283 121 6MB
English Pages [846] Year 2024
Table of contents :
Introduction
About the author
Data tables and Periodic table Data Table 1
Periodic Table of the Elements
Data Table 2
Questions
Chapter 1: Unit 3 Area of Study 1 – What are the current and future options for supplying energy?
Chapter 2: Unit 3 Area of Study 2 – How can the rate and yield of chemical reactions be optimised?
Chapter 3: Unit 3 revision paper
Chapter 4: Unit 4 Area of Study 1 – How are organic
Chapter 5: Unit 4 Area of Study 2 – How are organic compounds analysed and used?
Chapter 6: Unit 4 Area of Study 3 – Practical investigation
Chapter 7: End of Year trial paper
Solutions
Chapter 1: Unit 3 Area of Study 1 – What are the current and future options for supplying energy?
Chapter 2: Unit 3 Area of Study 2 – How can the rate and yield of chemical reactions be optimised?
Chapter 3: Unit 3 revision paper
Chapter 4: Unit 4 Area of Study 1 – How are organic compounds categorised and synthesised?
Chapter 5: Unit 4 Area of Study 2 – How are organic compounds analysed and used?
Chapter 6: Unit 4 Area of Study 3 – Practical investigation
Chapter 7: End of Year trial paper
Author: Patrick Sanders
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Introduction This book is a collection of hundreds of practice questions for the written examination in Chemistry Units 3 and 4. Some questions make reference to the VCAA Chemistry data book, which you can find online at the VCAA website. A revision paper for Unit 3 is presented as a separate chapter. At the end of the book there is a trial paper to cover both Units 3 and 4. This exam contains selected VCAA exam questions from 2010 – 2022 that are relevant to the new 2024 Unit 3 and 4 Study design. The VCAA 2023 examination has not been included in its entirety as not all the content is relevant to the 2024 Study design. As well as these questions from the official sources, a number of new questions have been written for each section. Within each area of study, the questions have been grouped under a number of major headings, for example ‘Types of fuels’ and ‘Energy from fuels’. At the end of each area of study, a test has been prepared. These are designed to allow students to complete a test on the whole of a area of study. Each test should take approximately 45–75 minutes. Questions should be attempted once the relevant theory has been completed. Answers have been included at the end of the book. For the end of year examination, the five areas of study may or may not be given equal weighting.
About the author Patrick Sanders graduated from the University of Melbourne with a Bachelor of Science majoring in Chemistry and Human Anatomy. Patrick is currently teaching VCE Chemistry while in the role of Associate Head of The Crowther Centre, Curriculum and Assessment at Brighton Grammar School.
Data tables and Periodic table Data Table 1 The Electrochemical Series
The Electrochemical Series The Electrochemical Series
E0 (in volt)
The Electrochemical Series
E0 (in volt)
F2(g) + 2e− ⇌ 2F−(aq)
+2.87
Al3+(aq) + 3e− ⇌ Al(s)
−1.67
H2O2(aq) + 2H+(aq) + 2e− ⇌ 2H2O(l)
+1.77
Mg2+(aq) + 2e− ⇌ Mg(s)
−2.34
Au+(aq) + e− ⇌ Au(s)
+1.68
Na+(aq) + e− ⇌ Na(s)
Cl2(g) + 2e− ⇌ 2Cl−(aq)
+1.36
Ca2+(aq) + 2e− ⇌ Ca(s)
O2(g) + 4H+(aq) + 4e− ⇌ 2H2O(l)
+1.23
K+(aq) + e− ⇌ K(s)
Br2(g) + 2e− ⇌ 2Br−(aq)
+1.09
Li+(aq) + e− ⇌ Li(s)
Ag+(aq) + e− ⇌ Ag(s)
+0.80
Fe3+(aq) + e− ⇌ Fe2+(aq)
+0.77
O2(g) + 2H+(aq) + 2e− ⇌ H2O2(aq)
+0.68
I2(g) + 2e− ⇌ 2I−(aq)
+0.54
O2(g) + 2H2O(l) + 4e− ⇌ 4OH−(aq)
+0.40
Cu2+(aq) + 2e− ⇌ Cu(s)
+0.34
Sn4+(aq) + 2e− ⇌ Sn2+(aq)
+0.15
S(s) + 2H+(aq) + 2e− ⇌ H2S(g)
+0.14
2H+(aq) + 2e− ⇌ H2(g)
0.00
Pb2+(aq) + 2e− ⇌ Pb(s)
−0.13
Sn2+(aq) + 2e− ⇌ Sn(s)
−0.14
Ni2+(aq) + 2e− ⇌ Ni(s)
−0.23
Co2+(aq) + 2e− ⇌ Co(s)
−0.28
Cd2+(aq) + 2e− ⇌ Cd(s)
−0.40
Cr3+(aq) + e− ⇌ Cr2+(aq)
−0.41
Fe2+(aq) + 2e− ⇌ Fe(s)
−0.44
Cr3+(aq) + 3e− ⇌ Cr(s)
−0.74
Zn2+(aq) + 2e− ⇌ Zn(s)
−0.76
2H2O(l) + 2e− ⇌ H2(g) + 2OH−(aq)
−0.83
Mn2+(aq) + 2e− ⇌ Mn(s)
−1.03
−2.71 −2.87 −2.93 −3.02
Periodic Table of the Elements
Numbers in parentheses are mass numbers of the most stable isotope of that element
Data Table 2 Physical Constants and Unit Conversions Avogadro’s constant
6.023 × 1023 mol−1
Molar gas constant
8.314 J K−1 mol−1
Charge on one electron
−1.60 × 10−19 C
Faraday constant
96 500 C mol−1
Physical Constants and Unit Conversions Molar volume of ideal gas at SLC (25 °C and 100 kPa)
24.8 L mol−1
Pressure unit conversions
1 atmosphere = 101 325 Pa = 760 mm Hg
Specific heat capacity of water
4.18 kJ kg−1 K−1 or 4.18 J g−1 K−1
Chapter 1: Unit 3 Area of Study 1 – What are the current and future options for supplying energy? Question 1/ 82 Which one of the following statements about fuels is correct? A. When fuels react, they all produce carbon dioxide. B. Heat energy is always released when fuels are burnt. C. All fuels are hydrocarbons. D. Fuels need pure oxygen to produce energy.
