depends

valence

going

up

electron

on

t he

shell.

t he

group

increases

going

up

group.

elements

reactive

in

Group

element

containing

●

of

t heir

t he

modern

electrons,

ability

reactivity

because

●

3

electrons.

valence

ability

●

in

wit h

of

regular

proper ties

atoms

Elements

seven

t he

elements

t he

at

called

Group

reactivity

going

●

Period

1869.

consists

t he

of

reactivity

because

●

in

number.

hydrochloric

t heir

The

in

valence

credited

in

number

in

chemical

Elements

t he

number

arrangement

●

Trends

elements

recurrence

table

This

elements

shells.

in

rows

elements

electrons.

●

t he

atomic

horizontal

●

is

is

table

proper ties

increasing

●

classifying

Mendeleev

period ic

chemical

●

periodicity

concepts

●

of

and

t he

Displacement

will

less

reactions

strength

a

of

how

undergo

reactive

oxid ising

measure

VII

displace

of

of

t he

easily

a

a

less

d isplacement

reactive

reactions .

element

from

a

A

more

compound

element.

Group

VII

elements,

substance

elements

where

takes

depend

oxidising

electrons

on

t he

relative

strengt h

from

is

anot her

substance.

●

The

oxidising

strengt h

of

Group

VII

elements

increases

going

up

t he

group.

●

Going

along

elements

●

Going

●

The

to

decreases

along

elements

Period

from

lef t

because

Period

increases

3

3

from

because

electronegativity

of

to

t heir

lef t

ability

to

t heir

right,

right,

ability

elements

in

t he

to

lose

t he

to

metallic

nature

electrons

non-metallic

gain

Period

3

electrons

increases

of

t he

decreases.

nature

of

t he

increases.

going

from

lef t

right.

63

Practice

exam-style

Practice

questions

The

exam-style

periodic

table

and

periodicity

questions

N

Multiple-choice

questions

Na

1

Elements

in

t he

modern

periodic

table

are

arranged

Mg

Si

Cl

in

Ca

order

of

Br

A

chemical

B

atomic

C

mass

reactivity The

periodic

table

showing

the

position

of

some

elements

number

a

i)

Name

two

elements

which

occur

in

t he

same

number

period. D

relative

atomic

State

t he An

element

of

atomic

number

20

is

expected

to

in

Group

II

of

t he

periodic

t he

reason

same

for

placing

t hese

two

period.

(1

a

transition

i)

Name

two

elements

which

occur

in

t he

same

in

Period

4

of

t he

periodic

State

a

A

I

reason

for

placing

t hese

two

mark)

elements

same

group.

(1

and

III

Element

I,

II

and

IV

I,

III

D

III

and

IV

3

valence

IV

element

X

electrons

in

its

and

correct

4

electron

position

in

above.

(1

Give

t he

electronic

conguration

of

a

calcium

atom.

only (1

e Which

element

shows

ver y

similar

chemical

Bot h

magnesium

and

calcium

react

acid.

barium? i)

A

Which

element

would

you

expect

to

react

B

(1

mark)

aluminium ii)

C

sulfur

D

magnesium

f

X

is

an

element

periodic

I

II

III

react

table.

ver y

ionise

react

below

X

calcium

would

be

vigorously

more

slowly

readily

wit h

in

Group

expected

wit h

t han

cold

II

of

t he

ii)

to:

A

I

only

B

I

and

C

II

D

I,

Explain

What

g

and

II

of

potassium

Explain

i)

Explain

reason

for

to

above.

(2

obser ve

added

to

an

if

an

aqueous

bromide?

your

t he

(1

obser vation

to

right

elements

for

t he

along

fact

Period

decreases

and

t hat,

3,

when

t he

t he

mark)

in

(2

reason

marks)

aqueous

above.

lef t

t he

t he

is

i)

marks)

moving

metallic

nature

non-metallic

increases.

(3

marks)

only

III

and

which

expect

solution

Total

only

15

marks

III

Extended

In

you

to e

chlorine

nature II

would

answer

of

from

acid

your

solution

f

water

calcium

hydrochloric

i)

of

5

more

sodium vigorously?

4

mark)

wit h

proper ties hydrochloric

to

t he

mark)

only d

and

has

Place

only gure

C

X

only

shells.

3

in

mark)

metal

c

B

t he

table

t he IV

(1

element

ii) III

in

mark)

table

group. II

mark)

elements

be:

b I

(1

mass ii)

2

Kr

increasing:

group

of

t he

periodic

table

are

t he

response

question

halogens 8

a

Outline

t he

contributions

of

Döbereiner

and

found? Mendeleev

A

Group

to

t he

development

of

t he

periodic

(4

B

Group

II

C

Group

VII

b

The

reactivity

table

D

Group

0

Which

of

t he

following

is

t he

most

of

increases

statement

and

6

by

calcium

elements

going

reference

wit h

in

down

to

Group

t he

t he

oxygen,

II

group.

of

reactions

water

and

t he

of

hydrochloric

(6

silicon

C

sulfur

D

phosphor us

Element

X

potassium

reaction

i)

Place

X,

Structured

position

gure

in

to

iodide

t he

be

to

displace

solution,

potassium

following

found

chlorine,

but

iodine

was

chloride

elements

going

iodine,

of

cer tain

elements

in

t he

periodic

Explain,

in

terms

was

to

displace

able

marks)

down

from

found

to

have

no

solution.

in

order

Group

as

VII:

uorine.

t hey

element

t he

gure

answer

t he

below.

Use

following

t he

information

questions.

of

oxidising

(2

iodine

strengt h,

marks)

from

t he

why

X

potassium

table

iodide given

found

question ii)

The

was

wit h

would

64

t his

magnesium

chlorine

B

is

periodic

electronegative?

c

7

marks)

Suppor t

acid.

A

table.

I

in

solution.

(3

marks)

t he

Total

15

marks

A5

Most

substances

Structure

occur

as

compounds

in

and

bonding

n a t u re . Objectives

Compounds

chemically

a re

with

formed

each

when

o t h e r.

atoms

The

combine

compounds

By

the

be

able

formed

a re

m o re

stable

than

the

f re e

of

explain

elements

why

chemical

w e re .

The

noble

gases

a re

an

exception

to

do

occur

in

n a t u re

as

atoms.

The

state

e l e c t ro n i c

of

the

noble

gases

is

the

their

will

atoms

form

bonds

how

atoms

form

chemical

name

the

three

types

of

re a s o n chemical

behind

you

bonds

●

configuration

topic

this; ●

they

this

to:

which

●

a re

end

s t a b i l i t y.

describe

●

chemical

work

●

of

out

binary

bonding

three

types

of

formulae

the

empirical

compounds

formulae

from

their

names.

A5.1

Chemical

Introduction

When

atoms

to

bond

bonding

chemical

wit h

eac h

bonding

ot her,

only

t he

o u t e r m o st

electrons,

k n ow n

a s va l e n c e e l e c t r o n s , a r e u s u a l ly i nvo lve d i n t h e p r o c e s s . A t o m s c o m b i n e He

wit h

eac h

3.2).

The

shell

is

is

t his

noble

t heir

are

t he

st a b l e

g i ve s

ga s

st a b l e

a to m s

t hem

a

electron

configuration

electronic

because

st a b l e

configuration.

o u t e r m o st

electronic

m o st

t heir

electronic

A to m s ,

shell

of

configuration

t he

o u t e r m o st

or

electron

configuration.

t h e r e fo r e ,

valence

f i r st

( Un i t

t hree

bond

shell.

noble

This

wit h

eac h

Fi g u r e

5 .1.1

××

Ne

××

fill

att ain

ga s e s

and

t he

t he

to

××

to

s h ow s

noble

full

called

ot h e r

ot h e r

ga s e s .

××

A to m s

ga i n

n e a r e st

st a b i l i t y

noble

ga s

to

if

t h ey

t hem

in

att ain

t he

t he

noble

per iodic

ga s

t able,

configuration

i.e.

t he

element

of

t he

t hat

is ××

c l o s e st

is

by

neon

and

n e a r e st

Fo r

noble

e xa mp l e ,

ga s

to

t he

n e a r e st

c hlor ine

is

noble

argon.

ga s

This

is

to

sodium

××

i l l u st r a t e d

××

××

××

××

××

×

Ar

××

5 .1. 2 .

××

Fi g u r e

t he

n u m b e r.

××

in

a to m i c

×× ××

××

××

●

gain

●

share

one

one

or

or

more

more

valence

gas

valence

electrons

××

××

××

××

structure

of

sodium

and

chlorine

to



Figure

of

5.1.1

helium,

The

neon

electronic

and

structures

argon

their

argon

conguration

This

valence

Ar

××

donate

noble

××

●

a

change.

electronic

and

××

achieve

chemical

the

neon

××

gases,

××

Comparing

noble

××

can

a

××

5.1.2

nearest

during

Cl

××

Figure

Atoms

×

Ne

××



××

××

××

××

Na

can

occur

electrons

electrons

wit h

in

to

from

anot her

by

bonding

three

ways.

anot her

anot her

wit h

They

ot her

atoms

can:

atom

atom

atom.

65

Chemical

bonding

Structure

During

!

Key

fact

are

A

chemical

attraction

results

their

bond

is

between

from

the

chemical

involved.

a

force

atoms

of

These

caused

toget her.

by

bonding,

bonds

t he

There

chemical

are

forces

redistribution

are

three

main

bonds

of

of

t heir

types

are

formed

attraction

of

between

between

electrons,

chemical

and

and

t he

t hey

bonding

t he

atoms

join

atoms

which

t he

atoms

bonding:

that

redistribution

●

ionic

bond ing ,

●

covalent

●

metallic

which

occurs

when

a

metal

bonds

wit h

a

non-metal

of

bond ing ,

which

occurs

when

two

or

more

non-metals

bond

electrons.

onic

and

bond ing ,

covalent

which

occurs

bonding

wit hin

bot h

metals.

result

in

t he

formation

of

chemical

compounds.

Chemical

Just

by

as

elements

ionic

or

Chemical

are

in

compound.

●

are

The

can

be

covalent

a

There

are

are

be

impor tant

as

well

various

formula ,

atoms

compound.

by

can

atomic

because

as

t he

types

symbols,

represented

of

by

t hey

ratio

tell

us

between

chemical

compounds

chemical

which

t he

formulae.

formed

formulae .

elements

elements

The

in

t hree

t he

main

below.

molecular

of

compounds

represented

compound

given

number

of

bonding

formulae

found

types

formulae

For

of

which

each

uses

element

example,

t he

subscripts

present

molecular

in

to

one

formula

give

t he

actual

molecule

of

water

of

is

a

H

O,

which

2

means

atom.

one

molecule

Ot her

of

molecular

water

contains

formulae

2

hydrogen

include

CO

for

atoms

carbon

and

1

oxygen

dioxide

and

2

C

H 6

●

O 12

The

for 6

structural

molecule

bonds.

atom

The

of

For

OCO

●

glucose.

t he

which

and

t he

between

compound

empirical

which

compound

example,

t he

shows

carbon

empirical

ratio

formula ,

us

t hat

formula

diagrammatic

lines

between

formula

t here

are

for

two

representation

t he

atoms

carbon

bonds

to

one

represent

dioxide

between

of

is

each

oxygen

atom.

which

elements

consists

using

a

str uctural

formula ,

t he

is

of

for

in

gives

t he

multiples

of

magnesium

t he

simplest

compound

t hese

smallest

chloride

is

whole

using

number

subscripts.

units.

MgCl

,

For

which

The

example,

tells

us

t he

t hat

2

magnesium

and

chlorine

are

present

in

a

ratio

of

1

to

2.

Example

The

t hree

types

●

Molecular

●

Str uctural

of

chemical

formula:

C

formula:

et hane

are:.

6

formula:

H

Empirical

for

H 2

●

formulae

H

H

C

C

H

H

H

CH 3

!

Key

fact

Writing

Valence

number

(valency)

is

A maximum

number

of

bonds

can

form

other

atoms.

when

it

binary

bonds

t he

of

binary

compounds

compound

empirical

is

composed

formulae

of

of

two

binar y

different

elements

compounds

using

only.

t he

We

can

concept

of

with

valence

atom

66

formulae

an

write atom

empirical

the

number

can

form.

or

valency,

which

is

t he

maximum

number

of

bonds

an

Structure

and

bonding

Chemical

bonding

The number of valence electrons an atom has determines its valence number.

This

is

because

of

chemical

in

forming

electrons

it

is

t he

bonds.

bonds,

an

valence

Since

t he

atom

electrons

atoms

valence

has

to

lose,

number

lose,

gain

which

gain

or

can

or

par ticipate

share

be

share

t heir

t hought

during

in

t he

formation

valence

of

as

t he

bonding.

electrons

number

The

of

valence

number of an element is related to its position in t he periodic table as shown

in



Table

T able

Group

5.1.1

Valence

number

Valence

n

5.1.1.

number

ot her

numbers

I

II

transition

1

2

variable,

metals

often

2

III

IV

V

VI

VII

0

3

4

3

2

1

0

words:

●

valence

number

of

elements

in

Groups



●

valence

number

of

elements

in

Groups

V

Since

same

bot h

types

number

element

in

of

t he

of

atom

valence

forming

a

electrons,

compound

must

be

to

V

to

V

compound

t he

sum



of

t he



8

must

t he

group



t he

lose,

number

group

gain

valence

or

number.

share

numbers

of

t he

each

equal.

Example

The

chemical

formula

of

aluminium

oxide

is

Al

O 2

●

●

●

Number

Valence

Sum

i.e.

To

of

t he

write

of

atoms

number

t he

of

of

t he

each

each

valence

sum

t he

of

element

element:



3.

3

(Group

),



2

(Group

V).

O



3

numbers

a

2,

O



2

of



O



formula

3

Al

Al

numbers: Al

valence

chemical

present:





of

3



2



t he

binar y

6,

6,

two

elements

compound,

is

follow

equal.

t he

steps

given

below.

1)

Determine

2)

Write

3)

Write

down

symbol

Write

5)

Write

Points

t he

to

●

There

●

f

1

●

t he

as

a

Some

The

by

a

e.g.

of

t he

symbol

valence

t he

numbers

symbol

of

t he

of

rst

t he

two

elements

element.

f

a

present.

metal

is

present,

write

its

rst.

t he

symbol

4)

t he

of

valence

t he

number

rst

symbol

t he

second

element

as

a

subscript

af ter

t he

element.

of

valence

t he

of

t he

second

number

second

of

element

t he

rst

directly

af ter

element

as

a

t he

subscript.

subscript

af ter

t he

element.

note

must

be

valence

no

number

subscript

of

t he

spaces

(see

transition

number

Roman

numeral

copper(II)

one,

example

valence

example

is

between

write

t hese

placed

indicates

t hat

symbols

only

t he

and

subscripts.

symbol

wit hout

t he

number

2).

metals

of

t he

have

is

in

more

t han

indicated

brackets

copper

has

in

af ter

a

one

t he

valence

name

t he

of

name

valence

number.

t he

of

compound

t he

number

of

metal,

2

(see

3).

67

Chemical

bonding

Structure

●

The

●

To

valence

write

t he

simplest

number

of

empirical

form,

t hen

hydrogen

formula,

cancel

to

if

its

and

t he

t he

transition

ratio

simplest

of

t he

form

element,

subscripts

(see

and

is

example

bonding

silver,

not

in

is

1.

its

4).

Examples

1

Magnesium

●

nitride

Determine

t he

●

Write

down

●

Write

t he

t he

valence

t he

symbol

valence

symbol

of

numbers

t he

of

number

rst

t he

of

of

rst

t he

element:

t he

two

elements

element:

second

present:

Mg



2

(Group

),

N



3

(Group

V).

Mg

element

as

a

subscript

af ter

Mg 3

●

Write

t he

symbol

of

t he

second

element:

Mg

N 3

●

Write

t he

symbol

valence

of

t he

number

second

of

t he

element:

rst

Mg

The

empirical

formula

of

element

as

a

subscript

Potassium

●

●

t he

magnesium

2

nitride

is

Mg

N 3

2

af ter

N 3

2

sulde

Valence

numbers

Empirical

of

formula

t he

of

elements:

potassium

K



1

(Group

),

S



2

(Group

V).

sulde

is

K

S 2

3

ron( )

●

●

bromide

Valence

numbers

Empirical

of

formula

t he

of

elements:

iron ()

Fe



3

(given

Br



1

(Group

bromide

is

FeBr

in

t he

name),

V).

. 3

4

Carbon

●

●

dioxide

Valence

numbers

Empirical

of

formula

t he

of

elements:

carbon

C



4

(Group

V),

O



2

(Group

V).

dioxide

is

CO

. 2

simplest

Summary

1

Explain

why

2

Explain

how

3

Name

4

Using

the

a

O 2

is

cancelled

to

4

questions

atoms

form

types

periodic

binary

sodium

form

atoms

three

your

following

(C

ratio.)

of

compounds.

compounds.

chemical

table

to

help

bonding.

you,

write

the

formula

of

each

of

the

compounds:

oxide

b

copper(II)

c

tetrachloromethane,

bromide

a

compound

formed

between

carbon

and

chlorine

68

d

aluminium

e

ammonia,

sulde

a

compound

formed

between

nitrogen

and

hydrogen.

its

Structure

and

A5.2

bonding

Formation

Formation

of

ionic

bonds

atoms.

Compounds

formed

by

ionic

ionic

bonds

Objectives

onic bonding involves t he transfer of valence electrons from metal atoms to

non-metal

of

bonding

are

known

as

By

the

be

able

end

of

this

topic

you

will

to:

ionic

●

explain

the

principles

of

ionic

compounds

bonding

The

principles

of

ionic

bonding

are

explained

as

follows. ●

●

Metals

are

valence

noble

●

found

to

electrons.

gas

t he

f

lef t

t hey

of

lose

t he

periodic

t heir

table

valence

and

most

electrons

have

t hey

can

1,

2

or

attain

3

Non-metals

are

found

to

t he

right

of

t he

periodic

table

and

most

how

cations

and

form

a

conguration.

explain

metal

atoms

non-metal

form

atoms

anions

●

name

●

describe

ionic

compounds

the

formation

of

ionic

have

bonds

5,

6

or

7

valence

electrons.

f

t hey

gain

electrons

into

t heir

valence

shell

●

t hey

can

attain

a

noble

gas

represent

shell

●

When

an

atom

loses

or

gains

electrons

it

forms

an

ion.

The

ions

now

charged

par ticles

because

t hey

no

longer

contain

t he

of

electrons

as

t he

number

of

deduce

When

t han

●

a

metal

atom

electrons.

When

a

The

non-metal

electrons

t han

loses

ion

electrons,

has

atom

protons.

a

gains

The

t he

positive

ion

has

formed

charge

electrons,

ion

a

ionic

the

empirical

formulae

compounds

protons. ●

●

using

same of

number

bonding

diagrams

formed ●

are

ionic

conguration.

and

t he

ion

negative

is

has

more

called

formed

charge

a

describe

sodium

the

structure

chloride

of

a

crystal.

cation

has

and

protons

is

more

called

an

anion

Examples

1

Lithium

When

now

is

in

Group

bonding

has

one

wit h

more



of

a

t he

periodic

non-metal,

proton

t han

table

lit hium

electron.

and

has

loses

its

one

valence

valence

Therefore

it

electron.

electron

carries

a

and

single



positive

charge,

,

and

is

represented

as

Li

.

t

is

known

as

t he

lit hium



ion

or

Li

ion.



3p

3p

4n

4n



lithium

atom

lithium

an

electron

ion



Li

(2,1)

Li

(2)





2

Nitrogen

electrons.

and

now

is

Figure

in

Group

When

has

5.2.1

V

Formation

of

bonding

t hree

more

t he

of

a

lithium

periodic

wit h

a

table

metal,

electrons

t han

ion,

Li

and

nitrogen

protons.

has

ve

gains

valence

t hree

Therefore

it

electrons

carries

a

3

triple

negative

charge,

3 ,

and

is

represented

as

N

.

t

is

known

as

t he

3

nitride

ion

or

N

ion.

3

7p

7p 

three

electrons

7n

nitrogen

7n

atom

nitride

ion

3

N

(2,5)

N

(2,8)

3



Figure

5.2.2

Formation

of

a

nitride

ion,

N

69

Formation

of

ionic

bonds

Structure

When

Key

!

naming

electrons,

fact

t he

t he

negative

name

changes

anions

from

formed

t hat

of

when

t he

and

non-metal

atom.

The

name

bonding

atoms

of

t he

gain

anion

2

always

Ionic

bonds

created

by

are

the

chemical

bonds

and

of

t he

attraction

between

charged

negatively

‘ide’.

bromide

For

ion

example,

(Br

t he

chloride

ion

(Cl

),

t he

oxide

ion

(O

)

).

t he

cations

charged

anions

compounds

formed

by

ionic

bonding,

t here

are

strong

electrostatic

the

forces positively

in

electrostatic

n forces

ends

of

attraction

between

t he

positive

cations

and

negative

anions.

and

in

These

ionic

forces

of

attraction

are

known

as

ionic

bonds

and

t hey

hold

t he

ions

toget her. The strengt h of t he ionic bonds accounts for t he proper ties of ionic

compounds.

compounds

(Unit

Examples

to

The

formation

and

potassium

cross

5.5).

show

of

the

sodium

nitride

by

formation

chloride,

ionic

of

magnesium

bonding

is

ionic

compounds

uoride,

shown

next

aluminium

by

means

of

oxide

dot

and

diagrams.

Sodium

Sodium

chloride

is

a

metal

wit h

one

valence

electron.

t

loses

t his

electron

to

form

a



positive

is

a

sodium

non-metal

negative

sodium

atom

to

in

seven

ion

t hat

accept

a

single

valence

which

loses

t his

has

has

one

electron.

positive

electrons.

a

single

electron

The

t

charge,

gains

negative

t here

empirical

will

one

formula

.

Chlorine

to

i.e.

be

Cl

to

.

For

one

sodium

form

a

each

chlorine

chloride

is,

shows

how

to

use

shell

diagrams

to

represent

t he

ionic

bonding

chloride.

–

+

××

××

××

××

Cl

××

××

××

××

Na

Na

××

sodium

of

Na

electron

charge,

need

×

1

i.e.

NaCl

5.2.3

sodium

which

wit h

chloride

atom

t herefore,

Figure

ion

Cl

××

atom

1

chlorine

atom

1

sodium

ion

1

chloride

ion

+

(Na)

Did

?

you

term

(Na

)

(Cl

)

know?



The

(Cl)

‘lattice’

refers

Figure

5.2.3

Ionic

bonding

in

sodium

chloride

to

t is important to note that NaCl is not a separate, individual entity. NaCl simply a

regular,

three-dimensional 

represents arrangement

of

the

ratio

of

Na

ions

to

Cl

ions

in

sodium

chloride,

i.e.

it

is

the

particles.

empirical formula. t can also be called the

Sodium

c hlor ide

formula unit of sodium chloride.

t hat

we

spr inkle

on

our

food

is

composed of tiny cr yst als t hat are cubic in shape. Eac h

−

=

−

Cl



of

t hese

cr yst als

is

made

up

of

millions

of

Na

ions



and

−

+

millions

of

Cl

ions

in

a

ratio

of

one

Na

ion

to

− one

Cl

way;

ion.

t hey

These

occur

ions

are

ar ranged

alter nately

in

in

rows

a

ver y

and

regular

columns.

+

+

=



Na

Eac h

+

−

Na

ion

is

bonded

+

to

six

Cl

ions

and

eac h

Cl



ion

is

bonded

to

six

Na

ions

by

strong

ionic

bonds.

− This

t hree-dimensional,

for ms strong

ionic

charged

ordered

ar rangement

lattice.

+

−

oppositely

ions



70

cr yst al

bonds

− between

a

Figure

5.2.4

Crystal

lattice

of

sodium

chloride

of

ions

Structure

and

Magnesium

Magnesium

bonding

Formation

of

ionic

bonds

fluoride

is

a

metal

wit h

two

valence

electrons.

t

loses

t hese

electrons

to

2

form a positive magnesium ion which has a double positive charge, i.e. Mg

Fluorine

to

form

For

is

a

each

negative

atoms

one

uoride

non-metal

is,

to

wit h

uoride

magnesium

uorine

accepts

a

atom

accept

electron.

t herefore,

seven

ion

t hat

t hese

The

valence

which

loses

two

has

two

electrons.

a

single

electrons

electrons

empirical

formula

gains

negative

t here

since

or

t

each

formula

will

one

charge,

i.e.

need

be

uorine

unit

of

.

electron

to

atom

F

.

two

only

magnesium

MgF 2

–

F F

×

2+

×

××

××

×

××

××

××

××

Mg

Mg

–

××

××

F

F

×

1

magnesium

2

fluorine

1

magnesium

2

fluoride

2+

atom,



Mg

Figure

atoms,

5.2.5

Aluminium

Ionic

F

ion,

bonding

in

magnesium

Mg

ions,

F

uoride

oxide

Aluminium

is

a

metal

wit h

three

valence

electrons.

t

loses

t hese

electrons

to

3

form

a

positive

Oxygen

is

a

aluminium

non-metal

ion

wit h

which

six

has

valence

a

triple

positive

electrons.

t

charge,

gains

two

i.e.

Al

.

electrons

to

2

form a negative oxide ion which has a double negative charge, i.e. O

each

has

total

six

aluminium

to

gain

of

six

two

electrons

electrons.

t herefore,

The

Al

O 2

To

as

simplify

in

Figure

atom

has

electrons,

and

to

lose

two

t hree

empirical

t hree

electrons

aluminium

oxygen

formula

or

atoms

atoms

will

formula

and

will

be

unit

each

be

oxygen

needed

needed

of

. Since

to

to

gain

aluminium

atom

lose

a

t hese

oxide

is,

. 3

t he

diagrams,

sometimes

only

t he

valence

electrons

are

shown,

5.2.6.

2–

×

O

O

×

3+

×

Al

Al

2–

×

×

O

O

3+

×

×

Al

Al

2–

×

×

O

O

×

2

aluminium

3

oxygen

2

aluminium

ions,

3

oxide

3+

atoms,



Figure

Al

5.2.6

atoms,

Ionic

O

bonding

Al

in

aluminium

ions,

2–

O

oxide

71

Writing

chemical

formulae

of

ionic

compounds

Structure

Potassium

Potassium

and

bonding

nitride

has

one

valence

electron.

t

loses

t his

electron

to

form

a

positive



potassium ion wit h a single positive charge, i.e. K

electrons.

t

gains

t hree

electrons

to

form

a

. Nitrogen has

negative

nitride

ve

ion

valence

which

has

3

a

triple

t hree

of

negative

electrons

potassium

charge,

to

one

nitride

i.e.

N

.

nitrogen

is,

Three

atom.

t herefore,

K

potassium

The

atoms

empirical

are

formula

needed

or

to

formula

lose

unit

N 3

+

K

K

3

+

×

K

N

×

×

+

K

3

K

potassium

1

nitrogen

3

potassium

ions,

1

nitride

+

atoms,



K

atom,

Figure

5.2.7

Summary

1

Explain

2

Use

bonding

in

potassium

ion,

3

K

N

nitride

questions

what

shell

Ionic

N

happens

diagrams

a

sodium

b

magnesium

and

to

during

ionic

represent

oxygen

to

form

bonding.

the

ionic

sodium

bonding

oxide,

Na

between:

O 2

and

nitrogen

to

form

magnesium

nitride,

Mg

N 3

3

4

the

be

able

●

end

this

topic

you

●

ionic

the

name

b

Give

the

formula

Describe

the

of

compound

the

unit

structure

Writing

will

the

the

names

common

and

formulae

cations

and

with

uorine.

compound.

of

of

the

the

compound.

crystal

chemical

lattice

of

sodium

formulae

of

chloride.

ionic

compounds

work

out

onic

compounds

formula

of

an

compound.

anions

●

an

Give

to:

give

of

of

forms

a

A5.3

Objectives

By

Calcium

2

the

formula

ionic

compound

write

the

name

compound

of

from

of

from

an

the

an

the

name

ionic

●

ionic

are

ionic

There

represented

compound

are

using

is

impor tant

also

empirical

known

points

to

as

note

formulae .

t he

The

formula

when

writing

empirical

unit

of

t he

formulae

of

compounds.

Metals

generally

generally

gain

lose

electrons

electrons

forming

forming

positive

negative

cations.

Non-metals

anions.

formula. ●

The magnitude of the charge on an ion is the same as the valence number.

Therefore, when writing formulae of ionic compounds, the magnitude of

the charge on the ion can be used in place of the valence number.

●

Not

all

atoms

were

72

ions

are

bonded

formed

from

toget her.

previously

known

one

These

as

atom.

ions

radicals).

are

Many

ions

known

as

are

made

from

polyatomic

several

ions

(t hese

Structure

●

When

writing

t he

Writing

formula

charges

types

atom

or

group

number

of

electrons.

The



bonding

positive

same

in

and

of

names

Tables

T able

and

5.3.1

5.3.1

Monovalent

must

formulae

and

of

equal

of

of

an

t he

atoms

t he

ionic

sum

compound,

of

t he

bonded

ions

t hat

toget her

you

are

of

must

required

lose

to

of

ionic

compounds

t he

since

or

bot h

gain

know

t he

are

given

cations

cations

Divalent

cations

Trivalent



hydrogen

H

lithium

Li

sodium

Na

magnesium

Mg

calcium

Ca

barium

Ba



Ag

aluminium

Al

3

2

iron(II)

Fe

copper(II)

Cu

zinc

Zn

tin(II)

Sn

lead(II)

Pb



silver

Fe

2

K

Cu

3

iron(III)

2



copper( )

cations

2



2



2



ammonium

sum

charges,

formulae

5.3.2.

Common

potassium

t he

negative

chemical

2

NH 4

2



T able

5.3.2

Monovalent

Common

anions

anions

Divalent

anions

Trivalent

anions

2

fluoride

F

oxide

O

chloride

Cl

sulfide

S

3

nitride

N

phosphate

PO

2

3

4

2

bromide

carbonate

Br

CO 3

2

iodide

sulfite

I

(sulfate(IV))

SO 3

2

hydride

sulfate

H

(sulfate(VI))

SO 4

2

hydroxide

dichromate(VI)

OH

Cr

O

2

nitrite

(nitrate(III))

7

✔

Exam

tip

NO 2

Success nitrate

(nitrate(V))

in

chemistry

depends

on

NO 3

being manganate(VII)

able

to

write

the

names

and

MnO 4

formulae

hydrogensulfate

of

compounds.

Knowing

HSO 4

hydrogencarbonate

HCO

ethanoate

CH

the

formulae

important

3

this

of

step

ions

is

towards

a

very

achieving

success.

COO

3

n order to write t he chemical formula of an ionic compound from t he name,

follow

1)

t he

steps

below.

Write down t he formulae of t he two ions t hat are involved from Tables 5.3.1

and

5.3.2.

2)

Rewrite

3)

Write

t he

t he

formula

outside

Write

formula

of

magnitude

of

required,

4)

given

t he

place

t he

t he

of

cation.

t he

bracket

formula

t he

cation,

t he

f

it

charge

is

a

polyatomic

(see

of

on

t he

polyatomic

cation

example

t he

omitting

anion

in

its

charge.

anion

as

cation

brackets

a

subscript

and

and

more

write

af ter

t han

t he

t he

one

is

subscript

4).

directly

af ter

t he

subscript,

omitting

its

charge.

5)

Write

t he

formula

required,

outside

magnitude

of

t he

place

t he

of

anion.

t he

bracket

t he

f

it

charge

is

a

polyatomic

(see

on

t he

polyatomic

anion

example

in

cation

as

anion

brackets

a

subscript

and

and

more

write

af ter

t han

t he

t he

one

is

subscript

5).

73

Writing

chemical

formulae

of

ionic

compounds

Structure

Points

●

f

to

t he

f

t he

bonding

note

magnitude

subscript

●

and

(see

ratio

simplest

of

of

t he

charge

examples

t he

form

2

and

subscripts

(see

example

is

one,

do

not

write

t he

number

1

as

a

3).

is

not

in

its

simplest

form,

t hen

cancel

to

its

6).

Examples

1

Aluminium

sulde

3

●

Write

down

t he

ions

●

Write

down

t he

formula

●

Write

t he

t he

involved:

magnitude

formula

of

t he

of

of

t he

t he

cation:

Al

2

,

S

cation

charge

wit hout

on

t he

its

anion

charge:

as

a

Al

subscript

af ter

Al 2

●

Write

t he

formula

of

t he

anion

wit hout

its

charge:

Al

S 2

●

Write

t he

t he

magnitude

formula

of

t he

of

t he

anion:

charge

Al

formula

unit

of

t he

cation

Calcium

a

subscript

af ter

aluminium

3

sulde

is

Al

S 2

2

as

S 2

The

on

3

iodide

2

●

ons

involved:

●

Magnitude

●

Formula

Ca

,



2

of

unit

t he

of

charges:

calcium

Ca



iodide

is

2,





1

CaI 2

3

Sodium

phosphate



●

ons

involved:

Na

3

,

PO 4



●

Magnitude

of

t he

charges:

Na

3



1,

PO



3

4

●

Formula

unit

of

sodium

phosphate

is

Na

PO 3

4

Ammonium

sulfate



●

ons

involved:

NH

2

,

SO

4

4



●

Magnitude

of

t he

charges:

NH

2



1,

SO

4

●

Formula

4

unit

of

ammonium



2

4

sulfate

is

(NH

) 4

SO 2

4



(The

polyatomic

ammonium

ion,

NH

,

is

placed

in

brackets

wit h

4

subscript

5

outside.)

Copper(II)

nitrate

2

●

ons

involved:

●

Magnitude

Cu

,

NO 3

2

of

t he

charges:

Cu



2,

NO



1

3

●

Formula

unit

of

copper ()

nitrate

is

Cu(NO

) 3

(The

polyatomic

nitrate

ion,

NO

,

is

placed

in

2

brackets

3

subscript

6

outside.)

Magnesium

carbonate

2

●

ons

involved:

Mg

2

,

CO 3

2

●

Magnitude

of

t he

charges:

Mg

2



2,

CO



2

3

●

Formula

unit

of

magnesium

carbonate

is

MgCO 3

(Mg

(CO 2

74

) 3

is 2

cancelled

to

its

simplest

ratio.)

wit h

t he

t he

Structure

and

Naming

The

name

bonding

ionic

of

an

Writing

chemical

formulae

of

ionic

compounds

compounds

ionic

compound

is

built

from

t he

cation

and

anion

names.

Examples

1

Al(OH)

is

composed

of

t he

aluminium

cation

and

hydroxide

anion.

ts

3

name

2

K

O

is

is

aluminium

composed

of

hydroxide.

t he

potassium

cation

and

t he

oxide

anion.

ts

name

2

is

3

potassium

Ca

(PO 3

f

t he

is

is

by

composed

of

t he

calcium

cation

and

phosphate

anion.

ts

2

calcium

cation

charge

its

) 4

name

oxide.

is

phosphate.

t hat

looking

of

at

a

t he

transition

subscript

metal,

af ter

t he

determine

anion

and

t he

use

magnitude

t his

to

of

its

determine

name.

Examples

1

FeCl 2

●

The

subscript

af ter

●

The

magnitude

of

t he

t he

chloride

charge

ion

on

is

t he

2.

iron

ion

must

be

2.

be

3.

2

2

●

The

cation

●

The

name

Fe(NO

must

of

t he

be

t he

iron (II)

compound

is

ion,

Fe

iron (II)

chloride.

) 3

3

●

The

subscript

●

The

magnitude

af ter

●

The

cation

●

The

name

of

t he

t he

nitrate

charge

ion

on

is

t he

3.

iron

ion

must

3

of

Summary

1

2

Write

the

must

chemical

iron(III)

b

calcium

c

sodium

d

ammonium

e

silver

f

zinc

g

potassium

h

copper(II)

a

iron (III)

compound

is

ion,

Fe

iron (III)

nitrate.

formula

of

each

of

the

following

ionic

compounds:

sulde

hydroxide

sulfate

phosphate

oxide

nitrate

(PO 3

AgCl

c

ZnI

d

Al(HCO

for

each

of

the

following

compounds:

) 4

b

manganate( VII)

carbonate

names

Mg

t he

questions

a

Write

t he

be

2

2

) 3

e

3

FeBr 3

f

FeSO

g

Cu

4

O 2

h

Pb(NO

) 3

2

75

Formation

of

covalent

and

metallic

bonds

A5.4

Objectives

By

the

be

able

end

of

topic

you

the

formation

of

Covalent

metal

covalent

shell

covalent

and

metallic

bonding

bonds

bonding

bonding

bonding

atoms.

covalent

involves

t he

Compounds

sharing

formed

of

by

valence

covalent

electrons

bonding

between

are

non-

known

as

compounds

diagrams

Non-metals write

●

of

and

will

bonds

represent

using

Formation

Covalent

covalent

●

this

to:

describe

●

Structure

formulae

of

are

found

to

t he

right

of

t he

periodic

table

and

have

4,

6

or

shell

5,

to

covalent

7

valence

electrons.

They

need

to

gain

electrons

into

t heir

valence

compounds

attain describe

●

metallic

the

formation

a

noble

gas

conguration.

of

bonds

Since all t he atoms involved in covalent bonding need to gain electrons, t hey

relate

●

the

properties

of

metals

achieve t his by approaching each ot her so t hat t heir outermost electron shells

to

the

bonding

in

metals.

overlap.

are

Any

t hen

valence

shared,

in

electrons

pairs,

pair of electrons forms a

are

Key

!

known

orbiting

electron covalent

bond

is

a

a

pair

formed

of

covalent bond

bond ing

pair.

Each

not

two

in

pairs

in

overlapping

t he

original

atoms.

Each

atoms

shared

and t he electrons in a covalent bond

bonding

shell

by

the

electrons

around

and

is

each

stable.

nucleus.

Two

Each

pair

atoms

atom

spends

may

now

share

has

one,

a

time

wit h

two

completed

bot h

or

t hree

outer

pairs

of

chemical

electrons bond

a

were

t he

fact atoms,

A

as

t hat

between

sharing

between

between

t hem.

of

two

Two

or

more

non-metal

atoms

can

bond

toget her

by

sharing

electron

atoms.

pairs.

When

molecules.

The

electrostatic

!

Key

bonding

fact

molecule

more

atoms

bonded

is

a

group

which

together

are

of

two

or

may

behave

chemical

as

a

reaction.

atoms

of

pairs

bond

t hey

wit hin

form

a

attraction

of

molecule

between

electrons.

toget her

by

separate,

Atoms

covalent

are

t he

of

individual

held

toget her

nuclei

t he

entities

same

of

t he

by

known

t he

atoms

element

or

of

as

strong

and

t he

different

bonding.

covalently

strongly

single

t his,

or

enough

Examples to

do

forces

pair

elements

A

t hey

unit

in

to

show

the

formation

of

covalent

a

substances

The

by

formation

means

Chlorine

of

of

dot

a

variety

and

cross

of

substances

by

covalent

bonding

is

shown

next

diagrams.

gas

Chlor ine

is

a

non-metal

wit h

se ven

valence

electrons.

t

needs

one

more

electron to ll its valence electron shell and attain a noble gas conguration.

Dur ing t he for mation of a chlor ine molecule, two chlor ine atoms come close

enough

pair

of

for

t heir

outer

electrons

for ming

chlor ine

a

is

electron

between

single

shells

t hem.

covalent

The

bond

to

overlap.

shared

between

pair

t he

The

two

orbit

two

atoms

around

atoms.

The

share

bot h

2

××

××

××

××

××

Cl

××

××

××

××

2

chlorine

atoms,

Cl

1

××

Cl

××

××

××

××

××

Cl

×

chlorine

Cl

molecule,

Cl 2



76

Figure

5.4.1

Covalent

bonding

in

chlorine

atoms

for mula

Cl

××

one

for

Structure

and

bonding

Formation

of

covalent

and

metallic

bonds

Water

Water

is

a

its

t

is

a

compound

non-metal

valence

needs

atoms

water

more

needed

hydrogen

for

electron

two

are

wit h

atom

is

H

formed

one

shell.

to

provide

shares

one

hydrogen

electron.

Oxygen

electrons

to

from

valence

is

ll

t he

a

its

and

valence

wit h

one

wit h

atoms.

more

six

electron

electrons

pair

oxygen

needs

non-metal

two

electron

t

valence

shell.

required

t he

oxygen

Hydrogen

electron

Two

by

to

hydrogen

oxygen.

atom.

ll

electrons.

The

Each

formula

O 2

H

O

H

O

H H

2

hydrogen

1

oxygen

1

water

molecule,

H

O

2

atoms,



H

atom,

Figure

5.4.2

O

Covalent

bonding

in

water

Methane

Met hane is a compound formed from carbon and hydrogen. Carbon is a non-

metal

wit h

electron

Four

Each

formula

valence

electrons.

Hydrogen

hydrogen

carbon.

The

four

shell.

atoms

are

hydrogen

for

needs

needed

atom

met hane

is

t

one

needs

four

electron

to

shares

to

provide

one

electrons

ll

t he

its

four

electron

pair

to

valence

ll

electrons

wit h

its

valence

electron

t he

shell.

required

carbon

by

atom.

CH 4

Oxygen

gas

Oxygen

needs

formation

for

t heir

two

an

outer

electrons

oxygen

of

electron

between

is

electrons

oxygen

shells

t hem,

to

ll

molecule,

to

its

two

valence

overlap.

forming

a

electron

oxygen

The

double

atoms

two

atoms

covalent

shell.

come

During

close

share

bond .

two

The

t he

enough

pairs

formula

of

for

O 2

H

× ×

××

××

×

C

H

×

H

O

O

×

× ×

H

1

methane

molecule,

CH

1

oxygen

molecule,

O

4



Carbon

Figure

needs

valence

electron

electrons

t he

carbon

Covalent

bonding

in

methane

and

oxygen

dioxide

Carbon

wit h

5.4.3

2

four

required

carbon

dioxide

is

electrons

shells.

by

and

oxygen

oxygen

carbon.

atom,

CO

Two

Each

forming

a

needs

atoms

oxygen

double

are

two

electrons

needed

atom

to

shares

covalent

two

bond.

to

provide

ll

t he

electron

The

t heir

four

pairs

formula

for

. 2

77

Formation

of

covalent

and

metallic

bonds

Structure

and

bonding

Nitrogen

Nitrogen

is

electrons

to

molecule,

a

non-metal

ll

two

its

wit h

valence

nitrogen

ve

electron

atoms

valence

shell.

come

electrons.

During

close

t he

t

needs

formation

enough

for

t heir

t hree

of

a

more

nitrogen

outer

electron

shells to overlap. The two atoms share t hree pairs of electrons between t hem,

forming

a

triple

covalent

bond .

The

formula

for

nitrogen

is

N 2

××

×× ×

×

××

× × O

×

× ×

1

carbon

dioxide

molecule,

CO

1

nitrogen

molecule,

N

2

The

Figure

drawing

simplied

shell

of

by

5.4.4

dot

Covalent

and

showing

diagram

are

bonding

cross

only

shown

in

in

carbon

diagrams

t he

to

valence

Figure

dioxide

represent

electrons.

and

nitrogen

covalent

bonding

Examples

of

t his

can

be

type

of

5.4.5.

O

C

N

O



2

N

O

H

Exam

✔

1

It

is

very

important

that

you

are

draw

dot

and

cross

water

molecule

show

the

bond

compounds.

T o

first

the

decide

ionic

is

or

if

from

a

this,

you

compound

covalent.

formed

formation

do

If

the

metal

carbon

dioxide

molecule

1

nitrogen

molecule

Figure

5.4.5

Covalent

bonding

in

water,

carbon

dioxide

and

nitrogen

showing

diagrams valence

to

1

able 

to

H

tip

only

in

must

is

Str uctural

covalent

compound

and

electrons

formulae

bond

str uctural

is

may

also

shown

formulae

of

be

by

a

used

line

molecules

are

to

represent

between

given

in

t he

molecules

two

Figure

in

atoms.

which

each

Examples

of

5.4.6.

a

H non-metal

formed

it

will

from

be

ionic,

non-metals

if

it

is

only

it

Cl will

be

metal

covalent.

usually

Remember

has

1,

2

or

3

that

Cl

H

O

H

C

has

4,

5,

and

6

or

a

7

non-metal

valence

electrons.

chlorine

Valence

Number

bonds

1

1

of

1

1

chlorine

1

1

formulae

of

chlorine,

water,

carbon

methane,

dioxide

oxygen,

nitrogen

carbon

dioxide

nitrogen

Unit

5.1

bonds

you

with

learnt

other

that

the

atoms

is

number

known

of

as

bonds

its

that

valence

an

atom

can

number.

form

This

is

when

shown

clearly by these dot and cross diagrams. Hydrogen has a valence number of one

and

the

diagrams

number bromine

Structural

oxygen

covalent

it

fluorine

5.4.6

methane

formed

n

hydrogen

N

H

water

Figure

and

number

N

usually



Element

O

valence

H electrons

H

a

of

two

show

and

it

the

forming

diagrams

one

covalent

show

it

bond.

forming

Oxygen

two

has

covalent

a

valence

bonds.

The

1

1

valence numbers and number of covalent bonds formed by the common non-

iodine

1

1

oxygen

2

2

sulfur

2

2

nitrogen

3

3

carbon

4

4

metals when bonding to form covalent compounds are given in Table 5.4.1.

Polar

and

Molecules

t he



T able

5.4.1

number

of

Valence

covalent

number

bonds

and

formed

atoms

atom

78

atoms

may

in

be

t he

attracts

polar

or

molecule.

electrons.

covalent

non-polar

as

molecules

a

result

Electronegativity

Oxygen,

nitrogen,

is

a

of

t he

electronegative

t han

atoms

of

uorine

ot her

electronegativity

measure

and

by

strongly non-metal

non-polar

elements.

of

how

strongly

chlorine

are

of

an

more

Structure

●

n

a

and

polar

electrons

of

the

bonding

molecule,

in

the

the

bond

molecule

negative

Formation

has

charge.

atoms

with

a

slightly

Water

(H

at

each

different

positive

O),

side

of

charge

ammonia

(C

H 2

OH)

and

covalent

The

and

(NH

2

ethanol

a

strengths.

),

result

one

bond

is

side

hydrogen

attract

that

has

one

a

of

covalent

glucose

(C

H 6

O

12

)

metallic

bonds

the

side

slightly

chloride

(HCl),

3

5

and

δ

molecules

are

all

polar.

6

O

●

n

non

a

attract

have

polar

molecule,

electrons

any

wit h

charged

t he

equal

sides.

atoms

at

strengt hs

Oxygen

(O

each

such

),

side

t hat

nitrogen

t he

(N

2

carbon

dioxide

(CO

)

and

met hane

The

formula

each

of

element

formula.

of

of

n

elements

a

covalent

one

some

are

molecule

),

same,

) and met hane (CH 3

(Cl

(CH

)

not

H

H

δ

),

δ

2

molecules

are

all

non-polar.



Figure

5.4.7

A

polar

water

molecule

compound

of

gives

t he

compounds

e.g.

water

t he

exact

compound,

t he

(H

O),

molecular

carbon

number

i.e.

it

is

formula

dioxide

of

t he

atoms

and

(CO

of

molecular

),

t he

Prefix

Number

mono

1

di

2

tri

3

tetr

4

pent

5

hex

6

of

atoms

ratio

ammonia

2

). n t hese compounds t he molecular and empirical 4

formulae

are

molecular

t he

same.

formula

of

n

ot her

glucose

is

compounds

C

H 6

The

does

chlorine

2

(NH

bond

compounds

molecule

covalent

t he

covalent

4

covalent

in

a

2

2

Formulae

of

name

formula.

placed

of

This

a

is

before

prexes

are

covalent

done

t he

given

compound

by

name

in

O 12

using

of

Table

t he

t he

but

t hey

its

are

not

empirical

t he

same,

formula

is

e.g.

t he

CH

6

O. 2

can

sometimes

prexes

element

to

di,

tri,

indicate

tetr,

which

and

t hey

are

its

so

molecular

on.

These

referring.

are

These



5.4.2.

T able

in

5.4.2

naming

Prexes

covalent

sometimes

used

compounds

Examples

●

CO

●

SO

is

t he

formula

for

carbon

monoxide.

is

t he

formula

for

sulfur

dioxide.

is

t he

formula

for

sulfur

trioxide.

2

●

SO

●

CCl

3

is

t he

formula

for

carbon

tetrachloride,

more

correctly

known

as

4

tetrachloromet hane.

●

N

O 2

t

is

a

you

is

t he

formula

for

dinitrogen

tetroxide.

4

good

come

names,

idea

to

across

e.g.

learn

t hem,

ammonia

t he

molecular

especially

(NH

)

and

formulae

since

some

met hane

(CH

3

of

covalent

cannot

be

compounds

derived

from

as

t heir

). 4

positive

Metallic

ions

bonding –

–

–

–

+ Metals

type

of

have

ver y

bonding

distinct

t hat

chemical

occurs

and

between

physical

t he

metal

proper ties

atoms.

as

The

a

result

type

of

of

+

t he

bonding

– +

between

metal

atoms

in

a

metal

is

known

as

metallic

bond ing

–

The atoms in a metal are packed ver y closely together to form a

–

–

–

–

metal lattice.

+

Because of this tight packing, the outer electron shells overlap and the valence

electrons

become

par ticular

atom.

delocalised,

These

i.e.

delocalised

they

are

electrons,

no

also

longer

associated

known

as

mobile

with

any

‘delocalised’

a

belong

‘sea’

to

of

the

electrons

lattice

as

a

which

whole.

move

around

Positive

within

metal

the

cations

metal

are

electrons

electrons, 

form

+

lattice

formed

Figure

5.4.8

The

structure

of

metals

and

from

the

metal atoms when the electrons become delocalised. The metal lattice is held

! together by the strong electrostatic force of attraction, known as the

Key

bond, which exists between the positive cations and the moving, delocalised,

The

negative

bond

electrons.

Figure

5.4.8

illustrates

the

bonding

in

metals.

metallic

force

t

is

impor tant

to

note

t hat

metals

are

still

made

up

of

atoms

and

not

created

of

t he

valence

even

electrons

t hough

t hey

have

are

no

not

been

longer

lost.

They

attached

to

a

are

still

t here

par ticular

by

is

the

attraction

in

cations

the

chemical

electrostatic

between

and

the

the

moving,

t he delocalised

str ucture

bond

ions positive

because

fact

metallic

negative

electrons.

atom.

79

Structure

and

properties

of

solids

Structure

The

way

in

which

understand

explained

Metals

●

Large

high

forces

of

amounts

Metals

t he

of

metal

t he

atoms

are

proper ties

of

bonded

metals

in

metal

given

in

lattices

Unit

bonding

helps

4.4.

us

These

to

are

below.

have

strong

●

some

and

have

melting

points

attraction

of

high

heat

and

between

energy

densities

are

boiling

t he

required

because

points

cations

t he

to

and

because

separate

atoms

are

of

t he

delocalised

t he

packed

electrons.

atoms.

ver y

closely

toget her.

Metals

●

are

electrons

which

These

are

Metals

●

t he

an

good

moving

carried

are

breaking

Use

shell

t he

electricity

moving

current

act

of

as

to

be

heat

heat

because

electrons

carried

because

carriers,

t he

act

delocalised

as

t hrough

of

t he

charge

t he

carriers,

metal.

delocalised

which

allows

electrons.

heat

to

be

metal.

and

t herefore,

atoms

t he

of

The

conductors

malleable

can

roll

metallic

Summary

1

move.

electrons

type,

t he

to

electric

t hrough

same

metal,

conductors

free

allows

Metals

●

good

are

ductile

all

of

over

because

t he

same

each

t he

size.

ot her

atoms

f

into

in

force

new

a

is

metal

are

applied

positions

to

all

of

t he

wit hout

bond.

questions

diagrams

a

hydrogen,

c

hydrogen

to

represent

covalent

H

bonding

b

phosphorus

d

carbon

in

the

following:

triuoride,

PF

2

3

bromide,

HBr

disulde,

CS 2

2

Draw

the

chlorine

shell

and

3

Explain

the

4

Explain

why

diagram

give

the

terms

of

the

formula

covalent

of

‘delocalised

metals

are

the

bonding

electron’

electrical

between

carbon

and

compound.

and

‘metallic

bond’.

conductors.

Objectives

By

the

be

able

end

of

this

topic

you

will

A5.5

●

describe

the

examples

●

relate

the

chloride

●

Structure

and

properties

of

solids

to:

of

its

the

examples

of

and

give

crystals

properties

to

describe

structure

ionic

of

structure

proper ties

atoms,

sodium

structure

simple

The

molecules

individual

chemical

and

give

molecular

of

an

or

ions,

par ticles.

bond

element

This

between

or

compound,

depend

means

t he

on

t hat

par ticles.

t he

t he

n

whet her

forces

of

is

composed

attraction

proper ties

addition,

it

depend

t he

between

on

t he

proper ties

of

t he

type

depend

of

on

t he arrangement of t he par ticles, for example, if t he par ticles are packed ver y

tightly

toget her,

t he

element

or

compound

will

have

a

high

density.

crystals

When ●

distinguish

between

ionic

t he simple

molecular

describe

the

way

structure

and

of

giant

describe

the

diamond

●

relate

of

of

and

and

graphite

the

crystals

because

pattern

●

ionic

●

simple

●

giant

identify

are

bonded

four

different

wit hin

t he

str uctures

solid.

They

based

are

on

known

t heir

par ticles

t hroughout

t he

are

arranged

str ucture.

The

in

four

a

t hree-dimensional,

types

of

solid

are:

cr yst als

●

met allic

molecular

term

molecular

cr yst als

cr yst als

cr yst als.

to

allotropy.

We

have

We

will

unit.

80

can

uses

structures

explain

we

par ticles

graphite

properties

diamond

their

●

the

structure

and

solids,

t he

molecular

crystals

●

which

give

ordered examples

in

crystals

as ●

considering

and

already

be

studied

studying

t he

t he

str ucture

str ucture

and

and

proper ties

proper ties

of

of

t he

metals

ot her

in

Unit

t hree

in

5.4.

t his

Structure

Ionic

Ionic

is

solids

composed

in

represented

by

sodium

n

are

a

Unit

ionic

as

a

result

lattice

in

repeating,

of

an

which

called

formulae

have

of

ionic

t he

bonding.

cations

t hree-dimensional

attraction

empirical

bonding

and

properties

of

solids

or

ionic

formula

ionic

cr ystal

and

An

ionic

anions

are

arrangement

bonds.

units.

onic

All

str ucture,

by

cr ystals

compounds

for

example,

chloride.

structure

form

an

forces

by

ionic

of

formed

regular,

electrostatic

formed

The

Structure

crystals

toget her

strong

are

bonding

crystals

cr ystal

held

and

5.2

you

sodium

and

studied

chloride.

properties

t he

ionic

You

may

of

bonding

sodium

between

remember

t hat

t he

chloride

sodium

and

sodium

chloride

chlorine

to

cr ystal



lattice

is

composed

chloride

ions

or

of

Cl

millions

ions

held

of

sodium

toget her

ions

by

or

strong

Na

ions

ionic

and

bonds.

millions

Also

t hat

of

t he



ions

are

in

formula

a

ratio

unit

for

of

1

Na

sodium

ion

to

1

chloride

Cl

is

ion

and

t hat

t he

empirical

formula

or

NaCl.



ionic



Figure

5.5.1

Crystal

lattice

of



Na



Cl

ion

ion

bonds

sodium

chloride

a)

The

i.e.

proper ties

t he

of

sodium

arrangement

chloride

and

can

bonding

of

be

its

explained

par ticles,

by

as

its

Solid

sodium

chloride

str ucture,

summarised

in –

Table



T able

5.5.1

Properties

of

Property

Explanation

High

The

melting

point

–

about

801 °C

high

the

to

weaken

and

The

to

sodium

melting

sodium

solid

Hard

+

–

+

5.5.1.

ions

point

and

these

is

due

to

chloride

forces

+

–

+

–

–

+

–

+

chloride

and

the

ions.

very

A

strong

large

separate

the

electrostatic

amount

ions

of

from

heat

each

forces

energy

other,

between

is

needed

allowing

the

melt.

sodium

and

chloride

ions

are

closely

packed

and

held

together

by

strong

+ brittle

electrostatic

crystal

forces

lattice,

the

making

ion

the

solid

hard.

layers

move

slightly

charges

come

to

When

with

pressure

respect

to

is

applied

each

to

other

the

–

–

and

+ ions

with

between

the

the

same

like

charges

and

the

lie

next

lattice

to

each

breaks

other.

apart,

i.e.

Repulsion

it

is

occurs

brittle.

+

Soluble

in

When

sodium

chloride

is

added

to

water

the

ions

can

separate

resulting

+

in

–

–

– water

sodium

water

chloride

molecules

being

soluble

attract

the

in

water.

negative

The

partial

chloride

ions

positive

and

the

ends

of

partial

the

polar

negative

+ ends

attract

the

positive

sodium

ions.

This

pulls

the

ions

out

of

the

–

lattice

+ and

the

crystal

molecules

water

a

and

dissolves.

new

The

forces

of

ions

become

attraction

surrounded

now

exist

by

between

the

water

the

ions

and

the

molecules.

Conducts

For

electricity

particles

substance

when

are

which

b)

to

are

conduct

able

to

an

electric

move.

In

current

molten

it

must

(melted)

contain

sodium

Sodium

chloride

dissolved

charged

chloride,

the

ions

– +

i.e.

molten,

NaCl(l),

or

no

longer

sodium

held

chloride

together

to

by

conduct

ionic

bonds

electricity

in

and

the

they

liquid

are

state.

able

to

When

move

allowing

sodium

water

+

Na

Cl

dissolved

in

water,

chloride

an

dissolves

aqueous

in

solution

water,

of

the

sodium

ions

move

chloride

to

freely

throughout

conduct

an

the

electric

water,

allowing

molecule

current.

 i.e.

Figure

5.5.2

What

happens

when

NaCl(aq)

sodium

chloride

dissolves

in

water

81

Structure

and

properties

of

solids

Structure

Simple

Simple

molecular

molecular

and

bonding

crystals

crystals

are

solids

composed

of

small

molecules.

Each

molecule is composed of only a few atoms bonded toget her by strong covalent

bonds. These molecules are t hen arranged in a regular, t hree-dimensional way

to

create

weak

a

These

of

molecular

attraction

intermolecular

formulae

are

Examples

●

simple

forces

ice,

of

used

to

simple

composed

lattice .

between

forces

hold

represent

water

t he

simple

molecular

of

The

t hem

small

as

wit hin

t he

lattice

intermolecular

molecules

molecular

cr ystals

molecules,

molecules

known

toget her.

have

forces .

Molecular

cr ystals.

include:

molecular

formula

H

O 2

●

iodine,

composed

of

iodine

molecules,

molecular

formula

 2

●

dr y

ice,

composed

of

carbon

dioxide

molecules,

molecular

formula

CO 2

●

glucose,

composed

of

glucose

molecules,

molecular

formula

C

H 6

Distinguishing

between

ionic

and

simple

O 12

6

molecular

solids

onic

t he

and

simple

different

summarised



T able

way

in

5.5.2

Property

molecular

in

which

Table

solids

t heir

have

ver y

par ticles

different

are

proper ties

bonded.

These

Comparison

Ionic

of

the

properties

of

ionic

and

solids

simple

Simple

NaCl,

KBr

molecular

molecular

Examples:

I

,

CO

2

of

chemical

bond

Ionic

bonds

These

are

are

very

found

between

ions.

strong.

Covalent

atoms

are

of

very

the

point

Have

the

a

high

strong

ions.

A

melting

ionic

large

needed

to

separate

allowing

amount

weaken

the

the

point

bonds

ions

of

heat

these

from

solid

to

because

between

of

the

energy

bonds

each

Have

of

is

and

other,

a

the

low

between

much

melt.

the

simple

when

Due

and

in

to

being

polar

are

Do

not

strong

the

ionic

move.

water

because

together

they

are

free

but

are

do

held

and

conduct

the

by

to

ions

ionic

move,

current

or

to

not

are

by

free

electricity

dissolved

no

bonds

which

be

solid

together

are

in

in

longer

and

allows

carried.

the

not

is

from

solid

the

because

forces

Not

needed

and

to

separate

other,

melt.

solids

e.g.

forces

weak.

each

to

the

bonds

between

point

forces

rule

e.g.

Some

sublime

iodine

‘like

and

in

in

dissolves

substances

solvents,

like’.

polar

e.g.

in

dissolve

iodine

tetrachloromethane.

conduct

move.

dissolves

dissolve

glucose

because

charged

to

are

energy

non-polar

state

found

Non-polar

dissolves

Do

Intermolecular

substances

water.

These

dioxide.

solvents,

solvents.

when

Polar

between

molecules.

heated,

Follow

soluble

solvents,

organic

(melted)

held

positive

water,

electricity

bonds

They

of

are

tetrachloromethane,

ions

molten

electric

e.g.

other

when

an

82

and

most

non-polar

conduct

because

to

in

kerosene,

gasolene

Conductivity

ions,

solvents,

insoluble

e.g.

composed

negative

occur

molecular

carbon

O

intermolecular

these

the

H

melting

molecules

allowing

Solubility

are

the

heat

weaken

solids

2

These

weak

solids

molecules.

strong.

attraction

,

2

bonds

in

molecules.

Melting

of

are

5.5.2.

Examples:

T ype

because

differences

electricity

they

particles

do

not

which

in

any

have

are

free

any

Structure

and

bonding

Investigating

ionic

Your

and

teacher

may

observation,

●

manipulation

will

(simple

be

in

solubility

use

and

supplied

this

conductivity

properties

of

solids

of

solids

activity

and

electrical

and

to

assess:

reporting

measurement.

with

sodium

solids),

solvent)

Figure

and

molecular

recording

molecular

(non-polar

shown

the

simple

●

Y ou

Structure

and

chloride

distilled

the

water

apparatus

(ionic

(polar

used

to

solid),

glucose

solvent),

test

and

iodine

tetrachloromethane

electrical

conductivity

5.5.3.

Method

1

Investigate

following

the

the

solubility

of

instructions

sodium

chloride,

iodine

and

glucose

by

below.

3

●

Place

5 cm

●

Add

small

of

a

glucose

Shake

●

Repeat

●

in

the

of

water

into

sodium

second

tube

thoroughly

each

chloride

and

and

a

of

to

three

the

crystal

observe

of

if

test

rst

tubes.

tube,

iodine

each

to

a

small

the

spatula

third

switch

tube.

substance

A

not.

experiment

using

tetrachloromethane

instead

of

water.

Investigate

shown

distilled

tubes

or

the

distilled

2

to

the

dissolves

of

spatula

the

electrical

Figure

5.5.3

conductivity

and

by

of

following

solutions

the

using

instructions

the

apparatus

beaker

below.

carbon

electrodes

Make

●

three

solutions

by

adding

three

small

spatulas

of

sodium solution

3

chloride

to

25 cm

of

distilled

water,

three

small

spatulas

of

glucose

3

to

to

of

distilled

water

and

one

crystal

of

iodine

to

25 cm

Place

the

switch.

not

the

and

3

Draw

up

4

What

can

a

an

test

table

you

three

into

ammeter

current,

conduct

them,

in

electrodes

If

electric

if

it

electric

the

to

the

sodium

record

not

a

two

all

beakers.

chloride

reading,

register

current.

other

conclude

separate

registers

does

a

Remove

solutions

your

the

the

for

the

solution

and

solution

reading,

Figure

then

conducts

the

electrodes

electrical

close

solution

and

the

type

of

solid

(ionic

●

the

type

of

solid

and

strong

a

covalent

gi ant

or

its

t hroughout

t he

bonds

does

conductivity.

simple

molecular)

and

its

solubility

?

conductivity?

in

a

composed

regular,

such

of

non-metal

t hree-dimensional

The

covalent

t hat

a

giant

bonds

bonded

arrangement

exist

molecular

atoms

between

cr ystal

is

to

t he

also

by

Did

macromolecule,

i.e.

formula

is

of

giant

●

diamond,

●

graphite,

is

form

atoms

known

as

it

is

a

molecule

composed

of

millions

of

atoms.

used

to

represent

giant

molecular

in

type

of

and

sand.

occurs

molecular

composed

of

cr ystals

carbon

silicon

composed

dioxide,

empirical

of

carbon

atoms,

composed

of

silicon

and

as

formula

empirical

oxygen

a

quartz.

Earth’ s

of

crust.

almost

the

main

all

Quartz

It

every

is

a

rock

component

of

this

crystalline

forms

large

These

ornamental

precious

C

formula

silica

form

that

is

known

almost

and

atoms,

are

beautiful

very

stones

gemstones.

is

purple

popular

and

For

semi-

example,

quartz,

citrine

is

C orange

and

rose

quartz

is

a

empirical pink

formula

known

abundant

The

yellow

●

also

most

cr ystals.

include:

atoms,

the

is

amethyst

also

the

Almost

in

crystals.

