Chem Lab Basics: Quick Study Guide 1423238648, 9781423238645

Table of contents :
HELPFUL ICONS
LAB SAFETY TRAINING
Safety Training
Be Prepared
Personal Responsibility
GENERAL LAB GUIDELINES
WORKING WITH CHEMICALS
Heating Labware
Liquid Reagent
Solid Reagent
EXPOSURE TO CHEMICALS
Possible Risks of Exposure
FIRST AID
Burn from Hot Labware
Cut from Broken Glassware
Skin Exposure to aChemical
Feeling Lightheaded orPassing Out
Burning Clothing
Summary
KNOW YOUR LAB REAGENTS
Safety Data Sheets (SDS) Formerly Known as MSDS
Chemical Storage Codes
Baker System
International Hazard Symbols
CHEMICAL SPILLS
On the Floor or Bench Top
On Your Clothing or Skin
WASTE MANAGEMENT
USEFUL CHEMICAL INFORMATION
Organic Compounds: General Rules
Organic Solvents
Properties of Inorganic Salts (Aqueous Solubility)
Flame Test
Acids
Bases
Properties of Air
pH Key equations
pH Range & Examples
Common Ions
Acid-Base Indicators
Physical Constants
PERIODIC TABLE
LAB MUST-KNOWS
Common Lab Equipment
How to Dispense Liquids
How to Use a Pipette
How to Dispense Solids
How to Use a Balance
How to Use a Gas Burner
How to Use a Hot Plate
How to Use a Gas Cylinder
SAFE USE OF LAB EQUIPMENT
DATA MANIPULATION
Lab Units & Conversion Factors
Metric Prefixes
Metric Base Units
Other Common Units
Metric Conversions
Significant Figures (Sigfigs)
Graphing (x, y) Data
Equation for a Line
Average or Mean Value
PREPARING A SOLUTION
General Guidelines
Dilute Solutions from Stock
Dilute Solutions from Pure Reagents
Dilutions of Acids & Bases

Citation preview

WORLD’S #1 ACADEMIC OUTLINE

Essentials of lab concepts, use & safety—including helpful hints & tips, plus ways to avoid common pitfalls & dangers

HELPFUL ICONS

Hints

Think Again

Danger

Pitfalls

LAB SAFETY TRAINING • Lab skill—like skill in sports, music, or art—does not come naturally to anybody. Success in each of these areas depends on discipline, practice, and training. In the chemistry lab, you encounter new equipment and varied types of chemical materials that require training if you plan to use them safely. • Remember, details are important in chemistry—and not just where numbers and calculations are concerned. Chemical names and formulas present a whole new lingo. You have to know these symbols and definitions to work in the lab.

One letter can mean a lot—chlorine, with an “n,” is a toxic gas; sodium chloride, with a “d,” is a harmless salt.

Safety Training • Safety is an integral part of working in the chemistry lab, and a responsibility shared by students and instructors. • Learning about safety is part of your education; skills you gain in the lab will serve you in future careers and in life…. If nothing else, they will make you a better cook!

Be Prepared

• Where is the lab exit? Every lab should have at least two exits. Know how to get out quickly in an emergency.

Never work in an isolated “corner” of a lab; upper-floor windows do not count as emergency exits. • Where is the nearest phone? You may need to call for help in an emergency. If so, dial 911 or your local emergency number.

Do not rely on the cell phone in your book bag—it may be on fire! • Where is the fume hood? You’ll need to use it for any noxious reagent.

Always use a hood when working with concentrated acids or aqueous ammonia. If the chemical has a pungent odor, or is a health risk, you need to use a hood. • Where are the eyewash station and safety shower? These are for washing skin and/or eyes exposed to chemicals. • Where is the fire extinguisher? You may need to use it to douse small fires. Check with your instructor on guidelines for using an extinguisher. Some fires require special treatment.

Sodium reacts with water, a common ingredient in most fire extinguishers.

Personal Responsibility Rule 1: Safety first! Your mistakes will likely harm you more than anyone else. Ask questions if you are not sure how to do something properly. Rule 2: Read the lab manual before class. Come to lab prepared to work on the assigned experiment. Rule 3: Always pay attention as you work. Watch other students; you are impacted by their mistakes. Rule 4: Don’t fool around. Injuries happen when people play jokes or games, or show off in the lab. Repairing broken instruments can cost thousands, and some chemicals are very dangerous if misused or accidentally mixed. Rule 5: Clean up your own mess. You are a partner in maintaining a safe lab.

Keys to a Clean Lab

• Keep your workspace clean and organized. • Wash labware with detergent; rinse with deionized or distilled water. Use a wash bottle to conserve water. Drain excess liquid and allow the labware to dry before storing. • Wash shared equipment before and after each use. • After each lab session, return reagents and equipment to the designated storage areas.

Use these icons to help navigate to important information!

GENERAL LAB GUIDELINES • Always work with instructor supervision. Never work in a lab alone. • Always wear goggles in the lab, even over eyeglasses; replace contact lenses with eyeglasses.

Contact lenses can absorb solvent vapors. If you do accidentally get chemicals in your eye, the contact lens can actually trap harmful chemicals between the lens and your cornea. So switch to glasses for lab sessions. • Wear an apron, lab coat, and gloves to limit your chemical exposure and to save clothing from chemical stains.

Select gloves to match the chemicals that you are using in the lab. Some gloves dissolve in certain organic solvents. Think about what happens when you expose a Styrofoam cup to acetone. Unless you want it stained, never wear your favorite new shirt to the lab.