Question 2/ 82 Which one of the following lists contains only fossil fuels? A. biogas, bioethanol, biodiesel B. coal seam gas, biogas, natural gas C. coal, petrol, diesel D. peat, wood, charcoal
Question 3/ 82 Propane is often used as a fuel in portable barbecues. The equation for the combustion of propane is: C3H8(g) + 5O2(g) → 3CO2(g) + 4H2O(g) For this reaction, the sign of ΔH is A. negative and the total chemical energy of the products is less than that of the reactants. B. positive and the total chemical energy of the products is less than that of the reactants. C. negative and the total chemical energy of the products is greater than that of the reactants. D. positive and the total chemical energy of the products is greater than that of the reactants.
Question 4/ 82 Which one of the following is not likely to be a biofuel? A. a gas mixture containing ∼96% methane and 4% carbon dioxide B. ethanol, C2H5OH C. methyl stearate, CH3(CH2)16COOCH3 D. a gas mixture containing approximately equal amounts of methane and carbon dioxide
Question 5/ 82 Below are four molecules that have been found in fuels. I cyclohexane, C6H12 II octane, C8H18 III methyl palmitate, CH3OOC(CH2)14CH3 IV ethanol, C2H5OH Which of these is/are not likely to be found in crude oil?
A. I and II B. I, III and IV C. III and IV D. II only
Question 6/ 82 The following is a list of fuels. I coal II biogas III natural gas IV biodiesel V bioethanol VI petrol Which of these are renewable fuels? A. II, IV and VI B. I, III and VI C. I, III and V D. II, IV and V
Question 7/ 82 [VCAA 2018 SA Q3] Which one of the following statements about fuels is correct? A. Petroleum gas is a form of renewable energy. B. Electricity can only be generated by burning coal.
C. Carbon dioxide is not produced when biogas is burnt. D. Biodiesel can be derived from both plant and animal material.
Question 8/ 82 [VCAA 2015 SA Q5] Which one of the following statements best defines a renewable energy resource? A. an energy resource that will not be consumed within our lifetime B. an energy resource that does not produce greenhouse gases when consumed C. an energy resource derived from plants that are grown for the production of liquid biofuels D. an energy resource that can be replaced by natural processes within a relatively short time
Question 9/ 82 [VCAA 2014 SA Q24] Methane gas may be obtained from a number of different sources. It is a major component of natural gas. Methane trapped in coal is called coal seam gas and can be extracted by a process known as fracking. Methane is also produced by the microbial decomposition of plant and animal materials. In addition, large reserves of methane were trapped in ice as methane hydrate in the ocean depths long ago. Methane is a renewable energy source when it is obtained from A. natural gas. B. coal seam gas. C. methane hydrate. D. microbial decomposition.
Question 10/ 82 [Adapted VCAA 2017 SA Q5] Which one of the following is a biofuel? A. ethanol produced from crude oil B. ethanol produced from plant material C. propane produced from natural gas D. electricity produced by hydropower
Question 11/ 82 [VCAA 2020 SA Q11] Which one of the following statements is correct? A. Crude oil can be classified as a biofuel because it originally comes from plants. B. Methane, CH4, can be classified as a fossil fuel because it has major environmental impacts. C. Ethanol, CH3CH2OH, can be classified as a fossil fuel because it can be produced from crude oil. D. Hydrogen, H2, can be classified as a biofuel because, when it combusts, it does not produce carbon dioxide, CO2.
Question 12/ 82 [VCAA 2018 SA Q14] An equation for the complete combustion of methanol is 2CH3OH(l) + 3O2(g) → 2CO2(g) + 4H2O(g) ΔH for this equation would be A. +726 kJ mol−1 B. −726 kJ mol−1 C. +1452 kJ mol−1
D. −1452 kJ mol−1
Question 13/ 82 Methane reacts with oxygen according to the following equation: CH4(g) + 2O2(g) → CO2(g) + 2H2O(l); ΔH = −890 kJ mol−1 The energy change for this reaction is best described as A. exothermic, because the net strength of the bonds in the products is greater than the net strength of the bonds in the reactants. B. endothermic, because the net strength of the bonds in the products is greater than the net strength of the bonds in the reactants. C. exothermic, because the net strength of the bonds in the products is less than the net strength of the bonds in the reactants. D. endothermic, because the net strength of the bonds in the products is less than the net strength of the bonds in the reactants.
Question 14/ 82 Which of the following equations best represents the incomplete combustion of ethanol? A. C2H5OH(l) + 3O2(g) → 2CO2(g) + 3H2O(g) B. C2H5OH(l) → C2H4(g) + H2O(g) C. C2H5OH(l) + 2O2(g) → CO2(g) + C(s) + 3H2O(g) D. 2C2H5OH(l) + O2(g) → 2C2H4O(g) + 2H2O(g)
Question 15/ 82
The partial oxidation of methane is one step in the production of methanol. 2CH4(g) + O2(g) → 2CO(g) + 4H2(g); ΔH = −74 kJ mol−1 The activation energy for this reaction is 32 kJ mol−1. The energy profile for this reaction is best represented by
A.
B.
C.
D.
Question 16/ 82 [VCAA 2017 SA Q29]
The following energy profile shows the results obtained during an enzyme-catalysed reaction. Each stage of the reaction is labelled: M represents the initial reactants, N represents a stable intermediate and P represents the final products.