Examples

know?

dioxide,

silica,

pure

empirical

you

component

as

a

solution

results.

electrical

are

lattice .

lattice

a

crystals

crystals

molecular

measure

of

clean

mineral

molecular

to

an

as

Gi ant

Apparatus

conductivity

the

Silicon

molecular

5.5.3

electrical

about:

●

Giant

tested

of 

tetrachloromethane

●

be

3

25 cm

to

rose-red

variety.

SiO 2

83

Structure

and

properties

of

solids

Structure

Structure

Diamond

to

four

is

The

in



carbon

consists

t hroughout

t he

bonds,

t he

5.5.3

Properties

melting

about

word

which

Greek

means

diamond

diamond

is

another

known

the

as

cut

using

make

is

covalent

hard

be

from

hard

of

each

Diamond

not

conduct

has

by

bonds

heat

other,

is

the

is

covalent

useful

industry

as

the

carbon

needed

allowing

hardest

of

in

the

between

energy

the

solid

naturally

bonds

diamond

to

diamond,

is

a

you

to

strengt h

melting

str ucture,

as

of

anot her

of

point.

summarised

occurring

often

are

these

very

strong.

forces

and

A

very

separate

large

the

atoms

melt.

between

is

atoms

solid.

the

used

The

carbon

The

valence

electrons

does

not

have

of

the

any

carbon

‘free’

atoms

in

hardness

atoms.

cutting

electrons

are

to

all

and

shared

conduct

is

This

due

to

the

property

is

high

very

drilling.

an

between

electric

the

atoms.

current.

a

corner

cutting,

to

gems

create

used

to

(b)

Figure

5.5.4

(a)

A

cut

diamond

and

(b)

ago

at

in

the

an

we

see

(if

depths

below

molten

mantle

where

temperature

Powerful

brought

Earth’ s

diamond

today

not

of

bonds

billions)

about

the

Earth’ s

rock

are

the

of

the

atom

pressure

both

magma

the

uncut

know?

carbon

Earth’ s

then

t he

high

cr ystal

polished

millions

kilometres

high.

of

A

one

technique

powder

diamonds

surface

and

ver y

it.

to

from

hard,

the

After

then

sparkling

formed

years

150

Because

a

its

weaken

covalent

of

around

bonded

covalently

jewellery.

Did

were

bonded

diamond

strength

Carbon



Most

atoms

bonds.

and

explained

(a)

?

tetrahedron

carbon

is

‘adámas’,

so

using

diamond

beautiful,

comes

word

bruiting.

diamond

a

atom

‘unbreakable’.

Because

of

Each

know?

‘diamond’

ancient

of

covalent

amount

electricity

the

can

in

t hese

strong

diamond

The

–

arranged

of

diamond

atoms.

extremely

Very

Does

The

by

is

Explanation

Extremely

you

atoms

Property

high

carbon

millions

cr ystal

of

3550 °C

Did

of

of

bonding

5.5.3.

T able

point

?

of

diamond

proper ties

Table

properties

composed

ot her

diamond

and

and

extremely

eruptions

diamonds

to

the

surface.



Structure

Graphite

is

and

also

Figure

5.5.5

properties

composed

of

Structure

of

carbon

of

diamond

graphite

atoms.

Each

atom

is

bonded

covalently

to three other carbon atoms, forming hexagonal rings of atoms which link up to

form at sheets or layers of carbon atoms. The four th electron of each atom is

not bonded to another atom and becomes delocalised. These layers of carbon

atoms

then

atoms

in

weak

forces

str ucture,

84

lie

the

as

on

top

layers

of

of

are

each

ver y

attraction.

summarised

other.

strong,

The

in

The

covalent

however,

proper ties

Table

5.5.4.

of

the

bonds

layers

graphite

between

are

can

held

be

the

carbon

together

explained

by

by

its

Structure

and

bonding

Structure

 Property

Explanation

Very

The

high

point

–

melting

about

3600 °C

from

in

Soft

covalent

amount

and

each

weak

over

Good

of

conductor

The

electricity

other,

the

fourth

Because

molten

act

of

These

this,

the

between

as

a

of

the

carbon

needed

the

in

a

to

solid

metals,

resulting

electron

crystal.

is

allowing

for

other

can

between

energy

forces

each

graphite

bonds

heat

containers

The

lubricating

of

to

e.g.

melt.

are

these

very

strong.

forces

Because

of

and

this,

A

very

separate

graphite

5.5.4

the

can

of

carbon

crystal

atoms

which

allow

feels

the

slippery.

layers

to

Because

slide

of

this,

lubricant.

each

moving

graphite

carbon

atom

electrons

is

used

as

can

is

delocalised

carry

allowing

electricity

electrodes

during

it

through

to

the

move

within

crystal.

electrolysis.

Did

Constructing

fit



together

models

of

sodium

chloride,

diamond

Figure

may

use

this

activity

to

and

Structure

Exam

of

graphite

tip

is

important

that

you

can

draw

measurement. and

supplied

with

similar

5.5.6

assess: It

(or

of

and

✔

manipulation

plasticine

form

layers

graphite

be

stable

graphite

layers

will

more

diamond.

forces

between

Y ou

a

atom

weak

●

is

than

know?

bond

carbon

teacher

you

layer

covalent

Your

graphite

used

carbon

how

of

solids

atoms

be

Graphite

graphite

Properties

of

large

?

one

properties

crucibles.

layers

‘soft’

atoms

weaken

T able

and

toothpicks

round,

soft

and

material

small,

to

use

different

as

coloured

atoms

or

pieces

of

describe

sodium

chloride,

graphite

ions).

their

the

and

that

properties

structure

diamond

you

and

can

uses

of

and

relate

to

their

Method structures.

Using

show

the

diagrams

their

●

sodium

●

diamond

●

graphite.

Use

the

Unit

5.5

to

help

you,

make

models

of

the

following

to

chloride

plasticine

represent

in

structure:

the

to

bonds

represent

between

atoms

or

ions

and

the

toothpicks

to

them.

85

Structure

and

properties

of

solids

Structure

and

bonding

Allotropy

Key

!

fact Diamond

t hey Allotropes

are

different

are

same

of

the

same

physical

bot h

graphite

made

are

out

of

known

t he

as

same

allotropes

element,

of

carbon.

carbon,

This

is

but,

in

t he

occurence

of

t hese

because

solid

state,

structural

t heir forms

and

element

in

carbon

atoms

are

bonded

differently.

The

different

the

allotropes

state.

is

known

as

allotropy

Because diamond and graphite are bot h composed of carbon atoms, t hey have

t he

Key

!

same

different

Allotropy

is

the

existence

structural

forms

t hey

proper ties.

have

physical

different

However,

cr ystal

t heir

atoms

str uctures

are

which

bonded

result

in

differently,

t hem

having

proper ties.

of

Several different

chemical

t herefore,

fact

of

ot her

elements

exhibit

allotropy.

These

include

sulfur

and

the

phosphor us, when in the solid state, and oxygen, when in the gaseous state. same

element

in

the

same

physical

state.

Summary

1

Did

?

you

Converting

to

diamond

dream

the

of

high

its

to

bonding

that

the

and

force

consuming

and

long

crystal

is

Potassium

structure

does

each

of

the

following

have?

b

Iodine

c

Ice

d

Graphite

e

Calcium

bromide

held

extremely

carbonate

temperatures

carbon

to

have

2

Why

3

Compare

4

Why

are

5

Why

can

can

sodium

chloride

dissolve

in

water?

change

meant

extremely

the

melting

points

of

an

ionic

solid

and

a

simple

molecular

solid.

time-

diamonds

extremely

hard?

energy-intensive.

Consequently

it

achieved

any

with

a

the

structure

process

of

a

graphite

throughout

However,

pressures

required

been

scientists

world.

type

know?

inexpensive

has

What

questions

has

not

real

yet

been

graphite

conduct

an

electric

current?

success.

Key

●

concepts

Atoms

bond

wit h

conguration,

●

Atoms

can

electronic

●

There

are

each

i.e.

lose,

t hat

gain

ot her

of

or

to

t he

share

attain

nearest

a

more

noble

valence

stable

gas

in

electrons

to

electronic

t he

periodic

attain

a

table.

stable

conguration.

t hree

main

types

of

chemical

bonding:

ionic,

covalent

and

metallic.

●

A

chemical

t he

●

●

redistribution

Chemical

can

be

There

are

V alence

form

Ionic

t hree

Metal

form

86

force

t heir

by

main

formulae

number

ot her

of

atoms

form

negative

of

valency

a

result

chemical

t hat

results

from

is

t he

positive

of

ionic

or

covalent

bonding

formulae:

molecular

formulae,

formulae.

t he

number

number

composed

called

atoms

formulae.

Valence

forming

ions

as

empirical

involves

between

electrons.

types

atoms.

atoms,

attraction

formed

and

or

of

chemical

compounds

bond ing

non-metal

●

of

a

compounds

wit h

formulae

●

is

represented

str uctural

●

bond

of

transfer

two

of

of

can

bonds

be

used

different

electrons

an

to

atom

write

can

empirical

elements.

from

metal

atoms

to

ions.

ions

called

anions

cations

and

non-metal

atoms

Structure

●

n

ionic

t he

●

A

●

onic

ions

lattice

metal

Atoms

forces

n

to

or

The

strong

electrons

Four

●

The

●

Simple

in

a

t he

of

as

attraction

ionic

solids

between

bonds,

an

t he

empirical

ions

made

arrangement

hold

shar ing

from

of

shared

of

formula

par ticles.

or

formula

present.

several

polyatomic

A

in

held

t he

a

atoms

bonded

ions .

electrons

pair

of

are

between

electrons

bonded

chemical

toget her

nuclei

electrons

cations

non-

for ms

a

of

by

t he

toget her

strongly

reaction.

t he

strong

atoms

and

electrostatic

t he

bonding

become

which

delocalised

remain.

These

and

are

able

delocalised

to

move

electrons

are

electrons.

force

of

attraction

cations

forms

between

t he

t he

metallic

delocalised

bond

which

holds

toget her.

metals

solid

of

are

due

str uctures

wit hin

t he

different

par ticles

result

t he

and

from

molecular

crystals

be

solid

t he

bonding

identied

str uctures

arrangement

bonding.

and

anions

composed

t hree-dimensional

wit hin

based

t he

on

way

to

forces

depend

of

They

are

t he

are

held

arrangement

are

intermolecular

t he

metal

t he

way

lattice.

t he

solids.

ionic

cations

to

can

t he

t hree-dimensional

Weak

which

unit

are

positive

of

which

regular,

lattice.

atoms

between

bonded

t heir

repeating,

●

t he

single

molecule

lattice

are

in

of

a

electrostatic

crystals

lattice

as

molecules.

mobile

proper ties

Ionic

of

are

known

regular

using

ratio

involves

as

metal

different

between

t he

forces

known

of

electrons.

proper ties

par ticles

are

valence

as

and

metal

●

represented

group

a

of

t he

known

The

anions,

properties

lattice.

compounds

for m

a

t he

also

●

is

pairs

metals,

t he

cr ystal

give

ions

attraction

between

●

are

behave

wit hin

of

electrostatic

t hree-dimensional

ionic

to

a

strong

negative

and

bond

molecule

pair

a

bond ing

atoms

enough

●

in

t he

and

in

which

These

covalent

●

of

ions

Covalent

A

is

compounds

toget her.

●

cations

toget her

bot h

Many

Structure

compounds,

cr ystal

unit,

●

bonding

positive

t hese

●

and

by

of

create

strong

a

in

ionic

a

bonding

of

an

ionic

regular,

bonds.

molecules

simple

t he

t he

composed

toget her

small

between

on

par ticles.

arranged

molecular

molecules

hold

t hem

toget her.

●

onic

and

●

Simple

polar

●

cr ystals

t hey

molecular

solvents

Gi ant

bonds

in

molecular

high

melting

electricity

cr ystals

and

molecular

covalent

giant

have

conduct

t hey

have

do

crystals

a

Diamond

and

graphite

are

●

Diamond

and

graphite

are

●

carbon,

Diamond

is

ver y

are

also

●

element,

not

regular,

lattice,

but

t heir

hard,

has

points,

when

low

or

melting

conduct

dissolve

of

points,

as

a

of

allotropes.

atoms

high

are

polar

in

most

in

solvents

water.

dissolve

any

non-metal

t hree-dimensional

known

in

dissolved

electricity

composed

examples

a

most

molten

in

non-

state.

atoms

arrangement

bonded

to

form

by

a

macromolecule.

giant

They

are

bonded

melting

molecular

cr ystals.

composed

of

t he

same

differently.

point

and

does

not

conduct

electricity.

●

Graphite

conduct

is

‘sof t’

and

lubricating,

has

a

high

melting

point

and

does

electricity.

87

Practice

exam-style

questions

Structure

7

Practice

exam-style

Multiple-choice

1

Which

of

calcium

t he

Ca

(PO

B

Ca(PO

2

A

isotopes

B

isomers

C

allotropes

following

is

t he

correct

formula

for

D

allomers

carbon

of

of

carbon

carbon

Structured

3

question

2

The

table

gives

t he

mass

number

and

atomic

number

of

4

Ca

(PO

3

X

of

)

four

The

are:

carbon

questions

8

2

of

PO

3

D

graphite

questions

)

4

4

Ca

and

bonding

phosphate?

A

C

Diamond

and

Y

elements.

)

4

2

formula

and

different

of

would

t he

compound

formed

between

Element

Mass

number

Atomic

fluorine

19

9

neon

20

10

aluminium

27

13

phosphorus

31

15

number

atoms

be:

a

i)

Which

element

would

not

be

capable

of

forming

compounds?

ii)

b

A

XY

B

X

Give

Two

an

ionic

Name

(1

reason

elements

form

i)

a

in

for

t he

your

table

answer.

are

(2

capable

of

mark)

marks)

bonding

to

compound.

t hese

elements.

(1

mark)

Y

3

ii) C

Give

t he

formula

of

t his

compound.

(1

mark)

XY 3

iii) D

X

By

means

bonding

A

two

B

a

occurs

c

between:

Two

and

a

i)

non-metal

ii) metalloid

and

a

4

An

two

cross

diagram,

show

atom

wit h

an

atomic

number

of

15

and

an

atom

a

in

covalent

Name

Give

formed.

table

are

(3

capable

of

atomic

number

A

form

a

B

form

an

elements.

formula

of

t his

compound.

Draw

a

dot

and

cross

diagram

to

show

C

form

a

D

not

of

9

covalent

bonding

in

ionic

metallic

bond

aqueous

wit h

solution

A

water

B

electrons

mark)

t his

Describe

t he

compound.

(2

marks)

i)

Why

is

bonding

aluminium

in

able

aluminium.

to

conduct

an

(2

marks)

electric

compound

can

Total

only

conduct

electricity

when

9

conduct

become

free

a

electricity

when

t hey

free

when

t hey

t he

lattice

are

are

response

Wit h

in

i)

aqueous

ii)

become

in

aqueous

b

marks

when

t hey

are

in

question

of

a

sodium

diagram

in

EACH

case,

describe

chloride

reference

each

sodium

to

of

t he

of:

graphite.

Wit h

i) free

aid

str ucture

explain

become

15

in

solution

protons

mark)

ot her

because:

molecules

ions

(1

lattice

each

solution

D

mark)

(1

compound

compounds

t he

(1

would:

Extended

C

to

t he

current?

onic

marks)

bonding

compound.

t hese

t he

is

t he

wit h

ii)

5

how

non-metals

d an

and

non-metal

iii) D

compound

elements

form

metals

metal

a

dot

3

t his

onic

C

a

Y

7

3

of

t he

t he

str ucture

and

type

of

(3

marks)

(3

marks)

bonding,

following:

chloride

is

able

to

conduct

electricity

aqueous

when

molten

(2

marks)

solution

ii)

6

Which

of

t he

molecular

following

is/are

t he

proper ties

of

a

simple

They

are

usually



They

conduct



They

have

A





iii)

soluble

electricity

in

in

water.

any

state.

is

able

to

conduct

electricity

in

state

compound?



graphite

(2

bot h

sodium

melting

c

Some

t he

types

chloride

and

graphite

have

points.

of

sand

high

(3

consist

of

silica,

SiO

.

solid

marks)

marks)

Silica

is

2

low

melting

points.

relatively

state and

and



C



and

D



has

a

does

high

not

conduct

melting

electricity

point.

in

Describe

any

t he

only

bonding B

hard,



which

you

would

expect

to

nd

in

silica.

only

(2 and



Total

88

only

mark)

only

15

marks

Chemical

equations

and

A6 reactions

Chemical

equations

use

symbols

and

formulae

to Objectives

represent

chemical

standards

for

change.

writing

There

chemical

are

universal

equations

which

make

By

the

be

able

for

chemists

all

over

the

world

to

interpret

of

this

the

understand

the

conventions

equations

written

by

others.

The

theory

behind

is

very

important

in

the

chemical

you

will

different

used

when

writing

chemical chemical

reactions

topic

to:

it

●

possible

end

industry.

It

●

write

equations

balanced

chemical

equations

reduces

the

risk

of

accidents,

can

improve

productivity ●

and

can

increase

the

yield

of

chemicals.

soluble

●

A6.1

A

Writing

chemical

using

formed

The

equation

symbols

reactants,

and

and

are

t he

and

any

all

on

t he

reactions,

i.e.

are

representation

The

lef t

chemical

chemicals

side

t he

of

t he

by

a

an

are

or

a

compound

insoluble

balanced

in

ionic

is

water

equations.

equations

chemical

are

equation

products,

separated

of

t hat

write

whether

reaction

reacting,

and

shown

t he

on

t he

i.e.

t he

chemicals

right

side.

arrow:

products

Understanding

that

shor t hand

products

reactants

Chemists

a

formulae.

shown

during

reactants

is

balancing

predict

use

person

the

chemical

same

reading

a

equations

conventions

chemical

when

equation

writing

will

chemical

understand

equations

exactly

so

what

it

means. The conventions used when writing chemical equations are as follows:

●

The

symbol

side

of

on

●

An

t he

A

plus

●

A

state

and

●

( )

on

is

t he

and

products.



solid

is

The

liquid



gas

(aq)



aqueous

conditions

a

above

specic

about

to

of

each

symbol

separate

or

reactant

formula

t he

state

is

of

reactants

catalyst.

wit hout

A

are

a

a

used

1 1.2.

t he

solution

for

is

a

up

t he

as

placed

each

on

t he

product

lef t

is

placed

from

t he

products.

and

t he

symbol

where

t he

or

state

water

reaction

to

temperature,

t he

each

right

product.

it

means

formula

of

t he

The

‘and’.

of

each

reactants

follows:

chemical

in

on

physical

are

specic

For

and

af ter

used

required

e.g.

catalyst

being

Unit

brackets

i.e.

reactant

wit h’

indicates

symbols

arrow,

each

‘reacts

in

This

which

in

separate

solution,

t he

catalysts

to

means

written



reaction

used

used

lef t

(l)

or

t he

‘produces’.

(g)

written

is

product.

(s)

Any

a

means

symbol

reactant

formula

and

side.

)

sign

sign

chemical

(

arrow

plus

or

equation

right

arrow

The

●

t he

a

is

occur

solvent.

can

specic

substance

reaction.

t he

You

which

will

be

pressure

speeds

learn

up

more

example,

898 °C

CaCO

(s)

CaO(s)



CO

3

This

shows

decompose

(g) 2

t hat

into

calcium

calcium

carbonate

oxide

and

requires

carbon

heating

to

898 °C

for

it

to

dioxide.

89

Writing

and

balancing

chemical

equations

Chemical

●

f

t he

reaction

NH

is

reversible,

Cl(s)

NH

4

●

will

The

equation

balance

When

learn

on

more

must

each

t he

AgNO

(g)

an

about



arrow

(

)

in



so

t he

t he

t hat

arrow

sections

equation,

following

(aq)

of

each

reactions

t he

is

number

t he

t hat

par t

in

same.

For

example,

of

6.2.

atoms

will

or

ions

learn

of

how

each

to

follow.

represents

a

word

or

a

statement.

example:

KCl(aq)

AgCl(s)



KNO

(aq) 3

equation

chloride

used.

Unit

You

3

The

is

reactions

HCl(g)

reversible

balance

side

equations

reading

Consider

double

and

3

You

element

a

equations

reads

solution

as

to

follows:

‘silver

produce

solid

nitrate

silver

solution

chloride

reacts

and

wit h

potassium

potassium

nitrate

solution’.

Balancing

You

should

chemical

have

noticed

equations

t hat

in

t he

t hree

chemical

equations

above,

t he

atoms are not changed during t he reactions. The way in which t he atoms are

bonded to each ot her changes, but t here is t he same number of atoms of each

element

created

When

on

nor

bot h

writing

atoms

of

sides

destroyed

each

a

of

in

each

chemical

element

equation.

chemical

equation,

on

t he

n

ot her

reactions,

right

you

side

t hey

must

of

words,

are

ensure

t he

atoms

only

t hat

equation

are

neit her

rearranged.

is

t he

t he

number

same

as

of

t he

number on t he lef t side. A chemical equation t hat conforms to t his is known

as

a

balanced

You

learnt

about

understand

2H

●

2H

●

H

chemical

how

represents

represents

equation .

writing

to

chemical

balance

two

one

formulae

chemical

atoms

of

hydrogen,

molecule

of

in

equations,

not

hydrogen,

Unit

5.

consider

bonded

To

t he

help

you

to

following:

toget her

consisting

of

two

atoms

of

2

hydrogen

●

2H

bonded

represents

toget her

two

molecules

of

hydrogen

and,

in

total,

four

atoms

of

2

hydrogen

H 2

●

3CO

represents

t hree

molecules

of

carbon

dioxide.

n

total,

t he

number

2

of

●

atoms

Ca(NO

of

) 3

each

element

represents

one

is

3C

and

formula

6O

unit

atoms

of

calcium

nitrate,

which

consists

2

2

of

one

Ca

ion

and

two

NO

ions;

t herefore,

t he

number

of

atoms

of

3

2H 2

each

●

element

2Ca(NO

) 3



Figure

6.1.1

Different

atoms

and

1Ca,

2N

represents

and

two

6O.

formula

units

of

calcium

nitrate.

n

total,

t he

2

representations

number of

is

of

atoms

of

each

element

is

2Ca,

4N

and

12O.

molecules

The number in front of each formula in t he list above is called t he

A

coefcient

equations.

to

produce

formulae

H

as

(g)

of

is

not

t he

hydrogen

written.

reaction

chloride

Coefcients

between

gas.

We

are

used

hydrogen

can

gas

summarise

when

and

t his

balancing

chlorine

reaction

gas

using

follows:



Cl

2

Studying

one

Consider

coefcient.

(g)

HCl(g)

2

t his

equation

we

can

see

t hat

t here

are

two

atoms

of

hydrogen

on

t he lef t side, but only one atom on t he right side. Also, t here are two atoms of

chlorine

on

t he

lef t

side,

but

only

one

atom

on

t he

right

side.

The

equation

is, t herefore, not balanced. f a coefcient, 2, is placed in front of t he formula

90

Chemical

for

of

equations

hydrogen

chlorine

H

(g)

chloride,

on



t he

Cl

2

The

t

ver y

cannot

be

t he

elements

writing

write

should

Write

now

two

atoms

of

hydrogen

and

two

balancing

chemical

equations

atoms

balanced.

t he

of

t heir

The

of

t hat

when

number

t he

of

always

balancing

balancing

atoms

coefcient

in

remain

balanced

and

be

note

must

of

front

t he

t he

of

a

t he

elements

formula.

formulae

can

The

only

be

subscripts

same.

chemical

chemical

equations

equations

equations,

t he

guidelines

outlined

followed.

correct

t he

– Seven

to

changing

When

note

gives

and

2HCl(g)

changed.

by

to

●

now

Writing

side:

(g)

is

How

below

t his

right

impor tant

changed

af ter

reactions

2

equation

is

and

chemical

formula

for

each

reactant

and

product,

taking

following:

t he

free

common

st ate.

These

elements

are

H

,

involving

any

of

t hese

exist

N

2

,

O

2

,

as

F

2

elements,

,

diatomic

Cl

2

wr ite

,

Br

2

t he

molecules

and



2

.

n

when

in

reactions

2

for mula

for

t he

diatomic

molecule.

–

n

reactions

atomic

wr ite

involving

symbol

of

t he

ot her

elements

element,

e.g.

if

in

a

t heir

free

reaction

st ate,

wr ite

involves

t he

magnesium,

Mg.

●

Separate

t he

●

Separate

each

●

Write

●

Star t

t he

reactants

and

reactant

state

and

symbol

balancing

t he

products

each

af ter

in

an

product

each

elements

by

by

reactant

t he

arrow.

a

plus

and

product

sign.

product.

immediately

af ter

t he

arrow

rst.

●

Any

polyatomic

ion

which

appears

unchanged

from

one

side

to

t he

2

ot her

can

be

balanced

as

a

unit,

e.g.

if

SO

appears

at

bot h

sides,

✔

4

consider

it

as

a

single

unit

(see

Example

It ●

f

any

compounds

contain

hydrogen

Exam

or

oxygen,

balance

is

essential

from

last

and

balance

oxygen

last

(see

Examples

2

and

f

any

elements

balance,

e.g.

occur

Fe,

Ca,

in

Cl

,

t heir

Use

of

coefcients

each

in

element

t he

leave

t hese

until

t he

ver y

last

to

of

the

each

lef t

and

formula

right

to

sides.

balance

The

t he

number

formulae

must

of

not

atoms

reactions

Always

same

2

front

on

state,

O

2

●

free

you

chemical

can

write

equations

for

3). all

●

that

hydrogen balanced

second

tip

4).

of

check

type

each

you

that

and

arrow,

and

the

correct

you

on

that

encounter.

have

number

element

the

will

of

both

you

the

atom

sides

have

of

given

be

state

symbol

for

each

changed. reactant

●

Check

t hat

t he

coefcients

are

in

t he

lowest

possible

and

product.

ratio.

Examples

1

Write

a

balanced

chemical

equation

for

the

reaction

in

which

magnesium

burns in oxygen to form magnesium oxide as the only product.

Write

t heir

each

t he

chemical

state

element

Mg(s)

formulae

symbols.



on

O

Af ter

each

(g)

of

t he

doing

side

of

reactants

t his,

t he

and

determine

products

t he

toget her

number

of

wit h

atoms

of

arrow:

MgO(s)

2

Reactants

Products

Mg



1

Mg



1

O



2

O



1

91

Writing

and

balancing

chemical

equations

Chemical

O

does

not

balance.

Mg(s)



O

Balance

by

placing

a

2

in

equations

front

of

t he

and

reactions

MgO

2MgO(s)

(g) 2

Reactants

Now

Products

Mg



1

Mg



2

O



2

O



2

Mg

does

2Mg(s)

not



O

balance.

Balance

by

placing

a

2

in

front

of

t he

Mg

2MgO(s)

(g) 2

Reactants

The

2

gas

a

(C



2

Mg



2

O



2

O



2

Write

t heir

is

now

balanced

H 3

on

Mg

equation

Write

Products

)

and

balanced.

chemical

oxygen

to

equation

form

t he

each

C

chemical

symbols

side

H 3

of

(g)

t he



O

8

formulae

and

of

t he

determine

reaction

and

between

propane

steam.

of

leaving

(g)

CO

2

(g)



H

2

C



1

H



8

H



2

O



2

O



2

elements

oxygen

t he

products

atoms

of

toget her

each

O(g)

CO

balance.

in

.

its

free

Balance

Balance

state

t he

t he

until

H

by



1



3

carbon

last.

and

Balance

placing

a

4

in

hydrogen

t he

C

front

by

of

H 3

(g)



O

8

t he

H

still

(g)

3CO

2

(g)



4H

2

O(g) 2

C



3

C





8

H



8

O



2

O



6

not

3

Products

H

does

a

O 2

Reactants

O

rst,

placing

2

C

wit h

element

Products

3

of

of

2



t he

and

number

C

t he

front

reactants

t he

arrow:

Reactants

in

t he

dioxide

8

state

None

for

carbon

balance.

Balance

by

3



placing

4

a



5

10

in

front

of

t he

O 2

C

H 3

(g)



5O

8

(g)

3CO

2

The

3



4H

C



3

C



3



8

H



8

O



10

O



6

t he

is

now

) 3

(aq)



4



10

balanced.

following

Ca(HCO

O(g) 2

Products

H

equation

Balance

(g) 2

Reactants

equation:



HCl(aq)

2

CaCl

(aq)



CO

2

(g)



H

2

O(l) 2

Determine the number of atoms of each element on each side of the arrow:

Ca(HCO

) 3

(aq)



HCl(aq)

2

CaCl

(aq)

92

Ca



1

H



2



CO

2



1



(g)



2

Reactants

3

Ca



1

H



2

1

C



2

C



O



6

O



2

Cl



1

Cl



2



1

H

O(l) 2

Products



3

Chemical

Star t

equations

by

arrow.

front

and

balancing

Ca

of

t he

balances,

t he

reactions

Writing

elements

but

Cl

does

in

t he

not

product

balance.

immediately

Balance

) 3

(aq)



2HCl(aq)

CaCl

2

(aq)

front

of

Ca



1

H



2

C



2

O



Cl



t he



CO

2

Ca



1

H



2

C



1

6

O



2

2

Cl



2



carbon

CO

Ca(HCO

.

) 3

2



and

4

hydrogen

Balance

t he

H

next.

by

Balance

placing

a

2

t he

in

C



by

front

(aq)



2HCl(aq)

CaCl

2

(g)



1

H



2

C



2

O



Cl



t he

of

(aq)





) 3

t his

is

O(l)



3

placing

t he

2CO

H

a

2

in

O

1

H



4

C



2

6

O



4

2

Cl



2



2

(aq)



(g)



4

2H

O(l) 2



2



6

balanced.

equation

NaOH(aq)

Al(OH)

3

(s)



NaNO

3

t he



2



now

reaction,

H

Products

Ca

following

Al(NO

n

in

2

1

2

Ca

equation

Balance

2

2

Reactants

4

equations

Products

2

The

chemical

t he

a

2

Reactants

t he

af ter

placing

balancing

HCl

Ca(HCO

Balance

by

and

NO

and

t he

OH

ions

are

(aq) 3

polyatomic

ions

which

3

remain

treated

unchanged

as

element

single

at

each

Al(NO

) 3

from

units

side

(aq)



one

when

of

t he

side

to

t he

ot her.

determining

t he

They

number

of

t herefore,

atoms

NaOH(aq)

Al(OH)

3

(s)



NaNO

3

Al

NO



1



3

of

(aq) 3

Products

Al

NO

3



1



1

3

Na



1

Na



1

OH



1

OH



3

Start with the product immediately after the arrow.

Balance by placing a

3 in front of the

OH

does not balance.

NaOH. Move on to the next product.

does not balance. Balance by placing a

3

in front of the

NaNO

3

3

Al(NO

) 3

(aq)



3NaOH(aq)

Al(OH)

3

Al

NO

State



3NaNO



1



3

Al

NO



1



3

3

Na



3

Na



3

OH



3

OH



3

is

now

symbols

(aq) 3

Products

3

equation

(s) 3

Reactants

The

each

arrow.

Reactants

NO

are,

of

balanced.

ionic

compounds

n Unit 5.5 you learnt t hat most ionic compounds are soluble in water. Some

ionic

compounds

involving

ionic

compound

is

are,

however,

compounds,

soluble

or

it

insoluble

is

ver y

insoluble

in

in

water.

impor tant

water.

f

it

to

is

When

know

writing

equations

whet her

insoluble,

t hen

t he

it

ionic

would

93

Writing

and

balancing

chemical

equations

Chemical

always

t he

t he



be

state

solubility

T able

6.1.1

Solubility

All

and

t he

of

state

(aq).

ionic

Solubility

symbol

Table

(s).

6.1.1

compounds

of

ionic

e.g.

f

it

gives

in

is

soluble

t he

it

would

solubility

and

reactions

usually

r ules

for

be

given

determining

water.

compounds

rule

compounds

soluble,

All

given

symbol

equations

in

water

Exceptions

of

Group

I

compounds

metals

of

are

lithium,

None.

sodium

potassium.

ammonium

Most

nitrates

compounds

and

are

ethanoates

soluble.

are

None.

soluble.

Silver

ethanoate

(CH

COOAg)

is

only

slightly

soluble.

3

Most

chlorides,

bromides

and

iodides

are

Those

soluble

(PbCl

of

)

lead

and

and

silver

lead(II)

are

insoluble.

bromide

(PbBr

2

soluble

Most

sulfates

are

soluble.

Those

in

of

(CaSO

)

hot

All

Exam

hydrogencarbonates

are

soluble.

Lead(II)

are

chloride

moderately

water.

lead

and

and

barium

silver

sulfate

are

insoluble.

(Ag

4

✔

)

2

SO

2

)

are

Calcium

slightly

sulfate

soluble.

4

None.

tip Most

carbonates

and

phosphates

are

Those

of

Group

I

metals

and

ammonium

are

soluble.

Those

of

Group

I

metals

and

ammonium

are

soluble.

insoluble

It

is

essential

that

you

learn

the Most

solubility

rules

so

that

you

metal

hydroxides

are

insoluble.

can Barium

hydroxide

(Ba(OH)

)

is

moderately

soluble,

2

give

the

correct

state

symbols

calcium

hydroxide

(Ca(OH)

)

is

slightly

soluble

and

2

when

This

writing

is

chemical

particularly

magnesium

equations.

important

ionic

metal

oxides

t hey

of

a

ions

Those

two

an

ion

●

an

element

very

slightly

of

Group

water

to

I

metals,

form

the

calcium

equivalent

and

barium,

react

hydroxides.

t he

end

atoms

up

in

a

or

ions

which

different

state

actually

from

take

t he

one

par t

in

in

a

which

known

form

be

in

a

may

as

a

to

free

form

an

insoluble

compound

wit hin

precipitate

covalent

conver ted

its

join

to

state

compound

an

atom,

may

be

i.e.

composed

it

may

conver ted

to

be

an

of

molecules

discharged

ion,

i.e.

it

may

ionised.

following

Write

2)

Rewrite

t he

steps

should

balanced

t he

individual

be

followed

chemical

equation,

but

when

equation

show

any

for

ions

writing

t he

t hat

ionic

equations.

reaction.

are

present

in

solution

in

solution

as

ions.

solution

3)

Delete

bot h

not

4)

any

sides

take

Rewrite

5)

t

Cancel

is

ions

of

par t

t he

change,

i.e.

t he

acid

which

t he

in

remain

equation.

t he

ionic

t hose

to

equation

which

note

(HNO

(aq))

unchanged,

These

are

i.e.

called

which

are

spectator

ions

and

t hey

to

t hat

and

showing

actually

t he

only

take

lowest

when

acids,

sulfuric

t he

par t

in

possible

acid

such

(H

3

as

SO 2

atoms

t he

or

ions

which

reaction.

ratio

if

necessar y.

hydrochloric

(aq)),

are

in

acid

(HCl(aq)),

aqueous

solution

4



t hey

ionise

to

form

on

do

reaction.

coefcients

impor tant

nitric

94

soluble.

example,

may

may

1)

precipitate

only

result,

solution

solution,

ions

a

For

in

●

The

Example

is

equations

show

as

●

be

a

and,

star ted.

t he

6.1.2

ionic

equations

two

●

in

insoluble.

with

reaction

formed

are

equations.

onic

Figure

)

when

Writing



(Mg(OH) 2

Most

writing

hydroxide

hydrogen

ions,

or

H

ions,

and

negative

anions.

Chemical

equations

and

reactions

Writing

and

balancing

chemical

equations

Examples

1

Write

t he

chloride

1)

ionic

Write

t he

Pb(NO

) 3

2)

equation

solution

Rewrite

to

balanced

(aq)



for

t he

produce

chemical

between

lead

lead

chloride

nitrate

and

2NaCl(aq)

PbCl

(s)



2NaNO

2

t he

equation

solution

sodium



2NO

showing

(aq)



sodium

solution.

ions

(aq) 3

present

in

solution

as

individual



(aq)

and

nitrate

equation:

2

2

Pb

reaction

insoluble

2Na

ions:



(aq)



2Cl

(aq)

PbCl

3

(s)



2Na

(aq)



2NO

2

(aq)

3



3)

Delete

t he

Na

(aq)

and

NO

(aq)

ions

since

t hey

remain

unchanged:

3

2

Pb



(aq)









2Cl

(aq)

PbCl

(s)





2

2

4)

Rewrite

t he

ionic

equation:

Pb

(aq)



2Cl

(aq)

PbCl

(s) 2

2

Write

t he

SO

(H 2

1)

ionic

(aq))

to

equation

produce

for

t he

2KOH(aq)



H

SO 2

between

sulfate

(aq)

K

4

2K

SO 2



2)

reaction

potassium

and

potassium

hydroxide

and

sulfuric

acid

water.

4

(aq)



2OH

(aq)



2H

2H

O(l) 2



(aq)



4

2

(aq)





SO

(aq)

2K

2

(aq)



SO

4







2OH

(aq)



2H

2

(aq)

(aq)



2H

4



O(l) 2

2







2H

O(l) 2



4)

2OH

(aq)



2H

(aq)

2H

O(l) 2



5)

OH

(aq)



H

(aq)

H

O(l) 2

3

Write

t he

(HCl(aq))

ionic

to

equation

produce

for

t he

Key

!

reaction

magnesium

between

chloride

and

magnesium

hydrogen

and

hydrochloric

acid

It

is

give

1)

Mg(s)



2HCl(aq)

MgCl

(aq)



H

2

2)

Mg(s)



2H

2

(aq)



2Cl

(aq)

Mg

the

that

you

correct

(g) 2



extremely

important

gas.

fact

(aq)



2Cl

(aq)



H

state

symbols

when

writing

ionic

(g) 2

equations



3)

Mg(s)



2H

and

2

(aq)



(aq)





H

that

(g)

the

equations

2

balance 

4)

Mg(s)



2H

2

(aq)

Mg

(aq)



H

(g) 2

Summary

1

Write

questions

balanced

a

Aluminium

b

N

c

CH

(g)



H

2



(g)

The

The

to

f

2

State

reaction

the

Na

b

KOH(aq)

CO 2

Ba(NO



H

O(g) 2

potassium

between

aluminium

between

Na 3



hydrogen

and

water

to

and

dioxide

oxygen

are

)

hydroxide

and

equations

HCl(aq)

(NH 4

and

then

) 4

write

NaCl(aq)



or

(NH

)

(aq)



SO 2

Na

(aq) 4

SO 2

K

SO 2

(aq) 4

(aq)



(s)

in

equation

H

water:

for

each

reaction:

O(l) 2

(g)



3

4

(HCl(aq))

4

NH

4

BaSO

acid

steam.

insoluble

ionic

(g)



hydrochloric

PO 3

the

CO

and

water.

2



2

potassium

produce

soluble

KMnO 3

and

to

3

3

produce

hydrogencarbonate

carbon

compounds

CO 2

following

(aq)

chloride,

following

)

4

c

(g) 2

between

the

Fe(NO

a

oxide

(g)

CO

aluminium

reaction

Balance

reactions:

gas.

3

3

NH

(g)

reaction

whether

AgI

following

aluminium

2

produce

The

the

3

O

hydrogen

e

for

oxygen

2

(g) 4

d

equations





NaNO

H

O(l) 2

(aq) 3

95

Types

of

chemical

reactions

Chemical

A6.2

Objectives

By

the

be

able

end

of

this

topic

you

identify

Chemical

the

seven

main

t ake

●

chemical

give

●

write

the

of

reactions

reactions

place

in

for m

our

an

integ ral

bodies,

suc h

as

par t

of

our

respiration

lives,

whic h

from

reactions

c hanges

energy,

to

complex

reactions,

whic h

produce

glucose

phar maceutical

reactions

examples

types

chemical

reactions

types

into

of

of

and

will

to:

t hat

●

Types

equations

of

the

chemical

balanced

different

products.

There

are

descr ibed

below.

se ven

main

types

of

c hemical

reactions

whic h

are

main

reactions

equations

types

of

for

chemical

Synthesis

reactions

reactions.

Synthesis reactions

chemically

A

to

synt hesis

form

Examples

a

reaction

A

of

are reactions in which two or more substances combine

single

is





O

generally

B

synt hesis

2Mg(s)

product.

symbolised

by:

AB

reactions

are

as

follows:

(g)

2MgO(s)

(g)

2FeCl

2

2FeCl

(s)



Cl

2

Decomposition

Did

?

you

down

being

islands

coral

largely

When

of

in

the

islands,

calcium

the

started

of

sugar

are

composed

carbonate.

industry

Barbados,

and

carbonate

roasted

calcium

in

oxide.

a

first

coral

was

lime

The

into

compound

or

if

an

juice

then

used

during

the

to

state

or

is

at

one

from

time

current

dissolved

decomposition

kilns

to

produce

calcium

was

island

a

A

in

A

clarify

the

cane,

major

(Unit

in

if

t he

compound

is

passed

aqueous

reaction

B

is

A

a

single

reactant

reaction

will

is

broken

occur

is

t hrough

solution

heated

t he

(t hermal

if

t he

compound

decomposition)

when

in

t he

liquid

(electrolysis).

generally

symbolised

by:



B

of

decomposition

reactions

are

as

follows:

cane

of

heat

(s)

CaO(s)

3

which



CO

(g) 2

heat

industry

)

(s)

2PbO(s)

2



4NO

(g)



O

2

(g) 2

2.5).

Single

A

single

displacement

d isplacement

in

its

of

(displaces)

will

free

●

state

always

reactions

A

metal

This

and

a

be

may

t he

type

of

of

Mg(s)

reaction

a

element

less

divided

displace

single

t his



involves

The

in

reactive

into

from

t he

type

CuSO

of

(aq)

single



2HCl(aq)

from

a

free

A

between

state

more

an

takes

reactive

compound.

element

t he

place

element

Displacement

from

a

compound

or

it

may

acid.

reaction

AX



can

generally

MgSO

(aq)

reaction



Cu(s)

4

ZnCl

(aq) 2

be

symbolised

B

displacement

4

Zn(s)

its

compound.

metal

an

BX

reaction

in

types.

displacement



t he

element

element

two

anot her

hydrogen

A

Examples

reactions

compound.

anot her

displace

can

displace

96

which

decomposition

oxide

3

the

reactions

island,

2Pb(NO within

are

products.

quarried

extraction

sugar

more

unstable,

CaCO sucrose

reactions

or

electric

Examples was

two

Caribbean,

A calcium

reactions

know? Decomposition

Many

(s) 3

2



H

(g) 2

are

as

follows:

by:

Chemical

equations

Writing

t hese

and

as

reactions

ionic

Types



Cu



2H

reactions

2

(aq)

Mg



Zn(s)

chemical

equations:

2

Mg(s)

of

(aq)



Cu(s)

2

(aq)

Zn

(aq)



H

(g) 2

n

t he

above

appears

●

A

examples,

above

non-metal

This

type

of

may

single

X

An

example

Cl

(g)

of



magnesium

hydrogen

in

displace

t he

anot her

displacement



AY

t his

of

single

2KBr(aq)

more

reactive

series

non-metal

reaction

AX

type

is

reactivity



can

t his

Ionic

Ionic

be

displacement

2KCl(aq)



Br

(g)

as



an

ionic

a

and

zinc

compound.

generally

symbolised

by:

reaction

is

as

follows:

(aq)

2Br

equation:

(aq)

2Cl

(aq)



Br

2

n

from

copper

18.1).

2

t his

Cl

t han

Unit

Y

2

Writing

(see

(aq) 2

example,

chlorine

precipitation

precipitation

is

more

reactive

t han

bromine.

reactions

reactions

are

sometimes

referred

to

as

double

d isplacement reactions . They usually involve two compounds which are in

solution,

An

ionic

AX

where

t he

compounds

precipitation



BY

reaction

AY



exchange

is

ions.

generally

symbolised

by:

BX

To have a successful ionic precipitation reaction, one or bot h of t he products

must

be

because

incapable

t hey

form

of

one

undergoing

product

t he

which

reverse

is

reaction.

insoluble,

known

This

as

a

is

generally

of

ionic

precipitation

reactions

are

as

precipitate

that

follows:

forms

result

AgNO

(aq)



KBr(aq)

AgBr(s)



KNO

3

BaCl

of

a

in

is

a

an

insoluble

solution,

chemical

solid

often

as

a

reaction.

(aq) 3

(aq)



Na

2

Writing

fact

precipitate A

Examples

Key

!

SO 2

t hese

as

(aq)

BaSO

4

ionic

(s)



2NaCl(aq)

4

equations:



Ag

(aq)



Br

2

Ba

AgBr(s)

(aq)

2

(aq)



SO

BaSO

(aq)

Neutralisation

Neutralisation

acid.

The

salt

acid

are

a

and

An

example

reactions

reactions

is

(s) 4

4

are

neutralised

reactions

by

t he

between

base

(or

a

alkali)

base

and

(or

t he

an

alkali)

products

and

an

formed

water.

of

a

NaOH(aq)

neutralisation



reaction

HCl(aq)

is:

NaCl(aq)



H

O(l) 2

Writing

t his

as

an

ionic

equation:



OH

(aq)



H

(aq)

H

O(l) 2

Redox

Redox

in

reactions

reactions,

which

reactions

or

oxidation–reduction

one

reactant

will

be

is

covered

reduced

in

more

and

t he

detail

in

reactions,

ot her

Unit

are

chemical

reactant

is

reactions

oxid ised.

Redox

9.

97

Types

of

chemical

reactions

Chemical

Reversible

Reversible

can

be

one

f

and

reactions

reactions

reactions

reversed

reactants

equations

occur

easily,

again.

Most

i.e.

when

t he

t he

direction

products

reactions

are

not

can

react

reversible;

of

to

a

chemical

produce

t hey

can

t he

only

change

original

proceed

in

direction.

a

reaction

is

reversible,

a

double

arrow

(

)

is

used.

n

a

reversible

reaction, we refer to t he for ward reaction as proceeding from lef t to right and

t he

A

reverse

reversible

A

For



ring

of

backward

reaction

B

NH

is

C

example,

ammonia

white

or

for ms

near

symbolised

ammonium

hydrogen

Cl(s)

proceeding

from

right

to

lef t.

by:

D

chloride

NH

4

ammonium

as

generally



when

and

reaction

(g)



chloride

is

heated,

it

decomposes

into

gases:

HCl(g)

3

chloride

the

top

f

t he

ammonia

temperature)

NH

(g)

and

t hey



hydrogen

react

to

chloride

form

HCl(g)

gases

ammonium

NH

3

are

cooled

(or

mixed

at

room

chloride:

Cl(s) 4

ammonium

The

chloride

reaction

is,

t herefore,

reversible

and

t he

equation

can

be

written

as

follows:

NH

Cl(s)

NH

4

n

Figure

6.2.1,

hydrogen

is

Bunsen

much

cooler

many

t he

and

can

6.2.1

chloride



HCl(g)

t he

ammonium

gases,

and

which

when

t he

chloride

diffuse

gases

up

reach

is

heated

t he

test

here,

it

forms

tube.

t hey

The

react

ammonia

top

and

Heating

ammonium

chloride

reversible

same

time

products.

enter

backward

reached

or

f

1

dynamic

t he

t he

are

a

inside

t he

occurs

stage

equal.

is

of

reaction

reaction

reaction

t hen

reactions

Balance

t hat

t he

leave,

around

reactions,

such

Summary

form

t he

a

and

tube

can

always

in

a

ring

of

directions

at

tube.

proceed

contains

sealed

reached

The

t he

system

where

reaction

t he

does

in

a

where

rates

not

bot h

mixture

of

stop

the

Mg(NO

) 3

b

Fe(s)



following

equations,

single

then

displacement,

(s)

MgO(s)

Zn(s)





classify

ionic

NO

2

the

reactions

precipitation

(g)

or

Cl

(g)

FeCl

HCl(aq)

NaOH(aq)

AgNO



(aq) 3

O

(g)

(s) 3

H

ZnCl

SO 2

e

substances

for ward

said

to

and

have

(aq)





(aq) 4

MgBr

(aq)

(g) 2

Na

SO 2

2

H

(aq) 4

AgBr(s)



H

O(l) 2



Mg(NO

) 3

(aq). 2

as

synthesis,

neutralisation

2

2

d



2

2

c

is

reactants

questions

reactions:

a

no

t he

and

of

equilibrium

decomposition,

98

of

bur ner

n

Figure

as

chloride

ammonium



(g) 3

Chemical

Key

●

equations

Chemical

The

t he

●

n

●

state

solid,

a

(l)

of

are

shown

each

for

representations

at

liquid,

each

are

are

t he

Ionic

lef t

of

an

ionic

equations

and,

t hey

Writing

chemical

reactions

of

chemical

reactions

using

equation

and

t he

products

on

any

determine

Spectator

t herefore,

gas

and

on

bot h

r ules

in

sides

in

for

must

of

t he

front

Formulae

which

given

(aq)

t here

placed

water.

is

can

These

be

aqueous

be

t he

formula

using

(s)

solution.

same

formulae.

never

used

are

its

number

of

equation.

of

must

af ter

to

useful

be

They

determine

in

are

used

changed.

t he

solubility

determining

state

compounds.

show

as

a

only

result,

t he

end

atoms

up

in

a

or

ions

which

different

actually

situation

take

from

t he

par t

one

in

in

star ted.

ionic

showing

for

product

equation

numbers

solubility

reaction

and

equations.

compounds

of

(g)

element

There

ionic

reactant

chemical

balancing

which

●

are

when

a

of

formulae.

balanced

symbols

●

of

Coefcients

of

●

equations

and

reactants

atoms

●

Types

right.

The

for

●

reactions

concepts

symbols

●

and

equations

ions

which

ions

t hat

ions

are

remain

involves

are

do

t he

writing

present

not

ions

in

change

which

unchanged.

do

These

t he

full

solution

in

any

not

are

as

rst,

but

ions

to

way.

take

lef t

equation

individual

par t

out

of

in

a

t he

reaction

nal

and,

ionic

equation.

●

There

are

seven

main

decomposition,

redox

●

A

and

●

A

A

its

An

ionic

A

of

A

a

is

to

redox

a

is

any

synt hesis,

precipitation,

neutralisation,

in

which

two

or

more

reactants

reaction

where

a

single

reactant

is

products.

reaction

compound

is

any

where

reaction

to

insoluble

reaction

t he

between

element

an

element

displaces

anot her

usually

produce

solid

a

t hat

involves

two

compounds

in

precipitate.

forms

in

a

solution,

of ten

as

a

reaction.

reaction

salt

reaction

reaction

more

reacting

an

a

reactions:

ionic

compound.

chemical

form

chemical

product.

or

precipitation

neutralisation

alkali)

●

t he

any

reaction

two

and

solution

precipitate

result

●

state

from

aqueous

A

into

is

single

d isplacement

free

element

●

a

of

displacement,

reactions.

reaction

form

down

single

in

●

to

decomposition

broken

●

reversible

synthesis

combine

types

single

and

occurs

occurs

when

an

acid

reacts

wit h

a

base

(or

water.

when

one

reactant

is

reduced

and

t he

ot her

is

oxidised.

●

A

reversible

can

be

reaction

reversed

reactants

easily,

occurs

i.e.

t he

when

t he

products

direction

can

react

of

to

a

chemical

produce

change

t he

original

again.

99

Practice

exam-style

questions

Chemical

Equations

Practice

exam-style

questions

Write

Which

of

t he

following

a

correctly

represents

The

sulfuric

reaction

acid

to

between

produce

sodium

sodium

and

NaOH(aq)



H

SO

2

B

2NaOH(aq) 

(aq)

NaSO

4

H

b

(aq)



H

4

SO

2

(aq)

Na

4

reaction

2NaOH(aq)



H

SO

2

(aq)

SO

The

reaction

(H

O(l)

(s)



2H

4

Na

each

of

t he

aluminium

chloride

as

and

t he

chlorine

only

to

product.

SO

between

(aq)),

aluminium

which

oxide

produces

and

sulfuric

aluminium

sulfate

4

2

2

4

between

aluminium

2

SO

2

and

water.

The

reaction

and

hydrochloric

O(l)

2

c C

for

and

water?

acid A

equation

t he

hydroxide

sulfate

chemical

reactions.

produce chemical

reactions

write

balanced

following

a 1

and

questions 6

Multiple-choice

to

equations

between

potassium

carbonate

solution

(aq)

4



2H

acid

(HCl(aq))

to

produce

O(l)

2

potassium

D

Na(OH)

(aq)



H

2

SO

2

(aq)

NaSO

4

chloride,

carbon

dioxide

and

water.

(aq)

4

d

The

reaction

between

et hane

(C

H

2



2H

(g))

and

oxygen

to

6

O(l)

2

make

2

Which

of

t he

following

compounds

is

soluble

in

copper(II)

B

magnesium

C

zinc

sulfate

The

reaction

nitrate

and

aqueous

potassium

The

reaction

and

ammonium

sulfate

solutions

to

make

of

lead(II)

lead(II)

sulfate

nitrate.

between

potassium

Aqueous

solutions

react

of

which

of

t he

following

sodium

B

zinc

to

form

a

chloride

sulfate

precipitate

when

and

and

copper(II)

magnesium

ammonia

hydroxide

to

form

solution

potassium

C

potassium

D

lead

hydroxide

nitrate

and

chloride

and

sodium

ammonium

The

reaction

between

(HCl(aq)),

which

h

The

reaction

between

hydroxide

following

water.

calcium

makes

and

hydrochloric

calcium

sodium

and

chloride

and

and

water

to

produce

hydrogen.

nitrate

The

reaction

between

magnesium

carbonate

hydrogencarbonate

t he

and

hydrogen.

i nitrate

gas

mixed?

sodium

Consider

solution

compounds

acid

A

sulfate

phosphate

g

4

steam.

hydroxide

calcium

would

between

potassium

and

sulfate,

3

and

carbonate

f

D

dioxide

water? e

A

carbon

solution

and

nitric

acid

reaction: (HNO

(aq)),

which

produces

magnesium

nitrate,

3

Mg(HCO

)

3

(aq)



2HCl(aq)

MgCl

2

(aq)

carbon

2



2CO

(g)



2H

2

The

best

ionic

equation

for

t his

reaction

dioxide

and

water.

O(l)

2

j

is:

The

reaction

and

sulfuric

and

water.

between

acid

(H

2

2

A

Mg



(aq)



2HCO

(aq) 

2H

2

(aq)

Mg

sodium

SO

(aq))

hydroxide

to

make

solution

sodium

sulfate

4

(aq)

3



2CO

(g)



2H

2

O(l)

2

7

Write

balanced

f,

and

ionic

equations

for



B

2HCO

(aq)



2H

(aq)

2CO

3

(g)



2H

2

O(l)

2



C

HCO

(aq)



2H

(aq)

CO

3

(g)



H

2

O(l)

2



D

HCO

(aq)



H

(aq)

CO

3

5

What

to

type



H

of

reaction

would

you

O(l)

2

consider

t he

following

be?

2Al(s)



3H

SO

2

100

(g)

2

(aq)

Al

4

A

a

neutralisation

B

a

single

C

a

double

D

a

synt hesis

(SO

2

reaction

displacement

reaction

displacement

reaction

reaction

)

4

(aq)

3



3H

(g)

2

g,

i

j

in

question

6

above.

t he

reactions

in c,

e,

A7

Chemistry

often

The

involves

mole

determining

the

concept

amount

of

a Objectives

substance

how

required

much

to

ammonia

produce

and

nitric

a

product.

acid

are

For

example,

required

By

the

be

able

1 kg

of

the

fertiliser

ammonium

nitrate?

to

of

an

devise

atom

is

another

so

small

method

that

of

chemists

measuring

have

the

dene

the

had

and

this

method

uses

the

amount

relative

calculate

●

of

dene

molar

The

mole

and

atomic,

will

relative

atomic

molecular

formula

relative

mass

mass

molecular

and

masses

the

terms

mole

and

mass

●

give

●

perform

Avogadro’s

constant

mass

moles,

Relative

you

mole. ●

A7.1

topic

terms

relative

formula

substances;

this

The mass,

mass

of

to:

to

●

produce

end

molecular

and

formula

calculations

masses

and

involving

number

of

masses particles.

Yo u

lear nt

in

Unit

scientists

use

known

relative

t he

A

as

mass

of

a

an

carbon-12

amu,

1.0 0

3. 3

m uc h

atomic

ato m

atom

t herefore,

t ha t

be cause

s malle r

m a ss .

wit h

wa s

unit

t he

ma ss

t han

They

a

on e -t welf t h

t he

a

atoms

to

designed

on e -t we lf t h

assign e d

of

g ram

t he

mass

mass

of

of

a

a

is

ex t remely

compare

s y st e m

ma ss

of

12.0 0

a

wh ic h

s mal l,

mas s es ,

c ompares

carbo n - 12

a tomic

carb o n - 12

t h eir

mass

a tom

has

a tom.

un i ts

a

or

ma s s

of

amu.

Relative

atomic

element

to

compara tive

mass

is

mass,

t herefore,

one-twe lf t h

valu e ,

given

t he

t he

re la tive

s y mb ol

compares

ma ss

of

a to mic

a

t he

mass

carbo n - 12

mass

has

no

of

an

a tom.

units.

atom

B ec au se

Relative

of

it

an

is

a

a to mic

A r

n t he denition of relative atomic mass given in t he Key fact box, we use t he

word

‘average’

because

relative

atomic

mass

takes

into

account

t he

Key

!

fact

relative Relative

atomic

mass,

A

,

is

the

r

abundance

nearest

same

each

whole

example,

When

of

t he

number,

relative

calculating

logic

isotope.

by

can

The

be

atomic

t he

found

mass

masses

comparing

relative

of

t heir

of

in

atomic

t he

periodic

calcium

covalent

masses

to

mass

is

and

t he

40

an

table

and

ionic

of

of

element,

on

page

uorine

compounds

carbon-12

to

360.

is

we

t he

For

19.

average

mass

element

compared

the

use

elements

composed

of

and

compounds

formed

by

of

an

one

atom

to

atom

of

an

one-twelfth

of

carbon-12.

t he

atom.

Key

! Molecular

mass

of

covalent

bonding

fact

are Relative

molecular

mass,

M

,

is

r

molecules.

We

use

t he

term

relative

molecular

mass

to the

compare

t he

mass

of

a

molecule

of

a

molecular

element

or

compound

t he

mass

of

a

carbon-12

atom.

Relative

molecular

mass

is

symbol

Compounds

of

formed

by

ionic

bonding

use t he term relative formula mass

ionic

an

element

compound

wit h

are

represented

by

formula

units.

an

molecule

or

compound

one-twelfth

determine

t he

one-twelf t h

relative

toget her

t he

relative

t he

molecular

atomic

the

mass

Since

values,

have

mass

of

a

carbon-12

Key

!

atom.

mass

or

relative

formula

mass,

masses

of

all

t he

elements

present

in

relative

no

molecular

and

formula

masses

are

fact

formula

mass

is

the

we

mass

of

one

formula

unit

t he

a

compound

compared

to

one-

comparative twelfth

t hey

carbon-12.

We

of

compound.

of

to compare t he mass of a formula unit of

average

add

to

atom

Relative

To

one

M r

an

of

given compared

t he

mass

wit h of

one-twelf t h

average

the

mass

of

an

atom

of

units. carbon-12.

101

The

mole

and

mass

The

mole

concept

Examples

1

Calculate

t he

relative

molecular

mass

of

nitrogen,

N 2.

N

consists

of

2

atoms

of

N.

2

∴

relative

molecular

mass

of

N



(2



14)



28

2

2

Calculate

t he

relative

molecular

mass

of

glucose,

C

H 6

C

H 6

O 12

∴

consists

6

atoms

of

H,

12

atoms

of

H

and

6

6.

atoms

of

O.

6

relative

C

H 6

3

of

O 12

molecular

O 12



(6



mass

12)



of

(12



1)



(6



16)



180

6

Calculate

t he

relative

formula

mass

of

magnesium

carbonate,

MgCO 3.

MgCO

consists

of

1

atom

of

Mg,

1

atom

of

C

and

3

atoms

of

O.

3

∴

relative

formula

MgCO



(1



mass

24)



of

(1



12)



(3



16)



84.

3

The

mole

We use different terms to represent a xed amount of somet hing, e.g. a dozen

apples

same

can

be

mole

large

Key

mole

is

of

to

12

apples

used

in

describe

atoms

or

a

and

a

pair

anyt hing,

mole

is,

and

chemistr y.

of

of

The

e.g.

a

molecules.

t herefore,

used

gloves

represents

mole

represents

mole

of

apples,

However,

mainly

as

a

a

a

a

two

mole

mole

gloves.

xed

The

number.

of

represents

measurement

t

gloves,

of

a

a

ver y

atomic

par ticles.

fact

Like A

used

is

number

sized

!

represents

concept

the

amount

of

relative

atomic

mass,

t he

mole

has

been

dened

using

t he

carbon-12

a

isotope because of its high abundance and stability. t was found t hat 12.00 g substance

that

contains

number

particles

the

same 23

of of

as

there

carbon-12

contains

6.0



10

atoms

of

carbon-12.

One

mole

represents

are 23

t he atoms

in

12.00 g

of

number

of

atoms

in

12.00 g

of

carbon-12,

i.e.

6.0



10

.

This

number

is

carbon-12.

known

as

A vogadro’s

constant ,

or

N A

23

n

ot her

words,

par ticles

Looking

of

at

t he

t he

‘amount’

●

‘par ticles’

n

t he

if

is

t he

denition

refer

t he

can

same

mole

amount

of

a

substance

t hat

contains

6.0



10

substance.

can

substance

●

a

to

a

to

t hat

mole

mass

substance

refer

way

of

t he

is

a

atoms,

it

was

in

of

a

t he

Key

fact

substance

box:

or

t he

volume

of

a

gas

molecules,

found

formula

t hat

units

12.00 g

of

or

ions.

carbon-12

contains

23

6.0



10

carbon-12

atoms,

it

was

found

t hat:

23

●

40 g

of

calcium

(Ca)

contains

6.0



10

Ca

atoms

23

●

28 g

of

nitrogen

(N

)

contains

6.0



10

N

2

molecules 2

23

●

180 g

of

glucose

(C

H 6

O 12

)

contains

6.0



10

C

6

H 6

O 12

molecules 6

23

●

84 g

of

magnesium

carbonate

(MgCO

)

contains

6.0



10

MgCO

3

formula

f

we

look

numerical

is

t he

NB

102

mass

When

3

units.

at

t he

value

of

masses

as

one

t he

mole

writing

t he

given

relative

of

above

mass

par ticles

mole

as

a

of

we

of

t he

unit,

it

see

t he

t hat

each

element

or

mass

has

compound

t he

and

substance.

is

usually

abbreviated

to

mol

same

each

The

mole

Molar

The

concept

The

of

one

mole

of

a

substance

is

known

as

its

a

compound

molar

mass,

or

!

M

Key

Molar

molar

mass

of

an

element

or

is

given

t he

unit

mass

mole

or

g mol

mass,

grams,

.

For

example,

because

12.00 g

of

carbon

fact

M,

is

the

mass,

in

grams

1

per

and

mass

mass

The

mole

of

one

mole

of

a

substance.

contains

23

6.0  10

carbon atoms, or 1 mol of carbon atoms, t he molar mass of carbon

1

is

12 g mol

The

molar

t hough

apples

are

mass

t hey

will

bot h

a

different,

of

are

be

as

Calculating

Looking

at

t he

different

dozen.

just

different

all

t he

This

t he

elements

mass

from

is

molar

of

t he

an

and

one

compounds

mole,

mass

because

mass

ndings

of

t he

of

a

is

as

will

t he

g rapes

of

atoms

t he

different

from

be

different

mass

dozen

mass

apple

just

of

even

of

t he

one

t hough

each

mass

even

dozen

t hey

element

of

a

is

g rape.

mass

above,

it

can

be

seen

t hat:

23

●

because

40 g

of

calcium

contains

6.0



10

Ca

atoms,

or

1 mol

of

1

Ca

atoms,

t he

molar

mass

of

calcium

is

40 g mol

23

●

because

28 g

of

nitrogen

contains

6.0



10

N

molecules,

or

1 mol

of

2

1

N

molecules,

t he

molar

mass

of

nitrogen

is

28 g mol

2

23

●

because

180 g

of

O

of

glucose

contains

6.0



10

C

H 6

O 12

molecules,

or

1 mol

6

1

C

H 6

12

molecules,

t he

molar

mass

of

glucose

is

180 g mol

6

23

●

because

84 g

of

magnesium

carbonate

contains

6.0



10

MgCO 3

formula

units,

or

1 mol

of

MgCO

formula

units,

t he

molar

mass

of

3

1

magnesium

carbonate

is

84 g mol

Therefore, t he molar mass of an element or compound is t he relative atomic,

molecular

More

or

formula

mass

amount

expressed

in

grams

per

mole.

examples

1

M(H

O)



(2



1)



)



64

)



(3



40)

)



(2



14)

16



18 g mol

2

1

M(CuSO



32



(4



16)



160 g mol

4

1

M(Ca

(PO 3

) 4



(2



31)



(8



16)



310 g mol

2

1

M((NH

) 4

Moles

Molar

mass

t he

of

an

(8



1)



12



(3



16)



96 g mol

mass

gives

us

element

or



3

and

mass

mass

CO 2

number

t he

or

of

relationship

compound.

moles

of

an

between

We

can

element

t he

use

or

number

t he

molar

of

moles

mass

to

and

t he

calculate

compound.