Do not store book bags, cell phones, or other electronic gear on the lab bench. They can interfere with your workspace and could be damaged by a chemical spill or accident. • Food, drink, and cosmetics should not be brought into the lab.

You would be eating any chemicals that accidentally get on your food or putting chemicals on your lips with the lipstick. • Before leaving, wash your hands after each lab session. • Do not take any lab chemicals home with you, even by accident.

You definitely do not want chemicals flavoring the burger and potato chips you have after lab!

• Wear closed-toe shoes and long pants to protect your feet and legs.

These precautions provide protection from spilled chemicals and broken glass. • Tie back hair and avoid bulky sleeves that interfere with work.

Remove any rings and other jewelry that may lessen your grip on beakers, test tubes, and other equipment. Some jewelry may be damaged by lab chemicals.

WORKING WITH CHEMICALS Heating Labware

• Use tongs to handle labware while it is heated by a burner or hotplate.

Hot lab items do not look hot. Touching hot glassware is a good way to spill the contents. • Allow the item to cool to room temperature before weighing it.

Hot items create air currents that alter the reading of a balance.

Liquid Reagent

• Cover beakers with watch glasses. • Use “boiling stones” to promote smooth boiling. • Flammable solvent: Take special care when heating flammable liquids with a hot plate; avoid using an open flame. • Handle test tubes with wire test tube holders.

Heating a liquid is not a race. Overly rapid heating can cause the solution to erupt into a boil, termed bumping, usually resulting in the liquid spilling onto the hot 1

plate or burner and the lab bench top, soaking your notebook, etc.

Solid Reagent

• Use weighing dishes on balances. • Cover weighing dishes to prevent loss, spills, or contamination.

Always record lab data in an organized notebook, including the number and unit.

EXPOSURE TO CHEMICALS

KNOW YOUR LAB REAGENTS

While working in the lab, you will use a number of reagents, giving ample chance for exposure to the harmful effects of chemicals. In some cases, exposure will be due to an accidental spill or breakage of equipment. Other limited exposure may come as a result of using the chemicals as directed. If you can smell a volatile chemical, it could harm you. Your sense of smell is very sensitive, reflecting your body’s sensitivity to all types of odors. This also reflects the efficiency of our biochemistry—and explains why we have adverse reactions to minute quantities of certain chemicals.

Some chemicals are toxic; all can cause harm if used incorrectly. Learn about reagents before using them in an experiment. Read your lab manual and textbook, and talk to your instructor. If in doubt, ask questions!

Possible Risks of Exposure

1. Identification: Includes name, manufacturer, contact number(s), and restrictions on use 2. Hazards: Includes all hazards and labeling requirements 3. Ingredients: Percent purity, if there are any stabilizers or denaturants 4. First aid measures: Both acute (immediate) and long-term effects 5. Fire fighting measures: Best tools to use when putting out fires involving this material 6. Accidental release measures: Protective equipment requirements; cleanup and containment 7. Handling and storage: How containers must be stored—includes incompatibilities 8. Exposure controls: Details personal protective equipment used (e.g., gloves, lab coat) and includes toxicity limits for exposure 9. Physical and chemical properties: Melting point, boiling point, formula, etc. 10. Stability and reactivity: Lists possible hazardous reactions and chemical stability 11. Toxicology information: Route of exposure and symptoms of acute and long-term exposure 12. Ecological information: How the chemical interacts in the natural world 13. Disposal considerations: How to treat and get rid of waste material safely 14. Transportation information: Restrictions on shipping or transporting material safely 15. Regulatory information: Some materials have special rules (e.g., alcohol, neurotoxins) 16. Other information: Date of SDS preparation or revision, other rules, etc.

• Inhaling chemical powder or vapor. Take care when working with any volatile solvents.

Remember, if you can smell it, it could be harming you. Know how to use a fume hood. • Ingesting solid or liquid chemicals by mouth.

You are not likely to make a meal of chemicals in the lab, but any chemical on your hands or face could end up inside you when you consume food after the lab session. • Puncturing your skin with a sharp object and possibly injecting chemicals into your body.

Chipped or cracked glassware should not be used. Chipped beakers, flasks, and pipettes can have sharp edges and are common sources of injury. Take special care when inserting glass tubing or a thermometer into a rubber stopper; always use a slit-stopper and lubricate the glass to ease insertion. If you have to force it, you may snap the glass tube and end up inserting it into your hand. • Absorbing chemicals through your skin.

Never handle any chemical with your bare hands. Examine all cases of exposure to solid or liquid reagents, and take the appropriate action to treat the harm to your skin. Some solvents—for example, DMSO (dimethyl sulfoxide)—easily pass through the skin and carry chemicals into your body. Use the correct gloves for the materials you are using!

Safety Data Sheets (SDS) Formerly Known as MSDS

• An SDS is a detailed description of everything you would ever want to know about a chemical. Copies of the SDS should be in the lab for all the chemicals you are using. • Prior to 2015, these were known as Material Safety Data Sheets and had similar information.

As of 2015, each SDS should have the same 16 sections.

Chemical Storage Codes

• Chemicals in the same color group can normally be stored together; exceptions are noted on the label. Health hazard Reactive and oxidizing

SPECIFIC HAZARD Oxidizer Acid Alkali Corrosive Use NO WATER Radioactive

Flammable Corrosive Minimal hazard

FIRST AID Check with your instructor for local guidelines—those are the rules that you must follow.

Burn from Hot Labware Minor: Apply cold water. Serious: Contact medical help.