Which one of the following statements is correct? A. The energy change from M to N is exothermic and the energy change from N to P is exothermic. B. The energy change from M to P is exothermic and the energy change from N to P is endothermic. C. The energy change from M to N is endothermic and the energy change from N to P is endothermic. D. The energy change from M to N is endothermic and the energy change from M to P is endothermic.
Question 17/ 82 When propane is used as a fuel (for example, as portable camping gas), it reacts with oxygen according to the equation C3H8(g) + 5O2(g) → 3CO2(g) + 4H2O(l) Compared with the energy of the reactants, the chemical energy of the combustion products will be A. higher and the reaction is endothermic. B. lower and the reaction is exothermic. C. higher and the reaction is exothermic. D. lower and the reaction is endothermic.
Question 18/ 82
[VCAA 2011 E2 SA Q6] In an endothermic reaction the A. reaction system loses energy to the surroundings. B. addition of a catalyst increases the activation energy. C. activation energy is greater than the enthalpy of reaction. D. energy required to break bonds in the reactants is less than the energy released when bonds are formed in the products.
Question 19/ 82 [VCAA 2020 SA Q27] The heat of combustion of ethanoic acid, C2H4O2 is −876 kJ mo1−1 and the heat of combustion of methyl methanoate, C2H4O2, is −973 kJ mo1−1. The auto-ignition temperature (the temperature at which a substance will combust in air without a source of ignition) of ethanoic acid is 485 °C and the auto-ignition temperature of methyl methanoate is 449 °C. Which one of the following pairs is correct? Compound with the lower chemical energy per mole ethanoic acid
Compound with the lower activation energy of combustion per mole methyl methanoate
ethanoic acid
ethanoic acid
methyl methanoate
methyl methanoate
methyl methanoate
ethanoic acid
Question 20/ 82 [VCAA 2021 SA Q24] Which one of the following statements describes the effect that adding a catalyst will have on the energy profile diagram for an exothermic reaction? A. The energy of the products will remain the same.
B. The shape of the energy profile diagram will remain the same. C. The peak of the energy profile will move to the left as the reaction rate increases. D. The activation energy will be lowered by the same proportion in the forward and reverse reactions.
Question 21/ 82 Detonators often contain lead azide, Pb(N3)2, because when heated or struck, lead azide decomposes very rapidly, according to the equation Pb(N3)2(s) → Pb(s) + 3N2(g); ΔH = −440 kJ mol−1 Compared with the total chemical energy of the products, the chemical energy of the lead azide will be A. higher because the reaction is endothermic. B. higher because the reaction is exothermic. C. lower because the reaction is endothermic. D. lower because the reaction is exothermic.
Question 22/ 82 [VCAA 2017 SA Q9] The nutrition information panel on a packet of muesli includes the information shown below. Nutrition information Average serving size = 45 g Average quantity per 100 g protein
13.2 g
fat, total
16.3 g
– saturated
2.9 g
carbohydrate, total
48.2 g
– sugars
17.4 g
dietary fibre
4.9 g
sodium
10.5 mg
Using the information above, the percentage energy content due to protein in an average serving size of this muesli is A. 31.2% B. 29.3% C. 14.0% D. 13.2%
Question 23/ 82 [VCAA 2022 SA Q3] The correct equation for the incomplete combustion of ethanol is A. C2H5OH(l) + 12 O2(g) → 2CO(g) + 3H2(g) B. C2H5OH(l) + 23 O2(g) → 2CO2(g) + 3H2(g) C. C2H5OH(l) + 2O2(g) → 2CO(g) + 3H2O(l) D. C2H5OH(l) + 3O2(g) → 2CO2(g) + 3H2O(l)
Question 24/ 82 In a laboratory experiment, 100 mL of ethane gas was mixed with 500 mL of oxygen gas at SLC and sparked. The reaction shown by the following equation occurred: 2C2H6(g) + 7O2(g) → 4CO2(g) + 6H2O(l) What would be the total volume of gas present when the reaction had cooled back to SLC? A. 200 mL
B. 350 mL C. 550 mL D. 650 mL
Question 25/ 82 [Adapted VCAA 2014 SA Q8] When hydrochloric acid, HCl, is added to aluminium sulfide, Al2S3, the highly toxic gas hydrogen sulfide, H2S, is evolved. The equation for this reaction is Al2S3(s) + 6HCl(aq) → 2AlCl3(aq) + 3H2S(g) If excess hydrochloric acid is added to 0.200 mol of aluminium sulfide, then the volume of hydrogen sulfide produced at standard laboratory conditions (SLC) will be A. 1.63 L B. 4.90 L C. 7.44 L D. 14.9 L
Question 26/ 82 Methane, CH4, ethane, C2H6, ethyne, C2H2, and propane, C3H8, have all been used as fuels. The enthalpy change for the balanced complete combustion reactions of these fuels is given by the following equations: CH4(g) + 2O2(g) → CO2(g) + 2H2O(l); ΔH = −890 kJ mol−1 2C2H6(g) + 7O2(g) → 4CO2(g) + 6H2O(l); ΔH = −3120 kJ mol−1 2C2H2(g) + 5O2(g) → 4CO2(g) + 2H2O(l); ΔH = −2600 kJ mol−1 C3H8(g) + 5O2(g) → 3CO2(g) + 4H2O(l); ΔH = −2208 kJ mol−1 When 1.0 g of each fuel is burned, then the fuel releasing the greatest amount of energy would be A. CH4
B. C2H6 C. C2H2 D. C3H8
Question 27/ 82 Both ethanol, C2H5OH, and methanol, CH3OH, have been suggested as alternative fuels for transport vehicles. The equations describing the complete combustion of ethanol and methanol are given below. C2H5OH(g) + 3O2(g) → 2CO2(g) + 3H2O(l); ΔH = −1368 kJ mol−1 CH3OH(g) + 32 O2(g) → CO2(g) + 2H2O(l); ΔH = −726 kJ mol−1 Separate experiments are conducted in which 1 mol of ethanol and 2 mol of methanol undergo complete combustion. In these experiments A. the combustion of methanol produces more carbon dioxide. B. more heat energy is released from the combustion of ethanol. C. more water is formed in the combustion of ethanol. D. the two experiments consume the same amount of oxygen.