Examples

1

Calculate

t he

number

of

moles

in

10 g

of

calcium

carbonate,

CaCO 3

First

calculate

t he

molar

mass

of

CaCO 3

1

M(CaCO

)



40



12



(3



16)



100 g mol

3

i.e.

mass

of

1 mol

CaCO



100 g

3

10

____

∴

number

of

moles

in

10 g



mol



0.1 mol

100

103

The

mole

and

mass

The

2

Calculate

t he

mass

of

0.2 mol

of

sulfuric

acid,

H

calculate

t he

molar

mass

of

H

SO 2

performing

1

SO 2

chemistry,

involving

the

including

mole,

it

)



(2



1)



32

you

show

each



(4

is

essential

step

of

i.e.

mass

of

1 mol

H

SO

statement.

down

a

set

by

You

of

making

must

not

numbers

a

what

you

are

98 g mol



98 g

mass

of

0.2 mol

of

H

SO



0.2



98 g



19.6 g

4

clear

just

put

without

Moles stating



4

2

clearly

16)

your

∴ working



4

those

2

that

4

calculations

M(H in

4

tip

First

When

concept

SO 2

Exam

✔

mole

and

number

of

particles

calculating.

23

The

number

can

calculate

t hat

t he

●

t he

t he

type

of

f

a

in

number

par ticle

substance

f

a

are

one

of

in

of

f

is

an

mole

is

par ticles

a

always

in

substance

element,

individual

substance

compound,

●

par ticles

any

6.0



10

number

depends

on

.

of

t he

Using

t his

moles.

type

of

fact

is

e.g.

a

e.g.

bonding

and

t he

noble

gases,

t hen

t he

atoms

molecular

water,

metals

element,

t hen

t he

e.g.

par ticles

oxygen,

are

or

a

molecules

covalent

made

up

atoms

a

substance

par ticles

are

is

an

ionic

formula

compound,

units

made

up

e.g.

of

sodium

chloride,

t hen

t he

ions.

Examples

1

Calculate

t he

number

of

atoms



10

in

0.5

mole

of

copper,

Cu.

23

1 mol

Cu

contains

6.0

atoms.

23

∴

2

0.5 mol

Calculate

Cu

t he

contains

number

0.5

of



6.0

moles

of



10

23

atoms

carbon



3.0

dioxide,



CO

,

10

atoms

t hat

contain

2

23

2.0



10

carbon

dioxide

molecules.

23

1 mol

CO

contains

6.0



10

molecules.

2

23

number

of

moles

in

2.0



2.0



10

6.0



10

__________

23

∴

10

molecules



mol 23



We

can

extend

number

●

of

1 mol

our

moles

of

calculations

or

water,

par ticles

H

O,

of

moles

inside

consists

of:

a

and

1 mol

of

2

H

●

atoms

2 mol

and

of

1 mol

potassium

0.33 mol

par ticles

compound.

H

O

For

to

or

t he

molecules,

or

2 mol

of

2

of

O

atoms

carbonate,

K

CO 2

units,

at

example:

consists

of:

2 mol

4 mol

of

K

of

K

3

CO 2

3

2



formula

look

ions

and

2 mol

of

CO

ions. 3

Exam

✔

tip

Example

It

is

essential

correct

in

your

unit

that

you

after

place

each

calculations,

the

value

given

especially

Calculate

t he

number

of

hydrogen

atoms

in

1.5 mol

of

met hane,

CH 4

your

1 mol

CH

contains

4 mol

H

atoms.

4

final

answers.

have

no

units

The

are

only

values

relative

that

atomic,

∴

1.5 mol

CH

contains

1.5



4 mol

H

atoms



6

mol

H

atoms

4

molecular

and

formula

masses. 23

1 mol Your

answer

wrong

the

104

unit

value

is

or

for

incorrect

no

unit,

relative

if

it

has

unless

mass.

it

H

atoms

contains

6.0



10

atoms.

the

is

23

∴

6 mol

H

atoms

contains

6



6.0



10

24

atoms



3.6



10

we

Remember

substance.

par ticles

●

of

atoms

in

The

mole

concept

Moles,

We

can

mass

now

number

The

of

and

combine

number

our

of

mole

and

mass

particles

calculation

of

moles

and

mass,

and

moles

and

par ticles.

Examples

1

Calculate

t he

number

of

molecules

in

1.8 g

of

water,

H

O. 2

1

M(H

O)



(2



1)



16



18 g mol

2

i.e.

mass

of

1 mol

H

O



18 g

2

1.8

___

∴

number

of

moles

in

1.8 g



mol



0.1 mol

18

23

1 mol

H

O

contains

6.0



10

molecules

2

23

∴

0.1 mol

H

O

contains

0.1



6.0



10

molecules

2

22



6.0



10

molecules

23

2

Calculate

t he

mass

of

1.5



10

molecules

of

hydrogen

chloride,

HCl.

23

1 mol

HCl

contains

6.0



10

molecules

23

1.5

number of moles in 1.5





10

__________

23

∴

10

molecules



mol



0.25 mol

23

6.0



10

1

M(HCl)

i.e.

∴



mass

1

of

mass



35.5

1 mol

of



36.5 g mol

HCl

0.25 mol



36.5 g

HCl



0.25



36.5 g



9.13 g

3

3

Calculate

oxide,

t he

Al

number

of

aluminium

ions,

Al

,

in

40.8 g

of

aluminium

O 2

3

1

M(Al

O 2

i.e.

)



(2



27)



(3



16)



102 g mol

3

mass

of

1 mol

Al

O



2

3

moles

in

102 g

40.8

_____

∴

number

of

40.8 g



mol



0.4 mol

102

3

1 mol

Al

O 2

contains

2 mol

Al

ions.

3

3

∴

0.4 mol

Al

O 2

contains

0.4



2 mol

Al

ions

3

3



0.8 mol

3

1 mol

Al

Al

ions

23

ions

contains

6.0



10

ions

3

∴

0.8 mol

Al

23

ions

contains

0.8



6.0



10

ions

23



Summary

1

Calculate

a

mass

of

Calculate

a

3

20 g

of

Calculate

10

ions

of:

sodium

sulfate,

Na

the

number

of

moles

b

number

of

1.2 mol

of

glucose,

4

C

H 6

O 12

6

in:

neon

the

b

SO 2

2



questions

the

0.25 mol

4.8

molecules

in

63.0 g

of

1.5 mol

magnesium

of

hydrogen

carbonate.

chloride,

HCl.

23

4

Calculate

Ca

(PO 3

5

the

mass

of

the

number

2.5



10

formula

units

of

calcium

phosphate,

) 4

2.

Calculate

of

molecules

in

34 g

of

ammonia,

NH 3

6

Calculate

the

number

of

chloride

ions

in

6.8 g

of

zinc

chloride,

ZnCl 2

105

The

mole

and

gas

volumes

The

A7.2

Objectives

By

the

be

able

end

of

this

topic

you

The

state

gas

volumes

Gases have ver y small masses because of t heir low densities, so chemists have

Avogadro’s

●

dene

molar

●

perform

relationship

occupied

by

t he

between

t he

number

of

moles

of

a

gas

and

t he

gas.

volume

calculations

and

t he

law

volume

moles

and

concept

will

to:

investigated

●

mole

mole

volumes

involving

of

gases.

n 181 1, Amedeo Avo ga dro notice d t h at a ll gase s un d er t h e same c on d iti on s

of

temperature

t he

same

and

number

pre ssure,

of

an d

mo le cules.

o cc u pying

He

propose d

t he

same

volume,

A vogad ro’s

con t ain

law

3

As

!

Key

at

fact

an

a

example,

using

temperature

of

Avogadro’s

25 °C

and

law,

we

pressure

can

of

say

t hat

101.3 kPa

100 cm

has

t he

of

same

oxygen

gas

number

of

3

molecules

Avogadro’s

law

states

that

as

of

100 cm

nitrogen

gas

at

25 °C

and

101.3 kPa.

equal 23

volumes

same

and

of

all

gases,

conditions

pressure,

number

of

of

under

the

temperature

contain

the

same

f

t he

number

1 mol

must

of

all

of

molecules

gases

occupy

t he

under

same

in

t he

each

gas

same

is

6.0



conditions

10

,

of

i.e.

1 mol,

it

temperature

follows

and

t hat

pressure

volume.

molecules.

Molar

The

volume

volume

of

one

mole

of

a

gas

is

known

as

its

molar

volume,

or

V m

!

Key

fact Molar

volume

is,

t herefore,

t he

volume

of

a

gas

which

contains

23

Molar

volume,

V

is

the

volume

6.0



10

molecules

of

t he

gas.

m

occupied

by

1 mol

of

a

gas.

Since

temperature

volume

of

●

will

and

depend

pressure

on

bot h

of

bot h

t hese.

affect

t he

Chemists

volume

mostly

of

a

work

gas,

wit h

molar

two

sets

conditions.

Stand ard

temperature

and

pressure ,

or

stp,

which

equates

to

a

o

temperature

of

0

C

(273 K)

and

a

pressure

of

101.3 kPa

3

Molar

●

Room

volume

at

stp

temperature

temperature

of

is

22.4 dm

and

25 °C

and

a

22 400 cm

or

rtp,

which

pressure

of

Molar

t he

volume

volume

volume

number

of

of

at

r tp

gives

a

gas.

moles

of

us

is

t he

We

a

24.0 dm

can

t he

to

(1

a

atmosphere).

3

or

24 000 cm

relationship

use

equates

101.3 kPa

3

Molar

atmosphere).

3

or

pressure ,

(298 K)

(1

between

molar

volume

t he

to

number

calculate

of

moles

t he

and

volume

or

gas.

Examples

1

Calculate

t he

volume

occupied

by

0.25 mol

nitrogen,

N

,

at

stp.

2

3

Volume

of

1 mol

of

N

at

stp



22.4 dm

2

3

∴

volume

of

0.25 mol

of

N

at

stp



0.25



22.4 dm

3



5.6 dm

2

3

2

Calculate

t he

number

of

moles

in

2.4 dm

of

oxygen

gas,

O

,

at

r tp.

2

3

Volume

of

1 mol

of

O

at

r tp



24.0 dm

2

2.4

_____

3

∴

number

of

moles

in

2.4 dm

of

O

at

r tp



mol



0.1 mol

2

24.0

We

can

moles,

106

now

mass,

combine

volume

our

and

calculations

number

of

wit h

par ticles.

t hose

in

Unit

7 .1

to

involve

The

mole

concept

The

mole

and

gas

volumes

Examples

1

Calculate

t he

volume

occupied

by

6.4 g

of

oxygen,

O

at

stp.

2

Calculate

t he

molar

mass

of

O

gas. 2

1

M(O

)



2



16



32 g mol

2

i.e.

mass

of

1 mol

of

O



32 g

2

6.4

____

∴

number

of

moles

in

6.4 g



mol



0.2 mol

32

3

volume

of

1 mol

O

at

stp



22.4 dm

2

3

∴

volume

of

0.2 mol

O

gas

at

stp



0.2



22.4 dm

3



4.48 dm

2

3

2

Calculate

t he

mass

of

600 cm

of

carbon

dioxide,

CO

,

at

r tp.

2

3

Volume

of

1 mol

CO

at

r tp



24 000 cm

2

600

_______

3

∴

number

of

moles

in

600 cm



mol 24 000



0.025 mol

1

M(CO

)



12



(2



16)



44 g mol

2

i.e.

mass

of

1 mol

CO



44 g

2

∴

mass

of

0.025 mol

CO



0.025



1.1 g



44 g

2

3

3

Calculate

t he

number

of

molecules

in

6.72 dm

of

ammonia,

NH

,

at

stp.

3

3

Volume

of

1 mol

NH

at

stp



22.4 dm

3

6.72

_____

3

∴

number

of

moles

in

6.72 dm



mol 22.4



0.3 mol

23

1 mol

NH

contains

6.0



10

molecules

3

23

∴

0.3 mol

NH

contains

0.3



6.0



10

molecules

3

23



1.8



10

molecules

22

4

Calculate

chloride

t he

gas,

volume

HCl

at

occupied

by

4.5



10

molecules

of

hydrogen

r tp.

23

1 mol

HCl

contains

6.0



10

molecules.

22

number

of

moles

in

4.5



4.5



10

6.0



10

__________

22

∴

10

molecules



mol 23



0.075 mol

3

volume

of

1 mol

HCl

at

r tp



24 dm

3

∴

volume

of

0.075 mol

HCl

at

r tp



0.075





1.8 dm

24.0 dm

3

Summary

1

Calculate

questions

the

ammonia,

mass,

volume

and

number

of

molecules

in

2.5 mol

of

NH 3

3

2

Calculate

the

number

3

Calculate

the

volume

of

of

atoms

16 g

of

in

4.8 dm

sulfur

of

neon

dioxide,

gas

SO

,

at

at

rtp.

stp.

2

3

4

Determine

the

mass

of

840 cm

of

oxygen

gas,

O

,

at

rtp.

2

107

The

mole

and

concentration

of

solutions

A7.3

Objectives

By

the

be

able

end

of

The

this

topic

you

The

You

explain

what

is

meant

of

a

have

already

explain

the

terms

a

solution

solutions

come

and

across

saturated.

ways

of

describing

However,

we

can

solutions

express

such

t he

as

dilute,

concentration

in

more

solutions.

precise

The

ways,

which

concentration

allow

of

a

us

to

perfume

solution

is

a

calculations

measure

of

t he

mass

quantity

concentration

of

solution

involving

●

concentration

by

of

concentration

and

concept

will

to:

concentrated

●

mole

mole

and

of

a

solute

dissolved

in

molar

a

xed

volume

3

of

solution

usually

used

is

1 dm

of

t he

solution.

The

volume

3

,

i.e.

1000 cm

concentration

dene

●

the

term

Concentration

standard

of

a

solution

can

be

expressed

in

two

ways.

3

solution

perform

●

●

calculations

involving

Mass

of

concentration ,

solution.

The

unit

which

for

gives

mass

t he

mass

of

concentration

solute

is

dissolved

grams

of

solute

in

1 dm

per

cubic

3

concentrations

of

solutions.

decimetre

●

Molar

of

solution

or

concentration ,

g dm

which

gives

t he

number

of

moles

of

solute

3

dissolved

in

1 dm

of

solution.

The

unit

for

molar

concentration

is

moles

3

of

solute

per

cubic

decimetre

of

solution

or

mol dm

t is ver y impor tant to note t hat concentration is expressed as t he quantity of

3

solute

in

1 dm

3

of

solution

and

not

in

1 dm

of

solvent.

Example

A

solution

of

sodium

hydroxide

contains

10.0 g

of

sodium

hydroxide

3

Did

?

you

dissolved

know?

in

1 dm

of

3

g dm

Molar

concentration

may

solution.

Express

t he

concentration

of

t he

solution

in

3

and

mol dm

also 3

The be

called

molarity

molarity.

is

M.

A

The

unit

solution

solution

contains

10.0 g

of

NaOH

in

1 dm

for

with

3

a

Therefore,

mass

concentration



10.0 g dm

3

concentration

be

or

described

‘1 M

of

1 mol dm

as

a

‘1

may

molar

To

solution’

determine

hydroxide

solution’.

t he

molar

concentration,

nd

t he

number

of

moles

of

sodium

present:

1

M(NaOH)

i.e.

Key

!

mass

of

1



23

mole



16



1



40 g mol

NaOH



40 g

fact 10

___

∴

number

of

moles

in

10.0 g

NaOH



mol 40

A

standard

solution

is

one

whose

 concentration

is

known

0.25 mol

accurately.

3

Therefore,

A

molar

standard

concentration



0.25 mol dm

solution

A solution whose concentration is known accurately is referred to as a standard

solution. A standard solution is made in a volumetric ask as shown in Figure meniscus

of

the

solution

3

7 .3.1.

These

asks

come

in

various

sizes,

e.g.

100

cm

,

3

250

cm

3

,

500

cm

and

3

etched

line

1 dm

indicating

.

A

known

mass

of

solute

is

added

to

the

ask

and

distilled

water

is

then

3

volume,

e.g.

250 cm

added until the solution reaches the mark on the neck of the ask.

3

To

make

mass volumetric

a

fixed

flask

volume

of

a

standard

solute

solution

required

must

which

be

does

not

calculated

have

a

volume

of

1 dm

,

rst.

contains

of

solution

Example when

the

the

meniscus

etched

3

e.g.

is

on

line,

Determine

t he

mass

of

potassium

carbonate

which

must

be

dissolved

in

250 cm 3

distilled

water

to

make

250 cm

of

potassium

carbonate

solution

wit h

3

concentration

of

3



108

Figure

7.3.1

A

volumetric

ask

1000 cm

0.2 mol dm

3

(1 dm

)

of

t he

required

solution

contains

0.2 mol

K

CO 2

3

a

t he

The

mole

concept

The

mole

and

concentration

of

solutions

0.2

_____

3

∴

1 cm

of

t he

required

solution

contains

mol

K

CO 2

3

1000

3

and

250 cm

of

t he

required

solution

contains

0.2

_____



250 mol

K

CO 2



0.05 mol

K

3

CO 2

3

1000

Therefore

0.05 mol

K

CO 2

is

required

to

make

t he

solution.

3

1

M(K

CO 2

i.e.

)



(2



39)



mass

of

1 mol

K

CO 2

∴

12



mass



16)



138 g mol

of



Therefore

0.05 mol

t he

mass

138 g

3

K

CO 2

of



Making

Your

a

K

CO

may

manipulation

use

and



138 g



6.9 g

required

is

6.9 g

3

standard

teacher

0.05

3

2

●

(3

3

solution

this

activity

to

assess:

measurement.

3

Y ou

are

going

Y ou

will

be

to

make

250 cm

3

of

sodium

carbonate

solution

with

a

concentration

of

0.1 mol dm

3

supplied

with

sodium

carbonate,

distilled

water,

a

balance,

a

sheet

of

weighing

paper,

a

100 cm

beaker,

3

a

glass

rod

and

a

250 cm

volumetric

ask.

Method

1

Calculate

the

above

to

2

Weigh

a

3

Weigh

the

4

Carefully

5

Add

6

Transfer

7

Rinse

8

help

of

mass

the

sodium

weighing

of

transfer

sodium

the

distilled

the

of

water

solution

glass

rod

to

the

with

three

Add

distilled

water

to

Place

the

bottom

stopper

on

of

stir

required

to

make

the

solution.

(Use

the

calculation

given

in

the

example

the

the

to

the

with

over

transfer

the

beaker,

the

in

your

calculation

making

glass

rod

sure

until

all

it

is

the

on

all

the

sheet

of

weighing

paper.

transferred.

sodium

carbonate

has

dissolved

completely .

ask.

water

line

meniscus

ask.

determined

solution

and

below

the

balance.

you

volumetric

times

just

a

carbonate

distilled

water

on

carbonate

and

distilled

the

paper

sodium

with

until

carbonate

you.)

sheet

some

drop

9

mass

is

Holding

in

the

on

the

the

beaker

these

and

washings

volumetric

the

transfer

to

the

ask.

the

ask

Add

washings

each

the

nal

to

the

ask.

Wash

the

beaker

time.

quantity

of

distilled

water

drop

by

line.

stopper

in

place,

invert

the

ask

three

times

to

mix

the

solution.

Calculations

We can extend our calculations involving solutions as shown in t he examples

below.

Examples

1

Calculate

t he

molar

concentration

of

a

solution

of

hydrochloric

acid,

3

HCl,

which

has

a

mass

concentration

of

9.125 g dm

1

M(HCl)

i.e.



mass

1

of



35.5

1 mol



36.5 g mol

HCl



36.5 g

9.125

______

∴

number

of

moles

HCl

in

9.125 g



mol



0.25 mol

36.5

109

The

mole

and

concentration

of

solutions

The

mole

concept

3

i.e.

number

of

moles

HCl

in

1 dm



0.25 mol

3

Therefore,

2

Calculate

which

molar

t he

concentration

molar

contains

6 g



0.25 mol dm

concentration

of

sodium

of

a

solution

hydroxide

of

sodium

dissolved

in

hydroxide

distilled

water

to

3

make

200 cm

Calculate

of

t he

solution.

molar

mass

of

sodium

hydroxide,

NaOH.

1

M(NaOH)

i.e.

mass



of

40 g mol

1 mol

of

NaOH



40 g

6

___

∴

number

of

moles

in

6 g

NaOH



mol



0.15 mol

40

3

200 cm

of

solution

contains

0.15 mol

NaOH

0.15

____

3

∴

1 cm

of

solution

contains

mol

NaOH

200

0.15

3

and

1000 cm

____

3

(1 dm

)

of

solution

contains



1000 mol

NaOH

200



0.75 mol

NaOH

3

Therefore

t he

molar

concentration



0.75 mol dm

3

3

Determine how many moles of sodium sulfate are present in 250 cm

of a

3

sodium sulfate solution which has a molar concentration of 0.2 mol dm

3

1 dm

of

solution

contains

0.2 mol

Na

SO 2

, 4

3

i.e.

1000 cm

of

solution

contains

0.2 mol

Na

SO 2

3

∴

4

0.2

_____

1 cm

of

solution

contains

mol

Na

SO 2

4

1000

0.2

_____

3

and

250 cm

of

solution

contains



250 mol

SO

Na 2

4

1000



0.05 mol

Na

SO 2

Therefore,

4

You

wish

number

to

make

of

a

moles

sodium

of

sodium

chloride

sulfate

solution

present

wit h

a

4



0.05 mol

molar

3

concentration

chloride.

of

What

Calculate

t he

0.25 mol dm

is

t he

molar

,

maximum

mass

of

but

you

volume

sodium

only

of

have

1 1.7 g

solution

chloride,

you

of

sodium

can

make?

NaCl.

1

M(NaCl)

i.e.

mass



of

23



35.5

1 mol





58.5 g

mol

58.5 g.

1 1.7

_____

∴

number

of

moles

in

1 1.7 g



mol 58.5



0.2 mol

3

Required

solution

has

a

molar

concentration

of

0.25 mol dm

,

3

i.e.

0.25 mol

NaCl

is

contained

in

1 dm

of

solution

3

or

0.25 mol

NaCl

is

contained

in

1000 cm

of

solution.

1000

_____

∴

1 mol

NaCl

is

contained

in

3

cm

of

solution

0.25

1000

_____

and

0.2 mol

NaCl

is

contained

in

3



0.2 cm

of

solution

0.25

3



800 cm

of

solution

3

Therefore, the maximum volume of solution which can be made is

110

800 cm

The

mole

concept

The

Summary

1

Dene

2

Calculate

the

mole

and

chemical

formulae

questions

terms

the

‘molar

mass

concentration’

concentration

and

and

‘standard

molar

solution’.

concentration

if

2.8 g

of

potassium

hydroxide

is

dissolved

in

3

distilled

water

to

make

up

500 cm

of

solution.

3

3

What

mass

of

calcium

chloride,

CaCl

,

needs

to

be

weighed

to

make

a

solution

of

volume

200 cm

and

2

3

concentration

0.1 mol dm

?

3

4

How

many

moles

of

sodium

carbonate

are

present

in

400 cm

of

sodium

carbonate

solution,

which

has

a

3

concentration

A7.4

The

Empirical

n

terms

of

of

0.25 mol dm

mole

and

and

?

chemical

molecular

moles,

a

chemical

formulae

Objectives

formulae

formula

shows

how

many

moles

of

By

the

be

able

each ●

element

combine

to

form

one

mole

of

t he

compound.

For

example,

H

O

n

Unit

2 mol

5.1

you

of

hydrogen

learnt

t hat

atoms

combined

chemical

formulae

wit h

can

1 mol

be

of

oxygen

written

in

atoms.

t hree

We

The

●

will

be

considering

empirical

ratio

between

formula ,

t he

atoms

two

of

which

or

t hese

gives

ions

in

ways

t he

t he

here.

explain

the

whole

number

terms

determine

molecular

atoms

onic

t he

of

each

element

compounds

ratio

of

Covalent

t he

formula ,

are

ions

which

present

always

wit hin

compounds

are

gives

in

one

mole

represented

t he

actual

●

by

of

number

t he

of

moles

will

empirical

formula

and

empirical

formulae

of

and

a

compound

mole

compound.

t he

you

composition

the

determine

the

composition

The

●

topic

molecular

molecular

simplest

this

percentage

main ●

ways.

of

to:

formula,

2

represents

end

percentage

of

a

compound.

of

compound.

empir ical

formulae ,

which

give

compound.

represented

by

molecular

for mulae .

The

empir ical

and molecular for mulae of covalent compounds may be t he same, e.g. water

(H

O),

ammonia

(NH

2

)

and

met hane

be

a

simple

molecular

whole

for mula

of

we

we

know

can

use

molecular

and

its

To

we

butene

know

is

multiple

C

H

t hese

to

work

t he

of

a

molar

of

out

t he

t he

or

of

its

t he

t he

molecular

empir ical

for mula

empir ical

for mula,

for mula

is

e.g.

2

elements,

empirical

t he

t he

CH

8

compound

mass

and

of

is

by

mass,

formula

different

of

from

compound,

we

in

a

t he

t he

can

compound,

compound.

empirical

use

t his

to

t hen

f

t he

formula

work

out

formula.

determine

of

propor tions

formula

molecular

moles

of

t he

t his

), 4

number

4

f

(CH

3

may

t he

each

empirical

element

formula,

present

and

we

t hen

need

to

calculate

determine

t he

t he

number

simplest

mole

of

ratio

elements.

Examples

1

A

sample

of

potassium,

empirical

mass

a

solid

4.34 g

formula

(g)

is

of

decomposed

chromium

of

t he

and

and

found

5.34 g

of

to

contain

oxygen.

6.52 g

What

is

of

t he

compound?

K

Cr

6.52

4.34

O

5.34

39

52

16

1

molar

mass

(g mol

)

6.52

4.34

____

number

of

moles

simplest

mole

ratio

2

5.34

____

 39

0.167

____

 52

1

0.083



0.333

16

4

111

The

mole

and

chemical

formulae

The

The

empirical

formula

is

K

of

2

To

each

On

determine

element

analysis,

6.7%

a

by

t he

t he

sample

hydrogen

and

4

simplest

smallest

of

concept

CrO 2

Note:

mole

mole

glucose

53.3%

ratio,

number,

was

oxygen.

found

The

divide

i.e.

t he

number

of

moles

0.083.

to

contain

molar

mass

40.0%

of

t he

carbon,

compound

is

1

180 g mol

f

t he

each

.

mass

Determine

of

t he

element

mass

t he

sample

can

be

(g)

is

molecular

assumed

expresses

in

formula

to

be

of

100 g,

glucose.

t hen

t he

percentage

of

grams.

C

H

40

6.7

O

53.3

12

1

16

1

molar

mass

(g mol

)

40

6.7

___

number

of

moles

simplest

The

mole

ratio

empirical

53.3

___



____

3.3



12

6.7



1

1

2

formula

of

glucose

is

3.3

16

1

CH

O 2

To

determine

t he

molecular

formula,

calculate

t he

molar

mass

of

CH

O: 2

1

M(CH

O)



12



(2



1)



16



30 g mol

2

1

M(glucose)



180 g mol

180

____

Ratio

between

M(glucose)

and

M(CH

O)





6

2

30

∴

t he

The

molecular

molecular

formula

formula

of

is

6



t he

glucose

is

empirical

C

H 6

Percentage

The

by

of

composition

each

composition

of

. 6

composition

percentage

mass,

O 12

formula.

element

water

in

shows

of

the

what

a

compound

compound.

percentage

indicates

For

of

the

the

example,

mass

of

a

the

percentage,

percentage

water

molecule

is made up of hydrogen and what percentage is made up of oxygen.

f

we

mass,

1 mol

1 mol

know

of

of

of

t he

each

t he

t he

formula

element

of

a

compound,

present

compound

and

can

t he

be

t he

percentage

calculated

mass

which

by

each

composition,

calculating

element

t he

mass

contributes

by

of

to

compound.

Examples

1

Calculate

t he

percentage

composition

of

hydrogen

1

M(H

O)



(2



1)



16



18 g mol

2

i.e.

mass

of

1 mol

H

O



18 g

2

Mass

of

hydrogen

in

1 mol

H

O



2



1

2

2

___

∴

percentage

hydrogen





100%

18



Mass

of

oxygen

in

1 mol

H

11.11%

O



16 g

2

16

___

∴

percentage

oxygen





100%

18



112

88.89%



2 g

and

oxygen

in

water.

The

2

mole

concept

Calculate

t he

phosphate,

The

percentage,

(NH

) 4

by

mass,

of

nitrogen

in

mole

and

chemical

reactions

ammonium

PO 3

4

1

M((NH

) 4

i.e.

PO 3

mass

)



(3



14)

of

1 mol

(NH

) 4

Mass

of



(12



1)



31



(4



16)



149

g mol

4

nitrogen

in

PO 3



149 g

4

1 mol

(NH

) 4

PO 3



3



14 g



42 g

4

42

____

∴

percentage

nitrogen





100%

149



Summary

1

On

analysis

Determine

2

A

liquid

28.19%

questions

a

compound

the

used

empirical

in

rocket

was

found

formula

fuel

is

of

to

contain

the

found

to

11.64 g

of

sodium,

16.20 g

of

sulfur

and

12.15 g

of

oxygen.

compound.

consist

of

3.04 g

of

nitrogen

and

6.94 g

of

oxygen.

The

molar

mass

of

the

1

compound

3

Calculate

is

92 g

the

mol

.

Determine

percentage

the

composition

molecular

of

formula

hydrogen,

sulfur

of

the

and

compound.

oxygen

in

sulfuric

acid,

H

SO 2

4

Determine

the

percentage,

by

mass,

of

carbon

in

aluminium

carbonate,

Al

(CO 2

A7.5

The

n

The

Law

Un i t

mole

of

6 .1

yo u

lear nt

reactions,

c hemical

e qu a t i o n

of

This

Key

is

t he

t hat

t h ey

t he

e qu a t i o n

summed

fact

chemical

Conservation

c hemical

side

and

up

in

a to m s

are

o n ly

number

m u st

t he

of

be

L aw

of

neit her

rear ranged,

a to m s

same

of

as

created

and

eac h

t he

d e st r oye d

when

element

number

C o n s e r vat i o n

nor

t hat

of

) 3

3

Objectives

Matter

are

of

t he

reactions

4

on

on

t he

M at te r

in

wr iting

t he

lef t

g i ve n

By

the

be

able

●

●

in

the

t he

●

this

Law

topic

you

will

of

Conservation

Matter

apply

the

mole

balanced

side.

b ox .

of

to:

state

of

a

r ight

end

concept

chemical

using

masses

apply

the

to

equations

mole

concept

to

mole

concept

to

ionic

equations

Since

all

t he

atoms

t hat

were

present

at

t he

beginning

of

t he

reaction

are ●

apply

the

present at t he end of t he reaction, it follows t hat t he total mass of t he products balanced

must

We

be

can

water.

t he

same

prove

The

as

t his

t he

using

balanced

total

t he

mass

of

reaction

equation

for

t he

original

between

t he

and

oxygen

to

make

●

using

volumes

of

apply

the

concept

balanced

is:

using

2H

(g)



O

2

This

(g)

2H

2

molecules

on

a

reactant

chemical

to

equations

concentration

of

solutions.

O(g)

of

H



1

molecule

of

O

bigger

and

scale,

product.

2

molecules

of

H

2

t he

The

coefcients

equation,

O 2

show

t he

t herefore,

number

of

moles

of

each

means:

! 2 mol

of

H



1 mol

of

O

2

2 mol

of

2

H

we

now

take

t his

a

step

Key

O

fur t her

and

use

our

mole/mass

relationship,

Law

Matter

neither

means:

during

2(2



1) g

of

H



1(2



16) g

of

2

4 g

of

H 2

O

2[(2



1)



16)] g

of

2



32 g

fact

2

The

it

gases

2

2

f

mole

means:

2

Or,

equations

reactants.

hydrogen

reaction

chemical

of

O

H

Conservation

be

a

that

created

chemical

matter

nor

of

can

destroyed

reaction.

O 2

36 g 2

of

states

of

H

O 2

113

The

mole

and

chemical

reactions

The

We

can

total

We

clearly

mass

can

of

see

t he

use

t hat

t he

original

balanced

mass

of

reactants,

chemical

t he

water

hydrogen

equations

produced

and

to

is

oxygen,

determine

mole

t he

i.e.

t he

concept

same

as

t he

36 g.

quantities

of

unknown reactants and products in a reaction. f t he quantity of one reactant

or

product

ot her

is

known,

reactants

Mass

and

and

it

is

possible

to

calculate

t he

quantities

of

any

of

t he

products.

chemical

reactions

When answering questions involving masses of reactants and products, you will

always be given the mass of one reactant or product and be asked to determine

the

mass

of

another

reactant

or

product.

To

do

this

we

use

our

mole/mass

relationship and the mole ratio from the balanced equation for the reaction.

The

1)

steps

Calculate

its

given

one

2)

involved

Use

t he

t he

t he

unknown

3)

Use

1),

of

4)

t he

and

t he

Use

Note:

write

f

number

number

and

you

t he

its

molar

and

ratio

of

have

is

t he

in

t he

2),

of

t he

to

t he

equation

reactant

t he

or

calculate

reactant

its

product

or

product

using

is

t he

mole

you

are

product

t he

or

ratio

products.

The

calculating.

found

number

product

of

in

step

moles

found

in

mass

equation

before

or

and/or

mass

reactant

unknown

follows:

question.

whose

to

as

reactant

determine

determine

given

are

reactants

known

step

t he

one

product.

chemical

known

in

to

or

mass,

been

The

given

known

unknown

found

moles

not

of

problems

t he

equation

product

reactant

of

mass.

been

t he

moles

molar

balanced

moles

have

or

of

mole

of

mass–mass

chemical

known

reactant

t he

3),

its

you

unknown

t he

step

and

mass

balanced

between

solving

number

mass

whose

in

for

you

t he

begin

reaction,

your

you

must

calculation.

Examples

1

Calculate

t he

magnesium

The

mass

in

balanced

2Mg(s)

of

excess

magnesium

O

formed

by

burning

12 g

of

oxygen.

equation



oxide

for

t he

(g)

reaction

is:

2MgO(s)

2

The

mass

of

t he

magnesium

1)

Find

t he

reactant,

oxide,

is

number

Calculate

t he

to

of

magnesium

be

moles

molar

is

known.

The

mass

of

t he

product,

determined.

mass

of

of

Mg

using

its

mass

and

molar

mass:

Mg.

1

M(Mg)

i.e.



mass

24 g mol

1 mol

of

Mg



24 g

in

12 g

12

___

∴

number

of

moles

of

Mg



mol



0.5 mol

24

2)

Use

t he

balanced

between

2 mol

∴

3)

Mg

1 mol

Use

to

t he

and

form

Mg

Mg

chemical

forms

t he

equation

to

determine

t he

mole

ratio

MgO:

2 mol

number

calculate

0.5 mol

114

Mg

of

MgO.

1 mol

moles

number

forms

MgO

of

of

0.5 mol

Mg

from

moles

MgO

of

1),

and

MgO

t he

mole

produced:

ratio

from

2),

The

mole

4)

concept

Use

t he

The

number

determine

t he

of

moles

mass

of

of

MgO

MgO

from

3),

and

its

molar

mass,

mole

and

chemical

reactions

to

produced.

1

M(MgO)



24

i.e.

of

1 mol

∴

2

mass

mass

Determine

of

sodium

of

CO 2

The



of

0.5 mol

t he

mass

40 g mol

MgO

of

of



MgO

40 g



sodium

when

t he

0.5



40 g

carbonate

sodium



20 g

required

carbonate

to

equation

(s)



for

t he

reaction

mass

of

wit h

23.4 g

excess

2HCl(aq)

is:

2NaCl(aq)



CO

3

reactant,

produce

reacts

acid.

balanced

Na

16

chloride,

hydrochloric

The



(g)



H

2

t he

product,

sodium

sodium

carbonate,

is

chloride,

to

be

is

known.

O(l) 2

The

mass

of

t he

determined.

1

1)

M(NaCl)

i.e.



mass

23

of



35.5

1 mol



NaCl

58.5 g mol



58.5 g

23.4

_____

∴

number

of

moles

in

23.4 g



mol



0.4 mol

58.5

2)

1 mol

Na

CO 2

forms

2 mol

NaCl.

3

1

__

3)



0.4 mol

Na

CO 2

forms

0.4 mol

NaCl



0.2 mol

Na

3

CO 2

3

2

1

4)

M(Na

CO 2

i.e.

)



(2



23)



mass

of

1 mol

Na

CO 2

∴

3

mass

Determine

of

0.2 mol

t he

magnesium

The

12



(3



MgCO



decrease

carbonate

balanced

equation



0.2

in

is

(s)

t he

106 g mol

106 g



106 g

mass

heated

for

t he



t hat

21.2 g

would

until

its

reaction

MgO(s)



CO

occur

mass

when

remains

21.0 g

of

constant.

is:

(g) 2

decrease

nd



3

3

The

16)

3

in

mass

decrease

in

is

due

mass,

to

t he

t he

loss

mass

of

of

carbon

carbon

dioxide,

dioxide

t herefore,

produced

to

must

be

mass

of

determined.

The

t he

mass

of

t he

product,

reactant,

carbon

magnesium

dioxide,

is

to

be

carbonate,

is

known.

The

determined.

1

1)

M(MgCO

)



24



12



(3



16)



84 g mol

3

i.e.

mass

of

1 mol

MgCO



84 g

3

21.0

_____

∴

number

of

moles

in

21.0 g



mol



0.25

mol

84

2)

1 mol

MgCO

forms

1 mol

CO

3

3)

0.25 mol

2

MgCO

forms

0.25 mol

CO

3

2

1

4)

M(CO

)



12



(2



16)



44 g mol

2

i.e.

mass

of

1 mol

CO



44 g

2

∴

mass

of

0.25 mol

CO



0.25



44 g



11.0 g

2

Therefore,

We

four

can

also

t he

decrease

apply

t he

in

mass

mole

is

11.0 g

concept

to

ionic

equations

using

t he

same

steps.

115

The

mole

and

chemical

reactions

The

mole

concept

Example

Calculate

t he

mass

of

lead(II)

hydroxide

t hat

could

be

produced

when

a

solution containing 3.4 g of hydroxide ions reacts wit h a solution containing

excess

The

lead

ionic

ions.

equation

for

t he

reaction

is:

2

Pb

(aq)



2OH

(aq)

Pb(OH)

(s) 2

The

of

mass

t he

of

t he

product,

hydroxide

lead(II)

ions

present

hydroxide,

is

to

in

be

t he

solution

is

known.

The

mass

determined.

1

1)

M(OH

i.e.

)



mass

16

of



1

1 mol



17 g mol

OH

ions



17 g

3.4

____

∴

number

of

moles

in

3.4 g



mol



0.2 mol

17

2)

2 mol

OH

ions

form

1 mol

Pb(OH) 2

3)

0.2 mol

OH

ions

form

0.1 mol

Pb(OH) 2

1

4)

M(Pb(OH)

)



207



(2



16)



(2



1)



241 g mol



241 g

2

i.e.

mass

of

1 mol

Pb(OH)



241 g

2

∴

mass

of

0.1 mol

Pb(OH)



0.1



24.1 g

2

Gas

Exam

✔

volumes

used must

pay

very

careful

the

conditions

under

to

determine

stp

or

the

involving

rtp,

to

correct

gases

ensure

value

unknown

and

volume

t he

of

mole

a

reactant

ratio

from

or

t he

product

using

balanced

t he

equation

t he

reaction.

occur,

that

for

t he

relationship

which

for reactions

use

reactions

attention

mole/volume

i.e.

chemical

A balanced chemical equation for a reaction which involves gases can also be

You

to

and

tip

you

When

answering

questions

involving

volumes

of

gases,

use

t he

same

four

molar

steps

as

are

used

in

solving

mass–mass

problems.

volume.

Example

Nitrogen reacts wit h hydrogen to produce ammonia. Calculate t he minimum

3

volume of hydrogen t hat would be required to react completely wit h 6.0 dm

of

nitrogen

The

at

balanced

N

(g)



r tp.

equation

3H

2

The

t he

(g)

reaction

2NH

2

volume

reactant,

for

of

is:

(g) 3

t he

hydrogen,

reactant,

is

to

be

nitrogen,

is

known.

The

volume

of

t he

ot her

determined.

3

1)

Volume

of

1 mol

N

at

r tp



24 dm

2

6.0

____

3

∴

number

of

moles

in

6.0 dm



mol



0.25 mol

24

2)

1 mol

N

reacts

wit h

3 mol

H

2

3)

0.25 mol

2

N

reacts

wit h

3



0.25 mol

H

2



0.75 mol

H

2

2

3

4)

Volume

of

1 mol

H

at

r tp



24.0 dm

2

3

∴

volume

of

0.75 mol

H

at

r tp



0.75



24.0 dm

3



18.0 dm

2

Problems can also be solved involving bot h mass and volume using t he same

four

116

steps.

The

mole

concept

The

mole

and

chemical

reactions

Example

Calculate t he volume of sulfur trioxide gas formed at r tp when 9.6 g of oxygen

reacts

The

wit h

excess

balanced

2SO

(g)

sulfur

equation



O

2

dioxide.

for

t he

(g)

reaction

2SO

2

is:

(g) 3

The mass of t he reactant, oxygen, is known. The volume of t he product, sulfur

dioxide,

is

to

be

determined.

1

1)

M(O

)



32 g mol

2

i.e.

mass

of

1 mol

O



32 g

2

9.6

____

∴

number

of

moles

in

9.6 g



mol



0.3 mol

32

2)

1 mol

O

forms

2 mol

SO

2

3)

0.3 mol

3

O

forms

2



0.3 mol

SO

2



0.6 mol

SO

3

3

3

4)

Volume

of

1 mol

SO

at

r tp



24.0 dm

3

3

∴

volume

of

0.6 mol

SO

at

r tp



0.6



24.0 dm

3



14.4 dm

3

Molar

concentration

and

chemical

reactions

A balanced chemical equation for a reaction which involves a solution whose

volume

t he

and

mass

same

of

four

molar

t he

steps

concentration

ot her

as

reactant,

for

solving

or

are

t he

mass

known

mass

and

or

can

also

volume

volume

be

of

used

a

to

determine

product,

using

t he

problems.

Examples

3

1

To

prepare

t he

salt,

sodium

sulfate,

a

student

adds

50 cm

of

sodium

3

hydroxide

sulfuric

The

solution

acid.

wit h

Calculate

balanced

equation

2NaOH(aq)



H

a

t he

for

SO 2

The

are

volume

known.

and

The

3

1)

1000 cm

mass

t he

(aq)

sulfate

SO 2

t he

product,

t hat

to

excess

would

form.

of

(aq)



2H

4

t he

reactant,

sodium

O(l) 2

sulfate,

sodium

is

to

be

hydroxide,

determined.

3

(1 dm

1 cm

2.0 mol dm

is:

Na

concentration

of

of

sodium

reaction

)

NaOH(aq)

contains

2 mol

NaOH

2

_____

3

∴

of

4

molar

mass

concentration

NaOH(aq)

contains

mol

NaOH

1000

2

_____

3

and 50 cm

NaOH(aq) contains



50 mol NaOH



0.1 mol NaOH

1000

2)

2 mol

NaOH

forms

1 mol

Na

SO 2

4

1

__

3)

0.1 mol

NaOH

forms



0.1 mol

Na

SO 2



0.05 mol

4

Na

SO 2

4

2

1

4)

M(Na

SO 2

i.e.

mass

of

)



(2



23)

1 mol

Na

SO 2

∴

mass

of



32



(4



16)



142 g mol

4

0.05 mol



142 g

4

Na

SO 2



0.05



142 g



7.1 g

4

117

The

mole

and

chemical

reactions

The

2

What

volume

when

20 cm

reacts

wit h

of

carbon

dioxide,

measured

at

stp,

would

be

mole

concept

produced

3

The

(CO 2

)

is

(s)

acid

aluminium

equation

3

volume

acid,

hydrochloric

excess

balanced

Al

The

3

of



for

wit h

a

concentration

t he

reaction

6HCl(aq)

is:

2AlCl

(aq)



3CO

3

and

molar

The

concentration

volume

1.5 mol dm

carbonate?

3

known.

of

of

t he

of

t he

product,

(g)



3H

2

reactant,

carbon

O(l) 2

hydrochloric

dioxide

is

to

be

determined.

3

1)

1000 cm

HCl(aq)

contains

HCl.

1.5

_____

3

∴

1.5 mol

1 cm

contains

mol

HCl

1000

1.5

_____

3

and

20 cm

contains



20 mol

HCl



0.03 mol

HCl

1000

2)

6 mol

HCl

form

3 mol

CO 2

∴

2 mol

HCl

form

1 mol

CO 2

1

__

3)

0.03 mol

HCl

forms



0.03 mol

CO



0.015 mol

CO

2

2

2

3

4)

Volume

of

1 mol

CO

at

stp



22.4 dm

2

3

∴

volume

of

0.015 mol

CO

at

stp



0.015



22.4 dm

2

3



Summary

1

Ethene

(C

C

H 2

If

2

2.8 g

)

burns

(g)

the

oxygen



following

3O

4

of

in

to

form

(g)

2CO

2

ethene

(g)

burn

in

excess

of

moles

in

b

calculate

the

number

of

moles

of

c

calculate

the

mass

d

calculate

the

volume

carbonate

calcium

Carbon

gas.

and

steam

of

carbonate

monoxide

the

carbon

of

carbon

is

gas

the

O(g) 2

2.8 g

of

ethene

dioxide

formed

formed

dioxide

into

mass

of

carbon

dioxide

decomposes

Calculate

Calculate

2H

oxygen,

number

heated.



2

the

of

dioxide

equation:

calculate

Calcium

carbon

4

to

a

when

3

questions

H 2

according

0.336 dm

formed

calcium

carbon

at

oxide

dioxide

stp.

and

carbon

released

dioxide

when

300 g

heated.

reacts

volume

with

and

oxygen

mass

of

gas

to

carbon

form

carbon

monoxide

gas

dioxide

required

to

3

produce

4

4 dm

Potassium

of

carbon

carbonate

dioxide

reacts

with

gas

at

nitric

rtp.

acid

(HNO

)

to

produce

potassium

3

nitrate,

carbon

dioxide

and

water.

Calculate

the

mass

of

potassium

3

chloride

formed

when

40 cm

of

potassium

carbonate

solution

3

concentration

118

of

0.5 mol dm

reacts

with

excess

nitric

acid.

with

a

The

mole

Key

●

concept

mole

and

chemical

reactions

concepts

Relative

masses

of

The

a

atomic

of

carbon-12

●

Relative

●

A

mole

mass,

atoms,

par ticles

t he

as

and

mass

and

formula

formula

units

mass

wit h

compare

one-twelf t h

t he

t he

mass

atom.

atomic

is

molecular

molecules

mass,

molecular

amount

t here

are

of

a

mass

substance

atoms

in

and

t hat

12.00 g

of

formula

contains

mass

t he

have

same

no

units.

number

of

carbon-12.

23

●

The

number

A vogadro’s

of

par ticles

number

or

in

a

mole

is

6.0



10

,

which

is

also

known

as

N A

●

Molar

●

The

mass

molar

is

t he

mass

molecular

mass

mass,

of

an

or

in

grams,

element

formula

or

mass

of

one

mole

compound

amount

of

is

a

t he

substance.

relative

expressed

in

atomic

grams

per

mass,

mole.

1

Molar

●

mass

is

A vogadro’s

conditions

given

law

of

t he

states

unit

t hat

temperature

g mol

equal

and

volumes

pressure,

of

all

gases,

contain

t he

under

same

t he

same

number

of

molecules.

●

Molar

molar

volume

volume

temperature

is

is

t he

t he

and

volume

same

occupied

for

all

gases

by

one

under

mole

t he

of

same

a

gas.

The

conditions

of

pressure.

3

●

Molar

volume

at

standard

●

Molar

volume

at

room

●

The

temperature

and

pressure

(stp)

is

22.4 dm

3

concentration

dissolved

in

a

xed

of

temperature

a

solution

volume

of

and

is

t he

a

pressure

measure

(r tp)

of

t he

is

24 dm

quantity

of

a

solute

solution.

3

●

Mass

concentration

gives

t he

mass

of

solute

dissolved

in

1 dm

of

3

solution.

●

Molar

Mass

concentration

concentration

gives

is

t he

given

t he

number

of

unit

g dm

moles

of

solute

dissolved

3

●

●

of

solution.

A

stand ard

A

standard

The

The

f

solution

t he

t he

of

atoms

atoms

of

t hen

formula

molar

of

a

mass

or

one

its

a

using

a

t he

volumetric

gives

present

formula

by

is

unit

mol dm

known

accurately.

ask.

t he

gives

in

simplest

be

from

known,

t he

one

mass,

can

different

is

t he

mole

ratio

compound.

compound

compound

given

concentration

a

elements,

is

is

compound

in

of

empirical

t he

whose

element

t he

compound

of

of

ions

each

of

concentration

made

formula

propor tions

known,

is

is

formula

molecular

moles

●

Molar

solution

empirical

between

●

in

3

1 dm

in

actual

mole

a

of

its

t he

f

empirical

molecular

of

compound.

compound

determined.

t he

number

are

t he

molecular

formula

formula

and

can

t he

be

determined.

●

The

by

●

percentage

mass,

The

L aw

created

●

The

of

element

in

t he

a

product

and

is

a

states

chemical

chemical

t he

can

it

and

indicates

t he

percentage,

t hat

matter

can

neit her

be

reaction.

equation

give

t he

mole

ratios

products.

products

known,

reactants

compound

compound.

Matter

a

equations

reactants

ot her

of

balanced

and

of

t he

during

reactants

chemical

or

in

Conservation

t he

unknown

reactant

composition

destroyed

coefcients

Balanced

any

each

of

nor

between

●

of

is

be

in

used

a

to

determine

reaction.

possible

to

f

t he

quantities

quantity

calculate

t he

of

of

one

quantities

of

products.

119

Practice

exam-style

questions

The

b

Practice

exam-style

Calcium

hydrogencarbonate

Ca(HCO

)

3

questions

(s)



The

mass

of

0.25 mol

of

potassium

carbonate

2HNO

t he

following

nitric

(aq)

Ca(NO

an

)

3

investigation

in

t he

(aq)



2CO

2

(g)



laborator y,

O(l)

2

8.1 g

of

calcium

a

hydrogencarbonate

student

to

excess

24.75 g

B

34.5 g

C

38.5 g

i)

acid.

Determine

t he

number

hydrogencarbonate D

of

used

moles

by

t he

of

calcium

student.

552.0 g (2

A

2H

2

is:

nitric

2

acid

equation:

3

added A

to

2

During 1

wit h

concept

questions according

Multiple-choice

reacts

mole

mass

of

32 g

of

ii)

oxygen:

Determine

23

A

contains

6.0



B

contains

2 mol

C

contains

6.0

D

contains

t he

oxygen

10

of

dioxide

atoms

iii)

oxygen

35.5 g

of

10

molecules

same

number

of

of

at

oxygen

molecules

of

oxygen

c

as

of

moles

of

marks)

carbon

(2

t he

volume

of

carbon

dioxide

r tp.

marks)

made

(1

Magnesium

produce

chlorine

number

made.

Determine

23



t he

reacts

wit h

magnesium

hydrochloric

chloride

and

acid

mark)

to

hydrogen.

n

3

anot her

investigation,

a

student

reacted

20 cm

3

3

What

is

t he

A

0.88 g

B

224 g

C

448 g

D

880 g

mass

of

448 cm

of

carbon

dioxide

at

stp?

of

hydrochloric

acid

wit h

a

concentration

of

3

1.5 mol dm

i)

Write

a

wit h

excess

balanced

magnesium.

chemical

equation

for

t he

reaction.

ii)

(2

Calculate

acid

t he

number

of

moles

of

marks)

hydrochloric

used.

(1

mark)

3

4

You

are

required

to

make

250 cm

of

a

solution

of iii)

sodium

hydroxide

which

has

a

concentration

Determine

t he

number

of

moles

of

magnesium

of chloride

produced.

(2

marks)

3

0.1 mol dm

.

What

mass

of

sodium

hydroxide

would iv)

you

need

to

weigh

Calculate

t he

mass

of

magnesium

chloride

out? produced.

A

(2

d B

1.0 g

C

4.0 g

On

analysis

24.45 g

of

empirical D

a

compound

iron

and

formula

was

10.55 g

of

t he

found

of

to

oxygen.

contain

Determine

compound.

A

t he

(2

marks)

15

marks

25.0 g

Total

5

marks)

0.1 g

compound

W

combined

of

W

is

of

t he

40

was

found

wit h

and

t he

7 g

of

to

consist

Z.

relative

f

t he

of

30 g

relative

atomic

mass

of

element

atomic

of

Z

is

mass

14,

Extended

8 following

is

t he

correct

empirical

formula

response

question

which

for

a

i)

What

do

you

understand

by

t he

term

‘standard

t he

solution’?

(1

mark)

compound? 3

ii) A

WZ

B

W

You

wish

to

carbonate

prepare

solution

250 cm

of

of

potassium

concentration

Z

2 3

0.8 mol dm C

W

t he

laborator y.

Determine

3

mass W

of

potassium

carbonate

required.

Z

3

2

(3

6

Hydrogen

reacts

wit h

oxygen

according

to

t he

iii)

following

Name

make

equation:

2H

(g)



O

2

(g)

2H

2

b

O(g)

A

volume

oxygen

of

reacts

steam

wit h

could

excess

8.96 dm

B

12.8 dm

of

apparatus

solution

wishes

to

you

would

in.

make

a

be

produced

at

stp

if

(1

sample

of

t he

to

mark)

lead(II)

chloride,

in

t he

laborator y.

insoluble

Determine

12.8 g

mass

reacting

wit h

3

of

a

a

lead(II)

solution

chloride

which

solution

containing

could

containing

excess

be

made

23.4 g

of

lead()

sodium

by

nitrate

chloride.

(6

3

C

marks)

use

hydrogen?

3

A

piece

your

student

t he of

t he

2

salt, What

t he

Z

2

D

in

marks)

17 .92 dm

3

D

c

25.6 dm

Ammonium

extensively

wit h

Structured

question

in

t he

This

question

is

concerned

wit h

t he

mole

and

By

in

and

ammonium

gardeners

nitrogen

growt h.

nitrogen 7

nitrate

by

t hey

as

need

calculating

each

of

t he

sulfate

fer tilisers

to

t he

make

to

protein

percentage,

fer tilisers,

are

supply

by

determine

used

plants

for

use

mass,

of

which

its would

be

t he

better

value

for

money

if

t hey

bot h

cost

application. t he a

Give

a

denition

for

t he

term

‘mole’.

(1

same

per

kilogram.

marks)

15

marks

mark)

Total

120

(4

A8

The

concept

of

Acids,

acids,

bases

and

salts

bases

has

been

and

salts

around Objectives

for

As

a

very

our

long

time;

knowledge

as

of

early

as

the

chemistry

has

17th

century.

developed,

By

the

be

able

of

a

compound

as

an

acid,

a

base

or

a

salt

explain

when

has

been

refined.

Acids,

bases

and

salts

are

used

in

of

our

lives.

Properties

was

have

not

always

and

until

somet hing

substance

a

in

few

known

hundred

common,

t hat

reacts

reactions

t hat

a

vinegar

years

t hey

wit h

of

acids

●

ago

bot h

base

and

t hat

contain

to

form

a

it

lemon

was

acids.

salt

juice

taste

discovered

An

and

acid

sour,

t hat

can

be

but

t hese

it

in

t heir

anhydrous

an

give

you

ionisation

acid

have

dened

as

a

form,

i.e.

not

dissolved

●

water.

in

the

in

in

acids

describe

the

acids

will

of

acids

water

terms

of

are

composed

with

properties

reactive

carbonates,

and

describe

which

the

can

dene

of

reactions

hydrogencarbonates

acids

water,

general

aqueous

metals,

●

Acids

the

dissolved

dene

of

People

topic

protons

●

A8.1

this

all ●

aspects

of

to:

the

●

classification

end

be

acid

ways

in

bases

classied

anhydride

and

give

of

examples

of

acid

anhydrides

covalent molecules and t hey may be solid, liquid or gas at room temperature.

●

Solids

include

citric

acid,

tar taric

acid

and

ascorbic

acid

(vitamin

C).

give

examples

of

acids

in

living

Liquids

systems.

include

sulfuric

acid

and

nitric

acid.

Gases

include

hydrogen

chloride

All acids have hydrogen in t heir formulae, e.g. nitric acid, HNO

gas.

and sulfuric 3

acid,

H

SO 2

.

Table

8.1.1

gives

t he

names

and

formulae

of

some

common

4

acids.



T able

8.1.1

Some

Name

acid

HCl

acid

H

SO

2

nitric

acids

Formula

hydrochloric

sulfuric

common

acid

4

HNO 3

phosphoric

acid

H

PO

3

methanoic

ethanoic

acid

4

HCOOH

acid

CH

COOH

3

(a)



Figure

(b)

8.1.1

(a)

Some

common

laboratory

acids,

(b)

some

common

household

acids

121

Properties

and

reactions

of

acids

Acids,

Ionisation

When

an

of

acid

is

acids

added

in

to

bases

and

salts

water

water,

t he

acid

molecules

ionise,

i.e.

t hey

for m



ions.

Acids

always

ionise

to

for m

hyd rogen

ions ,

or

H

ions,

and

negative



anions.

The

H

ions

t hen

become

att ac hed

to

t he

polar

water

molecules



for ming

hyd ronium

ions

or

H

O

ions

(sometimes

called

hydroxonium

3

ions).

Using

an

t he

ionisation

of

hydrogen

chloride

gas

to

form

hydrochloric

acid

as

example:



HCl(g)

water



H

(aq)



H



H



O(l)

H

2

O

(aq)

(aq)

3

hydronium

t he

Cl



(aq)

overall

reaction

can

be

summarised

ion

as:



HCl(g)



H

O(l)

H

2

For

simplicity,

it

O

(aq)



Cl

(aq)

3

is

usual

to

represent

t he

reaction

as

follows:

in

water



HCl(aq)

Ot her

examples

t hat

H

show

t he

(aq)



Cl

ionisation

(aq)

of

acids

are:



HNO

(aq)

H

(aq)



NO

3

(aq) 3



H

SO 2

(aq)

2H

2

(aq)



SO

4

(aq) 4



H

PO 3

(aq)

3H

3

(aq)



PO

4

(aq) 4



CH

COOH(aq)

CH

3

COO

(aq)



H

(aq)

3

1

A hydrogen atom,

H, has one proton in its nucleus and one electron spinning 1

around

single

!

Key

proton

electron,

acid

is

nucleus

in

since

it

t he

is

rst

energy

formed

by

a

shell.

A

hydrogen

hydrogen

atom

ion

losing

is,

its

t herefore,

one

a

valence

fact

an An

t he

a

proton

acid

leaving

to

only

donate

its

t he

nucleus

hydrogen

containing

ions,

or

t he

protons,

one

to

proton.

anot her

The

ability

reactant

can

of

be

donor.

used

to

When

dene

an

dissolves

an

an

acid

in

aqueous

acid

as

reacts,

water,

can

solution

being

t he

be

of

a

proton

hydrogen

given

to

donor.

ions,

t he

hydroc hlor ic

ot her

acid

or

protons,

react ant.

reacts

for med

For

wit h

when

example,

sodium

it

when

hydroxide,



t he

hydroc hlor ic

acid

gives

its

H

ions,

or

protons,

to

t he

OH

ions

of

t he

sodium hydroxide, for ming water. This can be summar ised by t he following

ionic

equation:



OH

(aq)



H

(aq)

H

O(l) 2

General

properties

of

aqueous

acids



The

presence

of

H

ions

in

aqueous

solution

gives

acids

t heir

proper ties. Aqueous solutions of acids are described as being

have

122

t he

following

●

t hey

have

a

●

t hey

change

●

t hey

have

a

sour

common

taste

blue

pH

proper ties:

litmus

value

of

to

red

less

t han

7

characteristic

acid ic

and t hey

Acids,

bases

and

salts

Properties

●

t hey

are

corrosive

●

t hey

are

electrolytes,

Chemical

Since

all

in

a

an

The

ions

salt.

acid

A

is

t he

is,

of

except

nitric

Reactive

of

(see

metals

aluminium,

This

can

reactive

When

as

produce

t

is

nitric

acid

dioxide

be

is

to

),

are

in

wit h

i.e.

an

acids

current.

aqueous

n

metal

all

ions

formed

or

t hese

acids

t he

have

reactions,

ammonium

when

ammonium

detail

solution,

of

t he

ions

hydrogen

to

ion

ion.

below.

reactive

above

metals

to

hydrogen

potassium,

sodium,

in

produce

t he

a

salt

reactivity

calcium,

and

series

magnesium,

lead.

by

t he

acid

react

remember

following

salt

wit h

and

reactions

it

acids,

t he

are

t hat

metals

not

or

t hose

summarised

wit h

in

compound

ion

react

evolved,

and

by

of

acids

reactants.

replaced

a

electric

reactions

metals

and



an

when

ot her

discussed

18.1),

t he

reacts

(NO

ions

metal

acid,

iron

i.e.

impor tant

a

are

metals

gas

heat,

by

metal

reactive

hydrogen

are

metals

Unit

zinc,

reaction

acid

conduct

aqueous

cer tain

reactive

hydrogen.

of

t herefore,

acids

with

t hey

hydrogen

wit h

replaced

react

Acids,

in

salt

reactions

Acids

form

reactions

hydrogen

form

reactions

acids

common

i.e.

and



effervescence

described

acid

produces

word

equation:

hydrogen

reactions

nitric

general

as

become

being

does

not

oxides

of

(bubbling)

hotter

is

seen

because

t hey

exothermic

react

in

t his

nitrogen,

way.

e.g.

When

nitrogen

hydrogen.

2

Example

Magnesium

reacts

wit h

sulfuric

acid

to

produce

magnesium

sulfate

and

hydrogen:

Mg(s)



H

SO 2

The

ionic

(aq)

MgSO

4

equation

for

t his

reaction



Mg(s)



2H

(aq)



H

4

(g) 2

is:

2

(aq)

Mg

(aq)



H

(g) 2

Acids

react

with

metal

carbonates

and

hydrogencarbonates

Acids react wit h metal carbonates and metal hydrogencarbonates to produce

a

salt,

carbon

dioxide

and

water.

These reactions can be summarised by the following general word equations:

carbon metal

carbonate



acid

salt





water



water

d ioxide

metal

carbon 

acid

salt

hydrogencarbonate

When

metal

effervescence

carbonates

is

seen

as

 d ioxide

and

carbon

hydrogencarbonates

dioxide

gas

is

react

wit h

acids,

evolved.

123

Properties

and

reactions

of

acids

Acids,

bases

and

salts

Examples

1

Potassium

nitrate,

K

CO 2

The

carbonate

carbon

reacts

dioxide

(aq)



2HNO

3

ionic

wit h

and

nitric

(aq)

2KNO

for

2

t his

(aq)



2H

reaction

(aq)

CO

(g)



H

O(l) 2

is:

CO

hydrogencarbonate

chloride,

) 3

ionic



2

(g)



H

2

Ca(HCO

The

potassium



(aq)

calcium

produce

3

3

Calcium

to

3

equation

CO

2

acid

water:

carbon

(aq)



reacts

dioxide

wit h

and

O(l) 2

hydrochloric

acid

2HCl(aq)

CaCl

2

(aq)



2CO

2

equation

for

t his

reaction

to

produce

water:

(g)



2H

2

O(l) 2

is:



HCO

(aq)



H

(aq)

CO

3

Acids

Did

?

you

know?