Cut from Broken Glassware Minor: Wash with soap; apply antiseptic ointment and a sterile bandage. Serious: Control bleeding by applying pressure with a sterile pad; contact emergency medical help. Be especially aware of the danger of chipped beakers and flasks. Also, take care when washing glass labware; it gets slippery and is easily dropped.

Skin Exposure to a Chemical Rinse with water; if a condition develops, contact medical personnel.

Feeling Lightheaded or Passing Out Move affected person to fresh air outside the lab; contact medical personnel if the condition persists. This can be a common problem when working with cylinders of compressed gases, such

as CO and CO2— even non-toxic gases such as He and N2 can displace the oxygen in a lab. Dangerous organic solvents should be used under fume hoods.

Burning Clothing Do not panic; drop to the floor and smother the flame. Use a safety shower to treat burns; contact emergency medical personnel. Do not use a fire blanket; these only complicate subsequent medical treatments for burns.

Summary Good lab planning and prevention of accidents is the best first aid. Read your lab instructions thoroughly before class and follow safety rules. Do not be heroic! Deal with cuts and minor chemical exposure promptly. Call emergency personnel for anything that is major.

HEALTH HAZARD 4 - Deadly 3 - Extreme danger 2 - Hazardous 1 - Slightly hazardous 0 - Normal material

3

FIRE HAZARD Flash Points: 4 - Below 73ºF 3 - Below 100ºF 2 - Above 100ºF, not exceeding 200ºF 1 - Above 200ºF 0 - Will not burn

1 2 OX ACID ALK COR W

W

REACTIVITY 4 - May detonate 3 - Shock and heat may detonate 2 - Violent chemical change 1 - Unstable if heated 0 - Stable

NFPA Hazard Codes (National Fire Prevention Association) (Highlights major chemical hazards)

Baker System Color Code

Directions

Warning

Health hazard (blue)

Store in secure (locked) poison area.

Chemicals that are toxic if inhaled, Cyanides and mercury ingested, or absorbed through the skin.

Flammable hazard (red)

Store in a “flammable liquids” storage area.

Chemicals that easily ignite; also, chemi- Acetone and organic cals that present an explosion hazard. solvents

Reactivity hazard (yellow)

Store in an area isolated from flammables and combustibles.

May react violently with air, water, or other substances.

Corrosive hazard (white)

Store in a corrosion-resistant area. Chemicals that react with skin or other Concentrated acids Separate acids and bases. exposed tissue. and bases Separate oxidizing acids from organic acids.

No serious hazard (green or orange)

May be stored in general storage.

None. Safe for use under most circumstances.

Sodium chloride and dextrose

Store with caution.

Reacts with other materials in that storage group; store each one separately.

Hydrogen peroxide with copper or iron

Incompatabilities (diagonal stripe)

Examples

Reactive metals, calcium, and sodium

International Hazard Symbols Starting in 2015, the new hazard symbols all have red borders on a white background, with a different pictogram depending on the particular hazard.

Safety is the top consideration in any chemistry lab. Make sure you know all of the safety codes and pictograms.

Physical hazards

Explosive

Flammable

Oxidizing

Compressed gas

Health hazards

Acute toxicity Corrosive Harmful Health hazard 2

Corrosive

Env. hazards

Hazardous to the environment

CHEMICAL SPILLS On the Floor or Bench Top

• Small spills: Wear gloves, neutralize with an acid or base, absorb using paper towels, and discard in a labeled bag. Make sure the gloves and bag are resistant to the chemical that was spilled. • Large spills: Notify the instructor. Wear gloves and shoe protectors and use a spill kit designed for the chemical. Your lab should be equipped with these items. • Clean up all spills promptly to prevent further accidents.

You do not want to track through any spill; it may dissolve your shoes!

On Your Clothing or Skin

• Assess the risk presented by the chemical. Dilute solutions of most reagents do not present a major health risk. Think about a 0.1 M NaCl vs. a 10.0 M HNO3. The former is harmless, whereas the latter can cause major skin and clothing damage. • If needed, remove the affected article of clothing, wash exposed skin with water, and apply first aid. Treat promptly to minimize harm. • If a large area is exposed, use the safety shower and then apply first aid. After first aid, follow up with professional medical treatment.

WASTE MANAGEMENT • “Waste” is a term with specific meaning in the chemical community. Federal, state, and local laws mandate how chemistry labs handle the excess solvents and other chemicals that are generated by chemists. Chemical waste may or may not be hazardous. • Follow the instructor’s directions for disposal of all lab materials. Most chemicals should not be poured down the drain. Your institution may be penalized by federal authorities if waste is not handled properly by you and other students. • Label all waste material as waste, but be sure to list the chemicals included in the waste material. Each type of chemical waste should have its own container to prevent mixing incompatible materials. Chemicals have different regulations and requirements for disposal depending upon the type of waste present. Mistakes as simple as unlabeled waste bottles can result in substantial fines! Unknown waste must be identified before it can be disposed of, which can be an expensive process. • All toxic metals and halogenated solvents must be collected for proper disposal. • Toxins may be active at very low levels. - 1 part per hundred (%) 1/100 1:100 - 1 part per million (ppm) 1/1,000,000 1:106 - 1 part per billion (ppb) 1/1,000,000,000 1:109 - 1 part per trillion (ppt) 1/1,000,000,000,000 1:1012 • Waste prevention: Use only the required amount of reagent. Excess material cannot be returned to the reagent jar; it is “waste.” Reagents are often expensive, so conservation helps keep lab costs low. • General rule: When in doubt, collect all solutions used in the lab in labeled waste bottles. Make sure that any chemical that is poured into the sink is not going to react in the sewer line or contribute to pollution. Most local water-treatment facilities monitor water from school labs.