Question 28/ 82 The heat of combustion for three methyl esters is given in the table below. Name
Formula
Methyl pentanoate
C4H9COOCH3
−3558
Methyl hexanoate
C5H11COOCH3
−4211
Methyl heptanoate
C6H13COOCH3
−4863
ΔH (kJ mol−1)
One of the molecules found in biodiesel is methyl stearate, C17H35COOCH3. The best estimate for the molar enthalpy change (in kJ mol−1) of methyl stearate is
A. −7178 B. −12 040 C. −12 632 D. −13 937
Question 29/ 82 [VCAA 2013 SA Q16] C(s) + O2(g) → CO2(g); ΔH = −393.5 kJ mol−1 2H2(g) + O2(g) → 2H2O(l); ΔH = −571.6 kJ mol−1 Given the information above, what is the enthalpy change for the following reaction? C(s) + 2H2O(l) → CO2(g) + 2H2(g) A. −965.1 kJ mol−1 B. −107.7 kJ mol−1 C. +178.1 kJ mol−1 D. +679.3 kJ mol−1
Question 30/ 82 [VCAA 2018 SA Q10] Bioethanol, C2H5OH, is produced by the fermentation of glucose, C6H12O6, according to the following equation. C6H12O6(aq) → 2C2H5OH(aq) + 2CO2(g) The mass of C2H5OH obtained when 5.68 g of carbon dioxide, CO2, is produced is A. 0.168 g B. 0.337 g
C. 2.97 g D. 5.94 g
Question 31/ 82 [VCAA 2014 SA Q23] Large deposits of methane hydrate have been discovered deep under the sediment on the ocean floor. It has been suggested that methane hydrate deposits could be commercially mined to provide a clean fuel once the trapped methane is extracted. Methane hydrate has a complex structure. The simplified formula for methane hydrate is CH4.6H2O. The amount of energy released by the complete combustion of methane extracted from a 1.00 kg sample of methane hydrate at SLC is A. 8.89 × 102 kJ B. 7.17 × 103 kJ C. 4.30 × 104 kJ D. 5.56 × 104 kJ
Question 32/ 82 [VCAA 2018 SA Q22] Four fuels undergo complete combustion in excess oxygen, O2, and the energy released is used to heat 1000 g of water. Assuming there is no energy lost to the environment, which one of these fuels will increase the temperature of the water from 25.0°C to 85.0°C? A. 0.889 g of hydrogen, H2 B. 3.95 g of propane, C3H8 C. 0.282 mol of methane, CH4 D. 0.301 mol of methanol, CH3OH
Question 33/ 82 [VCAA 2017 SA Q7] What is the total energy released, in kilojoules, when 100 g of butane and 200 g of octane undergo combustion in the presence of excess oxygen? A. 9760 B. 14 600 C. 17 300 D. 19 500
Question 34/ 82 Use the following information to answer Questions 35 and 36. Four identical vehicle models, 1, 2, 3 and 4, were tested for fuel efficiency using LPG, petrol (unleaded, 91 octane), E10 (petrol with 10% ethanol added) and petrodiesel. Carbon dioxide, CO2, emissions per litre of fuel burnt were also determined. The following table summarises the results. Vehicle model
Fuel
Fuel consumption (L/100 km)
CO2 produced (g CO2/L of fuel)
1
LPG
19.7
1665
2
petrol
14.5
2392
3
E10
14.2
2304
4
petrodiesel
9.2
2640
Question 35/ 82 [VCAA 2017 SA Q13] Using the information in the table above, which one of the following statements about petrodiesel is correct? A. It has the highest energy content.
B. It has the poorest fuel efficiency. C. It is a renewable energy source. D. It has the lowest CO2 emissions when burnt.
Question 36/ 82 [VCAA 2017 SA Q14] The use of which vehicle has the smallest impact on the environment, in terms of the grams of CO2 produced per 100 km? A. Vehicle model 1 B. Vehicle model 2 C. Vehicle model 3 D. Vehicle model 4
Question 37/ 82 [Adapted VCAA 2018 SA Q25] The molar enthalpy change for the combustion of pentan-1-ol, C5H11OH, is −3329 kJ mol−1. M(C5H11OH) = 88.0 g mol−1 The mass of C5H11OH, in tonnes, required to produce 10 800 MJ of energy is closest to A. 0.0286 B. 0.286 C. 2.86 D. 286
Question 38/ 82 100 mL of a gaseous hydrocarbon is mixed with 500 mL of oxygen at SLC At the end of the reaction, the gaseous mixture is returned to its original temperature and pressure. The final mixture consists of 300 mL of carbon dioxide and 100 mL of oxygen. The molecular formula of the hydrocarbon is A. C2H4 B. C3H4 C. C3H6 D. C3H8
Question 39/ 82 [VCAA 2020 SA Q18] An experiment was carried out to determine the enthalpy of combustion of propan-1-ol. Combustion of 557 mg of propan-1-ol increased the temperature of 150 g of water from 22.1 °C to 40.6 °C. The molar enthalpy of combustion is closest to A. −2742 kJ mo1−1 B. −1208 kJ mo1−1 C. −1250 kJ mo1−1 D. −1540 kJ mol−1
Question 40/ 82 [VCAA 2020 SA Q22] The combustion of which fuel provides the most energy per 100 g? A. pentane (M = 72 g mol−1), which releases 49 097 MJ tonne−1
B. nitromethane (M = 61 g mol−1), which releases 11.63 kJ g−1 C. butanol (M = 74 g mol−1), which releases 2670 kJ mo1−1 D. ethyne (M = 26 g mol−1), which releases 1300 kJ mo1−1
Question 41/ 82 [VCAA 2021 SA Q12] Butane, C4H10, undergoes complete combustion according to the following equation. 2C4H10(g) + 13O2(g) → 8CO2(g) + 10H2O(g) 67.0 g of C4H10 released 3330 kJ of energy during complete combustion at standard laboratory conditions (SLC). The mass of carbon dioxide, CO2, produced was A. 0.105 g B. 3.18 g C. 50.9 g D. 204 g