Acids

react

react

with

Any

reactive

metals,

that

react

salts

the

and

with

appear

salt

insoluble

acids

to

to

O(l) 2

bases

to

reactions.

produce

t

is

a

salt

impor tant

and

to

water.

note

t hat

These

are

base

a

a

is

known

metal

a

metal

hydroxide.

soluble

because

These

reactions

can

be

summarised

by

t he

following

general

word

equations:

dissolves.

metal

metal

When

bases

oxide

hydroxide

react

exothermic

wit h





acid

salt

acid

acids,

t he



salt

reactions

water



water

become

warmer

because

t hey

reactions.

Examples

1

Copper(II)

and

oxide

reacts

wit h

sulfuric

acid

to

produce

copper(II)

sulfate

water:

CuO(s)



H

SO 2

onic

(aq)

CuSO

4

(aq)



H

4

O(l) 2

equation:



CuO(s)



2H

2

(aq)

Cu

(aq)



H

O(l) 2

✔

Exam

tip n

t his

and It

is

extremely

important

that

a

reaction,

blue

t he

solution

black

copper(II)

forms.

This

is

oxide

because

appears

soluble

to

dissolve

copper(II)

slowly

sulfate

is

you 2

can

write

balanced

equations

acids.

good

word

so

T o

for

help

idea

to

the

you

products

for

to

do

memorise

given

know

each

produced

chemical

reactions

you

equations

that

the

the

in

it

is

a

general

this

of

the

must

also

common

learn

the

t he

solution

contains

blue

2

Sodium

hydroxide

chloride

and

ions.

reacts

wit h

hydrochloric

acid

to

produce

water:

NaOH(aq)



HCl(aq)

NaCl(aq)

formulae



H

O(l) 2

reaction.

equation:

of

acids. 

OH

(aq)



H

(aq)

H

O(l) 2

124

Cu

section

general

type

and

of

this,

onic You

as

oxide

bases

form

dissolve

produced

H

insoluble

or

carbonates



bases

wit h

neutralisation

(g) 2

sodium

are

Acids,

bases

and

salts

Investigating

Your

teacher

Properties

reactions

may

use

this

of

observation,

recording

●

analysis

interpretation.

Y ou

will

be

copper(II)

acid,

and

supplied

with

carbonate,

nitric

acid,

and

lime

to

water,

of

acids

assess:

reporting

magnesium

calcium

reactions

acids

activity

●

and

ribbon,

hydroxide,

test

tubes

zinc,

copper( II)

and

a

sodium

oxide,

wooden

hydrogencarbonate,

hydrochloric

acid,

sulfuric

splint.

Method

1

Reactions

between

an

acid

and

metals:

2

a

Place

2 cm

of

magnesium

if

b

it

becomes

Place

of

a

2

Repeat

Reaction

splint

gas.

pop

the

acid

Observe

the

in

a

test

tube

reaction.

Feel

and

the

add

a

piece

bottom

of

of

the

tube

to

see

hotter.

burning

hydrogen

squeaky

c

hydrochloric

ribbon.

If

and

at

the

ame

experiment

between

an

the

mouth

hydrogen

is

will

using

acid

and

be

a

a

of

being

the

test

tube

produced,

to

the

test

for

splint

the

will

presence

make

a

extinguished.

small

piece

of

zinc.

hydrogencarbonate:

delivery

tube

3

a

Place

2 cm

of

sulfuric

acid

in

a

test

cork/bung

tube

and

add

a

spatula

hydrogencarbonate.

of

test

tube

sodium

Observe

the

reaction.

b

Cork

the

running

test

tube

through

with

the

a

delivery

cork

into

a

tube

test

tube

dilute

sulfuric

of

colourless

Figure

8.1.2,

lime

to

water,

test

for

as

the

shown

acid

in

presence lime

sodium

of

carbon

dioxide.

If

carbon

dioxide

(calcium

hydrogencarbonate

is

water

hydroxid

solution)

being

produced,

a

white

precipitate

will



form

in

the

lime

Figure

sulfuric

3

Reaction

between

8.1.2

Reaction

between

water.

an

acid

and

a

acid

and

sodium

hydrogencarbonate

carbonate:

3

a

Place

b

T est

c

Observe

and

4

2 cm

add

for

Reactions

a

of

sulfuric

spatula

the

of

colour

between

an

in

a

copper( II)

presence

any

acid

of

test

carbonate.

carbon

changes

acid

and

tube

dioxide

Observe

as

occurring

in

step

during

the

the

reaction.

2

reaction.

bases:

3

a

Place

2 cm

hydroxide.

tube

b

to

Repeat

the

5

Record

for

Write

7

Explain

a

if

it

all

time

any

and

tube

felt

tube

and

observe

add

the

a

spatula

reaction.

Feel

of

calcium

the

bottom

of

the

a

the

spatula

tube

of

copper( II)

periodically

oxide

until

no

instead

further

of

calcium

changes

changes.

for

each

reaction,

including

the

results

of

the

tests

dioxide.

equation

changes

steps

test

and

using

shake

chemical

in

a

hotter.

colour

carbon

colour

you

in

observations

balanced

changes

the

becomes

This

your

any

acid

experiment

Observe

hydrogen

6

nitric

Shake

see

hydroxide.

occur.

of

you

1a

for

each

observed

and

in

reaction.

steps

3c

and

4b,

and

any

heat

4a

125

Properties

and

reactions

of

acids

Acids,

During

and

f

t he

experiment,

carbon

dioxide

hydrogen

is

you

learnt

how

to

test

for

t he

bases

presence

of

and

salts

hydrogen

gases.

produced

in

a

reaction,

it

causes

a

burning

splint

to

make

a

squeaky pop and to be extinguished. The ‘pop’ is t he sound of a small explosion

as

t he

hydrogen

2H

(g)



O

2

f

carbon

(g)

2H

is

lime

calcium

produced

water.

hydroxide,

and

(aq)



Acids

can

be

Inorganic

●

of

compounds

geological

do

not

origin.

contain

exceptions

Organic

An

of

the

and

●

carbon

compounds

biological

and

contain

animals.

carbon

to

form

steam:

a

reaction,

is

because

carbon

and

dioxide

water.

it

forms

t he

reacts

The

a

lime

white

water

wit h

calcium

precipitate

is

t his

a

when

solution

forming

carbonate

of

white,

forms

t he

(g)

CaCO

of

and

(s)



H

3

O(l) 2

acids

in

organic

a

variety

of

ways.

acids

and

be

classied

as

acid

inorganic

contains

a

acids

or

organic

non-met allic

acids.

origin,

They

e.g.

as

well

as

Most

organic

acids

it

are

hydrogen.

Examples

of

element

inorganic

or

polyatomic

acids

are

given

in

8.1.2.

is

t he

acids

contain

hydrogen

at

t he

t he

carboxyl

end

of

t he

group,

i.e.

carboxyl

COOH.

group

n

t hese

which

forms

t he



ion

when

t he

acid

dissolves

in

water.

Examples

of

organic

acids

are

from

given plants

t he

CO

classied

inorganic

Table

H

mainly

can

g roup

carbonates,

hydrogencarbonates

dioxide.

air

are

Most

carbon,

being

t he

know? Acids

Inorganic

in

2

Classification

?

in

O(g)

This

carbonate

2

you

oxygen

precipitate:

Ca(OH)

Did

wit h

2

d ioxide

into

insoluble

white

explosively

2

bubbled

calcium

reacts

in

Table

8.1.3.

always

most

contain



T able

8.1.2

Common

inorganic

acids



T able

8.1.3

Common

organic

acids

hydrogen. Acid

hydrochloric

nitric

acid

acid

Formula

Acid

HCl

methanoic

HNO

ethanoic

3

sulfuric

acid

H

phosphoric

acid

H

acid

lactic

4

acid

H

acid

H

dibasic

COOH

CH

CH(OH)COOH

acid

C

H

6

citric

acid

C

O

8

H

6

6

O

8

7

3

CO

2

Monobasic,

CH

SO

2

carbonic

acid

acid

ascorbic

4

HNO 2

sulfurous

HCOOH

3

PO

3

nitrous

acid

3

SO

2

Formula

3

and

tribasic

acids



Acids

!

Key

fact

per

can

also

molecule

be

classied

when

according

dissolved

in

to

water,

t he

number

known

as

of

t heir

H

ions

t hey

produce

basicity.

 

Basicity

is

produced

when

it

the

per

number

molecule

dissolves

in

of

of

H

●

A

monobasic

acid

produces

one

H

ion

per

molecule

when

it

dissolves

ions

in

acid

water.

Hydrochloric

acid

(HCl),

nitric

acid

(HNO

)

and

et hanoic

acid

3

(CH

water.

COOH)

are

examples

of

monobasic

acids.

3



●

A

d ibasic

water.

acid

Sulfuric

produces

acid

(H

two

SO 2

)

H

is

ions

an

per

molecule

example

of

a

when

dibasic

it

dissolves

in

acid.

4



●

A

tribasic

water.

acid

produces

Phosphoric

acid

t hree

(H

PO 3

126

H

) 4

is

ions

an

per

molecule

example

of

a

when

tribasic

it

dissolves

acid.

in

Acids,

bases

Dilute

Acids

A

●

and

can

and

salts

Properties

concentrated

also

d ilute

be

acid

one

reactions

of

acids

acids

classied

is

and

based

t hat

on

t he

contains

a

quantity

lot

of

of

water,

water

e.g.

Did

?

present.

hydrochloric

you

know?

acid, A

concentrated

acid

is

always

3

which

has

a

concentration

A concentrated acid

●

of

0.1 mol dm

,

is

dilute.

diluted

to

is one that contains very little water, e.g. hydrochloric

3

on

reaction

i.e.

Strong

and

weak

the

can

when

t he

also

be

A

●

strong

acid

A

●

weak

e.g.

We

and

is

classied

be

is

fully

sulfuric

acid

is

carbonic

will

dissolved

acid

based

on

t he

degree

of

ionisation

t hat

a

is

slowly

When

lot

to

of

an

acid

water ,

heat

the

energy ,

exothermic.

spattering

ionised

slowly

when

dissolved

in

water,

e.g.

only

at

can

This

be

of

hydrochloric

to

water

If

the

can

the

acid

water ,

is

the

absorb

added

larger

the

heat

volume

energy

produced.

par tially

and

and

occurs

water.

acid.

acid

looking

in

ionised

et hanoic

strong

and

when

dissolved

in

water,

acid.

weak

acids

in

more

detail

in

Unit

8.3.

Key

! Acid

acid

added

off

reaction

cause

dangerous.

acid

water .

being

gives

the

acids

can

Acids

adding

distilled

ionises

, is concentrated.

acid, which has a concentration of 12 mol dm

the

by

fact

anhydrides An

Cer tain

compounds

react

wit h

water

to

form

an

acid.

These

are

known

acid

which

as

anhydride

reacts

with

is

a

compound

water

to

form

an

acid.

acid

anhydrides

Acid anhydride literally means ‘an acid wit hout water’. Many acid anhydrides

are

acidic

oxides

of

non-metals.

Carbon

dioxide

(CO

),

sulfur

dioxide

2

(SO

),

sulfur

trioxide

(SO

2

)

and

nitrogen

dioxide

(NO

3

)

are

examples

of

acid

Did

?

2

you

know?

anhydrides:

Nitrogen

CO

(g) 2



H

O(l)

H

2

CO 2

in

carbonic

the

(g) 2



H



H

O(l)

H

2

(g)

SO 2

3

O(l)

H

2

(aq)

SO 2

acid

When

in

(aq)

the

H

O(l)

HNO

2

it

(aq)



HNO

2

it

rain

can

buildings

acid

nitric

water

living

to

with

come

some

Table



of

across

t hese

variety

in

of

our

8.1.4

Acid

acid

vitamin

H

O

8

acids

ever yday

Acids

in

living

C

In

many

fruits,

foods,

West

)

sweet

Methanoic

In

acid

ant

(HCOOH)

Important

e.g.

Indian

citrus

A

shortage

Lactic

acid

O

of

calcium

dissolve

them

to

It

acidic

make

as

it

can

for

soluble

also

certain

make

organisms.

These

are

We

also

to

aquatic

survive.

use

summarised

in

peppers,

to

vitamin

note

C

to

heat,

in

e.g.

the

diet

during

can

lead

cooking,

to

scurvy.

vitamin

C

is

destroyed

by

being

oxidised.

tomatoes,

the

leafy

)

hydrogencarbonate

is

sometimes

added

to

fruits

and

vegetables

to

improve

their

appearance

and

vegetables

venom

of

bee

and

texture.

This

neutralises

Causes

itching,

any

redness,

vitamin

swelling

C

and

present,

pain

reducing

around

the

the

vitamin

C

content.

sting.

stings

Produced

during

in

muscle

strenuous

cells

If

can

be

treated

by

hydrogencarbonate.

too

much

lactic

acid

applying

These

builds

a

paste

both

up

it

of

sodium

neutralise

prevents

the

hydrogencarbonate

or

calamine

lotion

which

contains

acid.

muscles

from

contracting

and

the

person

collapses.

activity

3

Ethanoic

(CH

living

points

of

exposure

zinc

6

made

slowly

cherries,

Stings

H

This

statues

6

green

3

in

activities.

Sodium

(C

cause

systems

On

6

vapour

rain.

systems

organic

Occurrence

Ascorbic

(C

the

8.1.4.

T able

or

a

acids

then

nitrate.

too

organisms

We

water

acid

in

vehicles.

acid

calcium

in

with

forms

present

motor

(aq)

reacts

acids

also

of

3

nitrous

of

is

reacts

air

carbonate

Examples

it

fumes

acid

and

2



naturally

lightning

4

sulfuric

(g)

and

exhaust

3

acid

2NO

made

when

acid

sulfurous

SO

is

atmosphere

occurs

SO

dioxide

(aq) 3

acid

COOH)

In

vinegar

Vinegar

is

enzymes

used

that

to

preserve

cause

decay

food

and

items.

inhibits

Being

the

acidic,

growth

of

it

has

a

low

bacteria

pH,

and

which

denatures

(destroys)

the

fungi.

3

127

Properties



T able

and

8.1.4

bases

Acids,

Occurrence

Citric

acid

H

6

of

O

8

In

citrus

fruits,

Important

e.g.

limes

Lime

)

(Fe

7

juice

O

2

)

in

points

is

used

the

rust

to

to

stains

(s)



3

iron(III)

rust

making

6H

stains

a

from

soluble

clothes.

Summary

Write

and

the

Give

three

4

Give

the

5

terms

Write

balanced

reaction

b

the

reaction

c

the

reaction

7

Why

does

is

and

‘acid

show

how

other

that

are

than

the

chemical

be

able

zinc

work

for

aluminium

to

preserve

hydrogencarbonate

a

an

2Fe

the

stain

acids

ionise

of

with

the

the

iron( III)

oxide

clothes:

(aq)



3H

O(l)

removed

when

placed

in

water:

sulfuric

acid,

hydrochloric

acid

topic

you

base

in

terms

of

react

are

typical

of

aqueous

acids.

with:

following:

and

hydrochloric

sulfuric

some

used

of

as

a

acid

and

nitric

acid

acid.

the

A8.2

this

which

hydrogencarbonate

foods

we

treatment

eat?

for

ant

Properties

stings?

and

reactions

of

bases

will

base

and

dene

acids

the

and

A

dene

reacts

out

carbonates.

hydroxide

to:

●

juice

acid

reactions,

when

magnesium

between

vinegar

of

●

lime

washed

3

(aq)

from

following

their

equations

between

between

sodium

end

the

b

Objectives

By

the

be

anhydride’.

formed

oxides

the

How

which

properties,

a

6

‘acid’

products

metal

in

can

acid.

3

a

acid

which

questions

equations

nitric

The

compound

2

oxide

(rust)

2

salts

note

remove



O

2

Dene

and

3

Fe

1

bases

(continued)

Acid

(C

reactions

can

be

water.

dened

Bases

are

as

a

substance

normally

metal

which

oxides

reacts

and

wit h

metal

an

acid

to

form

hydroxides.

a

salt

However,

protons

ammonia

is

also

classied

as

a

base.

Examples

of

bases

include

magnesium

alkali

oxide

(MgO),

copper(II)

oxide

(CuO),

magnesium

hydroxide

(Mg(OH)

)

and

2

give

●

the

general

properties

of

copper(II)

hydroxide

(Cu(OH)

). 2

●

aqueous

alkalis

describe

the

with

acids

●

dene

●

classify

an

reactions

and

of

bases

ammonium

amphoteric

oxides

into

salts

substance

acidic,

You

learnt

protons

t he

acid

and

Unit

t he

and

8.1

base,

t his

fact

t hat

when

forming

can

be

a

base

water.

used

to

reacts

The

wit h

base

dene

a

has

base

an

acid,

accepted

as

a

t he

t he

proton

acid

donates

protons

from

acceptor.

basic,

Using

amphoteric

in

to

t he

same

example

as

in

Unit

8.1,

when

hydrochloric

acid

reacts

wit h

neutral.



sodium

ions,

by

or

t he

hydroxide,

protons,

following

t he

from

ionic

OH

t he

ions

of

t he

hydrochloric

sodium

acid

hydroxide

forming

water,

accept

as

t he

H

summarised

equation:



Key

!

A

base

is

OH

fact

a

!

proton

acceptor.

in

alkali

water

(aq)

H

O(l)

bases

known

as

or

ions.

OH

are

soluble

alkalis.

When

in

water,

t hey

ot hers

dissolve

in

are

insoluble.

water,

t hey

a

base

form

a

which

dissolves

solution

common

hydroxide

(Ca(OH)

),

alkalis

(NaOH),

which

is

include

which

are

potassium

fully

moderately

soluble

soluble.

hydroxide

in

For

water,

OH

ions. 

NaOH(s)

128

bases

hydroxide



water

Na

(aq)



OH

(aq)

(KOH)

and

example:

2

containing

Soluble

form

are

ions,

fact

is

to

H

Alkalis

The

An



2

Some

Key

(aq)

and

calcium

sodium

hydroxide

Acids,

bases

and

salts

Properties

and

reactions

of

bases

When ammonia gas is added to water it reacts wit h water to form ammonium

hydroxide

(NH

OH),

which

is

also

an

alkali:

4



NH

(g)



H

3

O(l)

NH

2

Potassium

oxide

(aq)



OH

(K

O),

sodium

oxide

(Na

2

react

wit h

water

(aq)

4

to

O)

and

calcium

oxide

(CaO)

also

2

form

t he

equivalent

hydroxide.

For

example:



Na

O(s)



H

2

Like

on

●

acids,

t he

A

alkalis

degree

strong

A

weak

e.g.

of

2Na

can

be

classied

ionisation

alkali

hydroxide

●

O(l)

(aq)



2OH

(aq)

2

and

alkali

is

fully

sodium

is

only

t hat

into

strong

occurs

ionised

when

when

alkalis

t he

and

alkali

dissolved

in

is

weak

alkalis

dissolved

water,

e.g.

in

based

water.

potassium

hydroxide.

par tially

ionised

when

dissolved

in

water,

ammonia.



We

will

be

looking

at

strong

and

weak

alkalis

in

more

detail

in

Unit

Figure

8.2.1

These

products

contain

8.3. bases

General

properties

of

aqueous

alkalis

The presence of OH

ions in aqueous solution gives alkalis t heir characteristic

proper ties.

solutions

t hey

have

Aqueous

t he

following

●

t hey

have

a

●

t hey

change

●

t hey

have

●

t hey

are

corrosive

●

t hey

are

electrolytes,

●

t hey

feel

a

bitter

red

pH

Chemical

alkalis

are

described

as

being

alkaline

and

proper ties:

taste

litmus

value

soapy

of

common

to

of

i.e.

when

blue

more

t hey

t han

7

conduct

an

electric

current

touched.

reactions

of

bases

Since bases contain oxide or hydroxide ions, bases have common reactions with

certain other reactants. The reactions of bases are discussed in detail below.

Bases

Bases

react

react

These

with

wit h

acids

reactions,

following



Remember

to

which

general

base

acids

word

produce

you

looked

salt

when

salt

at

and

in

water.

Unit

8.1,

can

be

summarised

by

t he

equation:

acid

t hat

a

bases



water

react

wit h

acids,

t he

reactions

become

warmer

because t hey are exot hermic reactions. Also, any insoluble bases which react

to

produce

soluble

salts,

appear

to

dissolve.

Examples

1

Magnesium

chloride

oxide

and

MgO(s)

reacts

wit h

hydrochloric

acid



2HCl(aq)

MgCl

(aq)



H

2

onic

to

produce

magnesium

water:

O(l) 2

equation:



MgO(s)



2H

2

(aq)

Mg

(aq)



H

O(l) 2

2

Potassium

sulfate

hydroxide

and

2KOH(aq)



H

SO 2

onic

reacts

wit h

sulfuric

acid

to

produce

potassium

water:

(aq)

K

4

SO 2

(aq) 4



2H

O(l) 2

equation:



OH

(aq)



H

(aq)

H

O(l) 2

129

Properties

and

reactions

of

bases

Acids,

Bases

Bases

react

react

base

n

order

wit h



to

with

ammonium

ammonium

ammonium

react,

t he

and

salts

salts

salts

to

produce

salt

reactants

bases

salt

need

to

be

a

salt,



ammonia

ammoni a



and

water:

water

heated.

Examples

1

Copper(II)

chloride,

oxide

reacts

ammonia

CuO(s)



wit h

and

2NH

ammonium

Calcium

sulfate,

hydroxide

ammonia

Cl(s)

CuCl

Ca(OH)

(s)



reacts

ammonium

(NH

Your

●

teacher

will

paper,

be

a

may

wit h

SO 2



2NH

(g)



H

3

ammonium

sulfate

(s)

CaSO

4

reaction

use

this

recording

supplied

dry

copper(II)

O(l) 2

to

produce

calcium

(s)



2NH

4

between

(g)



2H

3

calcium

O(l) 2

hydroxide

and

chloride

observation,

Y ou

) 4

the

produce

water:

2

Investigating

(s) 2

and

to

water:

4

2

chloride

test

with

tube

activity

and

calcium

and

to

assess:

reporting.

hydroxide,

ammonium

chloride,

red

litmus

tongs.

Method

1

Place

2

Add

mix

Did

?

you

litmus

it

paper

reacts

form

gas

causes

to

with

turn

the

ammonium

moist

(g)



H

3

the

small

blue

water

because

present

hydroxide

O(l)

heat

paper

ammonia

hydroxide

ammonium

4

Look

5

Write

OH(aq) 4

6

Explain

Some

substance

substance

which

both

and

can

with

react

strong

is

chloride

the

and

test

tube.

shake

the

tube

to

mixture

If

the

and

while

mouth

ammonia

gas

of

is

heating

the

tube

hold

to

produced

test

the

a

piece

for

the

litmus

of

moist

presence

paper

will

red

of

turn

blue.

at

the

sides

of

the

test

tube

to

see

if

any

water

droplets

form.

a

balance

the

chemical

formation

of

oxides

equation

the

water

and

for

the

reaction.

droplets.

hydroxides

metal

wit h

oxides

acids

and

and

also

hydroxides

behave

as

can

acids

behave

as

because

bases

t hey

because

can

react

t hey

wit h

can

strong

a

with

alkalis.

These

substances

are

referred

to

as

being

amphoteric

alkalis.

The

and

●

following

general

hydroxides

The

word

equations

summarise

●

The

amphoteric

amphoteric

strong alkali

The



amphoteric

how

amphoteric

oxides

react.

substance

reacting

as

amphoteric oxide or hydroxide

130

in

fact

amphoteric

acids

of

calcium

is

react An

the

across

gas.

Amphoteric

!

spatulas

of

to

which

NH

2

Key

spatulas

solids.

Carefully

litmus

red

alkaline:

NH

two

small

know?

3

Ammonia

two

substance

reacting

as

a

base:



an

acid

salt

and

hydroxides

are

water

acid:

amphoteric oxide or hydroxide

oxides



listed

in

Table

salt

8.2.1.



water

Acids,



bases

T able

and

8.2.1

Amphoteric

aluminium

salts

Properties

Amphoteric

oxides

oxide

oxide

oxide

reactions

of

bases

hydroxides

Formula

Amphoteric

Al

aluminium

O

2

zinc

and

and

hydroxide

Formula

hydroxide

Al(OH)

3

3

ZnO

zinc

PbO

lead(II)

hydroxide

Zn(OH) 2

lead(II)

oxide

hydroxide

Pb(OH) 2

Examples

1

Aluminium

aluminium

hydroxide

chloride

Al(OH)

(s)



reacts

and

wit h

hydrochloric

3HCl(aq)

AlCl

3

2

Aluminium

to

produce

acid

to

(aq)



3H

3

hydroxide

sodium

NaOH(aq)

reacts

wit h

aluminate

Al(OH)



produce

water:

t he

and

O(l) 2

strong

alkali,

sodium

hydroxide,

water:

(s)

NaAlO

3

(aq)

2H



2

O(l) 2

sodium

aluminate

3

Zinc

oxide

reacts

wit h

hydrochloric

acid

to

produce

zinc

chloride

and

water:

ZnO(s)



2HCl(aq)

ZnCl

(aq)



H

2

4

Zinc

oxide

sodium

reacts

zincate

2NaOH(aq)

wit h

and

t he

strong

sodium

hydroxide,

to

produce

water:

ZnO(s)



alkali,

O(l) 2

Na

ZnO 2

(aq)

H



2

O(l) 2

sodium

zincate

Classification

So

far

in

t his

Anot her

unit

type

t herefore,

be

of

oxides

Acid ic

oxides

a

salt

you

are

and

oxides

have

oxide

classied

Acidic

form

of

as

for

of

across

exists,

acidic,

oxides

water,

come

also

acidic,

known

basic,

cer tain

as

basic

a

and

neutral

amphoteric

non-metals

and

amphoteric

oxide.

oxides.

Oxides

can,

neutral.

which

react

wit h

alkalis

to

Key

!

example, Acidic

2NaOH(aq)



CO

(g)

Na

2

CO 2

(aq)



H

3

O(l)

oxides

SO

(g)

also



H

3

react

wit h

water

O(l)

H

2

to

SO 2

form

an

acid,

for

(SO

)

and

nitrogen

Basic

oxides

for

dioxide

(NO

), sulfur dioxide (SO

), 2

). 2

are

oxides

of

metals

which



2HNO

(aq)

react

Cu(NO

3

wit h

acids

to

form

a

salt

and

!

) 3

(aq)



H

2

O(l)

few

basic

alkalis,

K

for

O(s)

2

oxides

which

react

oxides

also

react

wit h

water

to

form

a

hydroxide,

i.e.

t hey

and

are

with

oxides

acids

to

of

metals

form

a

water.

are



H

O(l)

2KOH(aq)

2

Examples

)

fact

example,

2

O

Key

Basic

salt

2

alkalis

water.

example,

CuO(s)

(Fe

and

certain

oxides

water,

A

salt

of

with

(aq)

3

Basic

a

oxides

react

example,

2

trioxide

form

are

which

4

Examples of acidic oxides include carbon dioxide (CO

sulfur

oxides

non-metals

2

to

Acidic

fact

of

and

basic

oxides

copper(II)

include

oxide

magnesium

oxide

(MgO),

iron(III)

oxide

(CuO).

3

131

Strength

of

acids

and

alkalis

Acids,

Basic

oxides

which

are

alkalis

include

potassium

oxide

(K

bases

O),

and

sodium

salts

oxide

2

(Na

O)

and

calcium

oxide

(CaO).

2

Amphoteric

!

Key

Amphoteric

acids Amphoteric

of

oxides

fact

certain

oxides

metals

are

which

the

and

oxides

strong

are

alkalis

t he

to

oxides

form

a

of

salt

cer tain

and

acids

and

strong

form

a

and

water.

alkalis

which

react

wit h

bot h

example,

with

PbO(s)



2HNO

(aq)

Pb(NO

) 3

(aq)



H

2

O(l) 2

to

2NaOH(aq)

salt

for

oxides

react

3

both

metals

water,



PbO(s)

Na

PbO 2

(aq)



2

H

O(l) 2

sodium

plumbate

The

t hree

amphoteric

oxides

are

aluminium

oxide

(Al

O 3

and

lead(II)

Neutral

!

Key

zinc

oxide

(ZnO)

(PbO).

oxides

fact Neutral

acids Neutral

oxide

), 3

oxides

are

oxides

or

oxides

are

alkalis.

oxides

These

of

cer tain

include

non-metals

carbon

monoxide

which

(CO),

do

not

nitrogen

react

wit h

monoxide

of

(NO)

and

dinitrogen

monoxide

(N

O). 2

certain

react

non-metals

with

acids

which

or

do

not

alkalis.

Summary

1

Dene

2

Give

the

three

aqueous

3

Write

questions

terms

‘base’,

properties,

‘alkali’

other

and

than

‘amphoteric

their

substance’.

reactions,

which

are

typical

of

alkalis.

balanced

chemical

equations

for

a

the

reaction

between

magnesium

b

the

reaction

between

calcium

c

the

reaction

between

sodium

the

following:

hydroxide

oxide

and

hydroxide

and

nitric

ammonium

and

zinc

acid

nitrate

hydroxide.

Objectives

4 By

the

end

of

this

topic

you

Calcium

calcium be

●

able

●

the

strong

give

difference

acid

and

examples

of

a

a

basic

oxide.

Explain,

using

a

chemical

equation,

why

basic.

strong

acid

and

Strength

of

acids

and

alkalis

acids

explain

the

difference

between

Aqueous

a

is

between

weak

A8.3 weak

●

is

oxide

to:

explain

a

oxide

will

strong

alkali

and

a

solutions

of

both

acids

and

alkalis

can

be

classied

as

strong

or

weak

weak

based on the degree of ionisation which occurs when they are dissolved in water.

alkali

You

●

give

examples

of

strong

must

not

confuse

this

with

concentration.

The

concentration

of

an

acid

or

and

alkali is based on the quantity of water present in the solution (see Unit 8.1).

weak

●

alkalis

explain

the

relationship

Strong between

the

pH

acidity,

alkalinity

and

weak

acids

and

scale

When

an

acid

dissolves

in

water,

its

molecules

ionise

to

form

hydrogen

ions,



●

give

the

acids,

values

weak

alkalis

●

pH

and

explain

acids,

weak

how

to

for

strong

or

of

a

Strong

determine

give

the

and

negative

anions.

acids

the

strong

acid

is

fully

ionised

when

it

dissolves

in

water.

This

means

colours

of

t he

in

acidic

acid

molecules

ionise

and

t here

is

a

high

concentration

of

H

ions

certain

t he

indicators

t hat

and

solution.

Hydrochloric

acid

is

an

example

of

a

strong

acid:

alkaline 

HCl(aq)

H

(aq)



Cl

(aq)

solutions.

Ot her

strong

acids

include

nitric

acid

(HNO

) 3

132

all



solution

of

●

ions,

strong

alkalis

A

pH

H

and

sulfuric

acid

(H

SO 2

). 4

in

Acids,

bases

Weak

A

and

salts

Strength

of

acids

and

alkalis

acids

weak

acid

is

only

partially

ionised

when

it

dissolves

in

water.

This

means

that the solution contains a mixture of acid molecules which have not ionised

and ions produced from the molecules which have ionised. The solution has a



low concentration of H

ions. Ethanoic acid is an example of a weak acid:



CH

COOH(aq)

CH

3

COO

(aq)

et hanoate

At

any

i.e.

t he



H

(aq)

3

one

time,

solution

only

about

contains

1%

1%

of

ion

et hanoic

et hanoate

ions

acid

(CH

molecules

COO

)

and

are

ionised,

hydrogen

ions

3



(H

)

and

99%

et hanoic

acid

molecules

(CH

COOH). 3

Most

organic

(HNO

),

acids

sulfurous

are

acid

weak.

(H

2

Strong

When

and

an

Strong

weak

alkali

hydroxide

A

SO 2

ions,

is

)

and

inorganic

carbonic

(H

include

CO 2

nitrous

acid

). 3

OH

to

water,

it

ionises

to

form

positive

cations

and

ions.

alkalis

strong

a

acid

3

alkali

is

fully

ionised

when

contains a high concentration of OH

of

acids

alkalis

added

or

Weak

strong

it

dissolves

in

water.

The

solution

ions. Sodium hydroxide is an example

alkali:



NaOH(aq)

Potassium

Weak

Na

hydroxide

(aq)

(KOH)

is



OH

(aq)

anot her

example

of

a

strong

alkali.

alkalis

A weak alkali is only par tially ionised when it dissolves in water. The solution

contains a low concentration of OH

ions. Ammonia is an example of a weak

alkali:



NH

(g)



H

3

Measuring

The

The

strengt h

pH

scale

solutions

greater

pH

of

The

is

pH

stronger

●

A

a

t he

strong

)

aqueous

pH

7

less

are

as

also

A

weak



OH

t han

7

a

neutral

t he

us

pH,

acids

or

wit h

are

considered

tells

lower

of

acid

scale

(aq)

alkali

t he

and

is

numbers

be

strong

ranging

to

alkaline.

Distilled

t he

stronger

be

An

acid,

using

from

acidic

0

or

is

pH

14.

scale.

Aqueous

t hose

wit h

a

solution

wit h

a

neutral.

alkaline

and

t he

to

and

aqueous

water

acidic

t he

alkalis

measured

considered

to

solution.

how

t he

solution

higher

t he

is.

pH,

n

t he

alkali.

acid

and

has

a

pH

sulfuric

close

acid

to

(H

3

●

(aq)

strength

number

dened

t he

(HNO

an

a

t han

scale

general,

NH 4

the

of

is

wit h

pH

7

O(l) 2

1,

SO 2

acid

has

a

pH

of

e.g.

hydrochloric

acid

(HCl),

nitric

acid

). 4

about

4

or

5,

e.g.

et hanoic

acid

(CH

COOH). 3

●

A

neutral

substance

has

a

pH

of

7 ,

e.g.

distilled

water

(H

O). 2

●

A

weak

alkali

has

a

pH

of

about

9

or

10,

e.g.

aqueous

ammonia

(NH

OH). 4

●

A

strong

and

alkali

potassium

has

a

pH

close

hydroxide

to

14,

e.g.

sodium

hydroxide

(NaOH)

(KOH).

133

Strength

of

acids

universal

pH

and

alkalis

Acids,

indicator

There

are

two

main

met hods

t hat

solution.

One

are

used

in

bases

t he

and

salts

laborator y

to

paper

measure

ot her

0

is

t he

a

pH

pH

of

a

is

universal

indicator

and

t he

meter.

very

acidic hydrochloric

1

Universal

●

acid

indicates

2

lemon

ind icator

t he

pH

of

is

a

a

chemical

solution

by

substance

colour,

i.e.

which

its

colour

juice acidic

orange

changes

depending

on

t he

pH

of

t he

solution.

Universal

juice

indicator

3

can

be

in

paper

form

or

solution

form.

When

vinegar

using

t he

paper,

a

small

piece

of

paper

is

dipped

into

t he

4

solution

and

its

colour

is

compared

wit h

a

pH

colour

char t.

slightly

black

5

coffee

Figure

acidic

8.3.1

different

shows

pH

t he

colour

of

universal

indicator

paper

at

values.

rainwater

6

A

●

pure

pH

meter

is

an

electronic

instr ument.

t

consists

of

a

neutral

water

7

measuring

sea

probe

connected

to

an

electronic

meter,

which

water

8 baking

soda

milk

magnesia

of

displays

t he

met hod

for

pH

reading.

A

pH

meter

is

a

more

accurate

slightly

determining

t he

pH

of

a

solution

t han

universal

alkaline

9 soap

indicator

paper.

10

11

Other 12

washing

soda

acid–alkali

indicators

alkaline

There

are

ot her

acidic

solution

ind icators

which

change

to

one

colour

in

an

13

oven

impor tant sodium

Figure

8.3.1

The

pH

you

is

may

met hyl

you

note

t hat

colour

t hese

in

an

solution,

t hey

only

indicators

alkaline

do

not

solution.

measure

t

t he

is

pH

a

indicate

if

it

is

acidic

or

alkaline.

scale

Litmus

Did

anot her

to

alkaline

hydroxide

of



and

very

cleaner

14

an

example

come

orange,

across

of

in

t his

t he

type

of

indicator.

laborator y

phenolpht halein

and

include

Ot her

indicators

met hyl

bromot hymol

orange,

blue.

These

which

screened

are

used

in

know?

neutralisation experiments to indicate t he neutralisation point (see Unit 8.5).

? The

compounds

which

and

are

the

and

be

in

fruit

in

They

colour

of

skins.

extracted

anthocyanins

acidic

purple-blue

conditions.

for

called

red



T able

parts,

Anthocyanins

cabbage,

and

acid–alkali

naturally

is

made

certain

e.g.

from

the

used

indicator.

occurring

by

of

8.3.1

Indicators

t heir

colours

in

acidic

and

used

in

the

alkaline

solutions

laboratory

Indicator

Colour

can

litmus

red

blue

as

a

of

in

acidic

solution

Colour

red

yellow

red

green

phenolphthalein

colourless

pink

bromothymol

yellow

blue

in

alkaline

solution

crude

Litmus

is

indicator

dyes

orange

red

screened

methyl

orange

a

which

from

blue

lichens.

Investigating

Your

teacher

observation,

●

manipulation

will

be

universal

orange

the

may

●

Y ou

134

and

8.3.1.

these

leaves

extracting

species

indicators

Table

flowers

methyl

plant

in

responsible

many

easily

common

given

conditions

alkaline

are

are

use

this

recording

and

supplied

indicator

and

acidity

and

alkalinity

activity

and

to

of

various

solutions

assess:

reporting

measurement.

with

paper,

samples

pH

phenolphthalein.

of

colour

solutions

chart,

red

to

be

and

tested,

blue

test

litmus

tubes,

paper,

methyl

Acids,

bases

and

salts

Salts

Method

1

Y ou

the

are

going

colour

and

of

to

measure

each

the

indicator

phenolphthalein

when

pH

in

of

each

the

each

of

the

solution.

solution

you

solutions

Only

are

use

and

methyl

testing

is

investigate

orange

colourless.

3

a

Place

b

Dip

a

tube

c

of

piece

and

to

Dip

piece

a

of

If

there

each

two

is

of

meter

3

Record

4

Classify

weak

a

of

each

alkali

Summary

1

What

2

Name

3

Describe

of

4

is

the

Give

the

values

a

the

in

neutral

a

the

the

four

test

solution

colour

with

in

the

tubes.

the

pH

rst

colour

blue

litmus

paper

into

the

solution

in

colours.

orange

use

each

into

of

solution.

other

that

each

two

the

you

and

phenolphthalein,

tubes.

meter

rinse

to

the

Observe

their

determine

measuring

the

colours.

pH

probe

of

of

the

reading.

table.

as

a

strong

acid,

a

weak

acid,

a

strong

alkali,

a

substance.

questions

strong

the

pH

colours

each

between

acids

scale,

alkaline

for

of

in

paper

of

their

methyl

after

results

the

piece

Ensure

water

tested

Compare

of

available,

difference

three

acidic,

the

substance

or

a

each

solutions.

your

pH

and

be

indicator

Observe

meter

to

colour.

the

of

into

distilled

all

its

red

drops

pH

the

in

universal

tube.

respectively,

2

solution

determine

second

Place

the

observe

chart

the

d

2 cm

and

of

of

and

the

strong

three

giving

the

neutral

methyl

a

acid

weak

range

and

a

weak

acid?

acids.

of

the

scale

and

the

pH

values

solutions.

orange

and

phenolphthalein

and

the

pH

following:

a

aqueous

ethanoic

c

aqueous

ammonia

acid

b

sodium

d

aqueous

hydroxide

solution

hydrochloric

acid.

Objectives

A8.4

You

Salts

have

molecule

one

already

when

hydrogen

learnt

t hey

ion

t hat

all

dissolve

per

in

molecule

acids

form

water,

and

e.g.

sulfuric

at

least

one

hydrogen

hydrochloric

acid

(H

SO 2

)

acid

ion

(HCl)

forms

two.

By

the

be

able

end

t hey

are

ions

can

known

hydrogen

ions

as

are

be

replaced

by

ot her

positive

replaceable

hydrogen

replaced

metal

by

or

ions .

ions

a

salt

is

●

dene

●

distinguish

the

when

acids

acids

ions

react

react

from

t he

and

be

of

classied

or

an

acid

a

normal

salt

●

explain

water

●

distinguish

of

crystallisation

t he

between

a

hydrated

ot her

and

decide

an

on

method

all

salt

between

and

and

anhydrous

only

of

the

most

salt

appropriate

preparing

a

salt

salts ●

can

term

formed.

Classification

whet her

will

These

●

Salts

you

4

When

ammonium

topic

forms

salt

reactant,

this

per

salt

hydrogen

of

to:

into

some

two

of

groups,

t he

normal

hydrogen

ions

salts

are

and

acid

replaced:

salts,

based

on

describe

of

●

preparing

describe

everyday

●

the

state

the

different

methods

salts

uses

of

salts

in

life

some

of

the

dangers

of

salts.

135

Salts

Acids,

Normal

Key

!

fact

and

salts

salts

Normal salts are formed when

by

bases

metal

or

ammonium

ions.

all of the hydrogen ions in an acid are replaced

For

example,

when

sodium

hydroxide

(NaOH)



reacts with sulfuric acid (H

SO 2

), if all of the H

ions in the acid are replaced by

4



A

salt

is

a

compound

formed

when

Na

ions, the normal salt, sodium sulfate (Na

SO 2

some

or

all

of

the

hydrogen

ions

2NaOH(aq)



H

SO 2

an

acid

are

ammonium

replaced

ions.

by

metal

), is formed:

4

in

(aq)

Na

4

SO 2

(aq)



2H

4

O(l) 2

or

All

acids

can

Acid

salts

Acid

salts

replaced

form

are

by

normal

formed

metal

or

salts.

when

the

hydrogen

ammonium

ions.

For

ions

in

an

example,

acid

when

are

only

sodium

partially

hydroxide



reacts

with

sulfuric

acid,

if

only

one

of

the

H

ions

in

the

acid

is

replaced

by

a



Na

ion, the acid salt, sodium hydrogensulfate (NaHSO

), is formed: 4

NaOH(aq)



H

SO 2

Only

The

dibasic

type

of

quantity

of

2 mol

was

of

and

salt

produced.

1 mol

The

of

tr ibasic

formed

each

sodium

acids

by

However,

acid,

can

For

acid

and

acid

1 mol

only

salt

phosphoric

of

in

two

different

hydroxide,

it

can

acid

form



H

1 mol

was

acid

salts.

t he

For

salts.

acids

t he

of

depends

two

acid

sodium

on

reactions

reacted,

t he

relative

above,

a

hydroxide

when

normal

reacted

salt

wit h

produced.

(H

PO

),

can

produce

one

normal

salt

4

example,

normal

O(l) 2

sulfuric

3

and

(aq)

tribasic

example,

and

when

an

form

dibasic

reactant.

acid,

NaHSO 4

hydroxide

sulfuric

tribasic

(aq) 4

salt,

in

t he

sodium

reaction

phosphate

wit h

(Na

sodium

PO 3

),

when

4



all

t hree

H

ions

are

replaced.

t

can

also

form

t he

two

acid

salts,

sodium



hydrogenphosphate

(Na

HPO 2

)

when

two

H

ions

are

replaced

and

sodium

4



dihydrogenphosphate

(NaH

PO 2

3NaOH(aq)

2NaOH(aq)

NaOH(aq)

Again,

you

which

salt

Table



8.4.1

T able

can

is

H



H



H

see

PO 3

shows

8.4.1

acid

acid

one

(aq)

PO 3

Na

(aq)

PO

t hat

Na

t he

(aq)

Salts

salts

formed

HCl

HNO

acid

acid

PO 2

relative

(aq) 4

NaH

quantity

by

formed

common

Salt(s)

by

t he

(aq) 4

of

t he

common

replaced:



3H



2H



H

two

O(l) 2

O(l) 2

O(l) 2

reactants

determines

CH

H 2

acids.

acids

formed

Anion

T ype

present

salt

chlorides

Cl

normal

salt

NaCl

nitrates

NO

of

Example

normal

salt

NaNO

COO

normal

salt

CH

2

normal

salt

3

3

COOH

ethanoates

3

sulfuric

(aq)

HPO

4

t he

is

4

2

3

ethanoic

ion

PO 3

4

3

H

4

4

Formula

hydrochloric

when

produced.

Acid

nitric



)

CH

3

3

SO

sulfates

4

SO 4

hydrogensulfates

COONa

Na

SO

2

acid

HSO

salt

4

NaHSO

4

carbonic

acid

H

CO

2

carbonates

3

4

2

normal

CO

salt

3

hydrogencarbonates

Na

CO

2

acid

HCO

salt

3

NaHCO

3

phosphoric

acid

H 3

PO

phosphates

4

3

3

normal

PO

salt

4

hydrogenphosphates

acid

salt

4

dihydrogenphosphates

H 2

136

Na

PO

3

2

HPO

Na

4

HPO

2

PO 4

acid

salt

4

NaH 2

PO 4

Acids,

bases

Water

Some

ions

of

salts

in

a

cr yst al

water

of

cr ystallisation

CuSO

Salts

contain

t heir

following

●

salts

crystallisation

containing

of

and

 xed

number

lattice,

known

cr yst allisation

can

be

given

in

water

as

are

t he

molecules

water

refer red

for mula

of

to

of

between

cr ystallisation .

as

hyd rated

t he

salts .

salt

as

shown

The

formula

t he

Salts

Water

in

t he

examples.

.5H 4

O

represents

hydrated

copper(II)

sulfate.

shows

2

2

t hat

of

for

ever y

2

mole

of

Cu

and

moles

of

water

SO

ions

wit hin

t he

cr ystal

lattice,

4

t here

are

CoCl

●

ve

.6H 2

.7H 4

FeSO

●

and

.7H

of

O

represents

O

represents

cr ystallisation

sometimes

becomes

copper(II)

heated

cobalt(II)

chloride.

hydrated

magnesium

sulfate.

hydrated

iron(II)

sulfate.

2

cr ystallisation

it

hydrated

2

4

Water

represents

2

MgSO

●

O

molecules.

t he

is

removed

powder y

sulfate

t hey

is

essential

colour,

and

by

its

cr ystals

become

of

to

colour

t he

may

bright

and

develop

cr ystals

heating,

are

white

t he

solid

also

blue

t he

cr ystalline

containing

loses

its

change.

and

have

it.

str ucture,

t his

cr ystalline

For

a

f

example,

regular

water

of

str ucture,

hydrated

shape.

When

powder y:

heat

CuSO

.5H 4

O(s)

CuSO

2

(s)

5H



4

O(g) 2

white blue

cr ystals powder

Salts

wit hout

water

Preparation

We

use

later

be

in

salts

t his

in

When

of

all

unit.

produced,

cr ystallisation

are

known

as

anhydrous

salts

salts

aspects

There

some

deciding

of

of

on

of

are

which

a

our

many

we

lives.

Some

different

will

preparation

be

of

t hese

met hods

discussing

met hod,

it

in

is

uses

by

will

which

t his

be

discussed

t hese

salts

can

section.

impor tant

to

know

t he

solubilit y of t he salt t hat is to be produced and t he solubilit y of t he compounds

whic h may be used to prepare t he salt. Met hods of prepar ing insoluble salts

differ

You

from

can

t hose

nd

a

table

Preparation

Insoluble

t he

of

salts

cations

t he

of

salt.

used

insoluble

can

This

is

prepare

summarising

of

t he

to

be

salt

prepared

being

known

as

soluble

t he

salts.

solubility

r ules

in

Unit

6.1.

salts

by

reacting

prepared

ionic

and

two

t he

solutions,

ot her

precipitation .

n

one

containing

an

ionic

containing

t he

anions

precipitation

reaction, t he two soluble salts in solution react to form an insoluble salt, i.e. a

precipitate,

wit h

and

sodium

nitrate

soluble

salt.

solution

For

to

example,

form

barium

insoluble

nitrate

barium

solution

sulfate

and

reacts

sodium

solution:

)

Ba(NO 3

onic

a

sulfate

(aq)



Na

2

SO 2

(aq)

BaSO

4

(s) 4



2NaNO

(aq) 3

equation:

2

Ba

2

(aq)



SO

(aq) 4

BaSO

(s) 4

137

Salts

Acids,

bases

and

salts

Method

The

1)

following

Choose

salt

two

and

Dissolve

3)

Mix

4)

Filter

5)

Wash

When

t he

t he

adding

wit h

t he

form

collect

for

preparing

containing

water

to

and

t he

to

anions

make

t he

t he

distilled

two

salts

nitrates

c hoose

above

t he

cations

salts.

required

to

make

t he

required.

solutions.

insoluble

salt

precipitate

water

insoluble

as

while

as

a

t he

it

is

precipitate.

residue

still

in

t he

lter

funnel

to

are

would

use

in

your

soluble,

be

a

preparation,

as

nitrate

and

a

preparation

are

to

all

supply

sodium

it

sodium

t he

salt

is

impor tant

salts.

cations,

to

supply

to

Therefore,

i.e.

t he

bar ium

anions,

sulfate.

prepare

Your

one

used

dr y.

all

to

t he

sodium

T o

to

t hat

salts

in

in

solutions

c hoosing

best

salts

residue

it

salts,

is

containing

mixture

leave

nitrate

e.g.

two

two

remember

t he

ot her

t he

t he

met hod

soluble

t he

2)

and

general

an

teacher

may

●

observation,

●

manipulation

Y ou

will

two

beakers,

be

insoluble

use

recording

and

supplied

a

this

lter

salt

by

activity

and

ionic

to

precipitation

assess:

reporting

measurement.

with

solutions

funnel

and

of

lter

barium

nitrate

and

sodium

sulfate,

paper.

barium

Method nitrate

solution

sodium

to

3

sulfate

1

Place

10 cm

of

sodium

sulfate

solution

into

a

small

beaker.

solution 3

2

Add

3

Using

4

Wash

10 cm

allow



Figure

8.4.1

insoluble

Preparation

salt,

barium

of

the

the

it

Record

6

Write

your

both

reaction

sulfate

are

●

direct

●

t he

●

t he

a

Salts

by

sulfate

138

precipitate

with

lter

distilled

and

paper,

water

swirl

lter

while

the

it

is

to

mix.

mixture.

still

in

the

lter

funnel

and

a

observations

balanced

as

you

chemical

prepare

equation

the

and

sample

an

ionic

of

the

salt.

equation

for

the

and

three

of

barium

of

the

insoluble

soluble

main

met hods

salt

that

you

have

prepared.

salts

for

preparing

soluble

salts:

combination

reaction

between

base

reaction

and

a

an

between

reactive

metal,

an

insoluble

carbonate

or

an

acid

a

soluble

base,

i.e.

an

alkali,

and

an

acid,

known

as

combination

composed

reacting

The

name

titration.

Direct

A

and

solution

dry.

all

insoluble

8.4.2

nitrate

the

There

Figure

funnel

residue

Preparation



barium

lter

to

5

of

metal

anions.

two

of

two

simple

elements,

supplies

t he

a

ions,

metal

cations

such

and

of

a

t he

as

metal

chlorides,

non-metal,

salt

and

t he

directly

can

be

wit h

non-metal

prepared

each

ot her.

supplies

t he

Acids,

For

bases

and

example,

passing

glass

a

salts

aluminium

stream

tube

as

Salts

of

dr y

shown

in

chloride

chlorine

Figure

can

gas

be

prepared

over

heated

a

fume

cupboard

foil

in

a

by

long

8.4.3.

aluminium

dry

in

aluminium

foil

chlorine

unreacted

in

chlorine

out

heat



Figure

The

8.4.3

Preparation

equation

2Al(s)

for



t he

3Cl

of

aluminium

reaction

(g)

is:

2AlCl

2

Since

is

an

t he

anhydrous

Reactions

Many

soluble

carbonate

●

occurs

salt.

chloride

with

or

in

This

and

is

absence

par ticularly

anhydrous

salts

can

be

of

any

moisture,

suitable

iron(III)

prepared

base

wit h

reactive metal

Mg(s)

t he

e.g.

an



an

●

cannot

potassium

is

Reacting

too

an

preparing

formed

anhydrous

by

reacting

acid

as

a

or

reactive

shown

in

t he

metal,

insoluble

examples

below.

and an acid, e.g. to prepare magnesium chloride:

2HCl(aq)

met hod

acid

salt

chloride.

MgCl

(aq)



H

2

This

for

t he

acids

insoluble

Reacting a

(s) 3

reaction

aluminium

chloride

be

sodium

(g) 2

used

to

prepare

salts,

because

salts

t he

of

ver y

reaction

of

reactive

t hese

metals,

metals

wit h

violent.

insoluble

carbonate

and

an

acid,

e.g.

to

prepare

calcium

nitrate:

CaCO

(s)



2HNO

3

●

Reacting

an

(aq)

Ca(NO

3

insoluble

CuO(S)



H

SO 2

) 3

base

and

an

(aq)

acid,

e.g.

CuSO

4

(aq)

CO

(g)



H

2

to

(aq)



2

prepare



H

4

O(l) 2

copper(II)

sulfate:

O(l) 2

n t hese reactions, t he nal product will only be a pure solution of t he required

salt

if

t he

achieve

to

t he

t he

reaction

t his

acid

is

by

until

reactant

to

has

reached

using

some

react

a

completion

reactant

remains.

wit h

and,

which

This

is

and

indicates

since

it

is

no

acid

insoluble.

t here

is

insoluble,

remains.

This

no

t he

One

reactant

more

acid

excess

way

is

will

to

added

lef t

for

remain

✔ undissolved

in

t he

solution

of

t he

Exam

tip

salt.

Being

able

to

describe

the

Method methods

is

very

used

to

important

prepare

for

salts

exams.

If

The following general met hod is used to prepare soluble salts using reactions

you

wit h

asked

Choose

the

appropriate

reactive

metal,

insoluble

carbonate

or

base to provide the

prepare

cations

and the appropriate acid to provide the

t he

excess

used.

3)

acid

solid

This

speed

into

a

remains

indicates

up

t he

beaker

and

t hat

reaction

and

add

t he

effer vescence

all

t he

when

acid

has

using

a

metal,

stops

if

reacted.

metal

or

a

carbonate

a

metal

Heating

or

or

base

until

carbonate

may

a

soluble

be

with

an

is

required

idea

to

the

salt

acid

using

and

insoluble

cations

reactants,

choose

the

you

a

can

a

carbonate

it

doesn’t

the

and

it

is

a

good

appropriate

carbonate

since

to

supply

reaction

an

acid

the

between

is

rapid,

base.

need

heating

and

visible

Dip a piece of blue litmus paper into t he solution to ensure all t he acid has effervescence

reacted.

The

Remove

t he

litmus

should

remain

excess,

unreacted

stops

when

the

blue. reaction

4)

how

anions choose

Place

to

describe

insoluble reaction

2)

to

acids. to

1)

are

solid

by

has

reached

completion.

ltration.

139

Salts

Acids,

5)

Collect the

a

hydrated

ltrate

salt

is

bases

and

salts

and evaporate the water over a beaker of boiling water. f

required,

evaporate

some

of

the

water

to

concentrate

the

solution and leave the concentrated solution to cr ystallise.

T o

prepare

Your

a

teacher

may

●

observation,

●

manipulation

Y ou

will

beaker,

be

an

soluble

use

salt

this

recording

and

supplied

by

reacting

activity

and

to

a

base

with

an

acid

assess:

reporting

measurement.

with

evaporating

samples

dish,

a

of

lter

copper( II)

funnel

oxide

and

lter

and

sulfuric

acid,

a

paper.

Method

Add

the

the

copper(II)

sulfuric

heating

more

acid

gently,

will

oxide

to

3

1

Place

2

Add

20 cm

of

sulfuric

acid

into

the

beaker.

while

until

no

copper( II)

oxide

to

the

acid

a

spatula

at

a

time,

heating

and

stirring

dissolve

gently,

oxide

3

until

in

Using

the

excess

4

Pour

5

Place

more

lter

funnel

ltrate

of

a

6

Record

piece

7

Write

8

T o

a

of

lter

i.e.

until

you

can

see

excess

copper( II)

paper,

collect

evaporating

heat

paper

and

over

the

the

it

the

mixture

Place

the

solution

remove

crystallise

evaporating

becomes

evaporating

to

to

the

ltrate.

dish.

until

leave

lter

the

dish

and

dish

a

concentrated.

containing

form

over

the

hydrated

crystals.

observations

balanced

chemical

anhydrous

evaporating

lter

and

and

solution

your

produce

the

water

sulfate

all

react,

and

oxide

into

boiling

concentrated

copper(II)

will

beaker.

copper( II)

the

beaker

no

the

dish

over

as

you

equation

copper( II)

a

prepare

beaker

for

the

sulfate,

of

the

reaction.

you

boiling

salt.

can

water

heat

until

the

all

ltrate

the

water

in

the

has

evaporated.

Filter

off

the

excess

copper(II)oxide

Titration

Potassium,

sodium

and

ammonium

salts

cannot

be

prepared

by

the

method

which you have just learnt for two reasons. Firstly, potassium and sodium react

in

a

violent

way

with

acids

making

the

reactions

too

dangerous.

Secondly,

potassium, sodium and ammonium carbonates and hydroxides are all soluble,

T o

produce

copper(II)

so

hydrated

sulfate

allow

when

the

excess solid crystals

days.

to

T o

form

over

a

of

boiling

over

a

Figure

8.4.4

preparation

sulfate

of

has

alkali

reached

until

t he

solution

involved

hydrated

in

is

completion.

added

to

and

no

more

acid

remains,

the

For

is

just

potassium

example,

neutral,

hydroxide

to

indicating

prepare

t hat

solution

potassium

t he

reaction

until

t he

sulfate,

resulting

sulfuric

solution

is

the

copper( II)

just

neutral:

crystals

2KOH(aq)



H

SO 2

The

colour

point.

to

The

change

a

of

xed

solution

(aq)

K

4

technique

neutralise

carbonate

140

completion

beaker

water

Steps

reached

sulfate

acid 

has

and the solution of the salt will then not be pure.

Potassium, sodium and ammonium salts are prepared by adding an acid to an

copper(II)

aqueous evaporate

dissolves

few

produce

anhydrous

reaction

the

an

indicator

used

to

volume

may

SO 2

also

used

determine

of

be

is

aqueous

used

(aq)

in



2H

4

O(l) 2

to

determine

t he

exact

alkali

place

of

is

t he

volume

known

t he

neutralisation

of

as

aqueous

a

acid

needed

titration.

alkali.

A

Acids,

bases

and

salts

Salts

Method

The

1)

general

Choose

and

2)

an

met hod

an

for

performing

appropriate

appropriate

alkali

acid

to

or

a

titration

soluble

supply

t he

is

as

follows.

carbonate

to

provide

t he

cations

anions

Measure a xed volume of t he aqueous alkali or carbonate using a pipette.

Run

e.g.

it

into

a

conical

ask

and

add

a

few

drops

of

indicator

solution,

phenolpht halein.

3)

Place

4)

Add

t he

t he

point

is

5)

Take

a

6)

Repeat

acid

acid

in

to

a

burette

t he

and

aqueous

take

an

alkali

or

initial

burette

carbonate

reading.

until

t he

neutralisation

reached.

nal

burette

reading

and

determine

t he

volume

of

acid

added.

3

of

t he

each

titration

ot her.

until

Average

you

t hese

have

t hree

volumes

volumes

to

of

acid

determine

t he

wit hin

volume

0.1 cm

of

acid

needed.

7)

Add t his volume of acid to t he xed volume of aqueous alkali or carbonate

wit hout

8)

t he

Evaporate

T o

t he

prepare

Your

indicator.

water

a

teacher

soluble

may

●

observation,

●

manipulation

from

use

salt

this

recording

and

t he

solution.

by

titration

activity

and

to

assess:

reporting

measurement.

3

Y ou

will

be

supplied

with

3

0.1 mol dm

sodium

hydroxide

solution,

0.1 mol dm

hydrochloric

acid,

phenolphthalein

3

solution,

a

25 cm

pipette,

a

conical

ask

and

a

burette.

Method

1

Rinse

2

Rinse

the

burette

with

some

hydrochloric

acid

and

ll

it

with

the

acid.

3

the

pipette

3

Add

4

T ake

5

Slowly

a

pipette

and

few

an

run

it

with

into

drops

initial

add

colourless.

of

the

the

sodium

conical

reading,

hydrochloric

The

hydroxide

solution

remembering

acid

neutralisation

solution.

Measure

25 cm

of

sodium

hydroxide

solution

in

the

ask.

phenolphthalein

burette

the

to

of

some

to

the

point

to

to

the

conical

take

conical

is

the

the

ask,

point

ask

reading

swirling

where

the

and

from

swirl

the

contents.

bottom

constantly,

colour

the

until

changes

of

the

the

meniscus.

solution

after

the

just

addition

turns

of

from

just

one

pink

drop

acid.

6

T ake

7

Discard

8

Repeat

a

nal

burette

the

reading

contents

of

the

and

determine

conical

ask

the

and

volume

rinse

the

of

hydrochloric

ask

acid

thoroughly

added.

with

This

distilled

is

your

rough

titration.

water.

3

your

titration

until

you

have

three

volumes

of

acid

which

are

within

0.1 cm

.

Each

time

you

can

add

the

3

acid

tap

rapidly

and

until

add

the

you

have

added

acid

drop

by

about

drop

until

less

1 cm

the

than

you

neutralisation

added

point

is

in

your

rough

titration,

then

almost

close

the

reached.

3

9

Average

the

three

volumes

of

acid,

which

are

within

0.1 cm

.

This

is

the

accurate

volume

of

acid

needed

to

3

neutralise

10

Repeat

25 cm

your

determined

11

Place

the

of

the

titration,

in

step

solution

9,

sodium

but

this

add

into

an

hydroxide

time

the

acid

do

not

drop

evaporating

solution.

add

by

dish

the

drop

and

Y ou

can

now

prepare

phenolphthalein

until

you

carefully

have

solution.

added

evaporate

the

all

the

the

salt.

When

correct

water

you

approach

the

volume

volume.

to

obtain

sodium

chloride.

141

Salts

Acids,

12

Record

your

results

in

a

table

like

the

one

opposite.

Titration

Burette

Write

a

chemical

equation

for

the

and

salts

number

reading

Rough

13

bases

1

2

3

reaction. 3

Final

reading/cm

3

Initial

reading/cm

3

Volume

of

acid

added/cm

safety burette filler these

allow

fill

valves

you

and

the

to

empty

when

pipette

pipette

is these

filled

to

this

graduations

mark measure

it

contains

how

exactly much

solution

3

25

cm

of

solution has

been

added

tap

conical

flask

(a)



Figure

8.4.5

hydroxide

(a)

Using

solution

hydrochloric

and

a

pipette

(b)

using

to

a

measure

burette

a

to

xed

add

a

volume

varying

of

sodium

volume



Figure

of

pink

acid

Preparation

You

learnt

wit h

of

earlier

sulfuric

acid

in

acid

t his

(H

SO 2

The

formation

of

2NaOH(aq)

a

H

SO 2

The

formation

of

NaOH(aq)



an

H

●

to

at

t he

produce

hydroxide

●

to

produce

hydroxide

f

t he

acid

a

SO

1 mol

an

acid

t he

same,

when

changes

hydroxide

0 .1

mol

dm

(a)

acid

is

solution

sodium

hydroxide

(NaOH)

reacts

salt:

Na

SO

NaHSO

salt,

t he

t he

O(l) 2

(aq)



H

t he

t hese

of

O(l) 2

two

reactions:

reactants

is

2 mol

of

sodium

acid

ratio

sulfuric

can

for

ratio

sulfuric

of

we

2H

4

equations

of



salt:

(aq)

of

(aq) 4

of

reactants

is

1 mol

of

sodium

acid.

sodium

a p p ly

t he

hy d r ox i d e

ratio

to

solution

vo l u m e s .

and

Fo r

t he

sulfur ic

e xa mp l e ,

3

use

from

hydrochloric

possibilities:

2

salt,

1 mol

concentrations

are

two

4

normal

to

sodium

when

are

(aq)

acid

balanced

to

t hat

t here

4

2

Looking

to

Phenolphthalein

colourless

4

normal



(b)

salts

unit

)

8.4.6

to

added

(b)

if

we

3

sodium

hy d r ox i d e

solution

and

0 .1

mol

dm

sulfur ic

acid:

3

●

to

produce

a

normal

salt,

we

would

react

50 cm

of

sodium

hydroxide

3

solution

wit h

25 cm

of

sulfuric

acid

3

●

to

produce

an

acid

salt,

we

would

react

50 cm

of

sodium

hydroxide

3

solution

wit h

50 cm

of

sulfuric

acid.