Remember—if you “sink it” today, you “drink it” tomorrow. Dilution is NOT the solution to pollution.

USEFUL CHEMICAL INFORMATION Liquid solubility rule: “Like dissolves like” Water, “the universal solvent,” is an excellent solvent for polar molecules like salts. Boiling point: 100.0ºC Freezing point: 0.0ºC Density: 1.00 g/mL at 4ºC Molar mass: 18.015 g Vapor pressure: 23.8 mm Hg, 25ºC

Organic Compounds: General Rules

• Nonpolar compounds (e.g., hexane and benzene) are soluble in nonpolar organic solvents, but insoluble in water. Oils tend to float on water (think about when you are washing oily or greasy dishes). • Polar compounds (e.g., amines, alcohols, and organic acids) tend to dissolve in water.

Organic Solvents Organic Solvent

Acetone Acetic acid Benzene Carbon tetrachloride Chloroform Diethyl ether Dimethyl sulfoxide (DMSO) Ethanol Ethyl acetate Ethylene glycol Hexane Isopropanol Methanol Toluene

Boiling Point

Density Molar Mass (g/mol) (g/mL)

56ºC 118ºC 80ºC 77ºC 61ºC 34.5ºC 189ºC

0.79 1.0446 0.88 1.594 1.4788 0.713 1.092

58.08 polar 60.052 polar 78.12 nonpolar 153.82 nonpolar 119.38 nonpolar 74.12 nonpolar 78.13 polar

79ºC 77ºC 195ºC 69ºC 82ºC 65ºC 111ºC

0.79 0.895 1.115 0.659 0.79 0.79 0.87

46.07 polar 88.11 polar 62.07 polar 86.18 nonpolar 60.11 polar 32.04 polar 92.15 nonpolar

Bases NaOH and KOH, hygroscopic pellets Commercial Reagent

NaOH Aqueous ammonia

Roughly 80% N2, 20% O2 Water content, variable: 1–4%

pH Key equations pH = -log10 [H+] pOH = -log10 [OH-] pOH + pH = 14 Water self-ionization: pKw = 14 Neutral pH of water = 7.0 = 1 × 10-7 M [H+] ions

pH Range & Examples Strong Weak Weak Strong Acid Acid Base Base Neutral 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 HO HCl, HNO H CO NH NaOH H SO HAc Ca(OH) KOH NaCl NH + Salts Ac- or CO 2- Salts 2

3

2

Soluble

Soluble

Forms hydroxide

Ca, Mg Sr, Ba Fe, Cu, Zn Pb(II) Hg(I) Ag

Soluble Soluble Soluble Insoluble Insoluble Insoluble

Insoluble Insoluble Insoluble Insoluble N/A Soluble

Soluble Insoluble Soluble Insoluble Insoluble Soluble

Insoluble Insoluble Insoluble Insoluble Insoluble Insoluble

Insoluble Insoluble Insoluble Insoluble Insoluble Insoluble

Blue: Copper (azure), lead, arsenic, and selenium Green: Copper (emerald), barium (yellowish), and zinc (whitish) Yellow: Sodium Red: Lithium (carmine), strontium (scarlet), and calcium (yellowish)

Acids Commercial Reagent

Hydrochloric, HCl Nitric, HNO3 Sulfuric, H2SO4 Acetic Glacial acetic Phosphoric

11.6 M 16.0 M 18.0 M 6.27 M 17.4 M 14.7 M

Pungent Oxidizer Dehydrating agent Vinegar smell

Safety notes—oxidizing acids should not be stored or mixed with organic acids. When diluting acids, always add the acid to the solvent. As the old saying goes, “Add acid to water, doin’ what you oughter.” 3

2

3

Charge

Soluble

Violet: Potassium, rubidium, and cesium

3

Common Ions

Soluble

Characteristic colors of ion in a flame

3

4

Carbonate Sulfide Phosphate Oxide Hydroxide Chromate

Flame Test

2

4

Soluble Alkali metals, ammonium Soluble Soluble Soluble Soluble Soluble Soluble

Pungent

Properties of Air

Properties of Inorganic Salts (Aqueous Solubility) Acetate Chloride Nitrate Bromide Fluoride Sulfate Perchlorate Iodide Chlorate

19.1 M 14.8 M

C2H3O2OH CO3 HCO3 NO3 NO2 O2 PO4 SO4 SO3 ClO4 NH4

112111232211+

Molar Mass

Acetate Hydroxide Carbonate Bicarbonate Nitrate Nitrite Peroxide Phosphate Sulfate Sulfite Perchlorate Ammonium

59.04 17.01 g/mol 60.01 g/mol 61.02 g/mol 62.01 g/mol 46.01 g/mol 32.00 g/mol 94.97 g/mol 96.97 g/mol 80.07 g/mol 99.45 g/mol 18.04 g/mol

Acid-Base Indicators Compounds that change color as the pH changes. Selection: Pick to match the pH range of the salt produced by a titration or other process. Name

Range

Acid-Base Color

Bromcresol green Methyl red Phenol red Thymol blue Phenolphthalein

4.0–5.6 4.4–6.2 6.4–8.0 8.0–9.6 8.0–10.0

Yellow-blue Red-yellow Yellow-red Yellow-blue Colorless-red

Physical Constants Avogadro’s number, NA: Mass of electron, me: Mass of proton, mp: Mass of neutron, mn: Planck’s constant, h: Electron charge, e: Faraday’s constant, F: Ideal gas constant, R for gas calculations: for energy calculations: Speed of light: Standard temperature and pressure (STP): Volume of ideal gas at STP: Typical room temperature:

6.022 × 1023 mol-1 9.110 × 10-31 kg 1.673 × 10-27 kg 1.675 × 10-27 kg 6.626 × 10-34 J s 1.602 × 10-19 C 96,485 C mol-1 0.082 L atm mol-1 K-1 8.314 J K-1 mol-1 2.9979 × 108 m/s 1 atm and 0ºC 22.414 L/mol 20–25ºC

Periodic Table PERIODIC TABLE

Solid

Liquid

Gas

232.0

1

H

1.008

Li

6.94

Lithium

11

Na

22.99

Sodium

19

K

39.10

Potassium

37

Rb

85.47

Rubidium

55

Cs

132.9 Cesium

87

Fr

223

Francium

Atomic Weight

Thorium

Name

18 2

13

2

Hydrogen

3

& quick reference

Radioactive Element

Th

Symbol

1

Artificially prepared

90

Atomic Number

Essential information condensed for lab use Essential information condensed for lab use & quick reference

4

5

Be

10.81

9.01

Beryllium

Boron

12

13

Mg

24.31

3

Magnesium

20

Ca

40.08

Calcium

38

Sr

87.62

Strontium

56

Ba

137.3 Barium

88

Ra 226

Radium

B

21

Sc

44.96

Scandium

39

Y

88.91 Yttrium

57

La

4 22

Ti

47.87

Titanium

40

Zr

91.22

Zirconium

72

Hf

178.5

138.9

Lanthanum

89

Ac 227

Actinium

Hafnium

104

Rf 267

Rutherfordium

5 23

6

V

50.94

24

Cr

52.00

7

8

25

26

Fe

Mn

54.94

Vanadium

Chromium

Manganese

41

42

43

Nb

92.91

Niobium

73

Ta

180.9

Tantalum

105

Db 268

Dubnium

58

Ce

140.1 Cerium

90

Th

232.0

Thorium

Mo

95.95

Iron

44

Ru

Tc 98

55.85

101.1

Molybdenum Technetium

Ruthenium

74

76

W

183.8

Tungsten

106

Sg 269

Seaborgium

59

Pr

140.9

75

Re

186.2

Rhenium

107

Bh 270

Bohrium

60

Nd

144.2

Os

190.2

Osmium

108

Hs 277

Hassium

61

Pm 145

9

10

27

28

Ni

Co

58.93

58.69

Cobalt

Nickel

45

46

Rh

Pd

102.9

106.4

Rhodium

77

Palladium

78

Pt

Ir

192.2

195.1

Iridium

109

Mt

Platinum

110

Ds 281

278

11

Cu

79

Au

111

Rg

282

200.6

Mercury

112

Cn 285

Ga

69.72

Gallium

49

In

114.8 Indium

81

Tl

204.4

Thallium

113

Nh 286

C

12.01 Carbon

14

Si

28.09 Silicon

32

Ge

72.63

Germanium

50

Sn

118.7 Tin

82

Pb

207.2 Lead

114

Fl

289

7

N

14.01

Nitrogen

15

P

30.97

Phosphorus

33

As

74.92

Arsenic

51

Sb

121.8

Antimony

83

Bi

209.0

Bismuth

115

Mc 289

Copernicium

Nihonium

Flerovium

Moscovium

62

65

66

67

68

63

Sm

Eu

150.4

152.0

64

Gd

157.3

96

Neptunium

Hg

Aluminum

31

6

15

Meitnerium Darmstadtium Roentgenium

95

Uranium

80

Gold

94

Protactinium

Cadmium

197.0

92

237

112.4

Silver

91

238.0

Cd

107.9

Gadolinium

231.0

48

Ag

Europium

Np

Zinc

47

Samarium

93

Zn

65.39

Copper

Neodymium Promethium

U

30

63.55

Praseodymium

Pa

12

29

Al

26.98

14

Pu

Am 243

244

Plutonium

Americium

Cm 247

Curium

Tb

158.9

Terbium

97

Bk 247

Berkelium

Dy

162.5

Dysprosium

98

Cf

251

Ho

164.9

Holmium

99

Es 252

Californium Einsteinium

Er

167.3 Erbium

100

Fm 257

Fermium

16 8

O

16.00

Oxygen

16

S

32.06 Sulfur

34

Se

78.96

Selenium

52

Te

127.6

Tellurium

84

Po 209

Polonium

116

Lv

293

Livermorium

69

Tm

168.9

Thulium

101

Md 258

Mendelevium

17 9

F

19.00

Fluorine

17

Cl

35.45

Chlorine

35

Br

79.90

Bromine

53

I

126.9 Iodine

85

At 210

Astatine

117

Ts

294

He

4.003 Helium

10

Ne

20.18 Neon

18

Ar

39.95 Argon

36

Kr

83.80

Krypton

54

Xe

131.3 Xenon

86

Rn 222

Radon

118

Og

294

Tennessine

Oganesson

70

71

Yb

173.0

Ytterbium

102

No 259

Nobelium

Lu

175.0

Lutetium

103

Lr

262

Lawrencium

LAB MUST-KNOWS Common Lab Equipment • Buret: Calibrated tube similar to a large pipette with a stopcock at one end. Used to measure how much liquid is added to a solution during an experiment. • Crucible: A container (usually ceramic) used to hold a solid chemical for heating it. • Fume hood: Device used to keep hazardous vapors away from users. Uses a buildingʼs vacuum system to pull air and other vapors into the hood and exhausts them safely away. • Funnel: Device used when transferring a liquid to a container with a narrow neck. Often used to hold filter paper when removing precipitates. • Hot plate/Magnetic stirrer: Device used to heat a liquid that has a rotating magnet in the base. The magnet spins a Teflon-coated stir bar inside the liquid to heat the solution more evenly. • Mortar: A container (usually ceramic) used to hold a solid chemical being crushed by a rounded pestle. • pH meter: Device with a detachable pH electrode that measures the pH of a solution. The electrode is first standardized using solutions of known pH, and then the electrode is submerged in an