Question 42/ 82 [VCAA 2021 SA Q22] 1 L of octane has a mass of 703 g at SLC. The efficiency of the reaction when octane undergoes combustion in the petrol engine of a car is 25.0%. What volume of octane stored in a petrol tank at SLC is required to produce 528 MJ of usable energy in a combustion engine? A. 3.92 L B. 11.8 L C. 15.7 L D. 62.7 L
Question 43/ 82 For each mole of oxygen consumed, which one of the following fuels produces the largest amount of carbon dioxide? A. methane, CH4 B. ethyne, C2H2 C. ethene, C2H4 D. propane, C3H8
Question 44/ 82 [VCAA 2019 SA Q26] The calibration factor of a bomb calorimeter was determined by connecting the calorimeter to a power supply. The calibration was done using 100 mL of water, 6.5 V and a current of 3.6 A for 4.0 minutes. The temperature of the water increased by 0.48°C during the calibration. 4.20 g of sucrose underwent complete combustion in the bomb calorimeter. The temperature of the 100 mL of water increased from 19.6°C to 25.8°C. M(C12H22O11) = 342 g mo1−1 The experimental heat of combustion of pure sucrose, in joules per gram, is A. 5.9 × 106 B. 7.3 × 104 C. 1.7 × 104 D. 1.2 × 104
Question 45/ 82
Use the following information to answer Questions 46 and 47. A solution calorimeter containing 350 mL of water was set up. The calorimeter was calibrated electrically and the graph of the results is shown below. Graph of temperature versus time during electrical calibration of solution calorimeter
The calorimeter was calibrated using a current of 2.7 A, starting at 60 s. The current was applied for 180 s and the applied voltage was 5.4 V.
Question 46/ 82 [VCAA 2020 SA Q9] What is the calibration factor for this calorimeter? A. 125 J °C−1 B. 820 J °C−1 C. 847 J °C−1 D. 875 J °C−1
Question 47/ 82 [VCAA 2020 SA Q10] This type of calorimeter A. has no heat loss. B. can be used for bomb calorimetry. C. requires electrical calibration in order to determine the calibration factor. D. measures energy changes that can be measured in a bomb calorimeter.
Question 48/ 82 [VCAA 2021 SA Q19] A food chemist conducted an experiment in a bomb calorimeter to determine the energy content, in joules per gram, of a muesli bar. A 3.95 g sample of the muesli bar was combusted in the calorimeter and the temperature of the water rose by 16.7 °C. The calibration factor of the calorimeter was previously determined to be 4780 J °C−1. The energy content of the muesli bar is A. 3.51 × 105 J g−1 B. 2.02 × 104 J g−1 C. 1.13 × 103 J g−1 D. 7.25 × 10 J g−1
Question 49/ 82 [VCAA 2022 SA Q2] A fuel undergoes combustion to heat water. Which of the following descriptions of the energy and enthalpy of combustion, ΔH, of the reaction is correct? Energy absorbed by water
ΔH negative
released by water
negative
absorbed by water
positive
released by water
positive
Question 50/ 82 [VCAA 2022 SA Q26] Calorimeter 1 and Calorimeter 2 were each electrically calibrated. The same current, voltage and time were used to calibrate each calorimeter. A reaction was undertaken in Calorimeter 1 and Calorimeter 2. The same amount and type of each reactant was used in both calorimeters. The following temperature versus time graphs were produced for the reaction in each calorimeter.
Which one of the following statements is correct? A. Only Calorimeter 1 can be used to calculate m. B. Calorimeter 2 has better insulation than Calorimeter 1. C. The calibration factor for Calorimeter 2 is higher than the calibration factor for Calorimeter 1. D. During the calibration, the temperature increase of Calorimeter 2 was greater than the temperature increase of Calorimeter 1.
Question 51/ 82 For which of the following species is the oxidation number of oxygen the lowest? A. Na2O2 B. H2O2 C. O2 D. H2SO4
Question 52/ 82 In which of the following reactions is nitrous acid, HNO2, behaving solely as an oxidising agent? A. 2H+(aq) + Zn(s) + 2HNO2(aq) → Zn2+(aq) + 2NO(g) + 2H2O(l) B. MnO2(s) + HNO2(aq) + H+(aq) → Mn2+(aq) + NO3−(aq) + H2O(l) C. 3HNO2(aq) → HNO3(aq) + H2O(l) + 2NO(g) D. 2Fe3+(aq) + HNO2(aq) + H+(aq) → 2Fe2+(aq) + NO3−(aq) + H2O(l)
Question 53/ 82 In which one of the following reactions does sulfur have the largest change in oxidation number? A. 2S2O32−(aq) + I2(aq) → S4O62−(aq) + 2I−(aq) B. 2SO2(g) + O2(g) → 2SO3(g) C. H2SO4(l) + 8HI(g) → H2S(g) + 4H2O(l) + 4I2(s) D. S(l) + O2(g) → SO2(g)
Question 54/ 82 A galvanic cell is set up as shown in the diagram below.
In this cell, the aluminium electrode will be the A. anode and negatively charged. B. anode and positively charged. C. cathode and negatively charged. D. cathode and positively charged.