Comparing t he two, to prepare t he acid salt we would need

of

142

acid

t hat

we

used

to

prepare

t he

normal

salt.

double t he volume

Acids,

bases

and

salts

Salts

Method

The

as

●

general

Determine

volume

●

Repeat

of

●

met hod

for

preparing

t he

acid

salt,

sodium

hydrogensulfate,

is

follows.

of

t he

sulfuric

Evaporate

t he

volume

sodium

titration

acid

t he

Summary

sulfuric

wit hout

acid

needed

solution

t he

using

indicator

to

a

neutralise

a

xed

titration.

and

adding

twice

t he

volume

determined.

water

of

of

hydroxide

from

salt

t he

solution.

preparation

You have just learnt t hat t here are several met hods t hat can be used to prepare

salts

and

it

is

impor tant

t hat

you

choose

t he

correct

met hod.

The

ow

char t

in Figure 8.4.7 outlines a series of questions to ask which will help you decide

which

met hod

to

choose.

Use

reactive

or

an

a

metal

insoluble



acid

carbonate

Is NO  the

acid

or

an

base an

insoluble

salt

Is



acid

anhydrous

NO the

salt

a chloride? YES

potassium,

sodium

Is YES

Use or

the

direct

ammonium

salt YES combination salt

soluble

?

in

Use

water?

NO

a

titration

Use

ionic

precipitation



Figure

Uses

8.4.7

of

Flow

chart

salts

in

for

the

preparation

everyday

of

salts

life

Salts play an extremely impor tant par t in our ever yday lives, from t he sodium

chloride

as



t hat

washing

T able

we

soda.

8.4.2

use

to

Table

Uses

of

avour

8.4.2

our

gives

food

to

t he

sodium

some

of

t he

uses

carbonate

t hat

we

use

salts.

salts

Salt

Use

Explanation

Sodium

An

Baking

hydrogencarbonate

in

(NaHCO

powder

)

of

ingredient

baking

powder

is

used

to

hydrogencarbonate

and

in

the

the

cake

mixture,

make

an

cakes

acid.

two

rise.

When

It

contains

mixed

compounds

with

react

the

forming

sodium

liquid

carbon

3

dioxide:



Figure

8.4.8

Washing

soda

is

a

salt



HCO

(aq)



H

(aq)

CO

3

The

carbon

heating

Sodium

carbonate

(washing

T o

soda)

soften

hard

water

Hard

dioxide

causing

water

calcium

forms

the

does

and

cake

not

)

added,

the



H

in

the

O(l)

2

cake

which

which

expand

some

of

us

have

in

our

homes

on

rise.

with

salts.

soap.

When

It

is

caused

sodium

by

dissolved

carbonate

is

2

and

Ca

bubbles

to

lather

magnesium

2

(NaCO

(g)

2

Mg

ions

precipitate

out

as

insoluble

3

calcium

and

magnesium

2

Ca

carbonate:

2

(aq)



CO

(aq)

CaCO

3

The

Calcium

carbonate

(limestone)

(CaCO

)

water

Manufacture

T o

of

quantities

cement

make

becomes

cement,

of

and

calcium

other

(s)

3

soft

will

lather

carbonate

materials

such

as

is

with

soap.

heated

silicon

with

dioxide

small

(sand)

in

3

for

use

in

the

construction

a

kiln

to

forming

about

1400 °C.

calcium

oxide

The

calcium

carbonate

decomposes

(quicklime):

industry CaCO

(s)

CaO(s)



CO

3

The

calcium

inside

small

the

kiln

amount

(g)

2

oxide

to

of

is

then

form

blended

clinker.

calcium

The

sulfate

with

the

clinker

is

(gypsum)

other

then

to

materials

ground

make

with

a

cement.

143

Salts

Acids,



T able

8.4.2

?

you

Magnesium

know?

(Epsom

(MgSO

Epsom

salt

derives

its

sulfate

salt)

.7H

4

O)

Use

Explanation

Various

Added

medicinal

relax

the

uses

strain,

town

of

to

the

where

salt

in

The

in

healing

a

bitter

power

saline

of

spring

heal

the

spring.

waters

chloride

and

were

realised

news

of

in

these

(NaCl)

Sodium

preservation

and

fish,

that

the

from

rapidly .

Epsom

salt

is

pain

used

and

inflammation,

to

ease

aching

help

cure

stress

limbs,

skin

and

ease

muscle

problems

T aken

orally,

Epsom

salt

is

used

as

a

and

saline

to

help

also

chloride

by

is

eliminate

used

to

toxins

from

withdrawing

water

is

preserve

the

water

unavailable

withdraws

water

from

for

from

the

the

food

body.

their

items,

cells

reactions

such

by

as

meat

osmosis

that

microorganisms

cause

which

so

decay.

cause

about preventing

them

from

growing.

powers Sodium

spread

cuts.

and

Food

decay,

1618

reduce

back

first

It

the

Epsom

soothe

Surrey ,

was

Sodium

discovered

water,

name

Epsom

the

bath

body,

help

laxative

England

salts

2

help

from

and

(continued)

Salt

Did

bases

nitrate

Food

Sodium

preservation

chloride

nitrate

and

sodium

nitrite

are

often

used

with

sodium

quickly )

(NaNO

and

to

preserve

meat.

They

destroy

certain

bacteria

that

3

developed

into

a

spa

town

and sodium

people

travelled

from

far

and

wide

to

nitrite

(NaNO

cause

)

severe

rancidity.

food

Sodium

poisoning

nitrite

and

gives

an

retard

the

attractive

development

red

colour

to

of

the

2

visit

Epsom

and

‘take

the

meat,

waters’.

Sodium

H

(C 6

benzoate

COONa)

e.g.

Food

Sodium

preservation

e.g.

ham

and

benzoate

fizzy

drinks

bacon,

is

used

and

fruit

and

to

adds

preserve

juices.

At

a

flavour.

foods

pH

of

benzoate

is

converted

to

benzoic

acid

(C

H

6

Calcium

sulfate

(gypsum)

Did

?

you

.2H

4

inhibits

the

Manufacture

Plaster

of

of

which

of

plaster

O)

Paris,

and

back

it

gypsum

more

was

centuries

used

in

of

which

used

By

than

9000

through

many

the

parts

1700s,

of

the

became

known

years

bones

as

the

of

when

plaster

a

broken

paste

and

is

building

centre

as

Paris

for

the

were

time,

made

plaster

the

of

walls

the

of

its

to

of

Paris

fate

as

houses

was

make

Fire

of

did

not

and

1666.

heated

plaster)

to

is

about

made

300 °C

of

to

calcium

remove

sulfate

the

in

and,

used

them

suffer

had

in

Bandages

are

then

impregnated

with

water

the

Paris

powder.

When

water

is

added

to

the

dry

bandage,

forms

then

heat

wrapped

Plaster

an

of

to

is

around

orthopaedic

Paris

the

given

is

dry

also

the

off.

The

damaged

bandage,

limb,

with

where

it

its

hardens

cast.

used

plaster

to

as

a

building

make

a

material.

paste

which

is

Water

used

is

to

and

coat

ceilings.

of

salts

by

to

law,

While salts play such an impor tant role in our ever yday lives, some have also

cover

been

implicated

the

in

causing

various

healt h

problems.

Table

8.4.3

summarises

so

of

t hese

dangers.

same

T able

8.4.3

Dangers

of

salts

Great

Salt

Dangers

Sodium

chloride

Sodium

nitrate

(NaCl)

(NaNO

)

Excessive

and

May

consumption

increase

a

person’ s

can

lead

risk

of

to

hypertension

developing

(high

blood

pressure).

cancer.

3

sodium

nitrite

(NaNO

)

Have

been

implicated

in

causing

brain

damage

in

children.

2

Sodium

H

(C 6

benzoate

Has

COONa)

May

1

Explain

2

What

3

Name

salts.

is

the

difference

of

most

each

the

increase

a

in

increasing

person’ s

risk

of

hyperactivity

developing

and

asthma

in

children.

cancer.

magnesium

anhydrous

Describe,

Describe

appropriate

salt

c

and

full

starting

we

calcium

c

magnesium

a

normal

method

the

write

a

two

salt

and

for

an

preparing

compounds

balanced

chloride

details,

with

use

the

sulfate

sulfate.

how

you

magnesium

following

you

chemical

chloride

giving

how

name

iron( III)

a

between

acid

salt.

crystallisation?

case

a

carbonate

5

implicated

questions

water

the

In

prepare

4

been

5

Summary

144

a

paste,

Paris

fireproof

the

and

it



London

which

Paris.

some

that

COOH)

5

microorganisms.

had

use

plaster

wood

Paris

of

forming

material

the

Dangers At

of

(gypsum

been

crystallisation.

walls

become

growth

Paris

has

added

world.

pH,

sodium

plaster setting

date

low

4.5,

2

is

origins

a

know? (CaSO

The

with

below

5

each

equation

b

lead( II)

d

potassium

would

of

would

the

following

choose

for

the

to

reaction:

sulfate

prepare

nitrate.

magnesium

nitrate.

salts

in

b

our

everyday

sodium

lives:

hydrogencarbonate

Acids,

bases

A8.5

and

salts

Neutralisation

Neutralisation

n Unit 6.2 you learnt t hat a

a

base

and

an

acid.

n

a

reactions

Objectives

neutralisation reaction is any reaction between

neutralisation

reactions

reaction

a

salt

and

water

are

By

the

be

able

end

of

this

topic

you

will

to:

always

●

explain

●

describe

a

neutralisation

reaction

formed. how

When a strong alkali reacts wit h a strong acid, t he reaction is complete when

neutralisation

neit her

an

alkali

nor

acid

is

present

in

excess.

At

t his

point

pH of 7 , i.e. t hey are neutral. This point is known as t he

or

end

t he

products

have

a

neutralisation point

point.

indicator,

temperature

●

describe

to

a

neutralisation

reaction

between

an

aqueous

alkali

and

an

acid,

t he

reaction

hydrogen

ions

remain

occurring

ions

in

of

t he

solution

is

between

acid.

as

These

spectator

t he

ions

ions.

hydroxide

react

For

to

ions

form

example,

of

t he

water

t he

alkali

and

t he

reaction

meter

using

and

change

how

we

use

reactions

in

our

t he daily

actual

out

reactions

pH

neutralisation

n

carry

lives.

and

ot her

between

sodium hydroxide solution and hydrochloric acid can be summarised by t he

following

chemical

NaOH(aq)



equation:

Key

!

HCl(aq)

NaCl(aq)



H

O(l)

A

2

fact

neutralisation

reaction

reaction

between

a

base

is

a

and

an



The OH

ions from the sodium hydroxide and the H

ions from the hydrochloric acid

to

form

a

salt

and

water.

acid react to form water, as shown in the following ionic equation:



OH

(aq)



H

(aq)

H

O(l) 2

Key



The

Na

and

Cl

ions

remain

in

solution

as

spectator

!

ions.

The reaction between t he hydroxide and hydrogen ions is described as being

The

an

point

exothermic

can

a

make

use

reaction

of

t his

fact

(see

Unit

when

12.1)

because

determining

t he

it

produces

heat

neutralisation

energy.

point

of

We

such

neutralisation

in

where

an

the

neither

reaction.

fact

point

acid–alkali

reaction

acid

nor

is

alkali

is

the

reaction

complete

is

and

present

in

excess.

Determining

acid–alkali

The

the

acid

point

in

an

reaction

neutralisation

aqueous

neutralisation

is

point

of

deter mined

a

by

reaction

between

perfor ming

a

an

aqueous

titration.

alkali

Dur ing

t he

and

an

titration,

t he volume of one solution required to neutralise a xed volume of anot her

solution

of

three

c hange.

using

is

deter mined,

ways:

We

using

will

now

temperature

Using

an

n

Unit

in

an

an

and

t he

neutralisation

indicator,

look

at

using

two

of

a

pH

t hese

point

meter

ways,

is

or

identied

using

using

an

in

one

temperature

indicator

and

c hange.

indicator

8.3

you

acidic

learnt

solution

t hat

and

an

ind icator

anot her

is

colour

a

in

substance

an

which

alkaline

has

one

colour

Did

?

performing

solution,

indicator

usually

are

a

t he

added.

titration

alkali,

The

is

using

placed

ot her

an

in

a

solution,

indicator,

a

conical

ask

usually

t he

know?

solution. The

When

you

xed

and

acid,

a

is

volume

few

of

drops

added

one

of

t he

from

t he

neutralisation

determined

instead

is

of

added

using

an

in

point

a

pH

indicator.

small

can

be

meter

One

quantities,

solution

e.g.

3

2 cm

,

to

a

fixed

volume

of

the

burette and t he indicator will change colour at t he neutralisation point. This

other

point

is

determined

when

t he

colour

changes

on

t he

addition

of

a

solution

solution

drop

of

solution

from

t he

and

the

pH

of

the

single changes

sharply

to

7

at

the

burette. neutralisation

point.

Phenolpht halein and met hyl orange are t he most commonly used indicators

to

determine

t he

neutralisation

point

in

a

titration.

145

Neutralisation

reactions

Acids,

Using

temperature

When

using

a

 xed

a

of

and

salts

change

temperature

volume

bases

one

change

solution

is

to

deter mine

placed

in

an

t he

neutralisation

insulated

point,

container,

e.g.

a

polystyrene cup, and its temperature is recorded. The ot her solution is added

3

in

small

t he

is

quantities,

solution

is

recorded.

in

e.g.

2 cm

quic kly

The

temperature

,

procedure

have

from

stir red

been

t he

af ter

is

burette.

eac h

continued

recorded.

Using

addition

until

This

is

t he

and

several

known

t her mometer,

t he

temperature

successive

as

a

drops

thermometr ic

titration

A

graph

added

To

draw

t

are

and

of

is

t hen

from

t he

An

one

t hrough

intersection

example

of

of

showing

temperature

against

t he

volume

of

solution

burette.

graph,

drawn,

one

drawn

t he

t he

t he

t he

a

points

t hrough

points

two

graph

are

t he

plotted

points

where

lines

is

which

t he

the

and

t hen

where

t he

temperature

neutralisation

might

two

be

straight

temperature

is

lines

is

of

best

increasing

decreasing.

The

point

point.

obtained

when

hydrochloric

acid

3

is

added

to

25 cm

of

sodium

hydroxide

solution

is

shown

in

Figure

8.5.1.

3

The

graph

shows

t hat

1 1.0 cm

of

hydrochloric

acid

is

needed

to

neutralise

3

25 cm

of

sodium

hydroxide

solution.

neutralisation the

temperature point

increases

acid

is

as

more

added

the

temperature

decreases

)C°(

acid

is

as

more

added

erutarepme T 0

2

4

6

8

10

12

14

16

18

3

Volume



Figure

8.5.1

Graph

of

hydrochloric

showing

acid

temperature

added

against

(cm

)

volume

of

hydrochloric

acid

3

added

to

25 cm

of

sodium

hydroxide

solution



The reaction between t he OH

in

t he

hydrochloric

acid

ions in t he sodium hydroxide and t he H

produces

ions

heat:



OH

(aq)



H

(aq)

H

O(l) 2



The

temperature

being

added

to

when

all

OH

This

is

reasons;

146

t he

t he

no

increases

react

wit h

ions

more

heat

acid

at

solution

heat

is

and

a

is

more

t he

have

neutralisation

completion,

as

OH

reacted

point.

being

lower

being

acid

is

ions.

and

The

t here

produced

to

t he

The

because

are

because

is

more

temperature

none

temperature

temperature

lost

added

t hen

t he

being

environment.

H

stops

lef t

in

t he

decreases

reaction

added

ions

solution.

for

has

which

are

increasing

t hree

reached

cools

t he

Acids,

T o

bases

and

salts

determine

Your

teacher

the

may

observation,

●

Neutralisation

neutralisation

use

this

recording

activity

and

to

point

by

using

temperature

change

assess:

reporting

manipulation

●

and

measurement

3

Y ou

will

be

supplied

polystyrene

cup,

a

with

and

a

analysis

●

and

interpretation.

3

1.0 mol dm

burette

reactions

sodium

hydroxide

solution,

3

1.0 mol dm

sulfuric

acid,

a

25 cm

pipette,

a

thermometer.

Method

1

Rinse

the

burette

with

some

sulfuric

acid

2

Rinse

the

pipette

with

some

sodium

hydroxide

and

ll

it

with

the

acid.

3

pipette

and

3

Using

4

Keeping

the

run

it

into

the

thermometer,

polystyrene

measure

and

solution.

Measure

25 cm

of

sodium

hydroxide

solution

in

the

cup.

record

the

temperature

of

the

sodium

hydroxide

solution.

3

solution

the

thermometer

with

the

in

the

thermometer

sodium

and

hydroxide

record

its

solution,

maximum

add

2 cm

of

acid

from

the

burette.

Quickly

stir

the

temperature.

3

5

Immediately

6

Repeat

step

quickly

as

7

Record

8

Use

5

another

until

you

2 cm

have

of

hydrochloric

recorded

four

acid,

quickly

successive

stir

drops

the

in

solution

and

temperature.

record

It

is

its

maximum

essential

that

temperature.

you

do

this

as

possible.

your

your

added.

add

results

results

Draw

to

two

in

a

table.

draw

a

straight

graph

lines

showing

of

best

the

temperature

of

the

solution

against

the

volume

of

sulfuric

acid

t.

3

9

10

11

Use

determine

the

volume

of

sulfuric

acid

why

the

temperature

of

the

solution

increased

b

why

the

temperature

of

the

solution

stopped

c

why

the

temperature

of

the

solution

decreased.

Suggest

ant

T able

Where

reasons

why

this

neutralisation

already

and

8.5.1

used

Antacids

studied

bee

neutralisation



to

a

have

treat

graph

needed

to

neutralise

25 cm

of

sodium

hydroxide

solution.

Explain:

Using

We

your

stings.

method

of

(use

an

ionic

equation

to

help

you)

increasing

determining

the

neutralisation

point

is

less

accurate

than

using

an

indicator.

reactions

how

neutralisation

Table

8.5.1

reactions

summarises

t hree

can

be

ot her

used

ways

to

we

use

reactions.

Using

neutralisation

reactions

Action

Antacids

are

taken

to

treat

indigestion

and

acid

reflux.

They

may

contain

sodium

hydrogencarbonate

(NaHCO

),

magnesium

hydroxide

3

[Mg(OH)

]

2

excess

T oothpaste

Acid,

aluminium

hydroxide

[Al(OH)

,

],

magnesium

carbonate

(MgCO

3

hydrochloric

produced

by

acid

in

bacteria

the

in

)

or

calcium

carbonate

(CaCO

3

).

They

work

T wo

active

the

ingredients

in

mouth,

causes

toothpaste,

tooth

sodium

decay

by

reacting

hydrogencarbonate

with

the

and

calcium

sodium

hydroxyapatite

[Ca

monofluorophosphate

(PO 4

(Na

)

the

The

sodium

hydroxide

ions

hydrogencarbonate

in

the

calcium

neutralises

hydroxyapatite

any

acid

forming

in

the

calcium

mouth.

The

fluoroapatite

fluoride

ions

(PO

[Ca 10

Ca

(PO

10

Acids

Soil

treatment

Most

do

plants

)

4

not

(OH)

6

grow

(s)



2F

(aq)

Ca

2

react

best

(PO

10

with

calcium

if

the

soil

fluoroapatite

is

neutral.

hence

Finely

)

4

the

F

6

(s)

the

2OH

6

in

F

the

sodium

]

in

tooth

2

),

help

reduce

3

monofluorophosphate

displace

]:

2

(aq)

2

tooth

ground



)

4

(OH)

6

FPO

2

decay.

neutralising

stomach.

10

enamel.

by

3

enamel

calcium

does

not

carbonate

decay.

(limestone,

CaCO

)

or

lime

in

the

form

of

calcium

oxide

3

(quicklime,

CaO)

or

calcium

hydroxide

(slaked

lime,

Ca(OH)

)

can

be

added

to

soil

to

neutralise

any

acids

present.

However,

lime

cannot

2

be

added

beneficial

at

the

effects

same

of

time



an

ammonium

fertiliser

because

the

two

react

to

make

a

salt,

ammonia

gas

and

water

which

eliminates

the

both:



CaO(s)

as

2NH 4

2

(aq)

Ca

(aq)



2NH 3

(g)



H

O(l)

2

147

Volumetric

analysis

Acids,

Summary

1

What

2

Outline

a

By

the

be

able

end

of

an

this

topic

you

a

how

three

4

Why

should

time

to

salts

you

would

reaction?

perform

a

neutralisation

b

indicator

Give

and

questions

neutralisation

3

A8.6

Objectives

is

bases

uses

of

lime

neutralisation

and

an

reactions

ammonium

reaction

temperature

using:

change.

in

our

daily

fertiliser

not

be

lives.

added

at

the

same

soil?

Volumetric

analysis

will

Volumetric

analysis

involves

performing

a

titration

to

determine

t he

exact

to:

volume of one solution, usually an acid, required to neutralise a xed volume

●

explain

●

determine

volumetric

analysis

of

the

mole

ratio

anot her

t he

which

●

reactants

determine

the

concentration

concentration

used

in

a

solution,

usually

an

aqueous

alkali

or

carbonate.

The

results

of

in

titration

can

t hen

be

used

quantitatively

in

one

of

two

ways:

combine

●

to

determine

t he

mole

●

ratio

to

determine

t he

molar

of

t he

in

which

t he

two

reactants

combine

mass

and

of

concentration

and

mass

concentration

of

one

molar

one

reactants.

reactant

titration.

Determining

The

mole

ratio

mole

in

ratios

which

reactants

combine

can

be

determined

using

a

titration if t he mass or molar concentration of bot h reactants is known, i.e. if

t hey

are

bot h

standard

solutions.

Example

3

During

a

titration

it

was

found

t hat

25 cm

of

potassium

3

concentration

0.6 mol dm

hydroxide

of

molar

3

was

neutralised

by

10 cm

of

sulfuric

acid

of

3

molar

concentration

reactants

.

0.75 mol dm

Determine

t he

mole

ratio

t he

number

of

moles

of

potassium

hydroxide

t hat

3

concentration

3

i.e.

1000 cm

of

KOH(aq)

1 cm



0.6 mol dm

3

(1 dm

)

KOH(aq)

contains

0.6 mol

KOH.

0.6

_____

3

∴

KOH(aq)

contains

mol

KOH

1000

0.6

_____

3

and

25 cm

KOH(aq)

contains



25 mol

KOH

1000



Calculate

t he

number

of

moles

of

0.015 mol

sulfuric

acid

KOH

t hat

reacted:

3

Molar

concentration

of

H

SO 2

3

i.e.

1000 cm

(aq)



0.75 mol dm

4

3

(1 dm

)

H

SO 2

(aq)

contains

0.75 mol

4

H

SO 2

0.75

_____

3

∴

1 cm

H

SO 2

(aq)

contains

mol

4

H

SO 2

4

1000

0.75

_____

3

and

10 cm

H

SO 2

(aq)

contains



10 mol

H

4

SO 2

4

1000



0.0075 mol

H

SO 2

148

which

combine.

Calculate

Molar

in

4

4

reacted:

t he

Acids,

Use

bases

t he

and

salts

number

0.015 mol

of

KOH

Volumetric

moles

reacts

of

each

wit h

reactant

0.0075 mol

to

H

determine

2 mol

KOH

react

wit h

1 mol

H

SO 2

mole

ratio:

SO 2

∴

t he

analysiss

4

. 4

The mole ratio in which t he reactants combine is 2 mol potassium hydroxide

to

1 mol

sulfuric

acid.

Determining

The

t he

concentration

concentration

mass

or

standard

t hat

you

molar

solution.

followed

of

one

reactant

concentration

This

in

is

done

your

of

by

used

t he

in

a

following

calculations

titration

ot her

in

reactant

t he

Unit

same

can

is

be

determined

known,

four

steps,

i.e.

i.e.

if

1)

it

is

to

if

a

4),

7 .5.

Examples

1

A

student

solution

performed

of

a

titration

hydrochloric

acid.

to

determine

The

student

t he

used

concentration

a

standard

of

a

solution

of

3

potassium

hydroxide

wit h

a

concentration

of

0.1 mol dm

and

added

3

t he

hydrochloric

The

results

of

t he

acid

to

25 cm

experiment

of

are

Titration

Burette

t he

potassium

shown

in

t he

hydroxide

solution.

table.

number

reading

Rough

1

2

3

21.5

20.5

41.0

20.4

0.0

0.0

20.5

0.0

21.5

20.5

20.5

20.4

3

Final

reading/cm

3

Initial

reading/cm

3

Volume

of

acid

Determine

Calculate

added/cm

t he

t he

molar

average

concentration

volume

of

of

t he

hydrochloric

hydrochloric

20.5



acid

20.5



acid.

used:

20.4

__________________

average

volume

of

HCl(aq)



(

3

)

cm

3

3



20.5 cm

3

i.e. it takes 20.5 cm

3

of hydrochloric acid to neutralise 25 cm

of potassium

3

hydroxide solution, which has a concentration of 0.1 mol dm

The

balanced

chemical

KOH(aq)



equation

HCl(aq)

for

t he

reaction

KCl(aq)



H

is:

O(l) 2

1)

Calculate

t he

number

of

moles

of

potassium

hydroxide

t hat

reacted:

3

Molar

concentration

3

i.e.

1000 cm

of

KOH(aq)



0.1 mol dm

3

(1 dm

)

KOH(aq)

contains

0.1 mol

KOH.

0.1

_____

3

∴

1 cm

KOH(aq)

contains

mol

KOH

1000

0.1

_____

3

and

25 cm

KOH(aq)

contains



25 mol

KOH

1000



2)

Use

t he

KOH

balanced

and

1 mol

equation

to

0.0025 mol

determine

t he

KOH

mole

ratio

between

HCl:

KOH

reacts

wit h

1 mol

HCl.

149

Volumetric

analysis

Acids,

3)

Use

to

t he

number

calculate

0.0025 mol

4)

Use

t he

t he

of

moles

number

KOH

number

reacts

of

of

of

KOH

wit h

moles

from

moles

of

of

1)

and

HCl

from

3)

mole

ratio

and

from

salts

2)

reacting:

0.0025 mol

HCl

t he

bases

HCl

and

t he

volume

used

to

3

calculate

t he

number

of

moles

of

HCl

in

1 dm

:

3

Volume

of

HCl(aq)

used



20.5 cm

3

i.e.

20.5 cm

HCl(aq)

contains

HCl.

0.0025

_______

3

∴

0.0025 mol

1 cm

HCl(aq)

contains

mol

HCl

20.5

0.025

3

and

______

3

1000 cm

(1 dm

)

HCl(aq)

contains



1000 mol

HCl

20.5



0.122 mol

HCl

3

Therefore,

molar

concentration

of

HCl(aq)



0.122 mol dm

3

2

A

student

found

t hat

20.0 cm

of

hydrochloric

acid

of

unknown

3

concentration

were

required

to

neutralise

25 cm

of

sodium

carbonate

3

solution

wit h

a

concentration

The

balanced

Na

CO 2

concentration

of

t he



0.12 mol dm

hydrochloric

chemical

(aq)

of

equation

.

Calculate

t he

mass

acid.

for

t he

2HCl(aq)

reaction

2NaCl(aq)

is:



CO

3

(g)



H

2

O(l) 2

3

1)

Molar

concentration

of

Na

CO 2

3

i.e.

(aq)



0.12 mol dm

3

3

1000 cm

(1 dm

)

Na

CO 2

(aq)

contains

0.12 mol

Na

3

CO 2

3

0.12

_____

3

∴

1 cm

Na

CO 2

(aq)

contains

mol

Na

3

CO 2

3

1000

0.12

_____

3

and

25 cm

Na

CO 2

(aq)

contains



25 mol

Na

3

CO 2

3

1000



0.003 mol

Na

CO 2

2)

1 mol

Na

CO 2

3)

0.003 mol

reacts

wit h

2 mol

3

HCl.

3

Na

CO 2

reacts

wit h

2



0.003 mol

HCl

3



0.006 mol

HCl

3

4)

Volume

of

HCl(aq)

used



20.0 cm

3

i.e.

20.0 cm

HCl(aq)

contains

0.006 mol

HCl.

0.006

______

3

∴

1 cm

HCl(aq)

contains

mol

HCl

20.0

0.006

3

and

1000 cm

______

3

(1 dm

)

HCl(aq)

contains



1000 mol



0.3 mol

HCl

20.0

HCl

3

Therefore,

molar

concentration

of

HCl(aq)



0.3 mol dm

1

M(HCl)

i.e.

∴

mass

mass

of

of



1



1 mol

35.5

HCl

0.3 mol



HCl



36.5 g mol

36.5 g



0.3



36.5 g



10.95 g

3

Therefore,

150

mass

concentration

of

HCl(aq)



10.95 g dm

Acids,

T o

bases

and

salts

determine

the

hydrochloric

Your

teacher

Volumetric

concentration

of

a

solution

analysis

of

acid

may

●

manipulation

●

analysis

use

and

and

this

activity

to

assess:

measurement

interpretation

3

Y ou

will

be

supplied

hydrochloric

acid

with

of

0.2 mol dm

unknown

sodium

concentration,

hydroxide

methyl

solution,

orange

indicator,

a

3

25 cm

pipette,

a

conical

ask

and

a

burette.

Method

1

Rinse

2

Rinse

the

burette

with

some

hydrochloric

acid

and

ll

it

with

the

acid.

3

the

sodium

3

Add

the

4

a

with

hydroxide

few

drops

some

solution

of

sodium

in

methyl

the

hydroxide

pipette

orange

to

and

the

solution.

run

it

conical

into

Measure

the

ask

25 cm

conical

and

swirl

of

ask.

to

mix

contents.

Carry

This

out

time

orange

much

5

pipette

a

titration

add

on

the

as

described

acid

until

one

drop

adding

the

of

in

the

practical

solution

acid.

If

just

it

activity

turns

turns

red

from

you

on

page

yellow

have

141.

to

added

too

acid.

Record

your

results

in

a

table

as

outlined

in

the

practical

activity

on

page

3

6

142

and

Use

this

average

volume

concentration

help

or

vitamin

C

packaged

iodine

to

of

three

volumes

calculate

the

the

of

acid

molar

hydrochloric

which

were

concentration

acid.

Use

the

within

and

0.1 cm

.

mass

examples

above

to

you.

Determining

The

the

vitamin

(ascorbic

fr uit

solution.

juices

odine

C

acid)

can

acts

content

content

be

as

of

vitamin

determined

an

by

oxid ising

C

tablets,

fresh

performing

agent

(see

a

Unit

fr uit

juices

titration

using

9.3)

during

t he

titration and oxidises t he ascorbic acid to dehydroascorbic acid. The ascorbic

acid

is

acts

as

a

C

H 6

O 8

During

xed

is

(aq)

t he

t he

longer

starch

it

to

is

of

t he

of

(aq)

C

brown

juice

immediately

where

a

all

since

in

of

The

iodine

or

a

t he

O 6

iodine

(aq)

of

t he

1 mol

colour

t he

fr uit

of

by

colour.



ions.

The

reaction

ascorbic

in

The

is

added

vitamin

ascorbic

has

t he

end

2H(aq)

acid

from

C

acid

just

to

of

burette

As

t he

colourless

reacted,

solution

point

t he

tablet.

and

t he



iodine

reacts

a

ions.

will

wit h

titration

to

iodine

is

no

t he

when

forms.

iodine

juice

a

acid

remains

just

of

t he

ascorbic

iodine

to



6

solution

solution

reduced

t he

blue-black

blue-black

acid

H 6

concentration

calculated

reduces

equation:

2

fr uit

produce

ascorbic

and

dehydroascorbic

reduced.

permanent

f

agent

following





titration,

point

be

t he

acid

volume

added

At

in

6

ascorbic

a

reducing

summarised

solution

or

solution

acid

reacts

is

known,

of

wit h

a

t he

vitamin

1 mol

of

concentration

C

tablet

can

be

iodine.

151

Volumetric

analysis

Acids,

T o

determine

Your

teacher

may

●

manipulation

●

analysis

and

be

the

Y ou

will

e.g.

grapefruit

vitamin

use

and

this

C

content

activity

to

of

a

fruit

bases

and

salts

juice

assess:

measurement

interpretation.

supplied

with

a

sample

of

a

fruit

juice

without

pulp,

3

juice,

iodine

solution

of

concentration

0.005 mol dm

,

3

1%

starch

indicator

solution,

a

25 cm

pipette,

a

conical

 ask

and

a

burette.

Method

1

Rinse

the

burette

with

some

iodine

pipette

with

some

of

solution

and

ll

it

with

the

iodine

solution.

Summary

questions 3

2

3

1

A

volume

sodium

of

40 cm

carbonate

Rinse

juice

of

solution

of

3

Add

the

in

the

ten

pipette

drops

of

and

run

starch

it

the

into

fruit

the

indicator

to

juice.

Measure

conical

the

25 cm

of

the

fruit

ask.

conical

ask

and

swirl

to

mix

the

3

concentration

0.2 mol dm

contents.

3

reacts

with

20 cm

of

nitric

4

acid

of

Carry

out

a

titration

as

described

in

the

practical

activity

on

page

141.

concentration This

time

add

the

iodine

solution

until

the

rst

permanent

trace

of

a

blue-

3

.

0.8 mol dm

Determine black

the

mole

ratio

in

which

combine.

A

of

is

obtained.

the

5 reactants

colour

Record

on

your

page

results

142

and

in

a

table

average

as

the

outlined

three

in

the

volumes

of

same

practical

iodine

solution

activity

which

3

2

volume

sodium

30 cm

hydroxide

3

of

were

solution

within

0.1 cm

.

of

6

Use

this

volume

to

calculate

the

molar

concentration

and

mass

3

concentration

0.4 mol dm concentration

of

ascorbic

acid

in

the

grapefruit

juice.

Use

the

examples

3

were

neutralised

by

20 cm

of on

sulfuric

acid.

Determine

concentration

of

the

pages

149–50

to

help

you.

the

sulfuric

You could adapt t he experiment which you have just performed to determine acid

in:

3

a

3

b

t he

effect

of

heat

on

t he

vitamin

C

content

of

a

fr uit

juice.

Planning

and

mol dm

designing

experiments

is

discussed

in

more

detail

in

t he

School-Based

g dm

Assessment

Key

section

on

t he

CD.

concepts



●

An

in

acid

An

●

Aqueous

●

acid

red,

is

substance

dibasic

An

●

We

which

use

a

forms

of

acids

react

water;

hydrogen

ions

(H

)

when

dissolved

across

a

some

be

or

of

t hese

7

taste,

and

metals

wit h

bases

change

conduct

to

as

to

form

that

organic

organic

form

organic

concentrated;

compound

variety

of

sour

hydrogencarbonates

classied

a

a

t han

reactive

react

dilute

is

donor.

have

less

and

and

may

tribasic;

of

wit h

carbonates

of

proton

value

anhydride

come

make

pH

acids

or

acid

a

acids

and

Aqueous

as

solutions

wit h

dioxide

●

dened

have

Aqueous

react

●

a

water.

●

to

152

is

in

in

a

salt

and

form

salt

strong

with

living

our

colour

electric

a

or

litmus

hydrogen;

carbon

water.

monobasic,

weak.

water

to

form

organisms

ever yday

of

current.

salt,

and

inorganic;

and

reacts

acids

acids

or

a

to

t he

an

an

and

acid.

we

activities.

Acids,

●

A

●

An

bases

base

and

salts

analysis

is dened as a proton donor.

alkali

is a base which dissolves in water to form a solution containing

hydroxide ions (OH

●

Volumetric

).

Aqueous solutions of alkalis have a bitter taste, change the colour of

litmus to blue, have a pH value greater than 7 , conduct an electric current

and feel soapy.

●

Bases react with acids to form a salt and water and react with ammonium

salts to form a salt, ammonia and water.

●

Amphoteric substances

●

Oxides

●

Strong acids and alkalis are fully ionised when dissolved in water.

●

Weak acids and alkalis are partially ionised when dissolved in water.

●

The strength of an acid or alkali is measured using the

can be classied as acidic, basic, amphoteric and neutral.

ranges from

●

can react with acids and strong alkalis.

pH scale

which

0 to 1 4

The stronger the acid, the lower the pH. The stronger the alkali, the higher

the pH.

●

Neutral substances have a pH of 7 .

●

Universal indicator or a pH meter is used to measure pH.

●

Other acid–alkali indicators have one colour in an acidic solution and

another colour in an alkaline solution.

●

A

salt

is a compound formed when some or all of the replaceable

hydrogen ions in an acid are replaced by metal or ammonium ions.

●

A

normal salt

replaced. An

is formed when all the hydrogen ions in an acid are

acid salt

is formed when only some of the hydrogen ions are

replaced.

●

Some salts contain water molecules trapped between their ions in the

cr ystal lattice. This is known as

water of crystallisation

●

nsoluble salts can be prepared by ionic precipitation.

●

Anhydrous binar y salts can be prepared by direct combination.

●

Potassium, sodium and ammonium salts can be prepared using a titration.

●

Other soluble salts can be prepared by reacting a reactive metal, an

insoluble carbonate or an insoluble base with an acid.

●

Salts play an extremely important part in our ever yday lives, but can also

be dangerous.

●

A

neutralisation reaction

is a reaction between a base and an acid to form

a salt and water.

●

The

neutralisation point

is the point in an acid–alkali reaction where the

reaction is complete and neither acid nor alkali is present in excess.

●

The neutralisation point of an acid–alkali reaction can be determined

during a titration by using an indicator, a pH meter or temperature

change.

●

Neutralisation reactions are used in various aspects of our daily lives.

●

Volumetric analysis

involves performing a titration to determine the

exact volume of one solution required to neutralise a xed volume of

another solution.

●

Results of a titration can be used to determine the mole ratio in which the

two reactants combine or to determine the concentration of one reactant.

●

The vitamin C content of a vitamin C tablet or fr uit juice can be

determined using a titration.

153

Practice

exam-style

questions

Acids,

9

Practice

exam-style

Multiple-choice

1

Which

of

t he

Magnesium

sulfate

can

be

prepared

bases

and

salts

by:

questions 

reacting

magnesium

carbonate



reacting

magnesium

nitrate



reacting

magnesium

wit h

A



and



B



and



C

,

D



wit h

wit h

sulfuric

sulfuric

acid

acid

questions

following

is

not

a

proper ty

of

sulfuric

acid.

hydrochloric only

acid?

A

t

turns

a

blue

B

t

is

C

t

reacts

strong

t

reacts

2

Which

of

magnesium

and

form

carbonate

dioxide

following

and

is/are

to

form

sodium





They

react

They

have

They

react

wit h

a

and



acids

pH

less

wit h

to

water.

t han

a

salt

of

aqueous

and

hydrogen.

7 .

ammonium

salts

Which

an

proper ties

form

only

to

form

a

of

t he

following

neutralisation

alkalis?





magnesium

10

sodium

carbon

t he

to

water.

wit h

chloride,

only

red.

electrolyte.

wit h

chloride

D

litmus

point

in

cannot

a

be

reaction

used

to

determine

between

an

acid

t he

and

alkali?

A

An

B

A

t hermometer

anemometer

C

A

pH

D

An

meter

indicator

salt, 3

11 ammonia

and

A

volume

of

of

25 cm

a

carbonate

solution

of

water. 3

concentration

A



and





C

,

and



D

3

A



neutralised

by

20 cm

of

3

acid

of

concentration

0.5 mol dm

.

The

mole

ratio

in

only which



was

only an

B

3

0.2 mol dm

and

t he

reactants

combine

is:

 A

1 mol

of

carbonate

to

1 mol

of

acid

B

1 mol

of

carbonate

to

2 mol

of

acid

C

2 mol

of

carbonate

to

1 mol

of

acid

D

3 mol

of

carbonate

to

1 mol

of

acid.

only

weak

acid

A

is

B

ionises

C

has

D

does

is

one

which:

dilute

fully

in

aqueous

solution 3

12



a

low

concentration

of

A

volume

of

10 cm

of

sulfuric

acid

of

unknown

ions

H

3

concentration not

ionise

in

aqueous

neutralised

25 cm

of

sodium

solution. 3

hydroxide 4

A

solution

which

has

a

pH

of

solution

concentration A

is

more

B

is

less

alkaline

t han

a

of

concentration

.

0.4 mol dm

The

1 1:

solution

wit h

a

pH

of

of

t he

acid

is:

12 3

alkaline

t han

a

solution

wit h

a

pH

of

A

0.1 mol dm

B

0.25 mol dm

C

0.4 mol dm

D

0.5 mol dm

9 3

C

is

more

acidic

t han

water 3

D

is

less

alkaline

t han

a

sodium

hydroxide

solution

of 3

t he

5

The

same

actual

hydroxide

concentration.

change

which

solution

occurs

reacts

wit h

when

sodium

sulfuric

acid

is:

Structured 

A

2Na

question

2

(aq)



SO

(aq)

Na

4

SO

2

(aq)

4



B

OH

C

2NaOH(aq) 

(aq)



H

(aq)

D

NaOH(aq)  H

H

13

O(l)

A

titration

is

used

to

determine

t he

volume

of

one

2

H

SO

2

Na

4

SO

2

(aq)

SO

2

(aq)

Na

4



2H

4

SO

2

(s)

O(l)

solution

Which

of

t he

following

acids

is

found

in

4

an

O(l)

solution.

Met hanoic

B

Et hanoic

neutralise

Titrations

a

xed

volume

of

can

be

used

as

a

means

of

soluble

salts

and

in

volumetric

analysis

t he

concentration

of

one

of

t he

solutions

acid During

a

titration,

t he

neutralisation

point

C

Lactic

D

Hydrochloric

determined

by

using

an

indicator.

acid

a

acid

What

is

meant

by

t he

neutralisation

point

of

titration? of

is

acid usually

Which

to

sting?

used.

7

anot her

preparing

2

ant

determine A

to

2

(aq)  H

cer tain 6

needed

t he

following

is

not

an

amphoteric

Lead(II)

B

Aluminium

C

ron(III)

D

Zinc

marks)

substance?

b A

a

(2

n

order

to

determine

t he

concentration

of

a

sodium

oxide

hydroxide

solution,

a

student

is

provided

wit h

two

hydroxide

solutions

labelled

X

and

Y.

oxide

hydroxide

–

X

is

aqueous

sulfuric

acid

wit h

a

mass

3

concentration 8

A

pure

sample

of

lead(II)

chloride

can

be

prepared

of

19.6 g dm

by

–

Y

is

a

sodium

hydroxide

solution

of

unknown

reacting:

concentration. A

lead

B

lead(II)

wit h

hydroxide

dilute

hydrochloric

C

lead(II)

nitrate

wit h

dilute

acid

hydrochloric

acid

To

determine

t he

concentration

of

Y,

t he

student

3

solution

wit h

sodium

chloride

titrates

t he

solution

X

against

readings

25.0 cm

from

t he

of

Y.

burette

The

gure

before

and

3

D

154

lead(II)

carbonate

wit h

hydrochloric

acid.

titration

using

25.0 cm

of

solution

Y.

shows

af ter

each

Acids,

bases

and

salts

Practice

c

0

17

2

19

4

Salts

can

be

prepared

i)

your 20

5

t he

before

wit h

answer

a

you

would

copper(II)

copper(II)

a

balanced

prepare

sulfate

a

in

variety

carbonate.

chemical

pure

t he

1

after

titration

nclude

would

before

to

your

(5

met hod

prepare

be

hydrated

different

if

i)

Using

t he

t he

table

in

for

copper(II)

2

marks)

you

sulfate

after

titration

(1

mark)

3

Total

Burette

sample

equation

cr ystals?

titration

of

laborator y

reaction.

How

wanted

after

by

23

ii)

before

how

anhydrous

star ting

3

laborator y

met hods.

Describe

of

18

t he

questions

22

different

1

in

exam-style

15

marks

readings

information

from

t he

gure,

complete

below.

Titration

number

1

2

3

needed

to

3

Final

burette

reading/cm

3

Initial

burette

reading/cm

3

Volume

of

solution

X

used/cm

(3

ii)

Calculate

t he

volume

of

X

marks)

neutralise

3

25 cm

iii)

of

Y.

Calculate

(1

t he

concentration

of

sulfuric

mark)

acid

in

3

solution

iv)

X

Calculate

used

v)

in

Write

in

t he

t he

a

mol dm

(1

number

of

moles

of

sulfuric

titration.

balanced

for

t he

Determine

t he

number

of

moles

mark)

reaction.

(2

vi)

acid

(1

equation

mark)

of

marks)

sodium

3

hydroxide

vii)

Calculate

in

t he

t he

of

25.0 cm

concentration

solution

of

Y

used.

(1

mark)

(1

mark)

sodium

3

hydroxide

c

How

in

b

i)

would

t he

in

solution

student

Y

use

in

t he

mol dm

.

titration

carried

to

prepare

a

pure

dr y

sample

of

sodium

sulfate

(2

ii)

to

prepare

a

pure

sodium

(1

Total

14

a

An

as

response

acid

a

can

proton

be

15

dened

acceptor.

as

a

proton

Explain

t he

donor

reason

and

for

acid

However,

t hey

marks

a

and

sulfuric

have

acid

different

are

pH

bot h

values.

base

EACH

(4

Carbonic

mark)

question

denition.

b

marks)

hydrogensulfate

solution?

Extended

out

above:

marks)

acidic.

You

are

3

supplied

i)

ii)

wit h

Suggest

Explain

a

a

solution

1.0 mol dm

pH

t he

value

reason

for

for

EACH

t heir

of

each

solution.

different

(2

pH

Give

one

way

suggested

pH

you

could

values

are

use

to

nd

correct.

out

if

marks)

values.

(2

iii)

acid.

marks)

your

(1

mark)

155

Oxidation–reduction

A9 reactions

Oxidation

and

reduction

reactions

form

a

very

important

Objectives

By

the

be

able

end

of

this

topic

you

will

part

of

our

everyday

photography,

●

describe

the

oxidising

action

and

of

common

in

●

example,

in

batteries,

all

these

dene

identify

of

reduced

and

electron

the

oxidised

electrons

and

are

the

rusting

being

of

cars.

transferred.

It

In

was

the

using

the

discovery

of

oxygen

that

the

chemistry

oxidation–reduction

reactions

was

understood.

reduction

transfer

reactant

and

reactions

after

behind

oxidation

terms

photosynthesis

everyday

activities

in

for

reducing

only substances

●

lives,

to:

A9.1

being

reactant

electron

Oxidation

and

reduction

–

an

introduction

being

transfer.

The

discover y

stepping

when

metals

oxides.

and

stone

The

in

are

laborator y

chemistr y.

burned,

term

preparation

Antoine

t hey

oxid ation

combine

was

used

of

oxygen

Lavoisier

wit h

later

to

was

a

(1743–94)

oxygen

dene

ver y

from

any

impor tant

discovered

t he

air

reaction

to

in

t hat

form

which

a

reactant gains oxygen. An example, according to t his denition of oxidation,

is

t he

reaction

gained

between

oxygen,

2Mg(s)



magnesium

forming

O

and

magnesium

(g)

oxygen

where

t he

magnesium

has

oxide:

2MgO(s)

2

The

removal

reaction

of

oxygen

because

reduction

was

t he

used

from

metal

to

a

metal

oxide

dene

any

was

oxide

was

reduced

reaction

in

to

described

t he

which

a

pure

as

a

metal.

reactant

reduction

The

loses

term

oxygen.

An example, according to t his denition of reduction, is t he reaction between

iron(III)

oxide

and

carbon

where

t he

iron(III)

oxide

has

lost

oxygen

to

form

iron:

2Fe

O 2

These

(s)



3C(s)

4Fe(s)



3CO

3

(g) 2

denitions

were

later

extended

to

include

reactions

involving

hydrogen.

Hydrogen is chemically opposite to oxygen, therefore, oxidation was dened as

a loss of hydrogen and reduction was dened as a gain of hydrogen.

With

the

discovery

of

protons,

neutrons

and,

most

importantly,

electrons,

scientists rened their denitions of oxidation and reduction, and the denitions

were

rened

again

using

the

concept

of

oxidation

number

or

oxidation

state.

You will be studying these denitions in detail later in this unit.

Oxidation

We

and

encounter,

our

ever yday

Action

Bleach

used

and

of

is

and

lives.

reduction

make

We

use

will

of,

look

in

our

many

at

everyday

oxidation

some

of

t hese

and

activities

reduction

added

bleaches

oxygen



Figure

the

has

9.1.1

statue

oxidation

156

of

started

The

copper

Marcus

to

turn

from

Garvey

green

is

which

made

because

bleach

stain

to

to

are

clothes

chlorine

bleaches

remove

their

to

remove

bleaches

containing

coloured

containing

hydrogen

stains.

The

sodium

peroxide

most

stains

colourless

by

oxidising

form,

hence

the

the

coloured

stain

(H

O

summarises how the chlorate(I) ion (ClO

The

).

(aq)



coloured

dye

Cl

(NaClO)

Both

or

dyes,

equation

) in a chlorine bleach works:

(aq)



colourless

types

2

chemicals,

disappears.

commonly

chlorate(I)

of

ClO

in

bleaches

2

of

reactions

below.

dye

in

the

below

Oxidation–reduction

reactions

Oxidation

and

reduction

–

an

introduction

Rusting

When iron and its a lloy, ste el, co me into con t ac t w it h oxyg en an d mo isture

t he

iron

xH

O),

is

oxidised

by

t he

oxygen

to

fo r m

hydra te d

ir on (I II)

oxid e

(Fe

O 2

ot her wise

known

as

r ust .

Given

sufficient

t ime

a nd

3

ex po su re

to

2

oxygen

r ust

and

and

Browning

As

so on

suc h

t he

as

moist ure ,

of

as

cut

f ruits

cer t ain

pot atoes,

air.

a ny

iro n

ob j ec t

w ill

even tu ally

oxid ise

e n tir ely

to

disinteg ra t e .

fr uit s

a re

Enzymes

and

in

suc h

pee led

t he

vege tab les

as

or

plan t

a pple s

cut ,

c ells

an d

t he

on

cu t

t he

ban an as,

su r f ac e

su r f ac e

is

of

or

cer t ain

ex p ose d

t he

veget ables

to

fr u it

oxyg en

or

in

ve get ab le



begin

to

oxidise

cer t ain

c hemica ls

in

t he

ce lls

to

brown

Figure

on

known

tur n

n

as

melanins .

These

melanins

c a us e

t he

cut

or

9.1.2

da maged

su r f ac e

exposure

cases,

appearance,

b rown in g

flavo ur,

is

qualit y

un desirab le

and

t aste.

b ec au se

Th e

it

me la n ins

cau se s

for med

c h an ges

a re

not

in

Did

?

in

some

case s

t h e ir

pro ductio n

is

use f u l

sinc e

it

con tr ib u tes

turns

in

the

brown

air

you

colour

and

flavour

of

ite ms

suc h

as

raisins,

pr u n es,

coffee,

t ea

and

are

pigments

to

of

eyes

skin,

of

hair,

and

scales,

animals.

ultraviolet

for

the

light

feathers

Exposure

stimulates

the

preservation production

Sodium

sulfite

enhance

and

flavour,

discolouration

pot atoes

bacter ia

dr ied

brown

responsible

coc oa.

and

being

dark

t he

colour

Food

know?

tox ic

to

black

and

of

fo o ds

shr imp.

oxidising

de stroyed

pot ato

s ulfur

pre s e r ve

by

The

bre at halyser

test

t he

te st ,

dic hromate(VI)

do

is

t he

as

t his

sh r imp

to

acid.

used

c r y st a ls

Any

(K

et h an o l

by

to

O

)

t he

in to

c hemicals

fr u it s,

Th ey

C

b r own ing

in

of

dic hromate(VI)

io n

tur ning

t he

cr yst a ls

g re en

(se e

dr ie d

oxidation

invo lve

reactio n s

electrons

electrons

to

was

was

t hat

sai d

said

to

to

a

in

)

Un it

lo ss

of

invo lved

h ave

produc e d

dur in g

leve l

have

of

in

t he

oran ge

be e n

b reat h

of

p ot assi um

t he

dr ive r ’s

acidified

b reat h

w ill

wit h

reduce

to

t he

green

c h romium(III)

io n

t he

(Cr

),

9.3).

Key

ele c tron s.

a

b ee n

be en

and

reduc t ion

can

fact

electrons

tran sfer

Th ey

of

oxid ised

develo ped

ele c tron s.

and

a

A

a

mo d el

su b st an c e

subst ance

t hat

for

by

an

is

in

a

being

t he

loss

of

loss

in

its

of

free

electrons

state

or

an

compound.

t h at

gained

reduced .

be

d ef ined

in

t er ms

of

ele c tron

Key

fact

t ran s fer, Reduction

oxidation

the

element

element

! Oxidation

skin

7

and

h ave

why

ju ic e

Oxidation

seemed

is

fr u its ,

By t h e tur n of t he 2 0t h ce nt ur y, c he mists realise d t h at ox id atio n reac tion s

always

which

sunlight.

p reven t

fr u it

! Oxidation–reduc tion

skin,

in

3

O 2

human

darkens

pigments

7

vapo ur s

(Cr

in

melanin

dr ied

2

orange

to

and

of

for m.

sample

whic h

spoilage

dr ie d

vit amin

a lco h o l

a

preservative s

preven t

ox id atio n .

t he

p reven t

reducing

food

or

j u ices,

p reven t

test

2

fr u it

c olo u rle ss

blow s

Cr

as

r ed u c e

p reven ting

a lso

by

t h eir

dr ive r

use d

and

and

They

2

sulfur ic

are

wine ,

vine ga r

ba c k

te st

n

to

a nd

pro c e ss

breathalyser

dr iver s.

suc h

ox idat io n .

produc t s

browning

diox ide

fre sh ne ss

Th ey

win e

The

lost

apple

oxygen

to

Melanins

t he

cut

to

brown.

many

and

A

compounds

electrons

and

re duc tio n

b ein g

t he

gain

is

the

gain

of

electrons

of by

an

element

in

its

free

state

or

an

electrons. element

in

a

compound.

157

Oxidation

and

reduction

–

an

introduction

Oxidation–reduction

reactions

A substance will not lose electrons unless t here is anot her substance available

✔

Exam

to

tip

gain

t he

electrons,

i.e.

for

ever y

oxidation

reaction

t here

will

always

reduction reaction. These oxidation–reduction reactions are known as

You

must

oxidation

electron

be

able

and

define

reduction

transfer.

remember

to

these

remembering

An

in

easy

reactions.

terms

way

definitions

two

words:

is

of

to

t he

The

oxid ation

electrons

is

Oxidation

Is

RlG

Reduction

half

known

t hat

equation

as

t he

only

and

shows

t he

reduction

t he

loss

equation

half

of

t hat

electrons

only

is

shows

t he

OlL

gain

as

of

equation

RlG

of

redox

reactions

Loss

Is

1

Gain

Burning

magnesium

2Mg(s)

in



oxygen:

O

(g)

2MgO(s)

2

The

Key

!

redox

reaction

is

a

Each

consisting

in

reduced

(MgO)

magnesium

which

and

the

one

of

produced

Mg

in

atom

t he

reaction

is

an

ionic

2

ions

loses

and

two

O

ions.

electrons

to

During

form

a

t he

reaction:

magnesium

ion.

chemical

Magnesium reaction

oxide

2

compound

●

A

magnesium

fact

reactant

other

is

(Mg)

is

oxid ised:

is

2

oxidised.

Mg

This

is



2e

more

Mg

correctly

written

as:

2

Mg

The

✔

Exam

Mg

overall

oxidation

2e

half

equation

is:

tip 2

2Mg(s)

When

and



writing

balanced

reduction

half

oxidation

equations

●

you

2Mg

Each

oxygen

form

an

atom

oxide

in

ion.

(s)

t he



4e

oxygen

Oxygen

(O

)

molecule

is

gains

two

electrons

to

reduced:

2

must

always

include

state

symbols 2

O and

the

it

is

important

number

balance

at

of

to

ensure

atoms

each

side

and

of



2e

O

that

charges

The

overall

reduction

half

equation

is:

the 2

O

(g)



4e

2O

(s)

2

equation.

2

Adding

zinc

Zn(s)

to



copper(II)

CuSO

sulfate

(aq)

solution:

ZnSO

4

The

zinc

sulfate

displaces

and

copper

Writing

in

t he

t he

During

●



t he

Each

Cu

Cu(s)

copper(II)

ionic

2

Zn(s)



4

t he

copper.

(aq)

equation

sulfate

for

t he

to

form

zinc

reaction:

2

(aq)

Zn

(aq)



Cu(s)

reaction:

zinc

atom

loses

two

electrons

to

form

a

zinc

ion.

Zinc

(Zn)

is

oxid ised:

2

Zn(s)

●

Each

Zn

copper (II)

ion

(aq)

gains



two

2e

electrons

to

form

a

copper

atom.

The

2

copper(II)

ions

(Cu

)

are

reduced:

2

Cu

3

Bubbling

Cl

(aq)



chlorine

(g)



2e

gas

2Cu(s)

t hrough

2KBr(aq)

potassium

2KCl(aq)

bromide



Br

2

The

t he

(aq)

displaces

chloride

t he

and

bromine

bromine.

in

t he

potassium

Writing

t he

reaction:

(g) 2

158

gas

potassium

Cl

solution:

2

chlorine

form



2Br¯(aq)

2Cl¯(aq)



Br

(aq) 2

ionic

bromide

to

equation

a

redox

known

by

Examples

OlL

equation

be

for

Oxidation–reduction

During

t he

Each

●

reactions

Oxidation

numbers

reaction:

bromide

bromide

ions

ion

(Br

loses

)

are

2Br¯(aq)

one

electron

to

form

a

bromine

atom.

The

oxid ised:

Br

(aq)



2e

2

●

Each

chlorine

form

a

atom

chloride

in

ion.

t he

chlorine

Chlorine

(Cl

)

molecule

is

gains

one

electron

to

reduced:

2

Cl

(g)



2e

2Cl¯(aq)

2

onic

the

bonding

non-metal

always

atom.

involves

Any

a

transfer

reaction

in

of

electrons

which

ionic

from

bonds

the

are

metal

formed

atom

is

a

to

redox

reaction. Using the reaction between sodium and chlorine as an example:

2Na(s)



Cl

(g)

2NaCl(s)

2

Each

●

is

sodium

atom

loses

one

electron

to

form

a

sodium

ion.

Sodium

(Na)

oxid ised:



2Na(s)

Each

●

a

2Na

chlorine

chloride

atom

ion.

in

(s)

t he

Chlorine



2e

chlorine

(Cl

)

is

molecule

gains

one

electron

to

form

reduced:

2

Cl

(g)



2e

2Cl

(s)

2

Summary

1

Dene

2

State

questions

oxidation

whether

and

each

reduction

of

the

in

terms

following

half

of

a

transfer

equations

of

electrons.

shows

oxidation

or

reduction:

3

a

Fe

2

(aq)



3e

b

Fe(s)

Fe



c

Br

(aq)

2Br

(aq)



3

(aq)

Fe

(aq)



e

2

d

2e

Cu



2e

Cu(s).

2

3

In

the

has

following

been

Br

redox

reaction,

state

what

Why

A9.2

Redox

(aq)



2KI(aq)

an

apple

turn

Oxidation

chemistr y

2KBr(aq)

For

water,

and

what



I

(aq)

is

no

when

it

is

cut

in

half?

numbers

in

Objectives

fur t her

reactions

example,

t here

brown

developed

oxidation–reduction

for m

oxidised

2

does

electrons.

been

reduced:

2

4

has

t he

did

when

not

reaction

change

in

t he

chemists

always

between

number

of

involve

recognised

t he

hydrogen

valence

transfer

and

the

be

able

end

t he

atoms,

●

dene

●

determine

on

any

i.e.

t here

is

no

transfer

of

valence

electrons.

However,

t he

●

reaction

is

denitely

a

redox

reaction

because

t he

reaction

involves

and

(g)



O

2

The

of

development

Oxidation

as

a

result

(g)

2H

2

model

will

oxidation

number

oxidation

numbers

formulae

dene

oxidation

terms

of

and

oxidation

reduction

of

oxidation–reduction

t he

concept

indicates

chemical

identify

redox

number

change

in

identify

the

reactions

using

a

O(g) 2

number

of

you

oxygen:

●

2H

topic

bot h

in

hydrogen

this

to

from

of

of

to:

of

oxygen

electrons

By

t hat

of

t he

bonding.

reactions

oxid ation

number

of

was

number

electrons

expanded

or

lost,

by

oxid ation

gained

or

t he

state.

shared

●

oxidised

reduced

oxidation

reactant

and

the

using

oxidation

a

number

being

reactant

change

being

in

number.

159

Oxidation

numbers

Oxidation–reduction

Oxidation

Key

!

oxidation

fact

sign

The

oxidation

element

that

an

have

if

atoms

it

were

was

is

the

atom

all

in

the

the

ionic

number

of

theoretical

of

the

and

the

is

placed

1,

always

2,

can

of

an

before

and

be

t he

t here

positive,

element,

is

number

always

negative

unless

a

to

t he

or

zero.

number

indicate

number

af ter

impor tant

role

if

it

t he

is

When

zero,

is

a

positive

sign,

i.e.

writing

plus

or

t he

or

t he

minus

negative,

number

1

is

written.

would

between

compound

e.g.

charge

element

bonds

composed

an

numbers

number

reactions

the

containing

Oxidation

numbers

compounds

as

you

play

will

an

learn

in

sections

t hat

in

t he

naming

of

cer tain

follow.

compound

entirely

of

ions.

Rules

Before

for

you

determining

can

learn

how

to

oxidation

recognise

numbers

redox

reactions

using

t he

concept

of

oxidation number, you must learn how to determine t he oxidation numbers

of

●

elements.

The

For

To

do

oxidation

t his,

a

set

number

of

of

r ules

each

need

atom

of

to

an

be

followed.

element

in

its

free

state

is

zero.

example:

oxidation

number

of

an

oxidation

number

of

each

Al

atom

N

in

atom

Al

in



0

N



0.

2

●

The

oxidation

to

t he

in

Al

number

charge

on

t he

of

each

ion.

For

simple

ion

in

an

ionic

compound

is

equal

example:

3

O 2

:

oxidation

number

of

each

Al

ion



3

ion



2.

3

2

oxidation

●

number

The oxidation number of

of

each

O

hydrogen when present in a compound is always

1 except when bonded to a metal in a metal hydride where its oxidation

number is

1, e.g. in sodium hydride (NaH) and calcium hydride (CaH

). 2

●

The

2

oxidation

except

in

number

of

peroxides

oxygen

where

it

when

is

1,

present

e.g.

in

in

a

compound

hydrogen

is

peroxide

always

(H

O 2

●

The

sum

of

t he

compound

is

oxidation

zero.

For

numbers

example,

of

in

all

H

elements

O,

t he

present

oxidation

in

). 2

a

number

of

each

2

atom

must

add

up

2(oxidation

●

The

sum

of

OH

ion,



0



(2)



0

(2)



(2)



0

number

oxidation

ion

t he

zero:

2(1)

t he

polyatomic

to

is

equal

oxidation

(oxidation

of

H)



numbers

to

t he

of

O)

(2)

of

all

charge

number

number

(oxidation

of



elements

on

each

number

t he

ion.

atom

(oxidation



of

O)

present

For

must

a

example,

add

number

in

of

up

H)

(1)

to

in

t he

1:



1



1

Following these r ules, the oxidation number of any element can be determined

from

the

formula

of

the

compound

or

polyatomic

ion

in

which

the

element

occurs.

Examples

1

Determine

t he

oxidation

number

of

sulfur

in

sulfur

dioxide

(SO

). 2

(oxidation

number

of

S)





0

(oxidation

number

of

S)



2(oxidation

2(2)



0

(oxidation

number

of

S)



(4)



0



4

∴

The

compound

sulfur

dioxide

number

oxidation

(SO

)

can

be

of

number

called

O)

of

S

sulfur( IV)

oxide

2

because

160

t he

oxidation

number

of

sulfur

in

t he

compound

is

4.

Oxidation–reduction

2

Determine

t he

reactions

oxidation

Oxidation

number

of

nitrogen

in

t he

nitrate

ion

(NO

numbers

). 3

(oxidation

number

of

N)



(oxidation

number

of

N)



3(oxidation

3(2)



(oxidation

number

of

N)



(6)



∴

The

nitrate

ion

(NO

)

is

more

number

oxidation

correctly

of

number

called

t he

O)

of



N

1

1

1

5



nitrate( V)

ion

3

because

3

t he

Determine

carbon

in

oxidation

t he

number

oxidation

met hane

(CH

of

nitrogen

number

in

t he

ion

is

of

).

5.

C



4(1)



0

C



(4)



0

∴



4

4

The

4

oxidation

Determine

number

t he

manganese

in

of

oxidation

t he

carbon

is

number

MnO

ion

4

of

and

C

name

Mn



4(2)



1

Mn



(8)



1



7

4

t he

The

∴

ion.

oxidation

number

manganate( VII)

in

5

t he

t he

chromium

oxidation

in

K

Cr 2

name

of

manganese

because

of

t he

is

7.