unknown solution to measure its pH. • Ring stand: Metal or ceramic stand with a vertical metal rod attached to the base. Used with a variety of components (clamps, ring clamps, clay triangles, buret clamps, wire gauze, etc.) to safely hold pieces of lab equipment when using them, particularly during filtration and heating. • Spectrophotometer: Device used to measure how different wavelengths of light interact with a solution. • Tongs and forceps: Devices (usually metal) used to safely grasp materials or labware that are hot or otherwise unsafe to touch. • Water bath: Device used to heat a pool of water to a specified elevated temperature.

• Use a funnel to transfer to a flask.

Without a funnel you get more material on the outside of the flask and table than on the inside, where it should be. • Measure volumes to the bottom of the meniscus (the curved surface of a liquid caused by surface tension of the liquid to the tube or container it is in). • Volumetric flasks or volumetric pipettes offer the highest precision measuring. They tend to be expensive and are used only for a single volume. • Graduated cylinders come in a variety of sizes with markings usually etched or molded into the sides of the container. They are relatively accurate and may be used to measure a fairly broad range of volumes. Graduated cylinders will be least accurate near the low end of their range. Generally use the smallest cylinder that will hold the volume you need. • Pipettes tend to be used for smaller volumes than graduated cylinders and

How to Dispense Liquids

• Choice of equipment depends on the desired precision. • Use a small beaker to obtain the necessary amount from the reagent bottle.

Try to avoid taking extra of the reagent. Imagine if every student in the lab used three times as much reagent as needed. 4

come in a variety of types. The three most common types are: - Serological pipettes, which measure volume from the bottom tip of the pipette to an etched or printed mark on the side of the pipette. All of the liquid should be removed to get a precise measurement. - Mohr pipettes, which have unlabeled space at the tip of the pipette that should not be counted in the pipette volume. For Mohr pipettes, a precise volume is measured from the bottom mark to the top desired mark. - Pasteur pipettes, which do not have markings and are made of cheap, flexible, inaccurate plastic. They should not be used for precise measurements. • Pipettemen are typically used for small volumes (less than 1 mL) and use a disposable plastic tip attached to a mechanical air displacement handle that is often color coded to a particular size. They are accurate to 1–3% of the stated volume and are most accurate in the middle of their range.

Lab Must-Knows (continued)

How to Dispense Solids

• Beakers (cup-shaped containers) and most flasks (Erlenmeyer flasks, round bottom flasks, vacuum flasks, etc.) have markings printed on them, but they are only approximate and should not be used for precise measurements.

Your data will be meaningless unless the balance is properly zeroed.

• Dispense chemicals from a reagent bottle using a spatula or scoopula. Do not return excess chemicals to the bottle, as this may contaminate the bottle. • Transfer the chemical to a weighing boat or weighing paper on a balance. Always use a fresh boat or balance to minimize contamination issues. • Be aware of the effects of air currents in the lab, especially if you are working in a fume hood. Your powdery solid could end up spread all over the table, instead of in your beaker, where it belongs. • Always clean up spilled chemicals immediately. One powdery white solid looks very much like another!

EX: If the dish has a mass of 5.0 g and the sample plus dish has a mass of 6.5 g, the mass of the sample is 6.5 g – 5.0 g = 1.5 g.

Step 1: Insert the tip of the pipette into the liquid. Use a suction bulb to draw liquid into the pipette, past the desired “mark” on the stem of the pipette. Step 2: Quickly replace the bulb with your finger; carefully release the vacuum and allow the liquid to drain from the pipette. Step 3: Stop the flow at the desired “mark.” Step 4: Insert the pipette into the flask and release the liquid. Under no circumstances should you ever pipette using mouth suction, even if you are pipetting water or harmless solutions. This creates a bad habit, and suddenly, while not thinking, you have just pipetted a mouthful of sulfuric acid.

Never weigh a hot object—the heat generates air currents that alter the measurement. Try not to use a balance directly under an exhaust vent or next to any device that blows air. Powder can scatter a long way, and fine particles might accidentally be inhaled if a strong breeze hits your powder at the wrong moment.

• Manual triple-beam and electronic balances are used in the lab. Use a balance that is appropriate for the mass you are trying to measure. Make sure that your balance has the precision you require. • Make sure that your electronic balance has the necessary capacity; otherwise, it will give you an error message. • Analytical balances with an enclosed weighing area are better for small weights (under a gram) because air currents will have less effect on the measurement. • Clean the pan with a soft brush; if the pan is stained, with the assistance of the instructor, remove and clean the pan. • Tare the balance before use (set the weight of the balance with weighing paper or weighing boat to zero); otherwise, all of your mass data will be incorrect. • Alternatively, tare the balance without a dish, add just the dish and preweigh it, and then add the sample and reweigh the sample and dish. Determine the sample mass by the difference.

How to Use a Gas Burner • Securely connect the burner to the gas supply with rubber tubing. • Gradually increase the gas flow and ignite the flame. • Adjust the air/gas mix to give a quiet, hot flame. The size of the flame should “fit” your application. Small test tubes only need a small flame. • The ideal flame is light blue in color. The hottest part of the flame is at the tip of the inner cone of the flame.