Question 55/ 82 A Cu/Cu2+ half-cell and a Zn/Zn2+ half-cell are connected using a salt bridge and the system is used to produce an electric current. The purpose of the salt bridge is to A. allow the reactants to make contact with each other. B. allow cations and anions to flow in and out of the two half-cells. C. provide essential reactants for the overall reaction. D. provide electrons to complete the circuit in the cell.
Question 56/ 82 The following information refers to Questions 57 and 58. Two galvanic cells are set up as shown in the diagram below.
Question 57/ 82 The strongest reducing agent present is A. Co B. Cu C. V D. Cu2+
Question 58/ 82 The voltage of a cell using the Co/Co2+ and V/V2+ half-cells would be A. 0.90 V with the V electrode negative. B. 0.90 V with the Co electrode negative. C. 2.14 V with the V electrode negative. D. 2.14 V with the Co electrode negative.
Question 59/ 82 A piece of steel plate is placed in each of four separate containers, each containing a different 0.50 M aqueous solution. The four solutions are Pb(NO3)2(aq), Zn(NO3)2(aq), AgNO3(aq) and Cu(NO3)2(aq). It is expected that the piece of steel will be coated with another metal in the solutions of A. Pb(NO3)2, AgNO3 and Cu(NO3)2. B. Pb(NO3)2 and AgNO3. C. AgNO3 and Cu(NO3)2. D. Zn(NO3)2 only.
Question 60/ 82 Three metals, R, S and T, have the following properties: • Metal R does not react with 1.0 M H2SO4 • Metal S will react with 1.0 M H2SO4 to produce H2, and also reacts with 1.0 M RCl2 solution to produce R • Metal T will react with 1.0 M H2SO4 to produce H2 but does not react with 1.0 M SCl2 solution. From this information the order of reactivity of the metals and H2, from the highest to the lowest, is A. R > H2 > T > S B. H2 > R > T > S C. S > H2 > T > R D. S > T > H2 > R
Question 61/ 82 [VCAA 2013 SA Q24] Three beakers, each containing an iron strip and a 1.0 mol L−1 solution of a metal salt, were set up as shown below.
A reaction will occur in beaker(s) A. I and II only. B. I and III only. C. II and III only. D. III only.
Question 62/ 82 [VCAA 2018 SA Q1] Which one of the following statements is the most accurate? A. All fuel cells are galvanic cells. B. All galvanic cells are primary cells. C. All secondary cells have porous electrodes. D. All fuel cells are more efficient than all secondary cells.
Question 63/ 82 [VCAA 2018 SA Q11] A galvanic cell is set up as shown in the diagram below.
When this cell is operating A. a gas forms at the Ag electrode. B. the mass of the Ag electrode increases. C. Ag+ ions move towards the Fe electrode. D. electrons move from the Ag electrode to the Fe electrode.
Question 64/ 82 [VCAA 2013 SA Q25] A student constructs the following galvanic cell.
The student predicts that the following overall reaction will occur. 2H2O2(aq) → 2H2O(l) + O2(g) However, no reaction is observed. This is most likely because A. the difference between the E° values is too small for a reaction to occur.
B. hydrogen peroxide will oxidise water in preference to itself. C. the student did not construct standard half-cells. D. the rate of the reaction is extremely slow.
Question 65/ 82 [VCAA 2018 SA Q12] The overall reaction for an acidic fuel cell is shown below. 2H2(g) + O2(g) → 2H2O(l) Porous electrodes are often used in acidic fuel cells because they A. are highly reactive. B. are cheap to produce and readily available. C. are more efficient than solid electrodes at moving charges and reactants. D. provide a surface for the hydrogen and oxygen to directly react together.
Question 66/ 82 [VCAA 2014 SA Q25] Consider the information below about the reaction of Ru2+ with various reagents. Ru2+(aq) + Fe2+(aq) → no observed reaction Ru2+(aq) + Ni(s) → Ru(s) + Ni2+(aq) Ru2+(aq) + Ag(s) → no observed reaction Ru2+(aq) + Cu(s) → Ru(s) + Cu2+(aq) Where would the following reaction be placed in the electrochemical series if the above tests were carried out under standard conditions? Ru2+(aq) + 2e− ⇌ Ru(s)
A. below −0.23 V B. between −0.44 V and −0.23 V C. between 0.77 V and 0.34 V D. above 0.77 V
Question 67/ 82 [VCAA 2014 SA Q26] Consider the following experiments that are carried out under standard conditions. Beaker I A strip of nickel metal is placed into a 1.0 M silver nitrate solution. Beaker II A 1.0 M copper(II) sulfate solution is added to a 1.0 M sodium iodide solution. Beaker III Chlorine gas is bubbled through a 1.0 M potassium iodide solution. It would be predicted that a reaction will occur in A. Beaker I only. B. Beaker II only. C. Beakers I and III only. D. Beakers II and III only.
Question 68/ 82 [VCAA 2015 SA Q24] The reaction between hydrogen peroxide and ammonium ions is represented by the following equation. 3H2O2(aq) + 2NH4+(aq) → N2(g) + 2H+(aq) + 6H2O(l) Which one of the following is the correct half-equation for the reduction reaction? A. H2O2(aq) + 2H+(aq) + 2e− → 2H2O(l) B. 2NH4+(aq) → N2(g) + 8H+(aq) + 6e−
C. 2NH4+(aq) + 2e− → N2(g) + 4H2(g) D. H2O2(aq) + 2H2O(l) → 2O2(g) + 6H+(aq) + 6e−
Question 69/ 82 [VCAA 2015 SA Q25] Solution I – 1.0 M NaCl Solution II – 1.0 M CuCl2 Solution III – 1.0 M MgCl2. Which solution or solutions above will react with Zn powder? A. Solution I only B. Solution II only C. Solutions I and III only D. Solutions I, II and III
Question 70/ 82 [VCAA 2017 SA Q6] The overall equation for a particular methanol fuel cell is shown below. 2CH3OH(g) + 3O2(g) → 2CO2(g) + 4H2O(l) The equation for the reaction that occurs at the cathode in this fuel cell is A. CO2(g) + 5H2O(l) + 6e− → CH3OH(g) + 6OH−(aq) B. CH3OH(g) + 6OH−(aq) → CO2(g) + 5H2O(l) + 6e− C. O2(g) + 2H2O(l) + 4e− → 4OH−(aq) D. 4OH−(aq) → O2(g) + 2H2O(l) + 4e−
Question 71/ 82 [VCAA 2018 SA Q29] The diagrams below represent combinations of four galvanic half-cells (G/G2+, J/J2+, Q/Q2+ and R/R2+) that were investigated under standard conditions. Each half-cell consisted of a metal electrode placed in a 1.0 M nitrate solution of the respective metal ion. The diagrams show the polarity of the electrodes in each half-cell, as determined using an ammeter. The results were then used to determine the order of the E° values of the half-reactions.