The

oxidation

ion

is

called

number

of

t he

manganese

ion.

Determine

of

ion

Mn

t he

O 2

number

2(1)



2Cr



7(2)



(2)



2Cr



(14)



0

2Cr



12

Cr



6

and 7

compound.

∴ The

oxidation

The

compound

oxidation

6

number

is

called

number

Determine

t he

of

of

chromium

potassium

chromium

oxidation

in

number

is

0

6.

d ichromate( VI)

t he

because

of

t he

compound.

of

S



3(2)



2

S



(6)



2



4

2

sulfur

in

t he

sulte

ion

(SO

)

and

3

suggest

The

be

an

alternative

oxidation

called

t he

Oxidation

Cer tain

t his

elements,

name.

and



it

is

is

its

T able

give

9.2.1

containing

Compound

of

done

ions,

by

sulfur

more

impor tant

in

is

ion.

4.

∴

The

a

to

naming

t han

one

compound

include

placing

Roman

t he

t he

ion

can

S

also

ion

and

naming

for

name

t he

t he

compounds

possible

or

ion

oxidation

oxidation

numerals

always

oxidation

t hat

in

ends

in

number.

contains

number

number

brackets

‘ ate’.

any

as

of

par t

t he

af ter

Tables

of

For

t hese

of

t he

element,

its

name.

9.2.1,

9.2.2

examples.

Names

of

compounds

manganese

Oxidation



T able

ions

Name

9.2.2

Names

containing

Compound

of

compounds

and

nitrogen

Oxidation



T able

ions

Name

9.2.3

Names

containing

Compound

Oxidation

number

number

of

of

of

Mn

manganese(IV)

N

NO

2

nitrogen(II)

NO

4

nitrogen(IV)

oxide

SO 2

of

compounds

and

sulfur

number

4

2

have

charge,

naming

9.2.3

MnO

number

when

This

wit hout

When

number

sulfate( IV)

elements

reason,

name

Name

S

4

sulfur(IV)

oxide

6

sulfur(VI)

oxide

4

sulfate(IV)

ion

6

sulfate(VI)

ion

oxide

2

KMnO 4

7

oxide

SO 3

potassium 2

NO

3

nitrate(III)

ion

SO

5

nitrate(V)

ion

SO

2

3

manganate(VII)

2

NO 3

4

161

Oxidation

numbers

Oxidation–reduction

Redox

Key

!

reactions

and

oxidation

reactions

number

fact f we consider t he loss or gain of electrons and a change in oxidation number,

we Oxidation

is

the

increase

oxidation

number

in

state

its

free

or

of

an

an

in

can

see

a

clear

link

between

t he

two.

the

element

element

in

Whenever

●

a

an

same

time,

atom

forms

atom

its

or

ion

oxidation

loses

electrons

number

it

has

increases.

been

For

oxidised.

example,

At

when

a

t he

sodium

compound.

increases

a

sodium

from

0

to

ion

1.

it

loses

The

one

sodium

electron

atom

has

and

its

been

oxidation

number

oxid ised:



Na

Key

!

oxidation

Reduction

is

the

oxidation

number

in

state

its

free

or

decrease

of

an

an

in

the

Whenever

●

element

element

in

time,

a

its

forms

compound.

a

an

numbers:

atom

oxidation

chloride

decreases

from

0

or

ion

is

Exam

easy

to

reduction

number,

ion

to

it

gains

1.

is

remember

a

you

electrons

decreases.

The

one

it

has

been

example,

electron

chlorine



For

and

atom

its

has

e

reduced.

when

a

t he

same

chlorine

atom

oxidation

been

At

number

reduced:

Cl

(0)

(1)

tip

when

make

it

it

that

decrease

because

anything,

Na

(1)

gains

number

numbers:

By considering t he

It

e

(0)

Cl

oxidation

✔



fact

in

oxidation

you

reduce

is

possible

to

change in oxidation number of each element in a reaction

determine

if

it

is

a

redox

reaction.

f

it

is

a

redox

reaction,

t he

oxidation number of one element will increase and t he oxidation number of

anot her

element

will

decrease.

less

Consider

t he

2Mg(s)

following



O

reaction

(g)

again:

2MgO(s)

2

We

can

write

magnesium

t he

ions

half

and

equation

show

t he

for

t he

oxidation

conversion

number

of

of

each

magnesium

to

below:

2

2Mg(s)

2Mg

(0)

(2)

Looking

atom

We

can

and

at

has

t his,

we

increased

write

show

t he

t he

can

see

from

half

(s)

0



t hat

to

t he

2.

equation

oxidation

4e

for

numbers

oxidation

Magnesium

t he

number

(Mg)

has

conversion

of

of

each

been

magnesium

oxid ised

oxygen

to

oxide

ions

below:

2

O

(g)



2

4e

2O

(0)

Looking

in

t he

(s)

(2)

at

t his,

oxygen

we

can

see

molecule

t hat

has

t he

oxidation

decreased

from

number

0

to

2.

of

each

Oxygen

oxygen

(O

)

has

atom

been

2

reduced

t is impor tant to note t hat in writing t he oxidation number of each element

we

disregard

number

of

a

any

Recognising

Changes

in

electrons.

subscripts

single

atom

redox

oxidation

The

or

or

ion

t he

are

not

numbers

We

element

reactions

number

oxidation

coefcients.

of

of

using

always

are

writing

t he

oxidation

only.

oxidation

brought

elements

in

about

covalent

numbers

by

a

transfer

substances

of

can

also change when t hey react to form ot her covalent substances. For example,

when

hydrogen

and

oxygen

react

2H

(g) 2

oxidation

162

numbers:

(0)

to



form

O

(g) 2

(0)

water:

2H

O(g) 2

(1)

(

2)

Oxidation–reduction

●

The

has

oxidation

increased

reactions

number

from

0

of

to

Oxidation

each

1.

hydrogen

Hydrogen

atom

(H

)

in

has

t he

been

hydrogen

numbers

molecule

oxid ised

2

●

The

oxidation

decreased

number

from

0

to

of

2.

each

oxygen

Oxygen

(O

)

atom

has

in

been

t he

oxygen

molecule

has

reduced

2

Redox

don’t

reactions

involve

which

a

number

by

1)

Write

t he

balanced

2)

Write

t he

oxidation

not

need

ions

3)

5)

to

is

t he

t he

f

t here

which

is

a

no

in

number

t he

which

of

has

increase

in

each

electrons

be

and

also

recognised

an

been

shows

been

a

t hose

using

which

oxid ation

reaction.

in

a

brackets

of

below

elements

in

it.

You

do

polyatomic

reaction.

increase

in

its

oxidation

number.

oxidised.

decrease

in

its

oxidation

number.

This

reduced.

oxidation

number

t he

numbers

during

shows

has

for

element

oxidation

element

which

of

can

equation

unchanged

oxidation

redox

transfer

below.

chemical

element

which

element

decrease

not

remain

a

electrons

outlined

element

Determine

is

steps

of

determine

which

Determine

This

4)

t he

involve

transfer

of

number

anot her

of

one

element

element,

t hen

and

t he

a

reaction

is

reaction.

Examples

1

Determine

been

which

reduced

in

CuO(s)

(2)(

element

t he

H



has

reaction

been

oxidised

between

(g)

Cu(s)

H



2

(0)

2)

and

copper(II)

which

oxide

element

and

has

hydrogen.

O(g) 2

(0)

(1)(

2)

reduced

oxidised

●

The oxidation number of each hydrogen atom in the hydrogen molecule

has increased from 0 to

1. Hydrogen (H

) has been oxidised.

2

2

●

The

oxidation

decreased

2

Determine

reduced

in

from

which

t he

CH

2

to

(g)

of

0.

element

reaction



4

(

number

2O

t he

Cu

ion

Copper(II)

has

been

between

oxide

(g)

t he

CO

2

and

and

(g)

has

oxide

been

which

has

reduced.

has

been

oxygen.

2H



2

(4)(

copper(II)

(CuO)

oxidised

met hane

(0)

4)(1)

in

O(g) 2

2)

(1)(

2)

oxidised

reduced

●

The

has

oxidation

increased

number

from

4

of

to

t he

4.

carbon

atom

Met hane

in

(CH

t he

)

met hane

has

been

molecule

oxid ised.

4

●

The

has

oxidation

decreased

number

from

0

of

to

each

2.

oxygen

Oxygen

atom

(O

)

in

has

t he

been

oxygen

molecule

reduced.

2

3

Determine

whet her

2AgNO

(aq) 3



(1)

Because

t he

following

MgCl

NO

(aq)

is

a

redox

2AgCl(s)



2

(2)(

t he

reaction

ion

1)

remains

(1)(

unchanged

in

1)

reaction

Mg(NO

or

) 3

not.

(aq) 2

(2)

t he

reaction,

i.e.

it

is

one

of

oxygen

in

3

t he

spectator

t he

ion

None

This

do

of

is

t he

not

ions,

not

a

t he

need

to

elements

redox

oxidation

be

has

numbers

of

t he

nitrogen

and

considered.

undergone

a

change

in

oxidation

number.

reaction.

163

Oxidising

and

reducing

agents

Oxidation–reduction

4

Determine

reduced

in

which

t he

Mg(s)

element

reaction

ZnSO



has

been

between

oxidised

and

which

magnesium

and

zinc

(aq)

MgSO

4

(0)

(aq)

been

sulfate.

Zn(s)



4

(2)

has

reactions

(0)

(2)

oxidised

reduced

2

Because

t he

SO

ion

remains

unchanged

in

t he

reaction,

t he

oxidation

4

numbers

of

t he

sulfur

and

oxygen

in

t he

ion

do

not

need

to

be

considered.

The

●

oxidation

Magnesium

number

(Mg)

has

of

t he

been

magnesium

has

increased

from

0

to

2.

oxid ised.

2

The

●

oxidation

from

2

to

0.

number

Zinc

of

each

sulfate

Zn

(ZnSO

ion

)

has

in

t he

been

zinc

sulfate

has

decreased

reduced.

4

Summary

questions

1

Dene

2

Determine

the

a

copper

in

b

sulfur

c

carbon

oxidation

in

and

reduction

oxidation

in

number

terms

of

oxidation

number.

of:

CuO

H

S 2

in

each

of

CO,

CO

,

H

2

d

nitrogen

e

chlorine

in

each

of

NH

,

Mg

3

in

each

of

AlCl

CO 2

N 3

,

and

C

3

H 2

and

NH

2

4

NaClO

and

KClO

3

3

Use

oxidation

reactions.

If

they

oxidised

and

a



Cl

(g)

number

are

the

to

3

determine

redox

reactant

whether

reactions

which

2KI(aq)

has

give

2KCl(aq)



I



3O

(g)

2Al

2

Mg(s)

reactant

are

which

redox

has

been

reduced:

(aq)



O 2

2HCl(aq)

(s) 3

MgCl

(aq)



H

2

d

following

2

4Al(s)

c

the

the

been

2

b

4

Cl

BaCl

(aq)



H

2

SO 2

(aq)

(g) 2

BaSO

4

(s)



2HCl(aq).

4

Objectives

By

the

be

able

end

of

this

topic

you

will

A9.3

n ●

dene

the

reducing

terms

agent

oxidising

dene

in

terms

any

redox

of

●

One

terms

oxidising

in

terms

oxidation

One

This oxidising

as

t he

reactant

as

t he

can

brings

about

oxid ising

brings

occur

simultaneously.

t he

oxidation

of

t he

ot her

reactant.

This

is

reduction

of

t he

ot her

reactant.

This

is

agent

about

reducing

generally

oxidised

and

of

compounds

A



oxidised

can

oxidising

reduction

t he

agent

be

B

symbolised

is

t he

as

reactant

follows,

t hat

has

where

been

A

is

t he

reactant

reduced:

agents

examples

which

and

and

been reducing

oxidation

number

recognise

give

agents

of

known

●

reducing

and ●

agent

reaction,

reactant

known

the

reducing

●

and

and

electrons

●

Oxidising

to:

act

as

agent

both

and

a

B

C



D

reduced

an

reducing

n

t he

above

reaction:

agent

●

describe

oxidising

164

tests

and

to

●

A

●

B

must

have

been

oxidised

by

B.

B

is

t he

oxidising

agent.

identify

reducing

agents.

must

have

been

reduced

by

A.

A

is

t he

reducing

agent.

t hat

has

Oxidation–reduction

Oxidising

Consider

and

t he

2Al(s)

reactions

reducing

example



Oxidising

of

aluminium

(g)

3Cl

agents

2AlCl

2

●

The

in

terms

reacting

of

has

been

wit h

chlorine

each

atom

An

because

has

lost

to

form

an

aluminium

ion

(Al

agents

by

fact

oxidising

the

t hree

3

electrons

Key

!

gas:

(s)

oxidised

reducing

electrons

3

aluminium

and

agent

oxidation

causing

of

an

brings

another

atom

or

about

reactant

ion

in

that

):

reactant

to

lose

electrons.

3

2Al(s)

The

2Al

chlorine

Chlorine

atoms

(Cl

)

is

(s)



brought

t he

6e

about

oxid ising

t his

loss

by

taking

t hese

electrons.

agent

2

●

The

chlorine

gained

one

3Cl

has

been

electron

(g)



reduced

to

form

6e

a

because

chloride

6Cl

each

ion

atom

(Cl

in

t he

molecule

Key

!

):

A

(s)

fact

reducing

agent

brings

about

2

the

The

aluminium

atoms

brought

about

t his

gain

by

donating

Aluminium

(Al)

is

t he

reducing

a

oxid ising

reducing

agent,

agent

Oxidising

t herefore,

causes

and

causes

anot her

reducing

anot her

reactant

to

agents

reactant

gain

in

another

reactant

causing

an

atom

or

ion

in

that

agent. reactant

An

of

t hese by

electrons.

reduction

to

lose

electrons

to

gain

electrons.

and

electrons.

terms

of

oxidation Exam

✔

tip

number

It

Consider

t he

example

of

magnesium

burning

in

oxygen

can

learn

2Mg(s)



O

(g)

(0)

(2)(

agent

2)

to

reduced

magnesium

has

been

oxidised

because

t he

oxidation

number

magnesium

atom

has

increased

from

0

to

2.

confusing

Oxygen

(O

)

is

well

as

reducing

them

know

out

that

electrons

of

to

try

to

oxidation

those

agent.

when

Oxidation

(OIL).

of

An

It

and

oxidising

is

better

needed.

Is

the

oxidising

Loss

agent

of must

each

as

and

work

Y ou

of

The

very

definitions

reduction

oxidised

●

the

2MgO(s)

2

(0)

be

again:

cause

this

loss

by

taking

these

t he

2

electrons.

oxid ising

agent

because

it

is

t he

reactant

t hat

caused

t he

increase

The

oxygen

has

atom

been

reduced

because

t he

oxidation

number

of

has

decreased

An

ion

agent,

anot her

number

of

because

from

it

is

0

t he

to

2.

Magnesium

reactant

t hat

(Mg)

caused

t he

is

of

in

an

t herefore,

atom

or

to

ion

causes

increase.

in

A

anot her

t he

oxidation

reducing

reactant

number

agent

to

of

causes

an

t he

atom

decrease

which

in

CuO(s)

(2)(

reactant

t he



H

is

t he

reaction

oxdising

between

(g)

Cu(s)

2

(0)

2)

agent

and

copper(II)



(0)

H

which

oxide

is

and

the

reducing

this

gain

reducing

by

agent

giving

itself

fact

oxidation

agent

of

brings

another

about

reactant

t he by

causing

the

oxidation

an

atom

ion

in

number

of

hydrogen.

O(g)

or

that

reactant

to

increase

2

(1)(

Is

electrons.

oxidising

the

agent

cause

The

Key

An

reducing

A

or

Examples

Determine

(RIG).

oxidation

!

1

must

electrons.

loses

reactant

Reduction

electrons

t he

decrease

number.

oxid ising

in

agent

that

each

agent

reducing

oxidation

itself

electrons.

know

Gain

oxygen

agent

number. Y ou

●

oxidising

in gains

oxidation

The

2)

reduced

oxidised

Key

! ●

Copper (II)

t he

oxide

hydrogen

atom

to

by

increase

(CuO)

is

causing

from

0

t he

t he

to

oxid ising

oxidation

agent

number

because

of

each

it

hydrogen

A

reducing

reduction

1.

causing ●

Hydrogen (H

fact

oxidised

agent

of

the

brings

another

about

reactant

oxidation

the

by

number

of

) is the reducing agent because it reduced the copper(II)

2

an

atom

or

ion

in

that

reactant

to

2

oxide by causing the oxidation number of the Cu

ion to decrease from decrease

2 to 0.

165

Oxidising

and

reducing

agents

Oxidation–reduction

2

✔

Exam

Determine

reducing

tip

Zn(s) It

is

better

to

work

out

which

agent

H



of

oxidising

t he

SO 2

is

t he

reaction

oxdising

between

(aq)

ZnSO

4

agent

zinc

(aq)



4

and

and

which

sulfuric

H

is

t he

acid.

(g) 2

the (0)

definitions

reactant

in

reactions

agent

(1)

(0)

(2)

and

oxidised

reducing

of

agent

oxidation

need

using

number

the

concept

when

reduced

you

them.

Sulfuric

●

acid

(H

SO 2

If

you

remember

involves

number,

an

an

that

increase

oxidation

in

oxidising

zinc

oxidation

agent

from

this

0

causing

to

)

is

t he

oxid ising

agent

because

it

oxidised

t he

4

t he

oxidation

number

of

t he

zinc

atom

to

increase

2.

must

Zinc

●

cause

by

(Zn)

is

t he

reducing

agent

because

it

reduced

t he

sulfuric

acid

increase. 

by

If

you

remember

that

number,

a

a

decrease

reducing

in

this

oxidation

number

of

each

H

ion

to

decrease

from

1

0.

oxidation

agent

must

3 cause

t he

reduction

to involves

causing

s

iron(III)

oxide

behaving

as

an

oxdising

agent

or

a

reducing

agent

when

decrease.

it

reacts

wit h

Fe

O 2

carbon

(s)

3CO(g)



3

(3)(

monoxide?

2)

(2)(

2Fe(s)

3CO



(g) 2

(0)

2)

(4)(

2)

oxidised

To

determine

t he

carbon

t he

behaviour

monoxide

has

of

iron(III)

been

oxide

oxidised

or

we

need

to

look

to

see

if

reduced.

The carbon monoxide has been oxidised. The iron(III) oxide (Fe

O 2

) is

3

behaving as an oxidising agent because it caused the oxidation number of

the carbon atom in the carbon monoxide (CO) to increase from

Substances

reducing

There

are

agents.

Sulfur

can

behave

as

both

oxidising

and

agents

some

Their

compounds

that

2 to 4.

compounds

behaviour

which

dioxide,

can

which

depends

behave

in

can

on

t his

act

t he

as

bot h

ot her

way

are

oxidising

reactant.

given

and

reducing

Examples

of

two

below.

SO 2

Sulfur dioxide usually acts as a

it

reacts

wit h

SO

(g) 2

reducing agent. This is seen, for example, when

chlorine:

Cl



(g) 2



2H

O(l)

H

2

SO 2

(aq) 4



2HCl(aq)

(0)

(

reduced

by

1)

SO 2

The

sulfur

each

dioxide

chlorine

When

it

sulde,

reacts

sulfur

2H

S(g) 2

(

reduced

atom

in

wit h

a

dioxide



SO

t he

t he

chlorine

chlorine

stronger

behaves

(g)

reducing

as

an

3S(s)

2

by

causing

molecule

agent

oxidising



to

2H

t he

oxidation

decrease

t han

from

itself,

0

such

number

to

as

of

1.

hydrogen

agent:

O(l) 2

(0)

2)

oxidised

by

SO 2

The

sulfur

dioxide

oxidised

t he

hydrogen

sulde

by

causing

t he

oxidation

number of t he sulfur atom in t he hydrogen sulde molecule to increase from

2

166

to

0.

Oxidation–reduction

reactions

Oxidising

and

reducing

agents



Acidified

hydrogen

peroxide,

H

/H

O

2

2

Acidied hydrogen peroxide is hydrogen peroxide solution to which sulfuric

acid

has

been

example,

added.

when

2K(aq) 

(

it

t

usually

reacts

H

O 2

wit h

(aq)

 H

2

behaves

SO 2

oxidising

(aq)



4

hydrogen

oxidation

it

agent.

This

is

seen,

for

2

(g)  K

SO 2

4

(aq)  2H

O(l) 2

(0)

by

H

O

2

When

an

iodide:

1)

oxidised

The

as

potassium

peroxide

number

reacts

of

wit h

oxidised

t he

a

2



ion

stronger

to

t he

potassium

increase

oxidising

from

agent

iodide

1

to

t han

by

causing

t he

0.

itself,

such

as

acidied

potassium manganate(VII), acidied hydrogen peroxide behaves as a

reducing

agent:

2KMnO

(aq)  5H

4

O 2

(aq)  3H

2

SO 2

(aq)

K

4

SO 2

(aq)  5O

4

(g)  2MnSO

2

(7)

reduced

by

H

t he

hydrogen

oxidation

T ests

There

O(l) 2

O

2

The

(aq)  8H

4

( 2)

for

are

chemical

peroxide

number

reduced

of

t he

oxidising

cer tain

in

a

agents

ver y

potassium

manganese

chemicals

reaction

t he

2

to

and

which

distinct

from

reducing

undergo

way,

manganate(VII)

decrease

e.g.

to

by

causing

2.

agents

oxidation

they

7

may

or

reduction

change

to

a

in

a

distinct

colour, they may form a par ticular precipitate or they may give off a par ticular

gas. Chemists use these chemicals to determine whether unknown substances

are oxidising agents or reducing agents. They do this by reacting the unknown

substance with these chemicals and obser ving the products. These chemicals

form

the

basis

of

tests

for

oxidising

agents

and

reducing

agents.

Examples

Potassium

iod ide

Potassium

iod ide

agent.

brown

There

when

because

(

)

is

t he

which

a

t he

solution,

solution

distinct

K (aq)

is

potassium

oxidising

dissolves

used

colour

agent

forming

in

t he

change

iodide

is

laborator y

in

t he

oxidised.

oxidises

t he

a

solution.

brown

to

test

solution

The

colourless

for

from

colour

iodide

an

oxidising

colourless

change

ion

(

)

to

occurs

to

iodine

2

(



(aq)

2

(aq) 2



2e

(0)

1)

oxidised

The

potassium

iodide

is,

itself,

a

reducing

agent.



Acid ied

potassium

manganate(VII)

solution,

H

/KMnO

(aq) 4

Acid ied

test

for

from

The

a

potassium

reducing

purple

colour

to

manganate(VII)

agent.

colourless

change

There

when

occurs

is

a

t he

because

solution

distinct

is

potassium

t he

used

colour

in

t he

change

in

laborator y

t he

manganate(VII)

reducing

agent

reduces

is

to

solution

reduced.

t he

pur ple

2

manganate(VII)

ion

(MnO

)

to

t he

colourless

manganese(II)

ion

(Mn

).

4

2

MnO

(aq)

Mn

(aq)

4

(7)

(2)

reduced

The

acidied

potassium

manganate(VII)

is,

itself,

an

oxidising

agent.

167

Oxidising

and

reducing

agents

Oxidation–reduction

T ests

for

oxidising

Table

9.3.1

chemicals

These



chemicals

T able

9.3.1

Reducing

for

agents

summarises

which

can

are,

t he

be

agents

used

agent

iodide

as

used

Visible

test

Potassium

names

used

t hemselves,

Reducing

agent

reactions

solution

colour

reactants

reducing

to

test

change

is

and

t he

for

changes

to

test

of

for

t he

main

oxidising

two

agents.

agents.

the

when

presence

of

an

oxidising

agent

Explanation

oxidised

Colourless

to

brown

The

(KI(aq))

colourless

iodine

(I

)

iodide

which

ion

(I

dissolves

)

is

oxidised

forming

a

to

brown

2

solution

2

Iron(II)



Figure

9.3.1

Potassium

iodide

sulfate

solution

Pale

green

to

yellow-brown

The

(aq))

to

4

colourless

to

brown

green

iron(II)

ion

(Fe

)

is

oxidised

3

(FeSO

from

pale

turns the

yellow-brown

iron(III)

ion

(Fe

)

when

oxidised

There

are

reactions,

oxidising



T able

several

agent.

9.3.2

Reducing

ot her

alt hough

These

Other

chemicals

t hey

are

are

common

agent

given

sulfide

in

Visible

gas

(H

S(g))

A

which

usually

reducing

is

Hydrogen

not

Table

behave

used

to

as

test

reducing

for

t he

agents

presence

in

of

an

9.3.2.

agents

change

when

agent

Explanation

oxidised

yellow

precipitate

forms

Yellow

insoluble

sulfur

(S)

is

2

produced

Concentrated

hydrochloric

acid

A

yellow-green

gas

is

evolved

Yellow-green

chlorine

gas

(Cl

)

2

is

(HCl(aq))

Others:

hydrogen

gas

(H

);

carbon

(C);

carbon

monoxide

(CO);

reactive

produced

metals

2

T ests

for

reducing

Table

9.3.3

chemicals

These



summarises

which

chemicals

T able

9.3.3

Oxidising

agents

can

are,

used

agents

for

test

potassium

manganate(VII)

as

used

and

t he

colour

reactants

oxidising

to

Visible

is

Acidified

names

used

t hemselves,

Oxidising

agent

t he

be

test

for

change

changes

to

test

of

for

t he

main

reducing

two

agents.

agents.

the

presence

when

agent

of

a

reducing

agent

Explanation

reduced

Purple

to

colourless

solution

The

manganate(VII)

purple

(MnO

)

is

reduced

to

ion

the

4



(H

/KMnO

(aq))

colourless

manganese(II)

ion

4

2

(Mn

Acidified

potassium

dichromate(VI)

Orange

to

green

)

The

orange



solution

(H

dichromate(VI)

ion

2

/K 2

Cr 2

O

(aq))

(Cr

7

2

O

)

is

reduced

to

the

7

3

green



Figure

9.3.2

(a)

manganate( VII)

colourless

potassium

orange

to

Acidied

turns

when

purple

reduced.

dichromate( VI)

green

potassium

from

when

(b)

to

Acidied

turns

from

reduced

(a)

168

(b)

chromium(III)

ion

(Cr

)

Oxidation–reduction

reactions

Oxidising

and

reducing

agents

There are several ot her chemicals which behave as oxidising agents, alt hough

t hey

are



are

not

given

T able

in

usually

Table

9.3.4

Oxidising

used

to

Other

common

oxidising

agent

sulfate

for

t he

presence

of

a

reducing

agent.

These

9.3.4.

Visible

is

Iron(III)

test

solution

agents

change

when

agent

Explanation

reduced

Yellow-brown

to

pale

green

The

yellow-brown

iron(III)

ion

3

(Fe

(SO

2

)

4

(aq))

)

(Fe

is

reduced

to

the

pale

3

2

green

Dilute

or

(HNO

(aq))

concentrated

nitric

acid

A

brown

gas

is

evolved

Brown

(NO

3

Hot

iron(II)

)

ion

(Fe

nitrogen

is

)

dioxide

gas

produced

2

concentrated

sulfuric

acid

A

pungent

gas

is

evolved

Sulfur

dioxide

gas

(SO

)

is

2

H

SO

2

(l))

which

turns

acidified

potassium

produced

4

manganate(VII)

Others:

sodium

chlorate( )

solution

(NaClO);

oxygen

colourless

gas

(O

);

chlorine

gas

(Cl

2

T o

investigate

Your

teacher

the

may

reactions

use

this

activity

●

observation,

recording

●

analysis

interpretation.

Y ou

will

be

and

supplied

dichromate( VI),

with

and

oxidising

to

manganese(IV)

oxide

(MnO

)

2

agents

and

reducing

agents

assess:

reporting

aqueous

potassium

of

);

2

iodide,

solutions

iron( II)

of

acidied

sulfate

and

potassium

acidied

manganate( VII),

hydrogen

peroxide

acidied

and

ve

potassium

test

tubes.

Method

3

1

Place

2 cm

solution,

of

acidied

shaking

as

potassium

you

add

the

manganate( VII)

solution,

until

solution

you

see

no

into

the

further

rst

test

colour

tube.

Slowly

add

3

2

Place

potassium

iodide

change.

3

2 cm

of

acidied

potassium

manganate( VII)

solution

into

the

second

test

tube,

2 cm

of

acidied

potassium

3

dichromate( VI)

iron(II)

as

sulfate

you

add

3

Record

in

4

Explain

the

T ables

5

Dene

a

2

In

in

and

on

the

each

of

reducing

into

the

the

until

original

for

9.3.3

the

third

fth

you

behaviour

tube.

see

colour

colour

above

tube,

to

of

Slowly

no

of

the

2Fe

b

2NO(g)

each

O

Give

an

agent

acidied

colour

you

iodide

solution

hydrogen

into

peroxide

the

fourth

solution

to

tube

each

and

2 cm

tube,

of

shaking

change.

and

the

observed

hydrogen

nal

in

colour

each

after

reaction.

mixing.

Use

the

information

given

in

peroxide.

questions

of

the

oxidising

agent

and

b

electrons

following

reactions

reducing

in

terms

identify

the

(s)

agent

of

oxidation

oxidising

number.

agent

and

the



3C(s)

3CO

(g)



4Fe(s)

2



2CO(g)

N

(g)



2CO



2HCl(aq)

(g) 2

MgCl

(aq)



H

2

3

add

solution

that

acidied

3

Mg(s)

potassium

you.

2

c

of

further

change

help

3

2 cm

agent:

a

2

the

terms

terms

the

reason

9.3.1

into

solution,

table

Summary

1

solution

the

a

Comment

solution

example

and

as

a

of

a

compound

reducing

which

(g) 2

can

act

both

as

an

oxidising

agent.

169

Oxidising

and

reducing

agents

Oxidation–reduction

Key

●

concepts

We

encounter,

our

of

ever yday

fr uits,

and

lives.

and

breat halyser

make

We

make

use

Oxidation–reduction

●

Many

●

Oxid ation

state

or

an

or

an

Oxidation

oxidation

●

dened

element

is

of

t hem

and

involve

as

in

dened

element

oxidation

t hem

in

in

and

reduction

r usting

bleaches,

food

and

reactions

t he

in

browning

preser vation

and

t he

a

t he

a

a

known

transfer

loss

of

of

as

redox

reactions

electrons.

electrons

by

an

element

in

its

free

compound.

as

in

are

t he

gain

of

electrons

by

an

element

in

its

free

compound.

reduction

can

also

be

dened

using

t he

concept

of

number.

Oxid ation

would

of,

reactions

reactions

is

Reduction

state

●

redox

use

encounter

test.

●

●

reactions

number

have

containing

if

it

all

t he

were

is

t he

t heoretical

bonds

ionic

between

and

t he

charge

t he

t hat

atoms

compound

in

was

an

atom

t he

of

an

element

compound

composed

entirely

of

ions.

●

n

any

redox

numbers

●

Oxid ation

in

●

its

free

free

An

is

A

oxid ising

●

An

●

A

●

An

will

always

be

a

change

in

t he

oxidation

an

an

as

an

as

a

is

t he

in

a

in

a

in

oxidation

number

of

an

element

compound.

decrease

element

agent

increase

element

in

oxidation

number

of

an

element

reactant

t hat

brings

about

t he

oxidation

of

agent

is

t he

reactant

t hat

brings

about

t he

reduction

of

reactant.

oxidising

reducing

agent

agent

oxidising

causes

causes

agent

t he

t he

causes

ot her

ot her

t he

reactant

reactant

oxidation

to

to

lose

gain

number

electrons.

electrons.

of

anot her

element

to

increase.

●

A

reducing

agent

causes

t he

oxidation

number

of

anot her

element

to

decrease.

●

The

distinctive

reduction

when

●

●

of

to

for

for

170

a

presence

iron (II)

presence

potassium

of

changes

are

t hat

compounds

and

t he

dichromate(VI)

presence

t he

iodide

test

Acidied

colour

cer tain

testing

Potassium

used

in

compound.

reactant.

reducing

anot her

or

dened

or

t here

elements.

dened

is

state

anot her

●

reaction

two

state

Reduction

its

●

of

of

accompany

allow

sulfate

of

an

reducing

agent.

are

or

agents

and

reducing

to

or

be

used

agents.

agents

which

can

be

agent.

acidied

which

oxidation

compounds

reducing

oxidising

manganate (VII)

oxidising

t hese

oxidising

t he

can

be

potassium

used

to

test

for

t he

Oxidation–reduction

reactions

Practice

8

Practice

exam-style

n

t he

following



4HNO

is:

a

gain

of

oxygen



a

gain

of

electrons



a

decrease

A



only

B



and

C

,

D



in

B

oxidation

number

C



D

only

following

undergoes

Copper

)

(aq)

statements

oxidation

A

2

B

4

C

6

D

8

number

of

sulfur

in

t he

O

S

ion

Copper

Copper

n

its

oxidation

tr ue?

oxidation

and

its

oxidation

reduction

and

its

oxidation

oxidation

and

its

oxidation

increases.

undergoes

increases.

experiments,

acidied

acidied

following

obser ved

solutions

sulfur

of

potassium

pairs

in

Colour

dioxide

potassium

name

of

t he

BrO

ion

was

bubbled

dichromate(VI)

t he

of

manganate(VII).

correctly

describes

t he

Which

colour

of

t he

changes

experiment?

potassium

Colour

of

potassium

manganate(VII)

is: A

orange

to

green

colourless

B

orange

to

green

pur ple

C

green

to

orange

colourless

D

green

to

orange

pur ple

to

pur ple

bromite(I)

bromate(I)

C

bromite(V)

to

colourless

to

to

pur ple

colourless

bromate(V)

10

4

is

and

3

and

B

D

copper

O(l)

2

decreases.

undergoes

separate

into

is:

3

A

about

2H



reduction

d ichromate(VI)

The

(g)

2

only

2

3

2NO



2

decreases.

undergoes

number



9

The

t he

number

2

2

of

Copper

number

and

Cu(NO

3

number





(aq)

questions A

Oxidation

reaction:

3

which

1

questions

questions Cu(s)

Multiple-choice

exam-style

Consider

t he

When

acidied

hydrogen

peroxide

solution

is

added

to

following: iron(II)

sulfate

solution:

2

M(s)

n

t he

reaction

represented



has

been



has

increased



has

A



only

B



and

C



D

,



above,

metal

M:

oxidised

gained

and

(aq)

M

in

oxidation

number

5

6

and

Which

of

t he

C

t he

oxidation

D

t he

acidied

Structured

following

causes

an

B

t

causes

a

C

ts

D

t

increase

loss

oxidation

which

iron(II)

green

solution

ion

is

number

formed

of

hydrogen

to

t he

t he

iron(III)

iron(II)

peroxide

is

ion

ion

decreases

acting

as

a

agent

question

a

The

gure

and

mineral

below

shows

t he

of

is

tr ue

in

about

oxidation

a

reducing

supplement

information

agent?

has

been

label

bottle.

on

a

multivitamin

lef t

Much

of

t he

out.

number.

electrons.

number

increases.

electrons.

of

t he

following

reactions

does

t he

oxidation

Each

number

is

oxidised



t

n

pale

only

A

gains

t he

electrons

11



a

B

reducing

only



A

of

nitrogen

show

t he

greatest

tablet

contains

increase? ……………………………

A

2NO(g)



(g)

O

2NO

2

B

4NO

(g)



O

2

(g)

2

(g)



2H

2

……………………………

O(l)

4HNO

2

(aq)

……………………………

3

Potassium

C

N

(g)



3H

2

(g)

2NH

2

iodide

0.1 mg

(g)

3

……………………………

D

2NH

(g)



3CuO(s)

N

3

(g)



3Cu(s)



3H

2

O(l)

2

……………………………

7

Which

A

of

t he

2Na(s)



following

2H

reactions

O(l)

is

not

a

redox

2NaOH(aq) 

H

2

B

Fe(s)

C

MgO(s)



FeCl

(aq)



2

H

SO

2

A

(g)

(aq)

H

(g)

A

2

MgSO

4

(aq)

4



H

C(s)



O

(g)

2

and

mineral

supplement

bottle

solution

hydrogen

O(l)

CO

is

made

of

peroxide

is

one

of

added

t he

to

tablets

t he

and

acidied

solution.

2

i) D

multivitamin

2

2HCl(aq)



reaction?

State

what

you

would

expect

to

obser ve.

(1

mark)

(g)

2

ii)

Write

an

ionic

half

equation

to

represent

reaction.

iii)

Wit h

a

b

Three

(2

reason,

represents

redox

t he

state

whet her

oxidation

reactions

are

or

t he

marks)

reaction

reduction.

represented

by

(1

mark)

t he

171

Practice

exam-style

questions

equations

given

substance

which

give

t he

reason

Oxidation–reduction

below.

has

for

For

been

your

EACH

reaction,

oxidised.

choice

n

based

name

EACH

on

t he

case,

oxidation

number.

i)

Zn(s)



2HCl(aq)

ZnCl

(aq)



H

2

(g)

2

(2

2

ii)

2Fe

marks)

3

(aq)



Cl

(g)

2Fe

(aq)



2Cl

(aq)

2

(2

iii)

(g)

2NH



3CuO(s)

N

3

(g)



marks)

3Cu(s)

2



3H

O(l)

2

(2

c

One

type

of

potassium

i)

For

t he

breat halyser

dichromate(VI)

what

pur pose

is

test

uses

marks)

acidied

cr ystals.

t he

breat halyser

test

used?

(1

ii)

Describe

t he

iii)

test

what

is

Explain

Using

would

obser ve

if

t he

t he

(1

chemistr y

oxidation

involved

in

(2

suggest

a

name

for

ion.

ClO

of

mark)

t he

test.

number,

mark)

result

positive.

breat halyser

d

you

marks)

t he

(1

mark)

2

Total

Extended

12

a

Dene

i)

ii)

b

response

oxidation

15

question

in

terms

of:

electrons

oxidation

Suppor t

Cl

number.

EACH

reference

to

(g)

t he



(2

denition

given

following

2Br

in a

above

marks)

by

reaction:

(aq)

2Cl

(aq)



Br

2

(g)

2

(4

c

‘Metals

are

oxidising

Use

your

reducing

agents

and

non-metals

marks)

are

agents.’

EACH

whet her

i)

marks

of

t he

t he

answers

2PbO(s)

reactions

above

based



below

statement

on

is

oxidation

C(s)

to

determine

tr ue.

Pb(s)

Give

reasons

for

number.



CO

(g)

2

(2

ii)

The

reaction

sulfate

d

You

are

an

respectively.

Describe

what

and

wit h

are

two

agents

tests

told

you

about

bottles

agent

are

a

and

carr y

Y.

X

Y

agent,

liquids.

out

to

conrm

(4

Total

172

marks)

and

reducing

colourless

could

X

labelled

and

marks)

copper(II)

(3

oxidising

Bot h

T WO

you

magnesium

solution.

provided

containing

between

marks)

15

marks

reactions

A10

Electrochemistry

is

Electrochemistry

the

study

of

the

relationship Objectives

between

An

chemical

reactions

electrochemical

reaction

and

is

electrical

one

which

energy.

By

the

be

able

electrical

energy

or

requires

electrical

energy

give

of

in

order

in

a

to

proceed.

From

the

reactions

that

to

produce

an

electrolysis

of

aluminium

electric

current,

the

the

to

to

the

is

important

in

produce

our

you

electrochemical

determine

reaction

will

series

metals

if

a

will

and

displacement

occur

their

between

compounds

aluminium, based

electrochemistry

topic

common

metals

oxide

this

occur ●

battery

of

to:

either

●

produces

end

lives.

on

positions

their

in

relative

the

electrochemical

series

●

determine

displace

A10.1

The

electrochemical

if

a

metal

hydrogen

on

its

position

electrochemical

electrochemical

series

of

an

acid

series based

The

will

from

in

the

series

metals ●

give

the

electrochemical

series

n Unit 5.2 you learnt t hat when atoms bond ionically, t he metal atom always of

loses

electrons

to

form

a

positive

metal

cation.

Some

metals

lose

more

easily

t han

ot hers.

When

metals

are

placed

in

order

of

ease

t hey

lose

electrons,

i.e.

ease

wit h

which

t hey

ionise,

a

series

determine

known

A

electrochemical

section

of

t he

series

of

metals

electrochemical

is

if

a

displacement

will

occur

non-metals

The

10.1.1.

more

forms.

which

back

are

at

to

easy

metals

when

t his

easily

Metals

conver t

Since

n

t hey

a

table,

metal

t he

top

atoms.

to

lose

react

t he

series

atom

of

t he

Metals

conver t

of

t he

common

ionisation

ionises,

at

t he

to

metals

is

given

their

compounds

their

relative

t he

form

increases

more

ver y

bottom

stable

stable

of

t he

going

are

ions

series

based

positions

in

on

the

in

series.

upwards.

t he

ions

which

form

are

t hat

hard

unstable

it

to

ions



T able

series

10.1.1

of

the

The

electrochemical

common

metals

atoms.

when

ot her

of

series

back

electrons

wit h

ease

and

created.

electrochemical

Table

between

as certain

t he

non-metals

wit h reaction

which

common

electrons ●

much

some

t hey

ionise,

substances,

i.e.

t hey

t hey

act

give

as

reducing

electrons

to

agents

t he

Metal

Cation

potassium

K

calcium

Ca

sodium

Na

magnesium

Mg

aluminium

Al

zinc

Zn

iron

Fe

lead

Pb

hydrogen

H

copper

Cu

silver

Ag



ot her 2

reactant.

The

more

easily

t hey

give

electrons,

t he

stronger

t heir

reducing 

power.

The

strengt h

as

a

reducing

agent,

t herefore,

increases

going

up

2

t he

series.

3

Potassium

is

highest

in

t he

series,

which

means

t hat

it

ionises

t he

most

2

easily,

forms

t he

most

stable

ions

and

is

t he

strongest

reducing

agent.

Silver

is

t he lowest in t he series, which means t hat it ionises t he least easily, forms t he

least

stable

ions

and

is

t he

weakest

reducing

2

agent. 2

We

can

make

chemical

use

of

t he

electrochemical

series

of

metals

to

predict

cer tain



reactions. 2



Displacement

A

met al

from

a

met al

ions

of

t he

been

displace

compound

is

of

will

a

stronger

t he

lower

lower

of

a

metals

met al

t hat

cont aining

reducing

met al.

met al

are

As

is

t he

agent,

a

it

in

met al.

t herefore,

result,

conver ted

below

lower

t he

to

electroc hemical

readily

higher

atoms,

t he

This

is

gives

met al

i.e.

t he

because

are

and

said

ser ies

higher

electrons

ionises

ions

t he

to

t he

to

t he

ions

have

d ischarged

173

The

electrochemical

series

Electrochemistry

Examples

1

Will

a

reaction

copper(II)

occur

sulfate

Magnesium

is

magnesium

can

Magnesium

is

if

a

strip

of

magnesium

ribbon

is

placed

in

solution?

higher

t han

copper

in

t he

electrochemical

series,

t herefore,

2

a

displace

stronger

t he

Cu

ions

reducing

from

agent,

t he

copper(II)

t herefore,

it

2

t he

Cu

ions

The

magnesium

d ischarged

Mg(s)



forming

CuSO

ionises

copper

(aq)

ionic

equation

MgSO

Mg(s)

copper(II)

sulfate

to



2

Mg

ions

and

t he

Cu

(aq)



Cu(s)

4

is:

2

blue

forming

atoms:

4

The

electrons

2

ions.

are

gives

sulfate.

Cu

2

(aq)

Mg

(aq)



Cu(s)

solution

The

transfer

of

electrons

is

shown

in

t he

ionic

half

equations:

magnesium

2

Mg(s)

Mg

(aq)



2e

2

Cu

colourless

As

t he

●

The

(aq)



reaction

2e

Cu(s)

proceeds

magnesium

t he

ribbon

following

gradually

are

gets

obser ved:

smaller

as

it

ionises

and

t he

magnesium 2

sulfate

pink



Figure

10.1.1

Mg

solution

copper

Magnesium

is

added

to

ions

●

A

●

The

pink

dissolve

solid

blue

in

builds

colour

of

t he

up

in

t he

solution.

t he

solution

copper (II)

as

copper

sulfate

is

solution

formed.

gradually

fades

as

2

copper( II)

sulfate

t he

solution

2

Will

a

blue

Cu

reaction

ions

occur

are

if

discharged

some

iron

from

lings

t he

are

solution,

placed

in

a

forming

solution

copper.

of

zinc

nitrate?

ron is

lower

than zinc in the electrochemical series.

Displacement

of

No

reaction will occur.

hydrogen



Metals

above

ions

an

in

hydrogen

acid,

in

forming

t he

electrochemical

hydrogen

gas

(H

).

series

Metals

will

below

displace

hydrogen

t he

will

H

not

2



displace t he H

ions. Metals above hydrogen are stronger reducing agents and



will

readily

give

electrons

to

t he

H

ions

of

t he

acid.

Metals

below

hydrogen



are

weaker

reducing

agents,

so

will

not

reduce

t he

H

ions.

Examples

1

Will

Zinc

a

reaction

is

higher

occur

t han

if

zinc

is

hydrogen

placed

in

t he

in

hydrochloric

electrochemical

acid?

series,

t herefore,



zinc

can

displace

t he

H

ions

from

t he

hydrochloric

acid.

Zinc

is

a



stronger

reducing

agent,

t herefore,

it

gives

2

zinc

ionises

hydrogen

forming

gas

(H

Zn

electrons

to

t he

H

ions.

The



ions

and

t he

H

ions

are

d ischarged

forming

): 2

Zn(s)



2HCl(aq)

ZnCl

(aq)



H

2

The

ionic

equation

is:



Zn(s)



2H

(g) 2

2

(aq)

Zn

(aq)



H

(g) 2

The

transfer

of

electrons

is

shown

in

t he

ionic

half

equations:

2

Zn(s)

Zn

(aq)



2e



2H

(aq)



2e

H

(g) 2

2

Will

a

reaction

Copper

will

174

is

lower

occur.

occur

t han

if

some

copper

hydrogen

in

turnings

t he

are

placed

electrochemical

in

sulfuric

series.

No

acid?

reaction

Electrochemistry

The

The

electrochemical

When

non-metal

electrons

to

electrons

atoms

form

much

a

series

bond

ionically,

negative

more

easily

of

series

non-metals

t he

non-metal

t han

electrochemical

ot hers.

non-metal

anion.

When

atom

Some

always

gains

non-metals

non-metals

are

gain

placed

in

order of ease wit h which t hey gain electrons, i.e. ease wit h which t hey ionise,

a

A

series

known

section

Table

The

of

10.1.2.

easier

forms.

hard

t he

n

a

electrochemical

t his

ions,

when

at

back

which

non-metals

agents

table,

non-metal

conver t

unstable

electrochemical

t he

Non-metals

to

Since

as

are

ease

atom

t he

to

gain

t hey

t he

top

of

t he

to

wit h

of

t he

some

at

stable

ver y

t he

to

t hey

is

created.

non-metals

increases

form

back

when

non-metals

more

series

conver t

ot her

of

ionisation

Non-metals

electrons

react

series

of

ionises,

atoms.

easy

series

going

are

stable

bottom

is

t he

ions

ions,

of

given

in

t he

t hat

which

series

substances,

t hey

i.e.

t hey

act

as

are

form

oxid ising

remove

T able

10.1.2

of

The

some

electrochemical

non-metals

Non-metal

Anion

fluorine

F

chlorine

Cl

bromine

Br

iodine

I

it

atoms.

ionise,



series

upwards.

electrons

from t he ot her reactant. The more easily t hey remove electrons, t he stronger

t heir oxidising power. The strengt h as an oxidising agent, t herefore,

going

up

t he

Fluorine

forms

lowest

least

We

is

t he

in

can

cer tain

highest

most

t he

stable

in

series,

ions

make

and

use

chemical

non-metal

series

from

higher

will

a

t he

stable

series,

ions

and

which

is

of

t he

which

is

t he

means

weakest

t he

means

t hat

strongest

t hat

it

ionises

oxidising

electrochemical

it

ionises

oxidising

t he

t he

agent.

least

most

easily,

odine

easily,

is

forms

t he

t he

agent.

series

of

non-metals

to

predict

reactions.

Displacement

A

increases

series.

of

non-metals

displace

compound

non-metal

is

a

a

non-metal

containing

stronger

which

the

is

lower

oxidising

below

it

in

the

non-metal.

agent,

electrochemical

This

therefore,

is

because

readily

the

removes

electrons from the ions of the lower non-metal. As a result, the higher non-metal

ionises, and the ions of the lower non-metal are discharged forming atoms.

Examples

1

Will

a

reaction

occur

if

chlorine

gas

is

bubbled

into

sodium

iodide

solution?

Chlorine is

higher

than iodine in the electrochemical series of non-metals,

therefore, chlorine can displace the 

ions from the sodium iodide.

Chlorine is a stronger oxidising agent, therefore, it removes electrons from

the 

ions. The chlorine

discharged

ionises

forming iodine (

forming Cl

ions and the 

ions are

): 2

Cl

(g)



2Na(aq)

2NaCl(aq)



2

The

ionic

equation

(g)



2

is:

(aq)

2Cl

(aq)

2





(aq) 2

transfer

Cl

(aq) 2

Cl

The



(g)

of



electrons

2e

is

shown

2Cl

in

t he

ionic

half

equations:

(aq)

2

2

(aq)



(aq)



2e

2

175

Electrical

conduction

Electrochemistry

2

Will

a

reaction

potassium

Bromine

will

If

is

lower

zinc

is

Explain

b

Give

c

a

What

the

able

end

of

occur:

topic

you

the

b

silver

c

iodine

d

bromine

Which



chlorine

a

solution

reaction

added

to

a

solution

of

in

t he

electrochemical

series.

No

reaction

of

copper( II)

nitrate,

a

reaction

occurs.

occurs.

chemical

of

metal

lead(II)

equation

colour

of

and

a

balanced

ionic

equation

for

the

copper( II)

nitrate

solution?

Explain

to

in

of

the

a

displacement

reaction

solution.

electrochemical

zinc

when

three

series

will

release

hydrogen

acid?

displace

occurred

Arrange

not

solution

iodide

the

to

or

solution

hydrochloric

found

whether

solution

chloride

metals

was

ease

nitrate

potassium

added

predict

nitrate

sodium

displacement

of

the

following,





the

X

to

calcium



when

A10.2

this

of

aluminium

order

be

is

occurs.

a

solution.

By

in

a

happens

will

no

Objectives

why

this

each

A

solution

questions

balanced

For

gas

4

bromine

reaction.

why

3

t han

placed

a

the

2

if

occur.

Summary

1

occur

chloride?

it

from

was

metals,

X,

zinc

added

zinc

nitrate

to

and

solution

magnesium

magnesium

in

but

nitrate

decreasing

ionisation.

Electrical

conduction

will

n

Unit

5

you

learnt

t hat

in

order

for

a

substance

to

conduct

an

electric

to:

current, it must contain charged par ticles which are able to move t hrough t he

●

distinguish

conductor

between

and

a

a

substance.

non-

can

conductor

●

distinguish

between

electrolytic

distinguish

electrolyte,

and

a

give

Conductors

between

a

weak

a

strong

can

include

electrolyte

examples

electrolytes,

be

are

substances

solids,

metals,

compounds

of

can

based

be

on

eit her

t heir

electrons

ability

or

ions.

to

conduct

to

pass

Materials

an

electric

liquids

which

graphite,

and

aqueous

or

allow

solutions.

electricity

molten

acids

ionic

and

Examples

of

t hrough.

compounds,

conductors

solutions

of

ionic

alkalis.

Non-conductors

are

substances

which

do

not

allow

an

electric

current

strong

weak

pass

t hrough.

Non-conductors

can

be

solids,

liquids,

solutions

electrolytes

and

gases.

Examples

of

non-conductors

include

non-metals

(except

non-electrolytes.

graphite),

176

par ticles

groups

non-electrolyte

to

and

two

metallic

●

●

charged

into

conduction

They

●

These

classied

current.

●

and

be

plastics,

covalent

substances

and

solid

ionic

compounds.

Electrochemistry

T o

Electrical

investigate

the

electrical

conductivity

of

conduction

various

substances Circuit

1 switch

Your

teacher

may

●

observation,

●

manipulation

Y ou

will

be

sulfate

a

and

e.g.

hydrochloric

with

rod,

and

to

assess:

reporting

circuit

wire,

a

sodium

acid,

activity

A

measurement.

copper

graphite

crystal,

this

recording

supplied

substances,

crystal,

use

components,

magnesium

plastic

chloride

ethanol

and

ruler,

a

samples

ribbon,

sodium

solution,

of

various

aluminium

chloride

copper( II)

foil,

crystal,

sulfate

an

a

iodine

copper( II)

solution,

solid

to

be

tested

dilute

kerosene.

Circuit

2

Method

1

switch

Draw

up

a

table

‘Prediction’

with

and

three

‘Results’.

columns

In

the

headed

rst

‘T est

column

substance’,

write

down

the

name

of A

each

test

column

a

substance

ll

in

your

that

you

prediction

have

of

been

whether

supplied

the

with.

substance

In

is

the

a

second

conductor

or

non-conductor. beaker

2

Connect

the

circuit

as

shown

in

Figure

10.2.1.

If

the

test

substance

is

a carbon

solid

use

Circuit

1

and

if

it

is

a

solution

or

a

liquid

use

Circuit

electrodes

2.

solution

3

Record

4

Compare

the

results

of

your

experiment

in

the

third

column

of

your

to

table.



your

predictions

with

the

Figure

10.2.1

When

and

ionic

created

electrolytic

compounds

contains

ions

melt

and

of

a

solid

and

to

a

test

the

liquid

conduction

or

is

circuits

tested

results.

conductivity

Metallic

T wo

be

dissolve

known

in

as

water,

an

t he

liquid

electrolyte.

or

solution

Electrolytes

are

conductors.

There

are

cer tain

differences

between

conduction

in

a

metal,

known

Key

! as

metallic

electrolytic

conduction ,

and

conduction

in

an

electrolyte,

known

An

conduction

electrolyte

that

forms

aqueous

Metallic

n

a

fact

as

ions

is

a

compound

when

molten

or

in

solution.

conduction

metal,

t he

delocalised

valence

electrons,

electrons

known

as

of

t he

mobile

atoms

are

electrons,

delocalised.

are

able

to

These

move

t hroughout t he metal. Metals are able to conduct an electr ic cur rent because

t hese mobile electrons

is

of

a

non-metal,

delocalised,

During

ionic

an

can move t hroughout t he metal. Alt hough graphite

conducts

an

electrons

(see

conduction,

t he

electr ic

Unit

metal

cur rent

because

of

t he

presence

5.5).

remains

chemically

unchanged

conduction

ionic

bonds

also

mobile

metallic

Electrolytic

When

it

and

compound

t hey

melts,

become

free

t he

to

ions

move

are

no

longer

t hroughout

t he

held

toget her

by

liquid:

heat 

NaCl(s)

Na

(l)



Cl

(l)

177

Electrical

conduction

Electrochemistry

Similarly, when an ionic compound dissolves in water, t he ionic bonds break

and

t he

ions

are

free

to

move

t hroughout

t he

solution:

water 

NaCl(s)

These

of

Na

electrolytes

mobile

ions

(aq)

conduct

which

are



Cl

an

able

(aq)

electric

to

current

move

because

t hroughout

t he

of

t he

liquid

presence

or

aqueous

solution.

During

electrolytic

chemically



T able

10.2.1

Metallic

Mobile

through

The

Metallic

electrons

the

metal

electrolyte

and

electrolytic

conduction

carry

remains

can

is

decomposed,

i.e.

it

is

the

electric

current

Mobile

the

chemically

of

an

between

ions

Strong

electrolytes

Strong

electrolytes

strong

of

in

t he

are

alkalis

concentration

unchanged

The

ions

conduction

carry

the

electric

current

through

electrolyte

electrolyte

decomposes

electrolyte

distinguish

of

compared

Electrolytic

metal.

concentration

acids,

t he

conduction

Strength

We

conduction,

changed.

fully

and

ions

strong

in

and

weak

electrolytes

based

on

t he

electrolyte.

ionised

soluble

solution.

when

ionic

For

dissolved

in

compounds.

water,

These

e.g.

have

strong

a

high

example:



HCl(aq)

Molten

Weak

Weak

e.g.

H

ionic

(aq)

compounds



are

Cl

also

(aq)

classied

as

strong

electrolytes.

electrolytes

electrolytes

weak

solution.

acids

For

and

are

only

weak

parti ally

alkalis.

These

ionised

have

a

when

low

dissolved

concentration

in

of

water,

ions

example:



CH

COOH(aq)

CH

3



T able

10.2.2

Examples

Strong

Acids

COO

(aq)



H

(aq)

3

of

electrolytes

electrolytes

Hydrochloric

acid

Weak

(HCl(aq))

electrolytes

Carbonic

acid

(H

CO

2

Nitric

acid

(HNO

(aq))

Ethanoic

3

Sulfuric

acid

(H

Alkalis

Potassium

Sodium

Salts

Molten

Sodium

Molten

hydroxide

178

solution

solution

(NaOH(aq))

(NaCl(aq))

bromide

bromide

(KOH(aq))

(NaCl(l))

solution

potassium

Potassium

(aq))

chloride

chloride

COOH(aq))

4

hydroxide

sodium

(CH 3

SO

2

acid

(aq))

3

(KBr(l))

solution

(KBr(aq))

Aqueous

ammonia

(NH 3

(aq))

in

Electrochemistry

Strong

Electrolysis

electrolytes

are

much

better

electrical

conductors

t han

weak

Summary

questions

electrolytes. The strengt h of an electrolyte can be tested wit h a simple circuit

which

has

a

light

bulb

(or

light

emitting

diode

(LED))

connected

to

a

batter y

1

and

two

electrodes

which

are

dipped

in

t he

electrolyte.

The

greater

Distinguish

a strengt h

of

t he

electrolyte,

t he

more

brightly

t he

bulb

will

between:

t he a

conductor

and

a

non-

glow. conductor

A

non-electrolyte

liquid

any

state

ions.

or

is

a

substance

dissolved

in

Non-electrolytes

which

water.

are

The

remains

liquid

or

non-conductors.

as

molecules

solution

Examples

when

does

of

not

in

the

b

metallic

contain

and

electrolytic

conduction

non-electrolytes

c

a

strong

and

a

weak

include liquids such as kerosene and gasoline, molten covalent substances such electrolyte.

as

wax

and

solutions

of

covalent

substances

such

as

ethanol

and

glucose.

2

Classify

as

Pure

water

a

each

strong

weak

of

the

following

electrolyte,

electrolyte

or

a

a

non-

electrolyte:

Pure

water

is

an

extremely

weak

electrolyte.

Water

undergoes

spontaneous



ionisation

into

H

ions

and

OH

ions.

At

any

one

time,

approximately

one

a

potassium

b

a

c

aqueous

d

kerosene

e

aqueous

chloride

solution

8

in

ever y

5.56



10

water

molecules

is

ionised:

solution

of

sucrose

ethanoic

in

water

acid



H

O(l)

H

(aq)



OH

(aq)

2



7

The concentration of H

ions and OH

As

next

you

will

learn

in

t he

unit,

ions in pure water is 1  10

t his

is

of

par ticular

3

mol dm

signicance

when

.

3 electric

current

is

passed

t hrough

an

aqueous

When

an

Why

is

pure

decomposed

current

into

is

simpler

passed

t hrough

substances,

i.e.

an

it

electrolyte,

undergoes

a

t he

electrolyte

chemical

is

By

the

be

able

as

end

takes

electrolytic

A

dene

batter y

or

place

cell

has

ot her

in

a

piece

three

d.c.

of

main

power

apparatus

known

as

an

electrolytic

cell.

●

components.

the

Two

electrodes

you

will

terms

electrolysis,

supply

t hat

connected,

via

wires,

to

provides

t he

take

t he

electric

current

into

and

out

ions

anion

present

and

cation

in

electrolytes

t he

electric

current.

●

batter y

or

power

predict

of

t he

will

the

electrode

drift

during

to

which

an

electrolysis

supply,

●

which

topic

cathode,

identify

ion ●

this

electrolysis

Electrolysis

●

of

to:

anode,

An

an

electrolyte?

change ●

known

water

weak

Objectives

Electrolysis

electric

acid.

electrolyte.

extremely

A10.3

nitric

an

electrolyte.

They

discuss

the

electrolysis

of

molten

must electrolytes

be

able

to

conduct

an

electric

current

and

are

usually

made

of

an

iner t

●

material

such

as

graphite

(carbon)

or

platinum.

The

anode

is

explain

of

to

t he

positive

terminal

of

t he

batter y

and

t he

cathode

is

connected

negative

The

electrolyte,

compound

mobile

discharge

discuss

the

electrolysis

of

certain

terminal. aqueous

●

preferential

ions

to

●

t he

the

connected

or

a

which

is

solution

a

molten

electrolytes.

ionic

containing

ions. battery

Key

!

fact

Electrolysis

which

is

is

occurs

passed

the

chemical

when

through

an

an

change

electric

current

electrolyte.

electrolyte

!

anode



Figure

10.3.1

An

electrolytic

cell

Key

fact

The

anode

The

cathode

is

the

positive

electrode.

cathode

is

the

negative

electrode.

electrodes

179

Electrolysis

Electrochemistry

electrons

around

from

flow

the

Mechanism

of

electrolysis

circuit

anode

to

e



e



During Light

electrolysis

bot h

anions

and

cations

are

d ischarged,

i.e.

bulb:

cathode



glows

t hey

brightly

lose

or

gain

electrons

to

form

neutral

atoms.

This

occurs

as

e battery

if

the

is

electrolyte

follows.

strong

e 

e

glows

the

e

dimly

if

The

●

electrolyte

anions

(negative

ions)

are

attracted

to

t he

anode

is

(positive

electrode).

The

anions

lose

electrons

to

t he

anode

weak e

e

and anode

()

cathode

(

form

atoms,

i.e.

t hey

are

discharged:

)

n

n

C

C

n

n

A

A

A



ne

n

C n n

A

C n

A

Oxid ation occurs at t he anode (OL). The anode electrolyte,

n

C

n

C n

CA(l

A

n

A

→

A



or

aq)

acts

as

t he

oxid ising

The

electrons,

agent

ne n

C

n

A

n

C



ne

→

C

n n

A

●

C

lost

by

t he

anions

to

t he

positive

at

t he

anode,

travel

n

C n

A n

n

C

n

C

C

t hrough

n

Figure

10.3.2

Mechanism

of

●

✔

tip

The

cations

electrode).

atoms,

It

can

be

confusing

to

try

to

terminal

of

t he

t hen

re-enter

t he

circuit

from

t he

negative

batter y.

terminal

of

electrolysis

t he

Exam

circuit

A

They 

t he

(positive

The

i.e.

batter y

ions)

cations

t hey

are

and

travel

are

gain

to

t he

attracted

t he

cat hode.

to

electrons

t he

cat hode

from

t he

(negative

cat hode

forming

discharged:

learn n

which

electrode

which

is

is

negative.

positive

It

is

C

and

better



it

out,

remembering

C

to

Reduction work

ne

that

occurs

at

t he

cat hode

(RG).

The

cat hode

acts

as

t he

reducing

the

agent electrodes

which

•

are

You

are

named

attracted

know

negative

that

to

after

anions

charge.

the

ions

them.

have

Anions

a

must

Electrolysis be

attracted

electrode.

must

be

to

The

called

the

positive

the

You

know

positive

that

electrode

cations

charge.

molten

electrolytes

Molten

electrolytes

contain

only

two

different

ions,

one

cation

and

one

anode

anion.

•

of

positive

have

Cations

Bot h

are

discharged

during

electrolysis.

a

must

Example be

attracted

electrode.

electrode

to

The

must

the

negative

negative

be

called

Electrolysis

of

molten

(fused)

le ad(II)

bromide

using

inert

g raphite

the

electrodes

cathode

2

The

At

ions

the

present

in

t he

molten

lead(II)

bromide

are

Pb

(l)

and

Br

(l).

anode:

The

Br

lose

electrons

ions

immediately

2Br

move

to

towards

t he

bond

(l)

anode

t he

covalently

Br

(g)

anode

forming



where

bromine

forming

t hey

are

atoms.

bromine

discharged,

Pairs

of

i.e.

bromine

t hey

atoms

molecules:

2e

2

Brown

At

the

fumes

of

bromine

are

evolved

at

t he

anode.

cathode:

2

The Pb

gain

ions move towards t he cat hode where t hey are discharged, i.e. t hey

electrons

to

form

lead

atoms:

2

Pb

Molten

180

(l)



lead

2e

forms

Pb(l)

around

t he

cat hode

and

drips

off.