Be especially aware of the risk of burns when working with a burner and hot labware.

How to Use a Hot Plate

• Plug the hot plate cord into the electrical outlet.

SAFE USE OF LAB EQUIPMENT • Lab equipment is delicate and expensive; learn to use it correctly. Ask for assistance if you need help.

Disciplined training is required for any activity requiring skill in science, sports, music, or art. You do not naturally serve aces at Wimbledon or shoot under par at the US Open Championship. • Do not use worn or frayed electrical cords.

This can lead to dangerous electric shocks and the igniting of other flammable materials in the lab. If you have equipment with these problems, contact the instructor. • Be aware of the risk of static electricity—it may harm computers and can ignite flammable solvents.

This is more of a problem in dry climates and in labs with carpeted floors (in the labs or in attached hallways). • Watch out for chipped or cracked glassware; discard it in the glass-recycle box. Broken glass is sharp and can easily cut through a trash bag.

Do not simply set it on “high” and then forget about it. The surface can get hot enough to melt lead.

Never weigh chemicals directly on the balance pan. Clean up any spilled chemical on or around the balance before you leave it.

How to Use a Balance

How to Use a Pipette

• Adjust the setting to give the temperature required for your application. • Use tongs to manipulate the labware on the hot plate. • Clean the hot plate surface after it has cooled.

Take care when using flammable solvents on or around a hot plate. If spilled on the hot ceramic surface, they can ignite.

How to Use a Gas Cylinder • Make sure that the cylinder is safely chained or otherwise attached to a wall or other secure object. • Check to see if the regulator attached to the gas cylinder is of an appropriate type. Normally the fittings will not screw onto the wrong type of cylinder, but this is not always the case. • Make sure all valves are closed, then slowly open the high-pressure valve. The high-pressure indicator should go up. Once it stops moving, open the valve fully, and then close it down by one turn of the valve. • Open the low-pressure valve and adjust the operating pressure with the regulator as needed. • Be careful with gasses, as they flow easily through the air. Make sure that gas is vented safely and that the lab has good air flow to prevent suffocation. • When finished, first turn off the lowpressure valve on the main cylinder, and then the high-pressure valve. • Never move a gas cylinder with the regulator attached! Always remove the regulator and replace the protective cover over the valve stem of the gas cylinder.

DATA MANIPULATION Lab Units & Conversion Factors

Ask your instructor for guidance with the disposal of any damaged lab equipment.

The metric system is used throughout science as the common system of measurement. All data has a “number” and a “unit”; without a unit, a measurement might be 7 millimeters or 7 kilometers—a huge difference! The metric units all have a base prefix followed by a unit of measure.

• Thermometer: Use a “non-mercury” thermometer for routine work.

Unless you are in need of measurements over 120ºC, you should never work with a mercury thermometer in your lab. Why work with a toxic heavy metal if you don’t have to?

Metric Prefixes Peta Tera Giga Mega Kilo Hecto Deca

• Refrigerator: Store chemicals in sealed containers; donʼt store food with chemicals.

Always follow your instructor’s guidance on storing items in the lab refrigerator.

P T G M k h dk

1015 1012 109 106 103 102 101

base unit

Metric Base Units

• Compressed-gas cylinders: Secure to a wall or bench; falling cylinders cause serious injuries.

If you need to use this type of equipment, your instructor will train you in the use of the valves and regulators. Check for possible chemical hazards associated with the gas (CO, CO2, H2, O2, etc.). 5

Mass

Grams

g

Volume

Liters

L

Distance

Meters

m

Temperature

Celsius

o

Energy

Joules

J

Pressure

Pascal

Pa

Time

Seconds

s or sec

Force

Newtons

N

C

Deci Centi Milli Micro Nano Pico Femto

dc c m µ n p f

10-1 10-2 10-3 10-6 10-9 10-12 10-15

Data Manipulation (continued)

Other Common Units Temperature

Kelvin

o

Energy

Calories

cal

K

1 cal = 4.184 J

K = 273.15 + C

Pressure

Bar

bar

100,000 Pa

Atmosphere

atm

1 atm = 101,325 Pa

mm mercury

torr

1 torr = 133.322 Pa

Pounds per square inch

psi

1 psi = 6895 Pa

o

o

1 atm = 760 torr = 14.7 psi

As to why scientists like the metric system, consider units for time. How many hours are there in 1,000,000 seconds? You can calculate it as 1,000,000 ÷ (60 × 24), but the answer isn’t obvious. How many kiloseconds there are in 1,000,000 seconds is much easier to solve: 1,000,000 ÷ 1,000 = 1,000 kiloseconds. Because the metric system is built on factors of 10, it is easy to summarize long numbers using short prefixes. Instead of saying 0.000000001 meters, say 1 nanometer.

Metric Conversions To convert metric units, take the numerical value of the starting prefix and divide by the numerical value of the ending prefix. It’s that simple. When converting between any units, always check your final answer using this simple rule: Do I have more of my smaller units? Think it through: if there are more meters than millimeters after the conversion, that is a serious problem.

Examples

• When converting 3 terabytes into megabytes, take the prefix for tera (1012) and divide by the prefix for mega (106).

10 = 3 × 10 megabytes. (To divide by exponents, subtract them.) (12−6)

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Double check: Are there are more megabytes than terabytes? Yes.

• When converting 16 micrometers into millimeters, take the prefix micro (10-6) and divide by the prefix milli (10-3).