Which of the following indicates the order of the half-cell reactions, from the lowest E° value to the highest? A. J/J2+, R/R2+, G/G2+, Q/Q2+ B. Q/Q2+, G/G2+, R/R2+, J/J2+ C. R/R2+, J/J2+, Q/Q2+, G/G2+ D. G/G2+, Q/Q2+, J/J2+, R/R2+
Question 72/ 82 [VCAA 2017 SA Q11] A galvanic cell consists of two connected half-cells that can produce an electron flow. Which combination of standard half-cell pairs would be expected to result in a cell potential of 1.41 V? Al electrode with Al(NO3)3
Ag electrode with AgNO3
Zn electrode with Zn(NO3)2
Ni electrode with Ni(NO3)2
Ni electrode with Ni(NO3)2
Al electrode with Al(NO3)3
Ag electrode with AgNO3
Zn electrode with Zn(NO3)2
Question 73/ 82 [VCAA 2019 SA Q8] Consider the following statements about galvanic and fuel cells. Statement number
Statement
1
The overall reaction is exothermic.
2
Electrons are consumed at the negative electrode.
3
Both the reducing agent and oxidising agent are stored in each half-cell.
4
The electrodes are in contact with the reactants and the electrolyte.
5
The production of electricity requires the electrodes to be replaced regularly.
Which one of the following sets of statements is correct for both galvanic cells and fuel cells? A. statement numbers 2 and 3 B. statement numbers 1 and 4 C. statement numbers 2, 4 and 5 D. statement numbers 1, 3 and 5
Question 74/ 82 [VCAA 2020 SA Q13] Hydrogen, H2, fuel cells and H2-powered combustion engines can both be used to power cars. Three statements about H2 fuel cells and H2-powered combustion engines are given below: I Neither H2 fuel cells nor H2-powered combustion engines produce greenhouse gases. II Less H2 is required per kilometre travelled when using an H2-powered combustion engine than when using H2 fuel cells. III More heat per kilogram of H2 is generated in an H2-powered combustion engine than in H2 fuel cells. A. II only B. I and II only C. III only D. I and III only
Question 75/ 82 [VCAA 2019 SA Q18] Which one of the following galvanic cells will produce the largest cell voltage under standard laboratory conditions (SLC)?
A.
B.
C.
D.
Question 76/ 82 [VCAA 2020 SA Q3] A diagram of an electrochemical cell is shown below.
Which of the following gives the correct combination of the electrode in the oxidation half-cell and the electrolyte in the reduction half-cell? Electrode (oxidation half-cell)
Electrolyte (reduction half-cell)
S
P
S
R
Q
R
Q
P
Question 77/ 82 [VCAA 2020 SA Q26] The following reactions occur in a primary cell battery. Zn + 2OH− → ZnO + H2O + 2e− 2MnO2 + 2e− + H2O → Mn2O3 + 2OH− Which one of the following statements about the battery is correct? A. The reaction produces heat and Zn reacts directly with MnO2. B. The reaction produces heat and Zn does not react directly with MnO2. C. The reaction does not produce heat and Zn reacts directly with MnO2. D. The reaction does not produce heat and Zn does not react directly with MnO2.
Question 78/ 82 [VCAA 2020 SA Q30] Consider the following half-equation. ClO2(g) + e− ⇌ ClO2−(aq) It is also known that: • ClO2(g) will oxidise HI(aq), but not HCl(aq) • Fe3+(aq) will oxidise Hl(aq), but not NaClO2(aq). Based on this information, Fe2+(aq) can be oxidised by A. Cl2(g) and I2(aq). B. Cl2(g), but not ClO2(g). C. ClO2(g) and Cl2(g), but not I2(aq). D. Cl2(g), ClO2(g) and I2(aq).
Question 79/ 82 [VCAA 2021 SA Q26] Different metal ion (aq)/metal (s) half-cells are combined with an In3+(aq)/In(s) half-cell to create a galvanic cell at SLC, as shown in the diagram below. The equation for the In3+(aq)/In(s) half-cell is In3+(aq) + 3e− ⇌ In(s)
Which of the following shows the half-cells in decreasing order of voltage produced when combined with the In3+(aq)/In(s) half-cell and In(s) is the negative electrode?
A. Mn2+(aq)/Mn(s), Al3+(aq)/Al(s), Mg2+(aq)/Mg(s) B. Mg2+(aq)/Mg(s), A13+(aq)/Al(s), Mn2+(aq)/Mn(s) C. Cu2+(aq)/Cu(s), Pb2+(aq)/Pb(s), Ni2+(aq)/Ni(s) D. Ni2+(aq)/Ni(s), Pb2+(aq)/Pb(s), Cu2+(aq)/Cu(s)
Question 80/ 82 [VCAA 2022 SA Q4] Which one of the following diagrams shows the common design features of a fuel cell?
A.
B.
C.
D.