Electrochemistry

T o

Electrolysis

electrolyse

(T eacher

molten

lead( II)

bromide

using

graphite

electrodes

demonstration) +

Your

teacher

may

observation,

●

use

this

recording

activity

and

to

assess:

reporting. anode

Y our

teacher

will

perform

the

−

following

()

(

)

cathode

experiment. bromine

gas

The

experiment

must

be

performed

in

a

fume

cupboard. molten

lead

Method

1

Place

2

Heat

3

Connect

the

circuit

4

Observe

the

product

5

Write

some

the

lead( II)

lead( II)

bromide

bromide

as

into

until

it

shown

a

crucible.

melts.

in

Figure

bromide

10.3.3.

heat

formed

at

each

electrode. 

an

ionic

Electrolysis

During

those

the

of

half

of

equation

aqueous

electrolysis

the

for

solute.

of

an

the

occurring

at

each

Figure

electrode.

lead( II)

10.3.3

Electrolysis

of

molten

bromide

solutions

aqueous

Because

reaction

water

solution,

the

undergoes

ions

present

spontaneous

are

not

only

ionisation,

an



aqueous solution always contains H

ions and OH

ions from the ionisation of

water molecules as well as the ions from the solute. As a result, aqueous solutions

always contain at least

n

t he

will

electrolysis

be

discharged

of

in

two different cations and

an

aqueous

preference

solution,

to

t he

two different anions.

one

ot her.

type

This

is

of

ion

of

known

as

each

charge

preferenti al

d ischarge.

Preferential

discharge

of

anions

There are three main factors which inuence t he preferential discharge of t he

anions

The

t hat

you

position

Considering

will

of

the

t he

be

studying:

ion

in

the

electrochemical

electrochemical

series

of

series

anions

given

in

Table

10.3.1,

ions

discharge.

ons



T able

series

at

t he

top

of

t he

series

are

t he

most

stable

and

t he

hardest

to

at t he bottom of t he series are t he least stable and t he easiest to discharge, i.e.

t he

ease

of

discharge

increases

10.3.1

of

The

electrochemical

anions

Anion

downwards. F

2

The

lower

t he

ion

in

t he

electrochemical

series,

t he

more

likely

it

is

to

be

discharged.

SO 4

NO 3

Cl

This

is

seen,

for

example,

when

we

look

at

the

electrolysis

of

dilute

sulfuric

Br

acid,

dilute

sodium

chloride

inert electrodes; the OH

solution

and

copper(II)

sulfate

solution

using

ion is preferentially discharged from each solution.

I

OH

The

concentration

The

concentration

preferentially

to

be

of

the

electrolyte

t he

discharged.

preferentially

solutions

of

electrolyte

There

discharged.

containing

halide

ions,

is

a

has

However,

i.e.

an

tendency

Cl

impact

for

t his

ions,

Br

t he

r ule

on

more

really

ions

and



which

ions

concentrated

only

are

ion

applies

to

ions.

181

Electrolysis

Electrochemistry

This

is

seen

when

we

compare

t he

electrolysis

of

dilute

sodium

chloride

solution wit h t he electrolysis of concentrated sodium chloride solution, bot h

using

iner t

discharged

electrodes.

n

but

concentrated

in

t he

t he

dilute

solution,

t he

solution,

OH

t he

ion

Cl

is

ion

preferentially

is

preferentially

discharged.

The

type

of

electrode

The type of anode chosen for t he electrolysis can affect t he reaction occurring

at

t he

anode.

f

t he

anode

is

inert,

for

example

graphite

or

not affect t he reaction occurring. However, if t he anode is

copper,

it

happens

This

is

using

an

at

when

There

is

cations 

T able

series

Cation

10.3.2

of

The

wit h

is

t he

electrolysis

main

you

t he

of

factor

will

be

t he

its

used,

anode,

discharge

one

in

compare

anode

copper

t hat

we

anode

iner t

Preferential

par t

process

it

does

active, for example

and

t his

affects

what

anode.

iner t

an

active

take

t he

seen

an

When

can

platinum,

electrolysis

electrolysis

t he

OH

anode

ion

of

copper(II)

using

is

an

sulfate

active

preferentially

solution

copper

anode.

discharged.

Wit h

ionises.

cations

which

inuences

t he

preferential

discharge

of

t he

studying:

electrochemical

cations

The

position

of

the

ion

in

the

electrochemical

series



K

Considering

t he

electrochemical

series

of

cations

given

in

Table

10.3.2,

ions

2

Ca

at t he top of t he series are t he most stable and t he hardest to discharge. ons at



Na

2

Mg

t he

bottom

t he

ease

of

of

t he

series

discharge

are

t he

increases

least

stable

and

t he

easiest

to

discharge,

i.e.

downwards.

3

Al

The

lower

t he

ion

in

t he

electrochemical

series,

t he

more

likely

it

is

to

be

2

Zn

discharged.

2

Fe

This

is

seen,

for

example,

when

we

look

at

t he

electrolysis

of

dilute

and

2

Pb 

concentrated

sodium

chloride

solution;

t he

H

ion

is

preferentially



H

discharged in bot h. Also when we look at t he electrolysis of copper(II) sulfate

2

2

Cu

solution;

t he

Cu

ion

is

preferentially

discharged.

We

will

now

look

at



Ag

examples

referred

to

above

in

greater

detail.

Examples

1

Electrolysis

Ions

of

d ilute

sulfuric

acid

using

inert

electrodes

present:



From

t he

H

SO 2

:

H

2

(aq)

and

SO

4

(aq). 4



From

t he

H

O:

H

(aq)

and

OH

(aq).

2

At

the

anode:

2

The

SO

ions

and

t he

OH

ions

move

towards

t he

anode.

The

4

OH

ions

are

preferentially

electrochemical

4OH

series

of

(aq)

discharged

182

occurs

2H

as

t hey

are

lower

anions:

O(l)



2

Effer vescence

because

oxygen

O

(g)



4e

2

gas

is

evolved

at

t he

anode.

in

t he

t he

Electrochemistry

At

the

Electrolysis

cathode:



The

H

ions

move

towards

t he

cat hode

where

t hey

are

discharged:



2H

(aq)



2e

H

(g) 2

Effer vescence

Relative

volumes

Comparing

from

are

occurs

t he

t he

anode

of

hydrogen

gases

two

to

as

is

evolved

at

t he

cat hode.

produced:

equations,

t he

gas

for

cat hode,

ever y

1 mol

of

4 mol

of

oxygen

electrons

and

transferred

2 mol

of

hydrogen

produced:

4OH

(aq)

2H

O(l)



O

2

(g)



4e

2



4H

(aq)



4e

2H

(g) 2

1

volume

Changes

of

in

oxygen

the

is

produced

for

ever y

2

volumes

of

hydrogen.

electrolyte:



The

sulfuric

OH

ions

acid

are

becomes

discharged

more

from

concentrated

it,

i.e.

water

because

is

being

H

ions

removed

and

from

t he



electrolyte.

Because

electrolysis

of

T o

electrolyse

(T eacher

of

sulfuric

t he

discharge

acid

dilute

is

of

referred

sulfuric

t he

to

acid

as

H

ions

t he

using

and

OH

electrolysis

inert

ions,

of

t he

water .

electrodes

demonstration)

oxygen

Your

teacher

may

use

this

activity

●

observation,

recording

●

analysis

interpretation.

Y our

and

teacher

will

perform

and

the

to

hydrogen

assess:

reporting

following

experiment.

Method

platinum

foils

1

Set

up

the

sulfuric

Hoffmann’s

acid

2

Observe

3

T est

the

as

the

gas

the

as

shown

in

Figure

10.3.4,

using

dilute

anode

electrolyte.

relative

given

voltameter

volume

off

at

the

of

gases

anode

to

given

off

see

it

if

at

is

each

splint.

The

splint

should

glow

brighter

oxygen

or

(–)

electrode.

by

using



a

Figure

10.3.4

showing

glowing

cathode

(+)

re-light

if

the

gas

the

Hoffmann’s

electrolysis

voltameter

of

dilute

is sulfuric

acid

oxygen.

4

T est

a

the

gas

burning

given

splint.

extinguished

if

off

The

the

at

the

splint

gas

is

cathode

should

to

see

make

a

if

it

is

hydrogen

squeaky

pop

by

and

using

?

be

Did

glowing

Explain:

relight

a

why

oxygen

b

why

hydrogen

c

why

the

was

produced

at

the

anode

(include

an

gas

6

What

volume

would

you

of

produced

hydrogen

expect

to

at

the

was

happen

cathode

greater

to

the

the

electrolyte

an

equation)

volume

as

to

because

the

glow

it

brighter

supports

or

the

equation)

(include

than

causes

splint

combustion,

was

know?

hydrogen. Oxygen

5

you

the

of

i.e.

burning,

of

the

splint.

oxygen.

reaction

proceeds?

183

Electrolysis

Electrochemistry

2

Electrolysis

Ions

of

d ilute

sod ium

chloride

solution

using

inert

electrodes

present:



From

t he

NaCl:

Na

(aq)

and

Cl

(aq).



From

t he

H

O:

H

(aq)

and

OH

(aq).

2

At

the

The

are

anode:

Cl

ions

and

preferentially

lower

in

t he

4OH

t he

OH

ions

discharged

electrochemical

(aq)

2H

move

because

series

O(l)



At

the

occurs

as

in

O

are

a

dilute

The

OH

ions

solution

and

are

anions:

(g)



4e

2

oxygen

gas

is

evolved

at

t he

anode.



Na

ions

and

preferentially

series

t hey

anode.

cathode:



The

t he

of

2

Effer vescence

towards

of

t he

H



ions

discharged

move

because

towards

t hey

are

t he

cat hode.

lower

in

t he

The

H

ions

are

electrochemical

cations:



2H

(aq)



2e

H

(g) 2

Effer vescence

Relative

volumes

Comparing

from

are

occurs

t he

t he

anode

produced,

of

gases

two

to

i.e.

as

gas

is

evolved

at

t he

cat hode.

produced:

equations,

t he

1

hydrogen

for

cat hode,

volume

of

ever y

1 mol

of

oxygen

is

4 mol

of

oxygen

electrons

and

produced

2 mol

for

transferred

of

ever y

2

hydrogen

volumes

of

hydrogen.

Changes

in

the

electrolyte:



The

ions

3

sodium

and

chloride

OH

Electrolysis

inert

Ions

ions

of

solution

are

becomes

discharged

concentrated

from

sod ium

more

concentrated

because

H

it.

chloride

solution

(brine)

using

electrodes

present:



From

t he

NaCl:

From

t he

H

Na

(aq)

and

Cl

(aq).



O:

H

(aq)

and

OH

(aq).

2

At

the

The

ions

anode:

Cl

ions

are

and

t he

OH

preferentially

concentrated

2Cl

ions

move

discharged

towards

because

t he

t hey

anode.

are

The

halide

Cl

ions

in

a

solution:

(aq)

Cl

(g)



2e

2

Effer vescence

At

the

occurs

as

Na

gas

is

evolved

at

t he



ions

and

preferentially

series

chlorine

of

t he

H



ions

discharged

move

because

towards

t hey

are

t he

lower

cat hode.

in

t he

The

H

cations:

(aq)



2e

H

(g) 2

Effer vescence

occurs

as

hydrogen

gas

is

evolved

at

t he

ions

are

electrochemical



2H

184

anode.

cathode:



The

yellow-green

cat hode.

Electrochemistry

Relative

volumes

Comparing

from

are

Electrolysis

t he

t he

in

to

i.e.

the

gases

two

anode

produced,

Changes

of

produced:

equations,

t he

for

cat hode,

equal

ever y

1 mol

volumes

of

of

2 mol

of

electrons

chlorine

chlorine

and

and

transferred

1 mol

hydrogen

of

are

hydrogen

produced.

electrolyte:



The

electrolyte

becomes

alkaline

because

H

ions

and

Cl

ions

are



discharged

form

from

sodium

it

leaving

an

excess

of

Na

ions

and

OH

ions,

which

hydroxide.

test

T o

investigate

the

effect

of

the

concentration

of

tubes

the electrolyte

electrolyte

(T eacher

Your

on

the

preferential

of

ions

demonstration)

teacher

may

use

this

activity

●

observation,

recording

●

analysis

interpretation.

Y our

discharge

and

teacher

will

perform

and

the

to

assess:

reporting

following

experiment. anode

cathode

Method

1

Set

up

an

electrolytic

electrodes

2

Place

an

and

dilute

inverted

cell

as

shown

sodium

test

tube

in

chloride

lled

with

Figure

10.3.5,

solution

dilute

as

using

the

sodium

inert

graphite

electrolyte.

chloride

solution



over

each

electrode

to

collect

the

gas

evolved

at

Figure

10.3.5

concentrated

3

T est

the

4

T est

the

gas

in

gas

the

in

tube

the

over

tube

the

over

anode

the

for

cathode

oxygen

for

Electrolysing

each.

using

hydrogen

a

glowing

using

a

splint.

(brine)

in

the

sodium

chloride

solution

laboratory

burning

splint.

5

Repeat

6

T est

the

the

experiment

gas

in

the

using

tube

over

concentrated

the

anode

for

sodium

chloride

chlorine

using

a

solution.

piece

of

Did

? moist

and

blue

then

litmus

paper.

If

the

gas

is

chlorine

the

paper

should

turn

Chlorine

white.

litmus

7

T est

the

gas

in

the

tube

over

the

cathode

for

hydrogen

using

a

a

form

piece

of

red

litmus

paper

into

the

electrolyte.

it

How

were

your

observations

in

the

two

turns

red

moist

and

reacts

then

with

hydrochloric

chloric( )

acid

Cl

H

(g)



2

9

know?

acid

the

similar

b

different?

Which

the

were

in

the

dilute

b

in

the

concentrated

each

Which

case,

ions

Explain

were

why

electrolyte

sodium

explain

experiments?

12

preferentially

a

In

11

ions

the

in

chloride

why

and

preferentially

Give

a

reason

litmus

step

discharged

sodium

(HClO):

O(l)

HCl(aq)

2

at

the

acids

turn

chloric( )

litmus

acid

red

HClO(aq)

and

oxidises

it

to

colourless.

anode:

solution

chloride

include

solution?

the

discharged

and

paper

to

and

experiments:

The

10

white

water

(HCl)



a

blue

burning

splint.

Dip

gas

paper

because

8

you

red

a

relevant

at

relevant

changed

the

equation.

cathode

in

both

equation.

colour

when

dipped

into

the

8

185

Electrolysis

Electrochemistry

4

Electrolysis

Ions

of

copper( II)

sulfate

solution

using

inert

electrodes

present:

2

From

t he

CuSO

:

Cu

2

(aq)

and

SO

4

(aq). 4



From

t he

H

O:

H

(aq)

and

OH

(aq).

2

At

the

anode:

2

The

SO

ions

and

t he

OH

ions

move

towards

t he

anode.

The

4

ions

OH

are

preferentially

electrochemical

4OH

series

of

(aq)

discharged

2H

O(l)



O

2

Effer vescence

At

the

occurs

as

are

lower

in

t he

(g)



4e

gas

is

evolved

at

t he

anode.

cathode:

Cu

ions

t hey

2

oxygen

2

The

because

anions:



ions

are

and

t he

preferentially

electrochemical

H

2

ions

move

discharged

series

of

towards

because

t he

t hey

cat hode.

are

lower

The

in

Cu

t he

cations:

2

Cu

A

pink

(aq)

deposit

increases

Changes

in

in



2e

of

Cu(s)

copper

builds

up

around

t he

cat hode

because

t he

blue

and

t he

cat hode

size.

the

electrolyte:

2

The

electrolyte

becomes

paler

blue

Cu

ions

are

2

discharged

from

it.

t

also

becomes

acidic

because

Cu

ions



ions

are

discharged

leaving

an

excess

of

H

and

OH

2

ions

and

SO

ions,

which

4

form

5

sulfuric

Electrolysis

acid.

of

copper( II)

sulfate

solution

using

active

copper

electrodes

Ions

present:

2

From

t he

CuSO

:

Cu

2

(aq)

and

SO

4

(aq). 4



From

t he

H

O:

H

(aq)

and

OH

(aq).

2

At

the

anode:

2

The

SO

ions

and

t he

OH

ions

move

towards

t he

anode.

However,

4

t he

anode,

being

made

of

copper,

is

active

and

t he

copper

atoms

ionise,

2

forming

Cu

ions,

t his

requires

less

energy

t han

discharging

t he

OH

ions.

2

Cu(s)

Cu

(aq)



2e

2

The

✔

Exam

in

size.

At

the

you

are

ions

go

the

The

writing

reactions

t he

electrolyte

and

t he

anode

gradually

decreases

cathode:

Cu

are



ions

and

t he

preferentially

H

2

ions

move

discharged

towards

because

t he

t hey

cat hode.

are

lower

The

in

Cu

t he

equations

electrochemical for

into

2

tip

ions

When

Cu

occurring

at

series

of

cations:

the

2

anode

always

and

cathode,

include

the

remember

correct

Cu

to

(aq)

2e

A

pink

deposit

of

symbols

increases

186

Cu(s)

state

in

size.

copper

builds

up

around

t he

cat hode

and

t he

cat hode

Electrochemistry

Changes

in

Electrolysis

the

electrolyte:

The electrolyte remains

unchanged. For ever y 2 mol of electrons transferred

2

from anode to cathode, 1 mol of Cu

ions enter the electrolyte at the

2

anode and 1 mol of Cu

T o

investigate

on

the

the

ions is discharged at the cathode.

effect

electrolysis

of

of

using

copper( II)

inert

and

sulfate

active

electrodes

solution

anode

(T eacher

Your

teacher

may

use

this

activity

●

observation,

recording

●

analysis

interpretation.

Y our

()

(

)

cathode

demonstration)

and

teacher

will

perform

and

the

to

assess:

reporting

following

experiment.

oxygen

pink

gas

builds

is

copper

up

evolved

around

at

cathode

the

the

Method anode

1

Set

up

an

electrolytic

cell

as

shown

in

Figure

10.3.6,

using

graphite graphite

electrodes

2

Observe

the

electrode.

blue

and

Repeat

4

Observe

5

Classify

6

How

anode

Also

litmus

3

copper( II)

the

as

and

the

cathode,

taking

the

colour

the

into

the

experiment

the

solution

observe

paper

the

sulfate

anode

electrodes

note

of

what

electrolyte

and

occurs

dip

a

at

each

piece

of

the

as

copper

cathode

inert

or

anode

electrodes.

and

the

colour

of

the

your

observations

in

()

(

)

cathode

electrolyte.

active.

the

were

electrodes

electrolyte.

electrolyte.

using

and

of

the

the

two

anode

experiments: pink

becomes

a

b

similar

different?

copper

builds

thinner

up

around

7

Why

was

the

reaction

experiments?

8

Why

did

9

Why

was

the

Include

litmus

there

experiment

a

but

occurring

the

paper

change

not

in

relevant

change

in

the

at

the

anode

in

the

two

of

in

the

step

copper

2?

electrolyte

in

the



rst

Figure

10.3.6

sulfate

solution

Dene

2

Give

the

term

3

formula

a

molten

b

dilute

Draw

a

4

sodium

labelled

Describe

solution

using

5

By

a

the

inert

anode

a

of

and

means

the

and

sulfuric

electrolysis

using

of

copper( II)

graphite

and

electrodes

state

the

in

the

electrolysis

graphite

graphite

of

sulfate

differences

an

of

chloride

copper( II)

when

symbol

acid

diagram

the

of

Exam

tip

electrolysis. It

the

Electrolysis

questions

✔ 1

electrodes

second? copper

Summary

the

cathode

equations.

colour

colour

different

of

the

ions

present

c

copper( II)

d

potassium

apparatus

solution

used

using

electrolysis

of

concentrated

in

each

sulfate

in

of

inert

dilute

sodium

is

line

important

diagrams

that

to

you

show

can

draw

electrolytic

cells

solution

laboratory

graphite

sodium

following:

solution

bromide

the

the

for

the

electrodes.

chloride

chloride

solution

electrodes.

equation

in

copper( II)

anode

each

sulfate

case,

show

solution

b

a

is

the

reaction

electrolysed

copper

occurring

at

using:

anode.

187

Quantitative

electrolysis

Electrochemistry

A10.4

Objectives

By

the

be

able

end

of

this

topic

you

Quantitative

electrolysis

will

The

volumes

of

gases

and

masses

of

substances

produced

during

electrolysis

to:

can be calculated using t he mole concept t hat you studied in Unit 7 . Michael

●

dene

●

calculate

and

the

Faraday

the

masses

produced

constant

volumes

of

of

gases

(1791–1867)

quantity

t he

quantity

symbol

Q

Each

you

of

of

and

electrons

Did

t he

rst

person

to

propose

t hat

t he

mass

of

a

electricity

passing

t hrough

t he

electrolytic

cell.

electrolysis.

The

?

was

substance produced at an electrode during electrolysis is directly propor tional

to

substances

during

Faraday

ow

electron

electricity,

is

measured

from

t he

owing

or

in

quantity

units

anode

t hrough

of

called

to

t he

t hese

electrical

coulombs,

cat hode

wires

has

charge,

C.

t hrough

an

is

During

given

electrical

electrical

t he

electrolysis,

charge

wires.

which

is

know? extremely small. n fact, t he electrical charge on one electron is so small t hat

18

when The

electrical

charge

on

1 C

of

electrical

charge

ows

t hrough

a

circuit,

6.25



electrons

10

one

have

owed.

19

electron

means

is

1.6

that



1 C

10

of

C.

This

electrical

charge

The quantity of electricity or electrical charge owing t hrough an electrolytic

1

___________

is

equivalent

cell

to

during

electrolysis

depends

on

two

factors.

19

1.6



10

electrons. ●

The

the

rate

of

ow

symbol

I

of

and

the

is

electrical

measured

charge,

in

units

i.e.

the

called

current,

amperes

which

(also

is

given

known

as

18

amps),

A.

owing

●

The

The

t he

A

for

of

of

following

of

1

amp

is

equivalent

to

1 C,

or

6.25



10

electrons,

1 s.

lengt h

quantity

current

time,

t,

t hat

electricity

t he

or

current

electrical

ows

charge

for,

can

measured

t hen

be

in

seconds,

calculated

s

using

formula:

quantity

of

electrical

charge

(C)



current

Q



I

i.e.



(A)



time

(s)

t

Example

Calculate

t he

ows

circuit

in

a

Current

Time

∴

!

of

fact

can

for

of

electrical

charge

t hat

ows

when

a

current

seconds

of

relate

electrons



20



60

electrical

t his

has.

to



The

Faraday

of

the

of

electrons,

constant

electrical

charge

is

on

the

size

one

mole

if



we

10

charge

moles

You

will

if

owing

we



consider

recall

t hat

2



t he

1 mol

1200 C



electrical

of

2400 C

charge

electrons

is

which

1 mol

equivalent

to

19

electrons.

have

96 500 C.

2.0 A

1200 s

23

6.0

of

20 min.

2.0 A

quantity

We

Key

in



quantity

1 mol

This

of

The

charge

electrons,

value

is

known

on

one

t hese

as

t he

electron

electrons

Farad ay

is

1.6

would



10

have

a

C,

total

t herefore,

charge

of

constant

1

i.e.

96 500 C mol

. 

Dur ing

electrolysis,

discharged

at

t he

a

cation

cat hode

wit h

a

according

to

single

t he

positive

following

charge,

i.e.

M

,

is

equation:



M



e

M



This

and

shows

form

t hat

1 mol

1 mol

of

M

of

or,

electrons

applying

is

required

t he

Faraday

to

discharge

constant,

1 mol

96 500 C

of

is

M

ions

required



to

discharge

discharging

96 500 C

188

is

1 mol

1 mole

of

of

required.

M

ions

anions

and

wit h

form

a

1 mol

single

of

M.

negative

This

also

charge

at

applies

t he

when

anode,

i.e.

Electrochemistry

The

to

following

calculate

and

examples

t he

electrolysis.

of

Molar

mass,

M

Molar

volume,

will

volumes

You

volumes

Quantitative

will

of

recall

show

gases

t he

how

and

we

can

masses

following

of

use

t he

Faraday

substances

quantities

t hat

constant

formed

relate

electrolysis

moles

during

to

mass

gases.



mass

V



of

1 mol

volume

of

of

a

substance.

1 mol

of

a

gas.

m

3

At

stp,

V



22.4 dm

3

,

at

r tp,

V

m



24.0 dm

m

Examples

1

Calculate

of

5

5.0 A

t he

ows

mass

of

lead

t hrough

produced

molten

at

lead(II)

t he

cat hode

bromide

for

when

16

a

current

minutes

and

seconds.

Determine

Current

Time

∴



in

t he

seconds

t he

of

electricity

t hat

ows:

5.0 A

quantity

Write

quantity

of



(16



60)

electricity

equation

for



t he



5



965 s

(5.0



965) C

reaction

at



t he

4825 C

cat hode:

2

Pb

From

t he

2 mol

∴

2

i.e.

(l)

of





2e

Pb(l)

equation:

electrons

96 500 C

193 000 C

are

required

form

form

1 mol

1 mol

to

form

1 mol

Pb.

Pb

Pb

1

________

∴

1 C

forms

mol

Pb

193 000

1

________

∴

4825 C

forms



4825 mol

Pb

193 000



0.025 mol

Pb

1

M(Pb)

i.e.

∴

2

f

2



207 g mol

mass

of

mass

an

of

34

at

Time

in



current

minutes

Determine

Current

t he

t he

207 g

Pb

of



0.025

2.5 A

and

24

at

quantity

is



207 g

passed

seconds,



5.175 g

t hrough

calculate

dilute

t he

sulfuric

volume

of

acid

for

oxygen

r tp.

of

electricity

t hat

ows:

2.5 A

quantity

for

4OH



anode

seconds

Equation

Pb

0.025 mol

electric

hours

produced

∴

1 mol

of

(2



60

electricity

t he

(aq)



reaction





at

2H

60)

(2.5

t he







60)

9264) C





24



9264 s

23 160 C

anode:

O(aq) 2

(34



O

(g)



4e

2

189

Quantitative

electrolysis

Electrochemistry

From

t he

4 mol

equation:

electrons

are

lost

in

forming

1 mol

O 2

∴

4



96 500 C

form

1 mol

O 2

i.e.

386 000 C

form

1 mol

O 2

1

________

∴

1 C

forms

mol

O 2

386 000

1

________

∴

23 160 C

forms



23 160 mol

O 2

386 000



0.06 mol

O 2

3

Volume

of

1 mol

O

at

r tp



24.0 dm

2

3

∴

volume

of

0.06 mol

O



0.06



24.0 dm

3



1.44 dm

2

3

A

solution

of

Determine

t hrough

t he

Determine

Current

Time

∴

in



copper(II)

t he

solution

t he

in

for

quantity

is

mass

32

of

electrolysed

of

t he

minutes

anode

and

electricity

10

t hat

using

if

a

copper

current

of

electrodes.

4.0 A

passes

seconds.

ows:

4.0 A

seconds

quantity

Equation

sulfate

decrease

for

of



(32



60)

electricity

t he



reaction



10

4.0

at





t he

1930 s

1930 C



7720 C

anode:

2

Cu(s)

From

t he

Cu

(aq)



2e

equation:

2

2 mol

electrons

are

lost

in

forming

1 mol

Cu

ions.

2

∴

2



96 500 C

form

1 mol

Cu

ions

2

i.e.

193 000 C

form

1 mol

Cu

ions

1

________

∴

1 C

forms

2

mol

Cu

ions

193 000

1

________

∴

7720 C

forms

2



7720 mol

Cu

ions

193 000

21



2

M(Cu

)

0.04 mol

Cu

ions

1



64 g mol

2

i.e.

mass

of

1 mol

Cu

ions



64 g

2

∴

mass

of

Therefore,

4

A

steel

0.04 mol

decrease

spoon

Calculate

the

electroplate

Calculate

needs

in

be

of

spoon

number

ions

mass

to

length

the

t he

Cu

of

0.04

t he



anode

electroplated

time

that

when

of



a

of



as

the



2.56 g

2.56 g

wit h

current

placed

moles

64 g

13 g

of

of

15 A

cathode

chromium

of

which

produced:

1

M(Cr)

i.e.



mass

52 g mol

of

1 mol

Cr



52 g

13

___

∴

number

of

moles

in

13.0 g



mol 52

190



chromium.

would

0.25 mol

have

the

to

ow

electrolytic

need

to

be

to

cell.

Electrochemistry

Equation

for

Industrial

t he

reaction

at

t he

applications

of

electrolysis

cat hode:

3

Cr

From

t he

3 mol

∴

3

i.e.

(aq)

electrons



3e

form

96 500 C

0.25



Therefore,

Calculate

quantity

Cr(s)

equation:

289 500 C

∴



1 mol

form

form

t he

t he

of

1 mol

1 mol

289 500 C

electricity

72 375 C



∴



of

taken

15 A

0.25 mol

Cr

electricity

for

(C)



Cr

Cr.

form

quantity

time

Cr.



time

72 375 C

required

72 375 C

current



to

(A)

ow





72 375 C

using

time

a

current

of

15 A:

(s)

(s)

72 375

______

time

s 15

t

would

take

Dene

2

Calculate

the

cathode

chloride

3

rtp

4

How

A10.5

hour

hour

20

2

is

●

extracting

●

purifying

minutes

magnesium

current

hours

the

a

a

of

40

volume

current

must

for

a

of

of

51

in

metals

25

25

seconds

seconds

of

of

that

ows

and

chlorine

2.5 A

25.6 g

to

ows

electroplate

the

spoon.

10.0 A

would

28

ow

copper

at

ways

t heir

in

deposited

molten

on

the

magnesium

seconds.

through

and

be

through

50

that

would

be

produced

concentrated

at

the

anode

sodium

seconds.

through

the

a

solution

of

copper( II)

cathode?

applications

many

from

5.0 A

minutes

current

produce

used

of

minutes

Industrial

Electrolysis

minutes

constant.

mass

solution

to

20

questions

when

for

long

sulfate

1

Faraday

when

chloride



the

Determine

at

4825 s

1

Summary

1



industr y

of

electrolysis

Objectives

By

the

be

able

i.e.

plating

one

metal

describe

wit h

anot her,

i.e.

used

coating

a

metal

wit h

its

oxide,

i.e.

now

look

at

will

how

each

of

t hese

in

to

electrolysis

extract

metals

can

from

ores

describe

be

will

you

anodising. ●

We

topic

electroplating their

●

this

electrorening

be ●

of

to:

ores

●

metals,

end

including:

more

used

how

to

electrolysis

purify

can

metals

detail.

●

describe

the

process

of

electroplating

Extraction

of

metals ●

Ver y

few

metals

are

found

in

t heir

free

state

in

t he

Ear t h’s

cr ust.

Most

describe

the

process

of

are anodising.

found

bonded

Minerals

from

to

ot her

which

elements

metals

can

in

be

ionic

compounds

extracted

are

known

known

as

as

ores.

minerals.

The

process

191

Industrial

applications

of

electrolysis

Electrochemistry

of

extracting

atoms,

i.e.

it

metals

is

a

from

t heir

reduction

ores

involves

conver ting

t he

metal

ions

to

process:

n

M



Metals

ions.

high

This

reason

from

in

t hese

t heir

t he

electrochemical

t hat

metals

ores.

and

is

where

example

oxide

(Al

is

O 2

a

to

of

of

ionise

met hod

the

molten

aluminium

t heir

molten

easily

difcult

to

of

form

to

reduction

ore

and

and

reduce

is

a

ver y

atoms.

to

extract

powerful

metals

above

stable

For

t his

t hem

met hod

aluminium

of

in

ores.

ore,

t he

metal

ions

move

towards

t he

discharged.

extraction

using

series

ver y

powerful

from

t he

are

are

extract

series

t hey

t he

),

need

ions

Electrolysis

electrolysis

cat hode

t heir

used

electrochemical

During

An

M

means

reduction

t he

ne

iner t

of

aluminium

graphite

from

its

molten

ore,

aluminium

electrodes.

3

The aluminium ions move towards t he cat hode where t hey are discharged to

form

molten

aluminium:

3

Al

(l)



The

molten

and

it

be

sinks

3e

aluminium

to

discussed

t he

in

is

which

bottom

more

Purification

Electrolysis

Al(l)

of

of

detail

forms

t he

in

is

denser

electrolytic

Unit

t han

cell

and

t he

is

molten

tapped

electrolyte

off.

This

will

18.2.

metals

ver y

useful

in

t he

production

of

pure

metals

from

impure

samples of t he metal. This process is known as electrorening. The principles

of

●

electrorening

The

impure

terminal

of

The

cat hode

●

The

electrolyte

●

The

●

anode,

The

metal

metal

●

The

t he

negative

is

as

is

follows.

made

t he

anode,

i.e.

it

is

connected

to

t he

positive

batter y.

a

ver y

is

an

t hin

sample

aqueous

of

t he

solution

pure

which

metal.

contains

ions

of

t he

metal

puried.

electrolyte

electrode,

metal

t he

●

being

positive

are

being

where

ions

which

are

are

ionises,

join

t he

discharged

builds

electrolyte

anode

active,

t hey

up

at

around

remains

removed

and

ot her

t he

t he

t hey

are

of

t he

metal

enter

t he

ions.

cat hode

where

t hey

form

t he

pure

cat hode.

unchanged

as

ions

metal

since

t he

discharged

metal

at

t he

ions

entering

it

at

cat hode.

power electrode,

the

anode,

a

bar

supply

●

the of

impure

Any

insoluble

impurities

present

in

t he

anode

fall

to

t he

bottom

of

t he

cathode,

copper a (1)

thin

sheet

(2)

of

cell

forming

a

sludge

which

can

be

removed.

pure

copper

An example of electrorening is t he purication of copper . This is illustrated

in Figure 10.5.1. The impure copper is t he anode (1) and t he cat hode is a t hin

2

sheet

of

sulfate

sludge

copper(II)

containing

The

pure

copper

(2).

The

electrolyte

copper

anode

of

copper

Cu(s)

Cu

(aq)



copper(II)

2e

2

ions,

The

Cu

ions

enter

t he

electrolyte

(aq)

forming

10.5.1

The

electrorening

pure

copper:

of 2

192

i.e.

ionises:

2+

Cu

copper

ions,

solution.

2

solution

flow

Figure

Cu

sulfate

impurities



contains

Cu

(aq)



2e

Cu(s)

and

are

discharged

at

t he

cat hode,

Electrochemistry

Electrore ning

hydrogen

in

t he

ions,

in

being

is

t he

ser ies

hydrogen

Industrial

only

suitable

for

electroc hemical

would

lower

in

not

t he

be

pur ifying

ser ies.

disc harged

ser ies,

would

Any

at

be

t he

metals

metal

whose

ions

cat hode

preferentially

ions

are

above

since

applications

of

electrolysis

below

hydrogen

t he

hydrogen

disc harged,

for ming

gas.

Electroplating

Electroplating

anot her

metal

from

object

be

made

of

The

t he

more

any

of

metal,

to

negative

be

The

anode

●

The

electrolyte

The

is

used

The

metal

metal

The

●

t he

As

a

for

anode,

electrolyte

●

pure

is

ions

t he

sample

an

to

t hat

made

similar

made

to

t he

of

one

eit her

appearance

usually

is

layer

out

object

ver y

or

is

of

to

make

being

brass,

t hose

of

cat hode,

metal

protect

on

t he

a

top

cheap

metal

electroplated

copper

or

of

original

steel.

can

The

electrorening.

i.e.

it

is

connected

to

batter y.

of

aqueous

active,

t hey

are

t he

metal

solution

electrolyte

ionises,

join

t he

discharged

builds

up

as

remains

removed

electrorening,

electrochemical

of

t hin

which

which

is

being

contains

used

ions

for

of

plating.

t he

metal

plating.

being

are

is

are

its

The

electroplated

where

which

anode

wit h

it

a

carried

improve

but

terminal

●

●

to

is

valuable.

electroplating

object

being

depositing

Electroplating

corrosion,

appear

principles

●

involves

metal.

series

a

at

t he

coating

t hey

only

be

are

of

t he

cat hode

since

where

t he

t he

whose

for

metal

enter

t he

ions.

at

ions

t hey

form

t he

pure

object.

metal

discharged

metals

used

ions

metal

around

unchanged

as

can

and

ot her

ions

t he

are

entering

it

at

cat hode.

below

hydrogen

in

t he

plating.

Examples of electroplating are chromium plating, silver plating, gold plating

and

nickel

plating.

Chromium

look

as

as

t he

plating ,

well

as

cat hode,

solution

of

or

chrome

protecting

t he

t hem

anode

is

chromium(III)

plating,

from

pure

sulfate

chromium

[Cr

(SO 2

The

chromium

anode

gives

steel

corrosion.

) 4

and

objects

The

t he

steel

a

shiny,

object

electrolyte

is

is

silver

placed

usually

a

]. 3

ionises:

3

Cr(s)

Cr

(aq)



3e

3

The Cr

ions enter t he electrolyte and are discharged at t he cat hode forming 

a

layer

of

chromium

on

t he

Figure

10.5.2

Chrome

plated

taps

object:

3

Cr

The

(aq)



3e

electrolytes

solutions

of

Cr(s)

used

nickel(II)

in

nickel

sulfate

plating

(NiSO

)

and

and

silver

silver

nitrate

plating

(AgNO

4

).

are

usually

During

t he

3

+ silver

process

of

silver

plating

illustrated

in

Figure

10.5.3,

t he

silver

anode

ionises: nitrate

the

object

electrolyte 

Ag(s)

Ag

(aq)



e

being

plated



The Ag

a

layer

(cathode)

ions enter t he electrolyte and are discharged at t he cat hode forming

of

silver

on

t he

silver

object:

anode



Ag

(aq)



e

Ag(s)



Figure

10.5.3

Electroplating

with

silver

193

Industrial

applications

of

electrolysis

Electrochemistry

Anodising

On

a

exposure

layer

of

to

air,

aluminium

aluminium

oxide

immediately

(Al

O 2

unreactive

a

result

The

it

and

adheres

protects

t hickness

objects

it

can

of

be

t he

t he

rmly

metal

aluminium

ar ticially

on

its

wit h

surface.

t he

This

oxygen

layer

is

to

form

relatively

3

to

from

)

reacts

t he

metal

attack

by

oxide

increased

by

below

and

oxygen

and

layer

a

on

process

t he

does

not

ake

moisture

surface

known

as

of

in

off.

t he

As

air.

aluminium

anod ising.

This

makes t he objects, such as window frames and saucepans, even more resistant

to

●

corrosion.

The

The

aluminium

hydroxide

●

The

t he

●

The

●

As

anodising

solution

cleaned

terminal

electrolyte

as

to

to

t he

is

be

clean

aluminium

positive

soon

ar ticle

process

of

anodised

and

ar ticle

t he

usually

a

electrolytic

involves

etch

is

is

following

pre-treated

t he

made

t he

steps.

using

sodium

surface.

t he

anode,

i.e.

it

is

connected

dilute

cell

is

solution

of

connected

sulfuric

up,

t he

acid.

aluminium

anode

3

begins

to

ionise,

forming

to

batter y.

Al

2

ions,

and

at

t he

same

time

t he

SO

ions 4

and

t he

OH

ions

in

t he

electrolyte

move

towards

t he

anode.

The

OH

3

ions

react

surface

of

wit h

t he

t he

Al

ions

forming

a

layer

of

aluminium

oxide

on

t he

aluminium:

3

Al(s)

Al

(aq)



3e

3

2Al



(aq)



3OH

(aq)

Al

O 2

The

silver-grey

attractively

aluminium

oxide

(s)



3H

(aq)

3

coating

readily

absorbs

dyes

cathode

anode

article

e.g.

a

()

to

–

be



Figure

Summary

Explain

why

Describe

3

the

Give

(

4

electrolysis

how

series

you

anodising

is

would

for

used

from

the

to

their

purify

occurring

equations

194

chromium

What

is

)

of

–

dilute

acid

aluminium

questions

reactions

the

The

at

a

the

extract

metals

high

plating

anodising?

in

the

ores.

sample

anode

reactions

that

of

silver.

and

the

occur

Include

b

nickel

the

equations

cathode.

at

the

during:

a

be

frame

10.5.4

electrochemical

for

can

coated,

window

sulfuric

2

it

aluminium

electrolyte

1

so

coloured.

plating.

anode

and

cathode

Electrochemistry

Key

●

The

electrochemical

The

t heir

A

atoms

higher

ionises

●

t he

and

metal

●

Metals

The

A

how

higher

from

not

it

t he

from

can

a

t he

an

in

t he

electrolysis

Electrolytes

are

to

a

list

of

metals

in

order

of

how

is

t he

ions

non-metals

in

gain

t he

stronger

series

is

gas;

from

more

easily

series

a

list

displace

metals

an

it

from

a

of

t he

below

acid.

non-metals

in

electrons.

electrochemical

are

its

non-metal

containing

to

t he

electrochemical

hydrogen

hydrogen

of

electricity

pass

in

electrochemical

t he

a

it

series,

powers.

metal.

forming

atoms

displace

allow

electricity

below

t he

series

compound

Conductors

is

reducing

lower

acid,

t heir

and

metals

electrochemical

its

metal

non-metal

ionises

of

t he

are

displace

easily

non-metal

allow

●

a

electrochemical

of

in

hydrogen

will

series

●

above

hydrogen

easily

●

is

stronger

displace

ions

order

●

of

electrons.

containing

hydrogen

The

series

lose

metal

t he

can

compound

●

applications

concepts

easily

●

Industrial

oxidising

below

t he

pass

it

lower

t hrough.

series,

t he

more

powers.

in

t he

electrochemical

non-metal.

Non-conductors

do

not

t hrough.

compounds

t hat

form

ions

when

molten

or

in

aqueous

solution.

●

Electrolytes

●

When

conduct

electricity

electricity

passes

because

t hrough

an

t hey

contain

electrolyte,

t he

mobile

ions

electrolyte

decomposes.

●

Metals

●

When

●

Strong

of

●

conduct

electricity

electricity

ions.

passes

electrolytes

Weak

of

Pure

ver y

is

t hrough

fully

electrolytes

concentration

water

are

because

a

a

t hey

metal,

ionised;

are

contain

t he

t hey

par tially

mobile

metal

contain

ionised;

electrons

remains

a

high

t hey

unchanged.

concentration

contain

a

low

ions.

weak

electrolyte

due

to

t he

ver y

low

concentration

of



H

●

and

●

is

of

t he

are

anode

lose

electrons.

The

cathode

Molten

Bot h

t he

chemical

t hrough

used

is

and

t he

during

positive

Oxidation

is

t he

gain

which

occurs

when

an

electric

electrolyte.

electrolysis

electrode.

occurs

negative

electrons.

electrolytes

are

change

an

to

conduct

electricity

in

to

and

electrolyte.

The

cat hode

●

is

passed

Electrodes

out

●

ions.

Electrolysis

current

●

OH

contain

discharged

during

at

Anions

t he

electrode.

Cations

Reduction

one

type

move

towards

t he

anode

and

anode.

occurs

of

move

at

cation

t he

and

towards

t he

cat hode.

one

type

of

anion.

electrolysis.



●

Aqueous

ions

electrolytes

from

t he

preference

●

Factors

●

The

t he

which

position

t he

to

of

water.

of

solute

type

of

ions

ion

of

as

well

each

as

H

charge

ions

will

be

and

OH

discharged

in

ot her.

anion

solution

position

preferential

One

inuence

t he

aqueous

contain

t he

in

t he

t he

and

whet her

cation

discharge

of

preferenti al

d ischarge

electrochemical

in

t he

t he

series,

anode

is

of

active

electrochemical

anions

t he

or

series

are

t he

concentration

of

iner t.

determines

t he

cations.

195

Industrial

applications

of

electrolysis

Electrochemistry

●

When

dilute

produced

●

When

if

t he

at

sulfuric

t he

sodium

is

at

●

●

t he

When

copper (II)

bot h

oxygen

is

sulfate

solution

produced

at

it,

Copper

is

produced

at

t he

volume

of

passing

t hrough

●

The

quantity

●

The

quantity

charge,

i.e.

Q

t



The

I

gas

electrolysis



of

of

t he

Farad ay

or

is

t he

using

t he

iner t

at

t he

electrodes,

oxygen

is

cat hode.

electrolysed

produced

produced

is

The

is

is

at

at

using

t he

anode.

iner t

anode,

electrodes,

if

it

Hydrogen

is

is

produced

cases.

oxygen

during

●

in

electrolysed

hydrogen

solution

dilute,

chlorine

cat hode

is

and

chloride

solution

concentrated,

acid

anode

if

mass

t he

cat hode

of

a

directly

electricity ,

electricity

constant

I,

is

is

electrolysed,

in

is

made

bot h

substance

Q,

t he

if

t he

anode

copper,

it

is

iner t,

ionises.

cases.

to

t he

at

an

electrode

quantity

of

electricity

cell.

is

measured

dependent

and

of

produced

propor tional

electrolytic

current,

is

anode

t he

size

time

of

on

t he

t he

in

coulombs,

t he

rate

current

electrical

of

C.

ow

ows

charge

of

for,

on

electrical

t,

i.e.

one

mole

of

1

●

electrons,

i.e.

ndustrial

uses

ores,

196

t he

96 500 C mol

of

electrolysis

purication

of

.

include

metals,

t he

extraction

electroplating

and

of

metals

anodising.

from

t heir

Electrochemistry

Practice

Practice

exam-style

Multiple-choice

1

Metal

X

was

containing

questions

to

displace

sulfate

of

Y.

metal

Y

However,

from

X

did

a

solution

not

displace anode

metal

t he

Z

from

a

following

A

X

B

Z

is

solution

is

higher

containing

Z

sulfate.

Which

cathode

of

correct?

in

t he

electrochemical

series

t han

Z. copper(II)

is

a

stronger

C

Y

is

higher

D

Y

is

a

in

reducing

t he

stronger

agent

t han

electrochemical

reducing

agent

series

t han

Which

of

t he

following

lists

consists

t han

X.

Z.

of

Electrolytic

State,

sodium

B

hydrochloric

chloride,

magnesium,

et hanol,

anode.

aqueous

sodium

D

kerosene,

hydroxide,

copper,

et hanoic

State,

During

electrolysis,

potassium

t he

what

you

relevant

would

obser ve

equation. (3

giving

a

reason,

what

you

would

chloride,

tap

reaction

which

takes

(2

f

a

current

of

5.0 A

ows

for

2

hours

8

minutes

water

place

at

40

seconds

t hrough

determine

t he

increase

Give

differences

t he

in

electrolytic

mass

of

t he

cell,

cat hode.

t he

B

reduction

C

oxidation

D

a

current

t hrough

would

electrolytic

cell

made

t he

anode

made

t he

cat hode.

a

be

A

2.7 g

B

5.4 g

of

5.0 A

silver

ows

nitrate

deposited

at

for

16

minutes

solution,

t he

what

and

mass

5

i)

seconds

of

Give

and

ii)

silver

you

would

obser ve

if

and

t he

t he

copper

electrode

graphite

C

10.8 g

D

27 .0 g

T WO

ONE

(2

a

0.75 mol

sodium

of

electricity

chlorine

use

response

Electrolysis

of

of

between

(2

of

anodising.

molten

is

during

is

needed

t he

to

produce

electrolysis

of

answer

molten

b

chloride?

Using

t he

chemical

a

72 375 C

discuss

chemical

B

96 500 C

products

C

144 750 C

The

of

EACH

Use

t he

show

electrolysis

Suppor t

your

and

wit h

of

iner t

t he

(4

Which

of

t he

can

following

A

ron

B

Anodising

be

puried

is

used

statements

by

to

is

incorrect?

c

The

The

electrodes,

following

on

t he

electrolysis.

position

of

ions

aluminium

items

from

t hem

items

more

appearance

Cutler y Electroplating

can

be

used

to

coat

steel

items

wit h

in

t he

electrochemical

layer

of

electroplating

wit h

a

layer

resistant

and

made

t he

to

make

of

steel

of

electrolyte.

(2

marks)

(2

can

be

anot her

corrosion,

t hem

is

marks)

to

metal

more

coat

to

improve

appear

of ten

used

make

t heir

valuable.

electroplated

of

nickel

followed

by

a

layer

of

wit h

a

silver.

silver.

i) Magnesium

of

of

a

layer t hin

concentration

process

metal

electrolysis.

protect

corrosion.

D

marks)

concentrated

193 000 C

ii)

C

marks

how

equations.

dilute

solutions

effect

of

of

to

process.

ionic

electrolysis

t he

process.

bromide

relevant

chloride

A

i)

is

15

mark)

question

potassium

wit h

sodium

a

marks)

(1

series.

6

was

marks)

electroplating

Total

8

quantity

differences

anode?

electrolysis

What

D

in

was

electrode

anodising.

Give

Extended

5

t hat

decomposition

c

f

T WO

displacement t he

4

marks)

is: iv)

A

in

marks)

(4 anode

at

marks)

obser ve

electrolyte.

and

3

a

acid iii)

molten

reason,

aluminium t he

C

a

nclude

graphite ii)

acid,

giving

cell

conductors? t he

A

sulfate

solution

X.

i) 2

questions

questions

found

t he

exam-style

can

be

extracted

from

its

ore

Draw

a

labelled

diagram

to

show

t he

apparatus

by

you

could

use

to

electroplate

a

steel

spoon

wit h

electrolysis.

nickel

using

nickel

sulfate

solution

(NiSO

(aq))

as

4

Structured

7

a

b

Dene

An

electrolyte.

use

as

Clearly

indicate

what

you

would

question

t he

term

electrolytic

wit h

t he

cell

copper(II)

graphite

‘electrolysis’. (1

anode

was

sulfate

and

a

set

up,

as

solution

copper

ii)

mark)

shown

as

t he

cat hode.

in

t he

gure,

electrolyte,

a

How

t he

long

anode

must

t hrough

t he

9.44 g

nickel?

of

and

a

t he

steady

electrolyte

cat hode.

current

to

coat

(3

of

4.0 A

t he

spoon

(4

Total

marks)

ow

wit h

marks)

15

marks

197

A11

Rates

of

reaction

Chemical

reactions

reactions

can

proceed

at

different

speeds.

Some

Objectives

By

the

be

able

end

of

this

topic

you

will

while

●

take

years,

such

as

the

rusting

of

cars,

to:

dene

what

is

meant

by

rate

of

others

explosion.

happen

Other

in

less

reactions

than

take

a

second,

place

at

such

varying

as

an

speeds

reaction

between ●

explain

how

reaction

●

explain

the

can

the

be

rate

of

which

measured

collision

these

two

extremes.

Knowing

the

speed

at

a

theory

reactions

occur

is

extremely

important

in

industry

for

to

maximise

productivity

while

minimising

costs

and

the

reactions

●

interpret

rate

curves

risk

for

of

accidents.

reactions.

A11.1

The

t he

Measuring

study

rate

of

of

t he

concentration

increases.

f

of

we

t he

increase

in

t he

decrease

or

The

rate

of

speed

reaction ,

a

t he

can

is

rates

at

which

called

increase

reaction

to

can,

chemical

of

occur,

we

in

can

be

t he

in

product,

t herefore,

decrease

as

decrease

a

reaction

kinetics.

decreases

t he

concentration

reaction

chemical

reactants

measure

a

of

occurs,

During

a

concentration

concentration

and

know

determine

t he

determined

concentration

of

how

rate

known

reaction,

of

a

a

products

reactant

long

of

as

t he

it

took

or

for

reaction.

by:

of

a

reactant

____________________________________

rate

of

reaction

 time

increase

taken

in

for

t he

decrease

concentration

of

a

product

____________________________________

or

rate

of

reaction



. time

!

The

Key

rate

change

fact

of

in

reaction

the

is

a

measured

concentration

of

Changes

in

are

property

products,

or

product

with

time

at

t hat

changes

can

be

are

not

which

measured

always

depend

to

increase

easy

on

to

t he

determine

measure.

nature

t he

rate

of

of

a

However,

t he

t here

reactants

reaction.

and

Some

of

t hat

can

be

measured

are:

if

one

of

t he

products

is

a

gas,

t he

volume

of

gas

produced

over

time

temperature.

can

●

be

measured

metal

and

if

of

one

decrease

reaction

●

if

a

an

t he

in

if

products

precipitate

t here

is

reaction

e.g.

●

if

t here

of

a

a

is

t he

gas

syr inge,

a

gas,

if

t he

reaction

carbonate

for ms,

t he

e.g.

a

reaction

between

a

reactive

t he

gas

can

and

be

an

appearance

reaction

between

is

allowed

measured

to

escape,

over

t he

time,

e.g.

a

acid

of

t he

sodium

precipit ate

t hiosulfate

can

be

and

acid

c hange

between

is

reaction

a

a

acid

mass

hydroc hlor ic

●

using

between

measured,

198

changes,

t he

a

●

stated

concentration

for

a

t he

reactant

ot her

taken

in

colour

pot assium

distinct

proceeds,

c hange

any

of

intensity,

iodide

in

t his

and

pressure,

t hese

can

be

can

be

acidi ed

measured,

hydrogen

temperature

measured

or

over

pH

as

time.

e.g.

t he

peroxide

t he

Rates

of

reaction

Collision

Chemical

and

t he

take

Measuring

theory

reactions

formation

place,

all

of

for

t he

new

t he

breaking

bonds

following

the reactant particles must

●

of

reaction

reactions

involve

of

rates

in

must

t he

of

original

products.

bonds

in

order

for

n

t he

a

reactants

reaction

to

occur:

collide with each other in order to break the

original bonds in the reactants so that new bonds can form in the products

the

●

reactant

activation

reactants

products

t he

●

and

(see

reactant

energy

in

par ticles

energ y

enable

Unit

to

break

collide

Unit

the

with

12.1),

par ticles

to

to

enough

break

have

energy,

the

known

original

enough

as

bonds

energy

to

in

the

form

12.1)

par ticles

produced

order

must

(see

by

must

t he

collide

collision

wit h

can

t he

be

correct

passed

on

or ientation

to

t he

so

t hat

original

t he

bonds

t hem.

Not all collisions occur wit h t he required activation energy or wit h t he correct

orientation

of

par ticles.

Therefore,

not

all

collisions

result

in

a

reaction

occurring. Collisions which result in a reaction are called effective collisions .

The

For

rate

of

a

reaction

example,

2H

(g)

in



O

2

The

t he

depends

reaction

(g)

on

2H

break

will

t he

t hen

(H

)

and

oxygen

atoms,

and

collisions.

oxygen

to

form

new

(O

)

molecules

forming

H

between

covalent

bonds

water

bonds

must

to

atoms

collide

form

wit hin

wit h

t he

between

covalent

new

break

H



O

O

H

t he

must

O

O 2

Figure

11.1.1

To

be

effective

an

to

molecules

Rate

f

a

The

and

reaction

t he

t he

between

each

covalent

molecules

This

hydrogen

and

form

H

O

H

2H 2

collision,

break

ot her

covalent

bonds

2H



each

molecules.

molecules.

must

H

t he

H

energy

water:

O(g)

oxygen

bonds

original

H

hydrogen

effective

2

covalent

allow

of

2

2

to

number

between

2

hydrogen

t he

hydrogen

and

collision

bonds

must

be

O 2

oxygen

must

wit hin

correctly

generate

t he

enough

hydrogen

orientated

to

activation

and

each

oxygen

ot her.

curves

measured

proceeds

and

proper ty

t he

is

plotted

proper ty

on

changes,

a

a

graph

rate

against

curve

is

time

as

t he

reaction

obtained.

gas

syringe

volume

measures

of

the

hydrogen

Examples

1

The

reaction

between

magnesium

and

hydrochloric

acid:

dilute

Mg(s)



2HCl(aq)

MgCl

(aq)



H

2

(g) 2

hydrochloric

f

magnesium

ribbon

is

added

to

hydrochloric

acid,

t he

volume

acid

of magnesium

hydrogen

gas

given

off

can

be

measured

in

a

gas

syringe

at

regular



inter vals

using

t he

apparatus

shown

in

Figure

1 1.1.2.

f

t he

volume

of

Figure

of

is

t hen

plotted

against

time,

t he

cur ve

in

Figure

1 1.1.3

may

be

11.1.2

Investigating

the

rate

gas reaction

between

magnesium

and

obtained. hydrochloric

acid.

199

Measuring



Figure

rates

11.1.3

gas

reaction

Graph

of

released

Rates

volume

against

of

of

reaction

50

time

45

mc(

3

)

hydrogen

of

40

sag

35

negordyh

30

25

fo

20

emuloV

15

10

5

0

0

60

120

180

240

300

Time

We

can

use

reaction

at

t he

values

different

on

t he

stages

graph

in

t he

increase

to

determine

reaction

in

360

420

480

(s)

by

volume

of

t he

using

average

t he

rate

general

of

formula:

hydrogen

______________________________

rate

of

reaction

 time

To

●

determine

t he

average

taken

rate

of

for

t he

t he

increase

reaction

in

t he

rst

minute

(60 s):

3

volume

of

gas

produced

in

t he

rst

minute



28 cm

3

28 cm

_______

∴

average

rate

of

reaction

in

t he

rst

minute

3





0.47 cm

1

s

60 s

To

●

determine

t he

average

rate

of

t he

reaction

in

t he

second

minute:

3

olume of gas produced in the second minute

3

 (38  28) cm

 10 cm

3

10 cm

_______

∴

average

rate

of

reaction

in

t he

second

minute

 60 s

3



This

clearly

decreases.

graph.

t he

The

discuss

2

wool

to

The

can

t hat

as

also

be

gradient

reaction

becomes

cotton

shows

This

is

shallower

t his

in

reaction

is

rapid.

t he

reaction

seen

steep

at

more

detail

between

in

as

calcium

at

t he

beginning

t he

t he

t he

proceeds,

looking

t he

However,

indicating

by

of

reaction

reaction

next

is

t he

0.17 cm

rate

of

gradient

t he

graph

progresses,

slowing

t he

or

1

s

reaction

slope

of

t he

indicating

t he

down.

gradient

We

will

section.

carbonate

and

hydrochloric

acid:

stop

CaCO

(s)



2HCl(aq)

CaCl

3

f

some

hydrochloric

balance,

be

cur ve

in



CO

calcium

at

acid

regular

Figure

is

poured

carbonate

is

inter vals.

1 1.1.5

may

be

into

a

added,

f

t he

(g)



H

2

conical

t he

mass

ask,

mass

is

of

t hen

O(l) 2

which

t he

is

on

reaction

plotted

a

can

against

time,

obtained.

)g(

calcium

acid

carbonate

noitcaer

hydrochloric

(marble

and

measured

t he

(aq) 2

chips)

fo ssaM

direct-reading

balance

Time

on

 

Figure

11.1.4

reaction

and

200

Investigating

between

hydrochloric

calcium

the

rate

Figure

11.1.5

Graph

of

(s)

mass

of

reaction

against

time

of

carbonate

Looking

at

reaction

proceeds,

t he

gradient

of

t he

graph

we

can

also

clearly

acid

t he

rate

of

t he

reaction

decreases.

see

t hat

as

t he

Rates

of

reaction

Measuring

Explanation

We

can

steep

at

see

that

the

of

the

both

shape

rate

beginning

of

cur ves

the

of

rate

have

reaction

a

of

reaction

curves

ver y

and

rates

similar

gradually

shape.

The

becomes

gradient

shallower

is

until

the cur ve eventually becomes horizontal. This shows that the rate of a reaction

changes as the reaction proceeds. We will now look at the reasons for this.

●

The gradient is steepest at the beginning of the reaction indicating that

the rate of the reaction is at its

highest. This is because the concentration

of the reactant particles is at its highest at the beginning of the reaction.

The frequency of collision between the particles is at its highest at the

beginning.

●

As the reaction proceeds, the gradient becomes shallower indicating that

the rate of the reaction is

decreasing. This is because the concentration of

the reactant particles is decreasing as the reaction proceeds. The frequency

of collision between the particles is decreasing as the reaction proceeds.

●

After a period of time the cur ve becomes horizontal, i.e. the gradient

becomes zero, indicating that the reaction has reached completion and

has

stopped. One of the reactants has been used up and there are no more

of its particles left to collide. The reactant which is used up in a reaction

is known as the

limiting reactant. The quantity of the limiting reactant

determines the quantity of the products produced.

T o

investigate

reaction

Your

the

change

in

rate

of

a

reaction

as

the

proceeds

teacher

may

●

observation,

●

manipulation

●

analysis

and

use

this

recording

and

activity

and

to

assess:

reporting

measurement

interpretation.

3

Y ou

will

be

supplied

hydrochloric

through

it

to

acid,

a

a

gas

with

4.0 g

conical

syringe,

of

calcium

ask,

a

a

cork

measuring

carbonate

with

a

crystals,

delivery

cylinder

and

a

tube

0.3 mol dm

running

stopwatch.

Method

1

Place

the

calcium

carbonate

crystals

in

the

conical

ask.

3

2

Measure

3

As

quickly

conical

as

ask

syringe,

4

30 cm

as

of

possible

with

in

hydrochloric

the

Figure

Record

the

volume

volume

remains

Record

your

pour

cork

the

gas

acid

which

11.1.2.

of

acid

At

in

the

the

into

has

the

in

a

the

conical

delivery

same

gas

measuring

time,

syringe

tube

start

every

cylinder.

ask

and

running

the

15

cork

to

the

the

gas

stopwatch.

seconds

until

the

✔

5

constant

results

in

a

for

three

table

and

consecutive

use

them

to

Exam

plot

a

graph

of

volume

of

When

drawing

obtained

gas

against

time.

Draw

a

curve

of

best

t

between

the

from

Using

your

graph,

rst

minute

calculate

the

average

rate

of

the

reaction

the

b

the

second

minute.

Explain

than

in

why

the

the

average

second

rate

of

the

reaction

is

higher

in

the

Explain

why

the

you

rst

line

of

necessarily

data

it

draw

a

is

curve

best

join

curve

or

line

smooth

or

straight

of

all

fit.

You

the

best

fit

do

points.

must

be

minute and

must

pass

minute. between

8

that

straight

not

A

7

using

for: or

a

graphs

experiments,

points. important

6

tip

readings.

curve

of

your

graph

eventually

becomes

horizontal.

close

as

the

points

possible

to

so

all

that

the

it

is

as

points.

201

Factors

affecting

rates

of

reaction

Rates

Summary

Dene

2

Give

two

ways

3

Give

two

methods

of

reaction

changes

the

be

able

end

of

What

5

Explain

this

topic

you

rate

identify

the

factors

which

rates

explain

affect

●

calculating

that

between

a

of

reaction.

the

rate

student

magnesium

of

could

a

reaction.

use

ribbon

to

and

determine

dilute

how

the

hydrochloric

rate

acid

time.

the

how

rate

collision

the

rate

Factors

theory

of

a

for

a

reaction

reaction

changes

affecting

state?

as

rates

the

of

reaction

proceeds.

reaction

of

a

of

reaction

describe

different

rates

changing

the

a

will

is

dependent

be

st udyin g

on

several

whi c h

can

factor s.

a f fec t

There

t he

r ate

are

of

four

a

main

r eacti on .

are:

of

●

concentration

●

temperature

●

sur face

●

presence

factors

reaction

experiments

determine

we

reaction

how

the

t hat

affect

These

●

of

by

to:

facto r s

the

meant

will

The

●

is

with

does

A11.2

Objectives

By

4

reaction

questions

1

what

of

effect

factor

to

area

(par tic le

size)

of

on

the

rate

or

absen c e

of

a

ca t aly st .

of

Light and pressure also affect t he rate o f c e r t ain re act ion s. For e xa mple , t h e a

reaction

reaction between met h a n e a n d c h lor ine (se e Unit 14.1) a n d p h otosynt h esis ●

interpret

graphical

are representations

of

bot h

t he obtained

in

initiated

by

ligh t ,

an d

as

t he

lig h t

in ten sity

in c rease s,

t he

r ate

of

data

studying

rates

reaction

incre a s e s.

Ch emic al

re ac tio n s

wh ic h

are

in it ia ted

or

sp eed ed

of

up

by

light

are

kn own

as

photochemic al

re actions .

reaction.

Pressure

affects

pressure

on

meaning

Did

?

you

know?

is

possibly

in

the

the

which

most

important

world.

green

It

is

the

plants

effective

carbon

water.

plants

make

dioxide

use

sunlight

reaction.

animals

and

to

would

both

bring

W ithout

no

oxygen

t he

collis io n s ,

reactio n

the

(g)



3H

2

rea c t a n t

gase ou s

t h eir

p ar ticle s

p er

st ate.

volume

un it

f

t he

dec reas es ,

vo lume.

As

a

t h ereby

b etwee n

increasing

n itrog en

t he

and

rate

of

t he

hyd rogen

to

re a c t io n .

for m

This

is

a mmon i a:

(g)

2NH

2

(g) 3

will

now

look

in

det ail

at

h ow

eac h

of

t he

ot h er

four

factor s

affects

t he

and

of

a

reaction.