10(-6− (-3)) = 16 × 10-3 millimeters. Double check: Are there more micrometers than millimeters? Yes. You can also work out the problems by canceling out units. Here again, there should always be more of the smaller units present. • Convert 4500 milligrams to grams.

Starting base is 10-3 (.001), ending base is (1), so 10-3 ÷ 1 = .001. 4500 mg × .001 g/mg. mg cancels out, leaving 4500 × .001 = 4.5 grams. Double check: Do I have more milligrams than grams? Yes. • Convert 1.5 meters to centimeters.

Starting base is (1), ending base is 10-2, so 1 ÷ 10-2 = 100. 1.5 m × 100 cm/m. m cancels out, leaving 1.5 × 100 = 150 centimeters. Double check: Do I have more centimeters than meters? Yes. • Convert 672 milliliters to kiloliters.

672 mL/L × .001 mL/L × .001 kL/L = 0.672 × 10-3 kiloliters. Double check: Do I have more milliliters than kiloliters? Yes. With any unit conversion, it is easy to use the wrong factor. Always double-check before using the data. The second reason scientists love the metric system is

converting between units. Have you ever heard the saying “A pint’s a pound the world around?” It’s convenient, as a US pint of water weighs just about a pound (1.04375 pounds, actually). In Britain, however, an imperial pint weighs 1.25 pounds. But why use 16 ounces in a pint or a pound anyway? For metrics, all units are able to convert into one another. EX: 1 milliliter = 1 cm3 (As everyone who watches medical dramas know: “Give me 3 cc’s of adrenaline.”) Converting between units and making such calculations is critical as one progresses in science.

Unit Interconversions

• Volume to cubic distances: 1 mL = 1 cm3 • Energy to temperature: 1 calorie = energy needed to raise 1 gram of water 1oC • Mass to volume: 1 gram = mass of 1 cm3 of water or 1 mL • Pressure to force: 1 Pa = 1 newton per square meter (m2)

Many other such conversion factors are used in chemistry, but also biology, physics, etc.

Significant Figures (Sigfigs)

• Record the number of digits appropriate for the measuring device, plus record one “approximate” digit. Exponents are always significant. • Add/Subtract: For the final answer: the number of decimal places is given by the datum with the fewest decimal places. • Multiply/Divide: For the final answer: the number of sigfigs is given by the datum with the fewest sigfigs.

Graphing (x, y) Data

• Set the ranges to use the entire graph page; label axes and clearly mark data points.

Equation for a Line y = mx + b, where: m = slope and b = y-intercept

Average or Mean Value

• Add all data values and divide by the number of data points.

With all lab data and calculations—think! Balances and flasks, like calculators, are not equipped with a brain to ask, “Does this number make sense?”

PREPARING A SOLUTION • Chemical reagents are often dispensed as solutions. You may need to prepare a solution from scratch, or prepare dilutions of “stock” solutions. The most common solution concentration unit is molarity, M. • A 1.0 M solution of NaCl contains 1.0 moles of NaCl in 1.0 liter of solution. • The number of moles of material in a given V of solution of molarity, M, is given by M × V.

EX: If you dispense 0.50 L of a 1.0 M NaCl solution, you are working with: 0.50 L × 1.0 mol NaCl/L = 0.5 moles of NaCl.

General Guidelines

• Use volumetric glassware. Add the reagent, dissolve it in some solvent, and then dilute to the “mark” on the flask with additional solvent. • Organize the essential information before starting to prepare a solution. Know all weights and volumes before you start measuring.

When you are standing at the balance is not the time to ask yourself, “How much of this stuff do I need?”

Liquid reagent—you can determine the mass from the dispensed volume and density of the liquid: Mass (g) = Vol (mL) × Density (g/mL) If you need the exact mass of the liquid reagent, weigh out the desired quantity using a balance.

Dilute Solutions from Stock Step 1: Select the volume, v-dil, and desired concentration, c-dil, that you need for the final solution. Step 2: Determine v-stock of reagent of concentration c-stock. Step 3: Use this equation to calculate v-stock: v-dil × c-dil = v-stock × c-stock. Step 4: Add enough solvent to dilute v-stock in a volumetric flask of volume v-dil.

Dilute Solutions from Pure Reagents Step 1: Select the desired concentration, C, and volume, V. Step 2: Determine the required number of moles of reagent: mol = C × V. Step 3: Calculate the mass (grams) of reagent from molar

U.S. $6.95 Authors: Mark Jackson, PhD, Frank Miskevich, PhD

NOTE TO STUDENT: This guide is intended for informational purposes only. Due to its condensed format, this guide cannot cover every aspect of the subject; rather, it is intended for use in conjunction with course work and assigned texts. BarCharts Publishing, Inc., its writers, editors, and design staff are not responsible or liable for the use or misuse of the .information contained in this guide All rights reserved. No part of this publication may be reproduced or transmitted in any form, or by any means, electronic or mechanical, including photocopying, recording, or any information storage and retrieval .system, without written permission from the publisher Made in the USA ©2018 BarCharts Publishing, Inc. 0518

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mass; mass (grams) = mol × molar mass. Remember, the molar mass is calculated from the chemical formula and the mass of each atom in the chemical. C6H12O6 = 6 × (12.011) + 12 × (1.008) + 6 × (15.999) = 180.156 g/mol Step 4: Prepare a solution using mass (grams) of the reagent, using a volumetric flask of volume, V.

Dilutions of Acids & Bases Always add an acid (or base) to water, slowly, while stirring. Heat is produced in the process. This is true for liquid concentrated acids, such as H2SO4 or HNO3, and solid bases, such as NaOH or KOH pellets. Concentrated H2SO4 is also a dehydrating agent.