When

co nsider ing

a

p ar ticu la r

f ac tor,

it

is

of

a

assu med

t h at

energy

about

ot her

factor s

a re

ke pt

co nst a nt .

the

no

and

food

animals

to

eat

Concentration

would

The have

t he

photosynthesis,

have

plants

mo re

in

in c rease d ,

by

all from

in

N

by

food

rate The

are

r eac t an ts

is

reactions

process

We combining

t h e re

bet we en

react ants

one

seen of

t hat

gaseous

result, t h e par ticl e s c o llide mo re fre quen tly an d t h is inc rease s t h e c h an c es

of

Photosynthesis

re a c t io n s

t he

for

gene ral

r ule

is

t h at

t he

higher

t he

concentration

rea ct a nt ,

t he

respiration.

higher

This

is

t he

rate

applies

in creased,

volume.

t he

As

a

c hances

of

t he

reaction.

par t ic ula rly

t his

me an s

result ,

of

t he

to

so lution s.

t ha t

t h ere

pa r t icles

e ffe c t i ve

f

a re

c o llide

co llisio n s,

t he

con c en tratio n

mo re

mo re

r eac t an t

frequen tly

t h erefore,

t he

of

a

par ticle s

r ate

w h ic h

of

t he

r eac t an t

per

unit

inc r eas es

r eac tion

increases.

f we measure t he rate of a rea ctio n a t differen t con c en tratio n s o f on e o f t h e

react ants, and plot t h e rat e a gain st c on c en tratio n , we g et a g raph similar to

t he one in Figure 1 1. 2.1. The g raph

202

cle arly sh ows t h at a s t h e con c en trati on

Rates

of

reaction

t he

rate

increases.

t

also

shows

t h at,

for

t h is

reac tio n ,

t he

r ate

of 1

reaction

is

directly

propor tional

to

t he

rates

of

reaction

s(

t he

affecting

)

increases

Factors

concentrat io n .

noitcaer fo etaR 3



T o

investigate

Your

teacher

the

may

●

observation,

●

manipulation

●

analysis

effect

use

this

recording

and

and

Figure

of

Rate

of

reaction

concentration

activity

and

11.2.1

to

on

against

the

Concentration

concentration

rate

of

a

will

be

)

reaction

assess:

reporting

measurement

interpretation.

3

Y ou

(mol dm

supplied

with

0.005 mol dm

3

potassium

iodide

solution,

0.01 mol dm

sodium

thiosulfate

solution,

a

3

solution

of

acidied

hydrogen

peroxide

3

25 cm

and

starch

with

a

hydrogen

peroxide

concentration

of

0.085 mol dm

,

two

3

measuring

cylinders,

one

10 cm

measuring

cylinder,

a

burette,

a

small

beaker

and

a

stopwatch.

Method

1

Place

the

sodium

thiosulfate

solution

into

the

burette.

3

2

Measure

sodium

25 cm

3

of

thiosulfate

potassium

solution

iodide

from

the

solution

burette

in

a

and

measuring

swirl

to

cylinder

mix

the

and

pour

it

into

the

beaker.

Add

1 cm

of

solutions.

3

3

Measure

4

Add

the

piece

5

of

25 cm

of

acidied

mixture

to

the

white

Observe

the

hydrogen

beaker

and

at

peroxide

the

same

and

time

starch

start

mixture

the

in

another

stopwatch.

measuring

Swirl

the

cylinder.

beaker

and

place

it

on

a

paper.

solution

in

the

beaker

from

above

and

as

soon

as

a

blue-black

colour

begins

to

appear

stop

the

stopwatch.

6

Record

the

time

7

Repeat

the

experiment

table

8

taken

for

the

four

blue-black

more

times

colour

using

to

the

start

to

volumes

appear.

of

potassium

iodide

solution

and

water

given

in

the

below.

Calculate

the

concentration

of

potassium

volume

of

iodide

solution

for

each

of

KI(aq)

using

the

following

formula:

Kl(aq)

_______________

concentration

experiment



3



0.005 mol dm

25

9

Calculate

the

rate

of

reaction

for

each

experiment

using

the

following

1

______________________________________

rate

of

reaction



Record

your

against

the

Volume

results

a

Volume

iodide

of

of

distilled

3

solution/cm

taken

table

concentration

of

potassium

in

1

s time

10

formula:

for

similar

the

blue-black

to

the

potassium

Concentration

potassium

of

dm

appear

below

solution.

Volume

of

and

Draw

sodium

thiosulfate

3

solution/mol

to

outlined

iodide

iodide

3

water/cm

one

colour

a

plot

a

graph

straight

Volume

of

hydrogen

to

of

show

best

acidified

peroxide

3

solution/cm

line

Time

and

the

t

rate

of

between

taken

blue/black

the

the

for

colour

Rate

mixture/cm

25

0

1

25

20

5

1

25

15

10

1

25

10

15

1

25

5

20

1

25

of

reaction/

3

starch

reaction

points.

1

to

appear/s

s

203

Factors

affecting

11

What

12

Explain

13

Use

can

rates

you

the

of

reaction

deduce

effect

Rates

about

that

the

effect

increasing

the

of

concentration

concentration

has

on

on

the

rate

the

of

rate

the

of

of

reaction

reaction?

the

reaction.

3

your

graph

to

determine

the

rate

of

the

reaction

at

potassium

iodide

concentrations

of

0.0022 mol dm

3

and

0.0044 mol dm

double.

Did

information

the

rate

given

.

In

of

theory,

your

below

to

if

the

reaction

help

concentration

double?

If

it

of

a

didn’t

reactant

double,

doubles,

can

you

the

rate

suggest

of

a

reaction

reasons

why?

should

Use

also

the

you.

During

t he

potassium

experiment,

iodide

to

t he

iodine

hydrogen

molecules

peroxide

(

oxidises

t he



ions

in

t he

): 2

2

(aq)



(aq)



2e

2

As

soon

back

to



as



an

iodine

molecule

is

formed

t he

sodium

t hiosulfate

reduces

it

ions:

(aq)



2e

2

(aq)

2

When all t he sodium t hiosulfate has reacted, iodine molecules remain in t he

solution

and

react

concentration

t he

same,

iodine

time

t he

has

t he

volume

blue-black

been

taken

wit h

and

for

concentrations

made

t he

of

starch

of

colour

each

same

produce

time.

n

of

iodide

a

blue-black

t hiosulfate

star ts

quantity

potassium

to

sodium

to

appear

your

solution

when

t he

experiment

iodine

to

be

colour.

used

same

you

Since

each

quantity

determined

produced

t he

time

using

is

of

t he

different

solution.

T emperature

The general r ule is t hat t he

t he

f

higher

t he

t he

rate

of

temperature

par ticles

gain

t he

at

kinetic

t he

par ticles

move

●

t he

par ticles

collide

sufcient

Combining

effective

which

energ y

●

wit h

higher t he temperature at which a reaction occurs,

reaction.

faster,

wit h

activation

t hese

two

collisions

a

has

t herefore

more

as

occurs

t he

t hey

energy,

energy

effects,

increase,

reaction

which

for

t he

is

collide

temperature

t herefore

the

rate

of

to

collisions

occur

react.

increases,

t he

reactant

frequently

more

par ticles

t he

effects:

more

t herefore

t he

increased,

following

t he

reaction

chances

increases.

of

For

some chemical reactions which occur at room temperature, if t he temperature

increases

f

we

10 °C,

measure

against

The

by

the

t he

rate

temperature

graph

reaction

clearly

rate

of

we

a

but

it

t he

reaction

reaction

get

shows

increases,

of

a

at

graph

that

as

shows

different

similar

the

that

approximately

to

temperatures

the

one

temperature

the

rate

doubles

is

and

shown

in

increases,

not

directly

the

1

) s( noitcaer fo etaR



204

Figure

11.2.2

Rate

of

(°C)

reaction

against

the

rate

rate

1 1.2.2.

of

the

proportional

temperature.

T emperature

plot

Figure

temperature

to

Rates

T o

of

reaction

Factors

investigate

Your

teacher

the

may

●

observation,

●

manipulation

●

analysis

effect

use

this

recording

and

and

of

temperature

activity

and

to

on

the

rate

of

a

will

be

rates

of

reaction

reaction

assess:

reporting

measurement

interpretation

3

Y ou

affecting

supplied

with

1.0 mol

3

dm

hydrochloric

acid,

0.05 mol dm

sodium

thiosulfate

solution

(Na

S 2

O 2

(aq)), 3

3

a

small

conical

ask,

a

50 cm

measuring

cylinder,

a

burette,

a

thermometer

and

a

stopwatch.

Method

1

Using

a

black

pen,

draw

a

cross

on

a

piece

of

white

paper.

Do

not

make

the

cross

too

dark.

3

2

Measure

50 cm

3

Pour

hydrochloric

the

of

sodium

acid

thiosulfate

into

the

solution

using

the

measuring

cylinder

and

pour

it

into

the

conical

ask.

burette.

3

4

Add

mix

5

1 cm

the

When

Look

6

of

the

two

down

7

the

before

8

the

to

the

and

to

the

are

conical

the

ask

mixed,

ask

conical

on

a

the

ask

of

the

precipitate

and

record

top

stop

the

and

at

of

sulfur

same

slowly

stopwatch

temperature

the

time

start

the

stopwatch.

Swirl

the

ask

to

cross.

of

the

as

forms

soon

mixture

as

in

which

the

the

gradually

cross

conical

is

no

ask

obscures

longer

and

the

cross.

visible.

record

the

time

taken

disappear.

experiment,

adding

Repeat

the

acid

place

measure

cross

Repeat

and

reactants

into

Immediately

for

hydrochloric

solutions

the

but

this

hydrochloric

experiment

three

time

heat

the

sodium

thiosulfate

solution

in

the

conical

ask

to

about

40 °C

acid.

more

times,

heating

the

sodium

thiosulfate

solution

to

about

50 °C,

60 °C

and

then

70 °C.

9

Record

your

results

in

a

table

and

calculate

the

rate

of

the

reaction

at

each

temperature

using

the

following

formula:

1

______________________________

rate

of

reaction



s time

10

Plot

t

a

graph

between

11

What

12

Explain

13

Use

can

double,

Given

can

chemical

deduce

graph

that

that

to

rate

about

of

for

the

if

the

suggest

products

equation

for

the

cross

to

reaction

effect

increasing

determine

double

you

the

the

taken

disappear

against

the

nal

temperature

of

the

mixture.

Draw

a

curve

of

best

points.

effect

approximately

14

show

the

you

the

your

to

1

the

the

the

the

temperature

temperature

rate

of

the

temperature

reasons

of

of

why?

reaction

is

reaction

the

on

at

increased

Use

are

has

on

the

the

rate

40 °C

by

and

10 °C.

information

sodium

rate

chloride,

of

of

the

the

reaction?

reaction.

50 °C.

Did

given

the

In

rate

below

sulfur,

water

to

theory,

of

help

and

the

your

rate

of

reaction

a

reaction

double?

If

it

should

didn’t

you.

sulfur

dioxide,

write

a

balanced

reaction.

During t he experiment, t he sodium t hiosulfate reacted wit h t he hydrochloric

acid

to

form

Na

S 2

Since

each

t he

O 2

(aq)

each



sulfur,

which

slowly

2HCl(aq)

built

2NaCl(aq)

up



and

S(s)

obscured



H

3

t he

O(l)

t he



and

cross

time.

n

concentration

disappeared

your

of

when

experiment

t he

t he

you

two

solutions

same

were

quantity

(g) 2

used

of

cross:

SO

2

volume

time,

made

insoluble

was

sulfur

determining

t he

t he

same

had

time

been

taken sulfur

for

t he

same

quantity

of

sulfur

to

be

produced

at

different

temperatures.

precipitate

cross



Figure

11.2.3

thiosulfate

Following

solution

and

the

reaction

hydrochloric

between

sodium

on

drawn

paper

acid

205

Factors

affecting

rates

of

reaction

Rates

Surface

area

The

general

rate

of

This

a

size

only

to

par ticles

n

of

t he

our

oxygen

t he

T o

t he

size)

smaller

in

t he

t he

t he

ot her

par ticles

of

a

reactant,

t he

higher

t he

ne

coal

same

solid

solid.

mass

of

par ticles

reactant.

t he

As

state.

Small

large

have

a

chances

mines,

e.g.

which

par ticles

investigate

t he

t he

solid

a

par ticles.

t he

effective

solids

par ticles

greater

result,

of

When

solid

f

surface

react,

have

t he

area

par ticles

a

par ticle

exposed

collide

collisions,

t he

larger

more

t herefore,

t he

increases.

spark,

air

t he

in

of

smaller

increases

and

Any

surface

t han

reaction

mills

reactants

t he

t he

which

ammable.

of

area

of

to

on

decreased,

frequently

rate

t hat

applies

occurs

surface

is

is

reaction

reaction.

reaction

total

r ule

(particle

of

of

could

our

the

t he

from

a

be

and

effect

nely

divided

cigarette,

explosive

can

our

and

initiate

because

of

a

coal

are

reaction

t he

large

highly

wit h

surface

t he

area

coal.

of

surface

area

on

the

rate

of

a

reaction

Your

teacher

may

●

observation,

●

manipulation

●

analysis

Y ou

will

be

use

this

recording

and

and

activity

and

to

assess:

reporting

measurement

interpretation.

supplied

with

5.0 g

of

small

calcium

carbonate

crystals,

5.0 g

of

3

large

calcium

ask,

a

cork

measuring

carbonate

with

a

crystals,

delivery

cylinder

and

a

tube

0.3 mol dm

running

hydrochloric

through

it

to

a

gas

acid,

a

conical

syringe,

a

stopwatch.

Method

1

Place

the

small

calcium

carbonate

crystals

in

the

conical

ask.

3

2

Measure

3

As

quickly

conical

as

ask

syringe,

4

30 cm

as

with

in

volume

remains

5

Repeat

the

6

Record

your

gas

7

8

Using

volume

time

of

of

gas

the

small

b

the

large

why

in

for

acid

which

At

in

for

the

of

the

into

a

measuring

the

conical

delivery

time,

syringe

every

use

cylinder.

ask

tube

start

consecutive

large

and

set

in

same

gas

three

table

each

has

the

the

using

a

acid

and

running

the

30

cork

to

the

the

gas

stopwatch.

seconds

until

the

readings.

crystals.

them

crystals.

to

plot

Y ou

a

can

graph

plot

of

both

volume

curves

axes.

graph,

a

Explain

cork

the

11.1.2.

constant

results

set

your

pour

experiment

against

same

the

Figure

the

the

hydrochloric

possible

Record

of

of

calculate

the

average

rate

of

the

reaction

for:

crystals

crystals.

the

average

rate

of

the

reaction

is

higher

for

the

small

crystals.

9

Explain

of

206

gas.

why

both

sets

of

crystals

produced

almost

the

same

volume

on

Rates

of

reaction

Presence

Cer tain

t he

Factors

or

absence

chemical

reaction.

substances

These

of

a

can

chemically

in

substances

industr y

unchanged

to

at

be

are

added

to

reactions

known

as

catalysts

increase

t he

end

to

alter

and

t he

t hey

rate

are

of

of

t he

t he

rate

of

reactions.

Key

!

catalysts

providing

an

activation

of

t he

t he

added

to

alternative

energy

collisions

increases

For

are

t han

occur

number

example,

normal

wit h

hydrogen

up

pat hway

t he

of

speed

are

reaction.

t he

for

2H

O 2

into

water

peroxide

and

(aq)

reaction

catalyst

alters

energy

(H

O

)

a

reaction.

reaction

(see

for

in

a

the

reaction

of

Unit

t he

which

12.1).

As

par ticles

given

They

lengt h

decomposes

ver y

work

requires

a

result,

to

react,

of

time.

slowly

fact

is

a

rate

substance

of

a

without

permanent

which

chemical

itself

undergoing

chemical

change.

by

less

more

which

at

room

2

oxygen:

2H

2

t he

collisions

2

temperature

rate

pat hway

sufcient

effective

of

used

Catalysts

any

Most

rates

catalyst

A

extensively

affecting

O(l)



O

2

(g) 2

The reaction can be speeded up considerably by adding manganese(IV) oxide

(MnO

).

The

manganese(IV)

oxide

acts

as

a

catalyst

and

it

is

chemically

2

unchanged

mass

of

of

t he

at

t he

end

of

manganese(IV)

t he

oxide

reaction.

is

When

exactly

t he

t he

reaction

same

as

it

was

has

at

nished,

t he

t he

beginning

reaction.

Enz ymes are biological catalysts made of protein molecules. They are present

in

t he

t hat

cells

would

of

all

living

ot her wise

organisms

occur

too

where

slowly

t hey

for

life

speed

to

up

chemical

reactions

exist.

Did

? catalytic

you

know?

conver ter

CO 2

T etraethyl

lead(IV)

was

first

mixed

N 2

with

H

gasoline

in

the

1920s

as

an

2

inexpensive

way

to

increase

engine

gases

performance

and

fuel

economy

by

from

preventing

engine

uncontrolled

combustion

ceramic

known

suppor t

cavities

‘honeycomb’

in

through

matrix

it

as

Pt

and

covers

Pd

of

Figure

few

Hence

‘antiknock’.

toxic

inter nal

fuel

has

the

nature

been

use

of

of

lead

phased

leaded

out

almost

area

react

A

the

compounds,

worldwide.



knocking’.

as

pass

catalyst

large

surface

known

which

Because gases

‘engine

became

11.2.4

A

together

catalysts

catalytic

forming

are

converter

harmless

added

in

a

car

exhaust

allows

harmful

pollutant

gases

to

in

the

USA

This

in

phasing

the

out

started

mid-1970s.

products

to slow

down

the

rate

of

a

reaction.

These

are

known

as

negative catalysts or inhibitors. They work by providing an alternative pathway

✔

Exam

tip

for the reaction which requires more activation energy than the normal pathway.

This decreases the number of effective collisions in a given length of time.

If

you

are

particular

An

example

of

a

negative

catalyst

is

tetraethyl

lead(IV)

((C

H 2

)

5

Pb),

to

be

added

prevented

to

gasoline

uncontrolled

(petrol)

for

combustion

use

of

in

the

internal

gasoline

combustion

so

that

to

explain

affects

the

how

rate

a

of

which chemical

the

reaction,

your

answer

engines. must

t

factor

4

a

used

asked

engine

be

based

on

the

collision

ran theory

for

reactions.

more smoothly.

Effect

The

be

effect

shown

Figures

used

changing

of

changing

on

1 1.2.5

remains

is

of

t he

and

rate

in

a

any

factor

curve

1 1.2.6,

unchanged.

up

factors

t he

for

and

rate

which

t he

t hat

of

t he

determines

curves

alters

reaction.

number

Remember

reaction

on

t he

n

moles

limiting

t he

rate

of

each

of

t he

of

of

reaction

t he

is

t he

products

can

graphs

limiting

reactant

quantity

a

in

reactant

one

which

produced.

207

Factors

affecting

rates

of

reaction

Rates

B

A

Original

B

Rate

rate

curve

tcudorp

increased



A

fo

one

ytitnauQ

the

a

the

a

or

temperature

reaction,

adding

by:

concentration

reactant,

solid

an

caused

the

decreasing

of



rate

increasing

of



reaction

curve

showing

increasing

of



of

or

the

particle

reactant,

size

or

catalyst.

Time



Figure

a

n

of

Figure

●

curve

showing

the

effect

of

any

factor

which

increases

the

rate

of

A

cur ve

any

one

is

single

t he

original

factor

as

cur ve

and

indicated.

B

cur ve

Looking

shows

carefully

t he

at

effect

what

t he

shows:

B

cur ve

higher

to

bot h

been

has

a

becomes

reach

cur ves

made

reactant

steeper

gradient

–

t his

is

because

t he

reaction

is

occurring

at

rate

B

cur ve

time

●

rate

1 1.2.5,

changing

a

A

reaction

graph

●

11.2.5

–

hor izontal

become

t his

was

sooner

–

t his

is

because

t he

reaction

takes

less

completion

is

not

horizontal

because

t he

when

the

original

same

quantity

number

of

of

moles

product

of

t he

has

limiting

changed.

A

Original

C

Rate

rate

curve

tcudorp

decreased

curve

showing

rate

a

caused

by:

A



decreasing

the

concentration

C

fo

of

ytitnauQ



one

of



the

a

the

reaction,

increasing

of



reactant,

decreasing

solid

adding

a

the

or

temperature

or

particle

reactant,

negative

size

or

catalyst.

Time



Figure

a

n

of

Figure

✔

tip

●

is

extremely

important

that

interpret

graphs

which

cur ve

of

C

C

has

at

A

cur ve

one

is

single

a

a

shallower

slower

becomes

time

bot h

to

cur ves

made

t he

effect

original

factor

as

gradient

of

any

factor

which

decreases

the

rate

of

cur ve

indicated.

and

cur ve

Looking

C

shows

carefully

at

t he

effect

what

t he

hor izontal

reach

–

t his

is

because

t he

reaction

is

rate

later

–

t his

is

because

t he

reaction

takes

completion

–

become

t his

is

horizontal

because

reaction.

reactant

208

the

when

the

same

quantity

of

product

has

show

been rates

showing

you ●

can

curve

shows:

cur ve

more

It

rate

any

occurring

Exam

A

1 1.2.6,

changing

graph

●

11.2.6

reaction

was

not

changed.

t he

original

number

of

moles

of

t he

limiting

Rates

of

reaction

Factors

Summary

1

2

3

Explain

how

b

decreasing

c

increasing

What

Explain

Key

The

rate

The

a

the

reaction

an

of

the

the

particle

size

of

concentration

increases

the

rate

of

a

reaction:

a

of

reactant

a

reactant.

catalyst?

a

catalyst

experiment

size

following

temperature

the

how

and

●

An

●

A

●

All

●

The

of

on

the

rate

reaction

or

product

collision

collide,

t he

t he

alters

you

of

effective

rate

of

a

a

a

the

could

rate

of

a

perform

reaction.

to

determine

the

effect

of

reaction.

t he

when

factors

temperature,

time

be

is

at

t hat

must

t he

t he

a

to

occur

one

t hat

same

as

t he

area

of

a

of

required

t he

reactants

activation

must

energ y

in

t he

formation

plotted

against

of

t he

product.

time.

shape.

t he

reaction

wit h

of

concentration

orientated.

time

reactant

rate

t he

par ticles

results

(par ticle

in

temperature.

t he

proper ty

decreases

affect

react,

wit h

basic

limiting

change

stated

correctly

changes

rate

surface

measured

measured

reaction

and

completion

main

have

a

states

must

shows

cur ves

rate

Four

t heor y

collision

curve

rate

is

wit h

collisions

par ticles

beginning

●

of

concepts

reactant

●

is

Describe

particle

●

each

increasing

a

rates

questions

a

b

affecting

a

is

proceeds.

until

used

chemical

size)

and

t he

is

fastest

at

t he

reaches

up.

reaction:

t he

t

reaction

concentration,

presence

or

absence

of

a

catalyst.

●

The

higher

t he

concentration

t he

temperature,

of

a

reactant,

t he

higher

t he

rate

of

a

reaction.

●

The

higher

●

The

smaller

●

A

catalyst

wit hout

●

Most

●

A

t he

is

a

itself

size,

substance

if

present,

catalyst,

if

t he

which

undergoing

catalysts,

negative

par ticle

t he

any

higher

alters

t he

up

t he

t he

slows

rate

t he

rate

rate

permanent

speed

present,

higher

of

a

a

a

of

t he

a

reaction.

reaction.

chemical

chemical

rate

down

of

of

reaction

change.

reaction.

rate

of

a

reaction.

209

Practice

exam-style

questions

Rates

6

Practice

exam-style

A

mass

of

5.0 g

of

powdered

zinc

will

react

of

t he

reaction

slowest

questions wit h:

3

A

Multiple-choice

3

30 cm

questions

of

0.1 mol dm

of

0.2 mol dm

of

0.3 mol dm

of

0.4 mol dm

3

B

20 cm

C

20 cm

D

10 cm

3

1

Which

of

t he

following

would

not

result

in

an

increase

3

in

t he

rate

sulfuric

of

acid

reaction

and

between

excess

magnesium

of

0.1 mol dm

carbonate

cr ystals

acid

sulfuric

acid

3

3

3

25 cm

sulfuric

3

sulfuric

acid

sulfuric

acid

3

at

28 °C?

A

ncreasing

t he

temperature

of

t he

acid

to

Structured

38 °C.

question

3

B

ncreasing

C

Using

t he

volume

of

t he

acid

to

40 cm 7

t he

same

mass

of

magnesium

a

An

experiment

was

set

up

to

investigate

what

effect

carbonate changing

various

factors

has

on

t he

rate

of

reaction

powder. between

D

ncreasing

t he

concentration

of

t he

acid

calcium

carbonate

and

hydrochloric

acid.

to The

reaction

was

carried

out

at

30 °C

in

a

conical

3

0.2 mol dm ask

2

An

aqueous

solution

of

hydrogen

peroxide

t hat

calcium

was

was

placed

carbonate

on

was

a

balance.

placed

in

A

mass

t he

ask

of

10.0 g

and

of

excess

3

decomposed

a

gas

t he

and

syringe.

total

t he

Which

volume

of

oxygen

of

t he

produced

following

oxygen

as

was

collected

graphs

measured

at

hydrochloric

in

added.

represents

various

regular

time

as

inter vals?

The

acid

ask

in

t he

concentration

and

inter vals

shown

of

and

its

contents

t heir

mass

was

1.0 mol dm

were

weighed

plotted

against

at

time,

gure.

306

)g(

emuloV

noitcaer

emuloV A

B

ssaM

Time

304

303

fo

Time

305

302

301

300

emuloV

emuloV

0

0

30

Time

Time

C

D

i)

The

rate

catalyst

is

best

described

as

a

substance

of

of

proceeds.

A

90

120

150

Time

Mass

3

60

against

reaction

Using

determine

which:

a

reaction

t he

t he

180

210

time

decreases

data

average

240

(s)

from

rate

of

as

t he

t he

t he

reaction

graph,

reaction

1

A

speeds

B

slows

C

takes

D

alters

up

t he

down

no

t he

par t

t he

rate

in

rate

of

rate

a

of

a

of

chemical

a

chemical

chemical

a

reaction

reaction

chemical

:

in g s

reaction

ii)

reaction

–

in

t he

rst

–

in

t he

second

Why

is

second

4

The

rate

of

a

chemical

reaction

independent

of

t he

size

of

rate

minute.

faster

in

(4

t he

rst

minute

minute?

marks)

t han

(2

t he

marks)

is: iii)

A

t he

minute

t he

par ticles

of

a

What

effect

would

repeating

rate

t he

t he

reaction

at

40 °C

solid have

on

t he

of

reaction?

(1

mark)

reactant iv) B

independent

of

t he

concentration

of

t he

By

referring

explain C

dependent

D

unaffected

on

t he

to

t he

collision

t heor y

for

reactions,

reactants your

answer

to

par t iii)

above.

temperature (3

by

a

v)

5

f

t he

wit h

temperature

sodium

following

at

which

t hiosulfate

is

hydrochloric

raised

by

acid

10 °C,

of

The

rate

of

t he

reaction

is

increased

B

The

rate

of

t he

reaction

is

decreased

C

The

rate

of

t he

reaction

is

doubled.

D

The

rate

of

t he

reaction

is

halved.

by

by

a

a

factor

factor

of

of

effect,

if

hydrochloric

t he

occurs?

A

What

any,

would

using

excess

3

reacts

which

have

on

your

answer.

t he

acid

rate

of

of

concentration

t he

reaction?

0.5 mol dm

Give

a

reason

(2

for

marks)

10. b

i)

What

is

a

catalyst?

(1

mark)

10. ii)

210

marks)

catalyst

Explain

how

a

catalyst

works.

(2

Total

marks)

15

marks

Rates

of

reaction

Extended

8

The

response

graph

which

below

was

reaction

acid

Practice

between

varies

over

out

t he

to

results

n

of

determine

magnesium

time.

questions

question

shows

carried

exam-style

t he

an

experiment

how

ribbon

t he

and

experiment,

rate

of

a

hydrochloric

excess

3

magnesium

ribbon

was

added

to

25 cm

of

hydrochloric

o

acid

at

35

regular

C

and

t he

volume

of

gas

was

measured

at

inter vals.

mc(

3

) sag fo emuloV Time

a

i)

ii)

b

Write

a

balanced

Account

Draw

a

could

for

labelled

be

set

up

t he

(min)

equation

shape

diagram

to

carr y

of

to

out

for

t he

reaction.

cur ve.

show

t he

t he

how

t he

(2

marks)

(4

marks)

apparatus

experiment.

(3

c

i)

Copy

on

t he

your

graph

expected

at

25 °C.

your

ii)

f

graph

draw

results

Make

onto

if

a

your

second

t he

sure

answer

cur ve

experiment

t hat

you

paper

to

show

was

distinguish

between

(2

experiment

was

repeated

again

t he

repeated

cur ves.

t he

marks)

and

marks)

wit h

o

magnesium

powder

what

if

effect,

any,

–

t he

maximum

–

t he

rate

Explain

of

instead

would

volume

evolution

your

answer

of

in

of

t his

of

have

gas

t he

each

ribbon

at

35

C,

on:

evolved

gas?

case.

(4

Total

marks)

15

marks

211

A12

Energetics

Chemical

energetics

is

the

branch

of

chemistry

that

Objectives

By

the

be

able

end

of

this

topic

you

will

deals

and

●

with

distinguish

between

exothermic

reaction

an

chemical

accompany

and

give

and

examples

of

exothermic

endothermic

explain

physical

processes

bond

reactions.

all

Energy

chemical

changes

reactions.

In

usually

fact,

in

some

reactions

the

energy

produced

is

more

important

than

the

products

of

the

chemical

reaction,

reactions

exothermic

endothermic

on

during

reaction

e.g. ●

changes

an

chemical endothermic

●

energy

to:

reactions

breaking

the

burning

of

fuels.

Energy

changes

can

take

many

and

and

based

forms,

e.g.

changes

in

heat,

light

and

electricity.

bond

forming

A12.1 ●

explain

what

enthalpy

●

explain

is

meant

change,

H

exothermic

endothermic

enthalpy

changes

during

reactions

Exothermic

and

Whenever

is

endothermic

reactions

and

reactions

t here

a

chemical

reaction,

t here

tends

to

be

a

change

in

energy

based

of on

Energy

by

t he

system.

The

energy

changes

in

chemical

reactions

are

usually

in

t he

change

form of heat energy, however, t hey may also be in t he form of light, electrical ●

draw

energy

prole

or diagrams

for

exothermic

nuclear

on endothermic

show

the

t he

energy

effect

of

adding

can

distinguish

which

between

two

types

of

reaction

based

occur.

If

t he

reaction

using

energy

produces

heat,

causing

t he

reaction

mixture

and

its

a

surroundings catalyst

We

changes

reactions

● ●

energy.

and

to

get

hotter,

t he

reaction

is

said

to

be

an

exothermic

prole

reaction.

Exot hermic

reactions

transfer

energy

to

t heir

surroundings.

diagrams.

●

If

the

its

reaction

reaction.

!

An

Key

to

its

reaction

surroundings

to

get

!

heat,

causing

colder,

Endothermic

the

reactions

the

causing

reaction

absorb

is

the

said

energy

to

reaction

be

from

an

mixture

their

surroundings.

causing

investigate

fact

teacher

exothermic

may

●

observation,

●

manipulation

and

endothermic

reactions

use

this

recording

and

activity

and

to

assess:

reporting

measurement.

3

Y ou An

endothermic

reaction

will

from

its

the

supplied

with

3

2.0 mol dm

hydrochloric

acid,

2.0 mol dm

hydroxide

solution,

zinc

metal,

potassium

nitrate,

sodium

hydroxide

surroundings,

pellets, causing

be

absorbs

sodium energy

and

endothermic

hotter.

Your

Key

get

releases

surroundings,

T o the

to

fact

exothermic

energy

absorbs

surroundings

surroundings

to

ammonium

chloride,

distilled

water,

a

polystyrene

cup

supported

in

get

a

beaker,

two

measuring

cylinders

and

a

thermometer.

colder.

Method

3

1

Measure

pour

it

25 cm

into

the

of

hydrochloric

polystyrene

cup.

acid

using

Record

a

the

measuring

cylinder

temperature

of

the

and

acid.

3

2

Measure

cylinder

and

25 cm

and

record

of

add

the

it

sodium

to

the

hydroxide

acid.

maximum

or

Stir

solution

the

minimum

in

solutions

the

other

with

the

measuring

thermometer

temperature.

3

3

Measure

another

polystyrene

amount

212

of

cup.

zinc.

25 cm

Record

Stir

and

of

hydrochloric

the

acid

temperature

record

the

of

and

the

maximum

or

pour

acid

it

and

into

add

minimum

the

a

cleaned

small

temperature.

Energetics

Energy

changes

during

reactions

3

4

Measure

pour

it

water

25 cm

into

and

Repeat

or

step

ammonium

Make

sure

6

Record

7

Classify

of

distilled

cleaned

add

maximum

5

the

a

small

4

using

you

your

amount

minimum

chloride

each

sodium

reaction

of

a

cleaned

cup.

measuring

Record

potassium

hydroxide

place

the

in

in

the

nitrate.

cylinder

temperature

Stir

and

and

of

record

the

the

temperature.

in

wash

results

water

polystyrene

a

of

the

pellets

potassium

polystyrene

cup

and

again

nitrate

between

in

using

each

each

case.

experiment.

table.

as

exothermic

or

endothermic.

zinc

is

added

sodium polystyrene hydroxide cup solution

hydrochloric



Figure

12.1.1

solution

is

Sodium

added

to

acid

hydrochloric

hydroxide



Figure

hydrochloric

12.1.2

hydrochloric

Zinc

is

acid

added

to

acid

acid

Examples

of

exot hermic

●

burning

of

●

neutralisation

between

reactions

include:

fuels

reactions

sodium

●

reactions

●

respiration,

between

hydroxide

between

reactive

which

releases

and

acids

and

bases,

hydrochloric

metals

energy

and

e.g.

t he

reaction

acid

acids

from

food

in

t he

cells

of

all

living

organisms

●

dissolving

sulfuric

Examples

●

t he

cer tain

substances

in

water,

e.g.

sodium

hydroxide

and

acid.

of

endot hermic

decomposition

decomposition,

decompose

into

●

photosynt hesis

●

dissolving

of

e.g.

reactions

compounds

calcium

calcium

in

cer tain

include:

oxide

plants,

salts

in

when

carbonate

and

which

water,

heated,

must

carbon

absorbs

e.g.

known

absorb

as

heat

thermal

in

order

to

dioxide

sunlight

ammonium

energy

chloride

and

potassium

nitrate.

Bond

breaking

and

bond

forming

In Unit 1 1.1 you learnt t hat a chemical reaction involves breaking t he original

bonds

in

t he

reactants

●

When

t he

original

●

When

new

bonds

bonds

are

is

making

bonds

are

reactants

energy

and

broken

absorbed

are

new

broken

formed

in

t he

bonds

in

t he

in

t he

products.

reactants,

products,

energy

energy

is

is

absorbed

released

products

bonds

are

energy

is

formed

released

213

Energy

changes

during

reactions

Energetics

In

●

Did

?

you

an

know?

t he

Average

bond

found

chemical

in

energies

data

can

be

amount

of

energy

in

new

absorbed

during

can

be

a

bonds

In

an

the

all

up

bonds

the

the

in

bond

bonds

in

in

new

t he

the

for

and

products

following

change

energies

all

bond

in

the



sum

in

extra

of

t he

to

break

released

energy

is

in

t he

released

surroundings

existing

forming

to

t he

increases.

reaction ,

is

t he

greater

energy

t han

absorbed

t he

energy

to

break

released

t he

in

existing

forming

in

t he

and

products.

t he

The

temperature

extra

of

t he

energy

is

absorbed

surroundings

from

t he

decreases.

Ever y

chemical

bond

has

a

specic

amount

of

energy,

no

matter

what

and

it

is

in,

known

as

its

bond

energ y.

The

amount

of

energy

which

formula:

of

reactant

energies

The

absorbed

energy

all

for

has

energy

t he

temperature

reactants

bonds

compound

applying

products.

t he

energy

t han

by

energies

reactants

the

t he

less

chemical

calculated

the

t he

endothermic

surroundings adding

in

and

is

books.

t he reaction

reaction ,

reactants

released

bonds or

t he

surroundings

●

The

exothermic

bonds

the

all

bond

sum

to

be

released

absorbed

when

to

t hat

break

bond

is

t hat

bond

is

t he

same

as

t he

amount

of

energy

formed.

of

products

Enthalpy

The

energy

symbol

but

change

it

H.

is

content

The

of

energy

possible

to

a

substance

content

measure

reaction. This is known as

of

t he

a

is

called

its

substance

change

in

enthalpy change

enthalpy

cannot

ent halpy

be

and

is

given

measured

t hat

occurs

t he

directly,

during

and is given t he symbol

a

H and

1

is

usually

The

expressed

ent halpy

change

ent halpy

i.e.

in

of

change

H



kilojoules,

of

In

an

i.e

of

reaction



t he

reaction

kilojoules

summarised



per mol,

by

t he

kJ mol

following

(total

ent halpy

of

products)

(total

ent halpy

of

reactants)

.

formula:



H reactants



H

energy

t he

ent halpy

of

t he

products

is

less

t han

t he

reactants:

H

products

extra

is

or

reactions

H

Therefore,

a

products

exothermic

ent halpy

reaction

H

reaction

Exothermic

a

kJ,

reactants

has

is

a

value

released

which

to

t he

is

less

t han

zero,

surroundings

and

i.e.

t he

H

is

negative.

temperature

of

The

t he

surroundings increases. Anot her way to t hink of t his is t hat since t he reaction

loses

energy,

H

is

negative,

i.e.

H

energy

of

ve.

content

reactants

ygrenE

H

ve

energy

of

Progress



An

example

value

of

H

of

is

an

Figure

12.1.3

exot hermic

given

af ter

t he

An

of

content

products

reaction

exothermic

reaction

is

t he

reaction

combustion

of

met hane

(t he

equation):

1

CH

(g)



2O

4

The

is

214

value

(g)

CO

2

for

completely

H

tells

burned

(g)



2

us

in

t hat

891 kJ

oxygen.

2H

O(g)

H



891 kJ mol

2

of

energy

is

lost

when

1 mol

of

met hane

Energetics

Energy

Endothermic

In

an

t he

i.e.

of

t he

H

reaction

t he

ent halpy

of

t he

products



from

is

greater

reactants

t he

surroundings

and

t he

H is positive. Energy

temperature

of

t he

surroundings

decreases. Anot her way to t hink of t his is t hat since t he reaction

H

is

positive,

i.e.

H

of

ygrenE

H

energy

of



example

of

an

Figure

content

products

ve

content

reactants

Progress

and

gains energy,

ve.

energy

An

t han

H

Therefore, H has a value which is greater t han zero, i.e.

absorbed

reactions

reactants:

products

is

during

reactions

endothermic

ent halpy

changes

12.1.4

endot hermic

An

of

reaction

endothermic

reaction

is

t he

reaction

reaction

between

hydrogen

iodine:

1

H

(g)



I

2

The

value

hydrogen

by

t he

(s)

2HI(g)

H



26.5 kJ mol

for

H

iodide

reaction

tells

is

us

made

t hat

26.5 kJ

during

represented

in

t he

t he

of

energy

reaction.

equation

is

The

would

gained

overall

be

when

energy

double

t his

1 mol

since

Reversible

In

a

it

shows

of It

may

a

reaction

of

hydrogen

iodide

being

be

very

confusing

value,

which

causes

to

think

an

of

increase

i.e.

made.

temperature

as

having

and

vice

that

an

a

of

its

surroundings

negative

versa.

Try

value

to

for

H

remember

reactions

reversible

reverse

2 mol

tip

absorbed

in

53 kJ,

Exam

✔

2

reaction ,

reaction

is

if

t he

for ward

endot hermic

and

reaction

vice

versa.

is

exot hermic,

The

H

value

t hen

given

t he

for

a

losing

and

exothermic

energy

if

you

minus

it,

to

lose

i.e.

its

reaction

anything

H

is

is

surroundings

–ve.

you

are

Similarly,

the

reversible reaction is for t he for ward reaction, i.e. t he reaction which proceeds

endothermic

from

lef t

to

right.

For

example,

t he

reaction

between

nitrogen

and

form

ammonia

is

gaining

hydrogen energy

to

reaction

from

its

surroundings

and

is: if

you

gain

anything

you

are

plus

it,

1

N

(g)



3H

2

(s)

2NH

2

(g)

H



–46.1 kJ mol

i.e.

3

H

is

ve.

This shows t hat t he for ward reaction which produces ammonia is exot hermic.

Therefore,

1 mol

of

t he

reverse

ammonia

is

reaction

made

is

endot hermic.

during

t he

reaction,

It

also

46.1 kJ

shows

of

us

energy

t hat

is

when

released.

! Energy

profile

Key

fact

diagrams Activation

The

energy

change

in

a

chemical

reaction

can

be

illustrated

wit h

an

energ y

amount

must

prole

d i agram.

The

diagram

shows

t he

energy

content

or

ent halpy

of

and

products,

H

and

t he

activation

energy.

Most

reactions

energy

to

get

t hem

star ted.

This

minimum

amount

of

energy

is

given,

normally

activation

energ y .

This

activation

energy

can

be

t hought

of

the

minimum

reactants

excess

possess,

in

of

what

order

bonds

to

start

breaking

in

the

called reactants

t he

in

is

that

need

for

some

energy

energy

t he

they

reactants

be

of

as

and

products

to

start

t he forming.

energy

The

for

amount

t he

The

barrier

of

of

reaction

are

reaction.

activation

reaction

general

a

and

energy

shown

is

prole

in

energy

not

does

included

diagrams

Figure

not

in

of

affect

t he

an

t he

overall

calculation

exot hermic

of

and

energy

t he

an

change

value

of

H.

endot hermic

12.1.5.

215

Energy

changes

during

reactions

Energetics

(a)

(b)

activation

energy tnetnoc

tnetnoc

AB + C

reactants

activation

ygrenE

ygrenE

–ve

H

A + BC

products

energy

H

A + BC

AB + C

products

Course



Figure

(a)

An

12.1.5

When

Energy

exothermic

Drawing

you

impor tant

of

prole

energy

are

you

Course

an

an

endothermic

energy

include

t he

formulae

of

t he

reactants

●

t he

formulae

of

t he

products

●

arrows

●

t he

An

value

example

hydrogen

is

of

H.

of

how

shown

t his

in

prole

activation

can

be

Figure

reaction.

diagram

following

t he

t he

energy

done

for

a

and

t he

specic

on

your

reaction

it

is

diagram:

H

reaction

between

nitrogen

and

12.1.6.

tnetnoc

(g) + 3H

2

for

information

activation

N

reaction

diagrams

●

indicating

of

diagrams.

(b)

profile

drawing

t hat

reactants

reaction

reaction,

+ve

energy

(g)

2

ygrenE

–1

=

H

– 46.2 kJ mol

2 NH

(g)

3

Course



Catalysts

In

Unit

rate

has

is

of

a

lower

a

effect

in

of

t he

a

catalyst

an

t he

because

of

catalyst

for

is

a

the

a

formation

substance

reaction

same

t he

of

t he

can

are

to

more

products)

be

shown

t hat

which

ammonia

for

when

effective

in

on

t he

pat hway.

react

t he

can

a

wit hout

pat hway

normal

energy

t here

in

reaction

alternative

t han

required

formation

using

diagram

energy,

energy

t he

reaction

diagrams

t han

provides

up

prole

a

of

energy

have

speeds

t hat

terms

activation

par ticles

result

In

Energy

profile

learnt

catalyst

reaction

t hat

you

activation

less

reactant

12.1.6

energy

reaction.

because

The

and

1 1.2

a

requires

t he

Figure

of

a

is

reaction

As

a

t hey

lengt h

prole

t he

used

catalyst.

This

which

result,

more

collide,

collisions

same

energy

increase

catalyst

and

(collisions

of

time.

diagrams.

It

is

impor tant to note that although the reaction has a lower activation energy, as

shown in the diagrams in Figure 12.1.7 , the energy values for the reactants and

products

216

remain

unchanged,

therefore,

the

value

for

H

remains

the

same.

Energetics

Calculating

activation

energy

activation

activation without

a

without

a

energy

catalyst activation

a

changes

energy

catalyst

with

energy

energy

catalyst with

a

catalyst

reactants

tnetnoc

tnetnoc

ygrenE

ygrenE

H

ve

H

ve

products reactants

Course



Figure

(a)

an

of

12.1.7

reaction

Energy

exothermic

Summary

1

Explain

Course

prole

reaction,

diagrams

(b)

an

with

and

endothermic

without

a

of

reaction

catalyst.

reaction.

questions

what

is

meant

by

an

exothermic

reaction

and

an

endothermic

reaction.

2

Explain

exothermic

a

bond

b

enthalpy

3

Give

4

Draw

breaking

the

a

fully

on

and

endothermic

bond

reactions

by

reference

to:

forming

change.

formula

Indicate

and

used

labelled

your

to

calculate

energy

diagram

enthalpy

prole

what

diagram

effect

change.

for

adding

a

the

following

catalyst

reaction.

would

have.

1

2H

(g)



O

2

(g)

2H

2

O(g)

H



241.8 kJ mol

2

Objectives

A12.2

Calculating

energy

changes

By

the

be

able

●

In

t he

laborator y,

t he

energy

c hange,

or

ent halpy

c hange,

in

a

end

of

be

deter mined

dene

by

measur ing

t he

heat

c hange

t hat

occurs

dur ing

known

as

t he

he at

of

re action .

We

cannot

measure

t he

or

ent halpy,

of

t he

react ants

and

products

directly.

the

calculate

t he

heat

of

reaction

by

measur ing

t he

c hange

However,

in

occurs

dur ing

a

terms

heat

the

of

solution

formula

to

calculate

change

of

a

heat

calculate

heat

unit

you

will

learn

how

to

determine

heats

of

reaction

such

as

of

neutralisation

from

explain

why

data

the

and

t he

heat

of

solution

experimentally.

In

heat

of

t he

neutralisation

heat

reaction

changes

reaction. experimental

t his

heat

neutralisation

temperature

●

In

specic

of

we

●

whic h

heat

give

the

can

will

energy ●

content,

you

t he and

reaction,

topic

reaction capacity,

can

this

to:

for

the

reaction

t hese

between

a

strong

acid

and

experiments you will measure t he change in temperature which accompanies

strong

t he

neutralisation

reaction

between

a

strong

acid

and

a

strong

alkali

and

of

a

solid

in

water.

You

can

t hen

use

what

is

known

as

t he

describe

capacity

to

determine

t he

change

in

ent halpy

for

t he

speci c

heat

capacity

of

a

substance,

c,

is

t he

the

same

experiments

determine

the

heat

of

reaction.

neutralisation

The

always

specic

to

heat

is

t he

●

dissolving

alkali

quantity

of

heat

and

heat

of

required solution

to

raise

t he

temperature

of

a

unit

mass

of

t he

substance

by

1 °C

or

1 K.

We ●

usually

take

t he

unit

mass

of

t he

substance

as

1 g

and

measure

give

the

when

in

deg rees

Celsius.

This

being

t he

case,

speci c

heat

capacity

is

given

joules

per

g ram

per

deg ree

Celsius

or

J g

calculating

.

Using

water

as

neutralisation

speci c

heat

capacity

of

water

is

and

heat

of

an solution

t he

made

heat

1

°C

1

example,

the

t he of

1

units

assumptions

temperature

4.2

J g

o

from

experimental

1

C

.

This

means data.

t hat

it

takes

4.2

J

of

heat

energy

to

raise

t he

temperature

of

1 g

of

water

by

1 °C.

217

Calculating

energy

changes

Energetics

If

Key

!

we

heat

fact

t he

The

specific

heat

capacity

know

of

substance

heat

energy

is

quantity

required

temperature

substance

the

of

by

a

to

unit

1 °C

temperature

q,

of

t he

from

change,

substances

t he

specic

T,

using

reacting,

heat

t he

m,

capacity

following

we

of

can

t he

determine

substances,

c,

t he

and

formula:



m



c



T

of

raise

mass

or

mass

of

q a

t he

reaction,

the

of

the

Measuring

1 K.

To

measure

heats

t he

heat

apparatus

known

container

whic h

sur roundings

being

The

a

general

xed

be

heat

reaction

t he

is

out

is

and

used.

released

of

if

a

t he

heat

A

by

exot her mic,

reaction

made

met hod

volume

it

into

of

maximum

or

of

solution

calor imeter

a

reaction

or

heat

reaction

polystyrene

above

determining

water

reactants

minimum

to

or

calorimeter

The

temperature

given

for

solution

t he

t hermometer.

The

neutralisation

c alor imeter

is

cup

is

a

an

piece

escaping

from

t he

into

t he

sur roundings

endot her mic.

because

of

insulated

A

simple

polystyrene

is

a

insulator.

pouring

a

by

can

of

a

reaction

prevents

t he

absorbed

calor imeter

good

if

as

of

are

to

can

t hen

t he

t hen

heat

of

of

be

reaction

used

measuring

temperature

change

calculate

and

heats

be

t he

its

mixed

reached

in

involves

t he

t he

calculated

cylinder,

temperature

calorimeter

reaction

and

measuring

measuring

initial

in

in

a

used

in

is

using

and

t he

measured.

t he

formula

reaction.

Assumptions

In

t he

experiments

you

will

be

carr ying

out

to

determine

t he

heat

of

neutralisation and heat of solution, you will make t hree assumptions in your

calculations.

●

The

density

of

a

dilute

aqueous

solution

is

t he

3

1 g cm

●

The

This

specic

means

heat

t hat

●

i.e.

4.2

Negligible

J g

heat

surroundings

Heat

!

Key

of

t he

capacity

1

water,

same

as

water,

i.e.

3

.

of

a

mass

of

dilute

1 cm

of

aqueous

solution

solution

is

is

1 g.

t he

same

as

1

°C

is

lost

during

to

t he

t he

surroundings

or

absorbed

from

t he

reaction.

neutralisation

fact The

neutralisation

reaction

between

a

strong

acid

and

a

strong

alkali

is

an

exot hermic reaction. The amount of heat produced per mole of water formed The

heat

heat

of

change

1 mol

of

neutralisation

which

water

is

occurs

produced

is

the

when

in

in

t he

between

an

acid

is

known

as

t he

heat

of

neutralisation

a

In reaction

reaction

and

calculating

t he

heat

of

neutralisation,

t he

initial

temperature

of

an

bot h

solutions

must

be

measured

and

averaged

to

determine

t he

initial

alkali.

temperature,

must

be

and

t he

number

of

moles

of

water

produced

in

t he

reaction

calculated.

Example

3

A

volume

of

50 cm

of

sodium

hydroxide

solution

of

3

1.0 mol dm

concentration

3

and

temperature

26.0 °C

is

added

to

50 cm

of

hydrochloric

3

acid

t he

of

concentration

maximum

neutralisation

218

temperature

and

and

1.0 mol dm

draw

an

of

t he

temperature

solution

energy

prole

is

33.2 °C.

diagram

for

27 .0 °C.

Af ter

Determine

t he

mixing,

t he

reaction.

heat

of

Energetics

The

Calculating

balanced

equation

NaOH(aq)



for

t he

reaction

HCl(aq)

energy

changes

is:

NaCl(aq)



H

O(l) 2

Determine

t he

number

of

moles

of

water

made

in

t he

reaction:

3

1000 cm

of

NaOH(aq)

contain

1.0 mol

NaOH

1.0

_____

3

∴

50 cm

of

NaOH(aq)

contain



50 mol

NaOH



0.05 mol

NaOH

1000

3

And

1000 cm

of

HCl

contains

1.0 mol

HCl

1.0

_____

3

∴

50 cm

of

HCl(aq)

contain



50 mol

HCl



0.05 mol

HCl

1000

From

t he

1 mol

equation:

NaOH

reacts

wit h

1 mol

HCl

forming

1 mol

H

O 2

∴

0.05 mol

NaOH

reacts

wit h

0.05 mol

HCl

forming

0.05 mol

H

O 2

i.e.

0.05 mol

H

O

is

produced

in

t he

reaction.

2

Determine

t he

heat

of

neutralisation:

3

Total

∴

volume

mass

of

of

solution 

solution,

m



50



50



100 cm

100 g

26.0



27 .0

___________

Average

initial

temperature,

T



°C



26.5 °C

1

2

Final

temperature,

T



33.2 °C

2

∴

temperature

increase,

T



T

–

T

2



(33.2

–

26.5) °C

1

Specic

Using

q

heat



heat

m



c

evolved

capacity



in

of

t he



6.7 °C

1

solution,

c



4.2 J g

1

°C

T,

forming

0.05 mol

H

O



(100



4.2



2814



2.814 kJ



6.7) J

2

J

2.814

______

∴

heat

evolved

in

forming

1 mol

H

O 

kJ

2

0.05



56.28 kJ

1

i.e.

The

heat

t herefore,

The

heat

of

neutralisation,

neutralisation

t he

energy

of

reaction

prole

was

diagram

is

H



negative

56.28 kJ mol

because

t he

is

shown

increased,

below:

activation

NaOH(aq)

temperature

exothermic



energy

HCl(aq)

tnetnoc ygrenE

1

H



56.28 kJ mol

NaCl(aq)



H

O(l)

2

Course

of

reaction

219

Calculating

energy

changes

Energetics

T o

determine

Your

teacher

the

may

●

observation,

●

manipulation

●

analysis

heat

use

this

recording

and

and

of

neutralisation

activity

and

to

assess:

reporting

measurement

interpretation.

3

Y ou

will

be

hydroxide

and

a

supplied

solution,

with

a

3

1.0 mol dm

calorimeter

sulfuric

(polystyrene

acid,

2.0 mol dm

cup),

a

potassium

measuring

cylinder

thermometer.

Method

3

1

Measure

the

2

dry

50 cm

of

sulfuric

acid

in

the

measuring

cylinder

and

pour

it

into

calorimeter.

Measure

and

record

the

temperature

of

the

acid

using

the

thermometer.

3

3

Measure

50 cm

measuring

4

Pour

the

solution

Record

6

Calculate

7

to

the

that

the

the

reaction

calculation

The

an

the

hydroxide

of

solution

temperature

the

initial

density

as

prole

for

cleaned

the

calorimeter

the

and

temperature

stir

the

change.

reached.

of

the

heat

the

and

to

for

the

the

two

solutions

and

use

increase.

acid

diagram

neutralisation

into

specic

page

in

temperature.

watching

calculate

sulfuric

previous

its

temperature

and

water,

solution

record

while

temperature

between

energy

heat

the

same

on

hydroxide

and

thermometer

average

calculate

both

9

Measure

maximum

are

Draw

the

the

Assuming

8

potassium

potassium

with

5

this

of

cylinder.

capacity

heat

of

potassium

help

the

of

the

solution

neutralisation

hydroxide.

for

Use

the

you.

reaction.

reaction

should

be

approximately

1

56.3 kJ mol

.

If

your

value

is

lower

than

this,

can

you

suggest

reasons

why?

The

heat

of

neutralisation

for

t he

reaction

between

any

strong

acid

and

any

acids

and

1

strong

alkali

is

always

about

56.3 kJ mol

.

This

is

because

strong

strong alkalis are fully ionised in aqueous solution and t he common reaction

t hat

releases

heat

in

all

cases

is:



OH

(aq)



H

1

(aq)

H

O(l)

H



56.3 kJ mol

2

The equation for t he neutralisation reaction between sodium hydroxide and

sulfuric

acid

is:

2NaOH(aq)



H

SO 2

(aq)

Na

4

SO 2

(aq)



2H

4

O(l) 2

In this reaction, 2 mol of water are produced. The heat of neutralisation is still

1

about 56.3 kJ mol

in

the

The

equation

heat

of

is

, however, the overall heat change for the reaction shown

about

1 12.6 kJ,

neutralisation

thermometric

temperatures

titration

of

t he

acid

can

i.e.

also

explained

and

double

be

in

alkali

t he

heat

determined

Unit

must

8.5.

be

In

of

neutralisation.

from

t his

t he

results

met hod,

measured

and

t he

t he

of

a

initial

point

of

intersection of t he two lines of best t on t he graph represents t he maximum

temperature

220

recorded

during

t he

reaction.

Energetics

Heat

When

Calculating

of

a

energy

changes

solution

solid,

liquid

or

gas

dissolves

in

a

solvent,

t here

is

usually

a

change

in

Key

!

fact

ent halpy. This ent halpy change which occurs when 1 mol of solute dissolves The

in

In

a

solvent

is

known

calculating

be

measured

t he

and

as

heat

t he

heat

of

of

solution

solution,

exact

t he

quantity

initial

of

heat

change

temperature

solute

dissolving

of

t he

must

water

be

of

solute

t he

number

of

moles

of

solute

can

be

solution

of

solvent

is

occurs

dissolves

in

the

heat

when

such

1 mol

a

volume

must

known

that

further

dilution

by

the

so solvent

t hat

of

which

produces

no

further

heat

calculated. change.

Example

3

A

student

water.

The

minimum

heat

for

of

t he

dissolves

initial

5.35 g

solution

of

Determine

t he

ammonium

temperature

temperature

solution

of

of

of

16.4 °C

ammonium

t he

is

chloride

water

recorded

chloride

and

is

by

in

100 cm

22.5 °C.

t he

draw

student.

an

of

Af ter

energy

distilled

mixing,

Determine

prole

a

t he

diagram

process.

number

of moles

of

NH

Cl

dissolved:

4

1

M(NH

Cl)



53.5 g mol

4

i.e.

mass

of

1 mol

NH

Cl



53.5 g

4

5.35

_____

∴

number

of

moles

in

5.35 g



mol



0.1 mol

53.5

Determine

t he

Mass

heat

of

Initial

of

water,

solution:

m



100 g

temperature,

T



22.5 °C

1

Final

temperature,

T



16.4 °C

2

∴

temperature

decrease

( T)



T

–

T

1



22.5

–

16.4 °C

1

Specic

Using

q

heat



heat

m



capacity

c



absorbed

of

t he



6.1 °C

2

solution,

c



4.2

J g

1

°C

T,

in

dissolving

0.1 mol

NH

Cl



100



2562



4.2



6.1

J

4

J



2.562 kJ

2.562

______

∴

heat

absorbed

in

dissolving

1 mol

NH

Cl



kJ



25.62 kJ

4

0.1

heat

of

solution,

H



Exam

✔

1

i.e.

25.62 kJ mol

It

is

essential

tip

that

you

give

The heat of solution is positive because t he temperature decreased, t herefore,

the

t he

reaction

was

correct

unit

energy

the

heat

of

endothermic

neutralisation

The

for

prole

diagram

is

shown

below:

are

for

or

calculating

producing

dissolving

solution.

the

heat

1 mol

1 mol

of

of

(aq)



Cl

(aq)

4

you

change

water

solute,



NH

Since

or

the

unit

1

will

tnetnoc

It

is

always

also

be

J mol

essential

1

or

that

kJ mol

you

.

indicate

activation

whether

energy

1

H



or

ygrenE

your

Cl(s)



reaction

by

is

exothermic

putting

a

25.62 kJ mol

negative

NH

the

endothermic

or

positive

sign

before

value.

water

4

Course

of

reaction

221

Calculating

energy

changes

Energetics

T o

determine

Your

teacher

may

●

observation,

●

manipulation

●

analysis

Y ou

will

use

and

of

this

solution

activity

and

to

assess:

reporting

measurement

interpretation.

supplied

calorimeter

heat

recording

and

be

the

with

(polystyrene

potassium

cup),

a

nitrate,

measuring

distilled

cylinder

water,

and

a

a

balance,

a

thermometer.

Method

3

1

Measure

into

the

dry

2

Measure

3

Using

water

4

Stir

100 cm

and

the

in

the

of

distilled

water

in

the

measuring

cylinder

and

pour

it

calorimeter.

record

balance,

the

the

temperature

weigh

12.1 g

of

of

the

water.

potassium

nitrate

and

add

it

to

the

calorimeter.

solution

with

the

thermometer

while

watching

the

temperature

change.

Summary

questions

5

Record

6

Calculate

7

Assuming

as

1

Dene

the

the

water,

the

a

heat

of

neutralisation

b

heat

of

solution

Is

specic

heat

the

to

in

heat

of

capacity

solution

of

of

the

solution

potassium

is

the

nitrate.

same

an

on

a

the

previous

potassium

reason

for

your

page

nitrate

to

an

help

Use

the

you.

exothermic

or

endothermic

reaction?

answer.

Draw

an

energy

prole

diagram

for

the

solution

process.

assumptions

10 made

the

heat

capacity.

9

are

decrease.

specic

calculate

dissolving

Give

What

the

reached.

following:

8

2

temperature

temperature

that

calculation

c

minimum

By

reference

for

the

to

bonds

breaking

and

bonds

forming,

explain

the

reason

experiment

determine

the

heat

enthalpy

change

which

occurred

when

potassium

nitrate

of dissolved

in

water.

neutralisation?

3

Why

is

the

heat

of

When neutralisation

between

and

for

sodium

hydrochloric

the

a

solute

●

hydroxide

Bonds

the

acid

break

same

as

the

heat

in

between

surroundings.

which the

dissolves

a

solvent

t he

following

events

occur.

reaction

break,

e.g.

In

the

the

when

par ticles

case

of

sodium

of

the

ionic

solute;

this

compounds,

chloride

dissolves

it

in

absorbs

is

the

water

energy

ionic

it

is

from

bonds

the

ionic

of 

bonds neutralisation

for

the

between

potassium

sulfuric

It

was

found

that

of

the

Cl

ions

which

break.

In

the

case

substances,

it

is

the

intermolecular

forces

between

the

of

molecules

break,

e.g.

between

when

the

ethanol

ethanol

dissolves

molecules

in

water

that

it

is

the

intermolecular

break.

when ●

4.0 g

and

acid?

forces

4

ions

hydroxide

that and

Na

reaction

covalent between

the

ammonium

The

intermolecular

also

absorbs

forces

between

t he

solvent

molecules

also

break;

t his

nitrate

energy

from

t he

surroundings.

3

dissolved

in

50 cm

of

distilled

●

water,

the

Attractions

t he decreased

from

27.4 °C

molecules

Determine

solution

for

the

heat

ammonium

energy

energy

reaction

is

absorbed

for

the

ions

or

process

to

t he

molecules

is

called

of

t he

solute

solvation

and

and

it

surroundings.

exot hermic

if

more

energy

to

break

if

more

t he

bonds

energy

is

in

t he

is

released

solute

absorbed

process.

solvent

222

t he

This

during

solvation

t han

and

solvent.

The

reaction

is

prole

endot hermic diagram

between

solvent.

nitrate

is an

t he

of

The

draw

formed

of

to

releases

21.6 °C.

and

are

temperature

t han

is

released

during

solvation.

to

break

bonds

in

t he

solute

and

Energetics

Key

●

Exothermic

reactions

mixture

its

and

Endothermic

t heir

●

bonds

are

an

an

The

The

energy

t han

energy

an

broken

in

heat

to

in

get

t he

in

of

energy

forming

reaction,

energy

t he

released

a

change

t han

The

H



exot hermic

a

reaction

The

H

is

zero,

A

proceed

to

The

●

The

H

The

of

●

t he

t he

of



To

m

in

t he

by

heat

a

absorbed.

to

absorbed

called

can

energy

from

When

new

break

bonds

is

less

new

to

break

bonds

is

bonds.

enthalpy

and

is

given

t he

be

measured

and

is

given

t he

H

,

t herefore,

H

is

less

t han

reactants

H

>

chemical

is

t he

H

, t herefore,

H

is

greater

reactants

reaction

minimum

from

heat

c

in



a

of

can

be

illustrated

by

an

amount

of

energy

required

for

a

a

of

is

can

determine

in

t he

route

required

for

t he

for

a

reaction

to

substance

in

t he

quantity

mass

be

enables

us

to

determine

temperature.

of

heat

heat

from

t he

capacity

using

energy

substance

calculated

T,

of

t he

t he

by

required

1 °C

masses

of

t he

or

of

to

1 K.

t he

substances,

c,

formula:

T

in

solution

produces

energy

alternative

specic

neutralisation

dissolves

a

unit

t he

activation

energy.

change

q,

m,

of

an

temperature,

produced

of

less

capacity

reaction ,



amount

providing

capacity

reacting,

of

is

heat

solvent

●

reaction

positive.

requires

change

heat

solute

is

temperature

heat

water

The

t he

absorb

bonds.

forming

is

is

absorbed

new