Question 81/ 82 [VCAA 2022 SA Q6 Galvanic cells and fuel cells have A. the same energy transformations and both are reversible. B. the same energy transformations and both produce heat. C. different energy transformations but galvanic cells produce electricity. D. different energy transformations but fuel cells use porous electrodes.
Question 82/ 82 [VCAA 2022 SA Q8] Unlike direct combustion of fuel, fuel cells A. can be recharged. B. do not produce greenhouse gases. C. require electrical energy to overcome the activation energy barrier. D. do not have direct contact between the oxidising and reducing agents.
Question 83/ 82 [VCAA 2022 SA Q14] The discharge reaction in a vanadium redox battery is represented by the following equation. VO2+(aq) + 2H+(aq) + V2+(aq) → V3+(aq) + VO2+(aq) + H2O(l) When the vanadium redox battery is recharging A. H+ is the reducing agent. B. H2O is the oxidising agent. C. VO2+ is the reducing agent. D. VO2+ is the oxidising agent.
Question 84/ 82 [VCAA 2022 SA Q18] A student wants to investigate a galvanic cell consisting of Sn4+/Sn2+ and Ag+/Ag half-cells. Which one of the following combinations of electrodes and solutions will produce an operational galvanic cell? Sn4+/Sn2+ half-cell
Ag+/Ag half-cell
Electrode Sn
Solution(s) 1 M Sn(NO3)2
Electrode graphite
Solution 1 M AgNO3
Sn
1 M Sn(NO3)4, 1 M Sn(NO3)2
graphite
1 M AgNO3
graphite
1 M Sn(NO3)4, 1 M Sn(NO3)2
Ag
1 M AgNO3
graphite
1 M Sn(NO3)4
Ag
1 M AgNO3
Question 85/ 82 [VCAA 2022 SA Q30] Consider the following half-equations, which are not in standard electrode potential order. HCrO4−(aq) + 7H+(aq) + 3e− ⇌ Cr3+(aq) + 4H2O(l) HBrO(aq) + H+(aq) + e− ⇌ 12 Br2(aq) + H2O(l) 2IO3−(aq) + 12H+(aq) + 10e− ⇌ I2(aq) + 6H2O(l) BrO3−(aq) + 6H+(aq) + 6e− ⇌ Br−(aq) + 3H2O(l) The following is also known: • I2 reacts with BrO3− and HBrO but not with HCrO4−. • Br− reacts with HBrO but not with IO3−. Platinum electrodes were used in each half-cell. Which one of the following galvanic cells will produce the highest potential difference?
A.
B.
C.
D.
Question 1/ 29 Methane and methanol will both burn in air. The reactions are described by the equations CH4(g) + 2O2(g) → CO2(g) + 2H2O(l); ΔH = −890 kJ mol−1
2CH3OH(g) + 3O2(g) → 2CO2(g) + 4H2O(l); ΔH = −1452 kJ mol−1 (a) If 2 mol of methane and 2 mol of methanol are completely burned in separate experiments, which experiment will release the most energy? (1 mark) (b) If each of the above reactions is used to produce 1000 kJ of energy, which one will release the most carbon dioxide? (2 marks) (Total = 3 marks)
Question 2/ 29 The reaction between hydrogen and oxygen is described by the equation 2H2(g) + O2(g) → 2H2O(g); ΔH = −484 kJ mol−1 (a) Draw an energy level diagram showing how the energy of the reactants is related to that of the products. Your diagram should also show ΔH and an activation energy. (3 marks) (b) Describe how the strength of the bonds in the reactants is related to the strength of the bonds in the products. (1 mark) (c) Would you expect the magnitude of the enthalpy change for the reaction 2H2(g) + O2(g) → 2H2O(l) to be greater than, less than or the same as the heat change in the first reaction? Explain your answer. (2 marks) (Total = 6 marks)
Question 3/ 29 Glucose is a very important energy source and is present in many foods. It is oxidised according to the equation below.
C6H12O6(s) + 6O2(aq) → 6CO2(g) + 6H2O(l); ΔH = −2803 kJ mol−1 (a) The energy required by a typical VCE chemistry student is about 13 500 kJ per day. If all of the student's energy is derived from the oxidation of glucose, as shown above, calculate the mass of glucose required each day. (2 marks) (b) The label on a bottle of fruit juice cordial indicates that 50.00 mL of the cordial yields 350 kJ of energy. If glucose is the only source of energy in the cordial, calculate the concentration of glucose in g L−1. (3 marks) (c) (i) According to the label on a packet of breakfast bars, each breakfast bar weighs 36.7 g, of which 66.7% is carbohydrate. If all of the carbohydrate is present as glucose, calculate the amount of energy that could be obtained from the combustion of the glucose in the breakfast bar. (3 marks) (ii) If the breakfast bar yields a total of 615 kJ, what percentage of the energy comes from the combustion of the carbohydrate? (1 mark) (Total = 9 marks)
Question 4/ 29 One substance used in detonators is lead azide, Pb(N3), because when given a shock (either thermal or mechanical), it decomposes rapidly according to the equation: Pb(N3)2(s) → Pb(s) + 3N2(g); ΔH = −436 kJ mol−1 (a) Would you expect the bonds in Pb and N2 to be stronger than those in Pb(N3)2 or weaker? Explain your answer. (2 marks) (b) Draw an energy level diagram showing how the energy of the reactants is related to that of the products. Your diagram should also show ΔH and an activation energy. (3 marks) (c) 10.0 g of lead azide rapidly decomposes in a volume of 5.00 mL. (i) Calculate the amount of energy released by this decomposition. (1 mark) (ii) Calculate the mass of the gas product.
(2 marks) (Total = 8 marks)
Question 5/ 29 A student is asked to determine the heat of combustion of methanol, CH3OH, using the apparatus shown below. 300 g of water is placed in a metal can. The can is clamped above the flame from a spirit burner. The temperature of the water is measured before and after heating by the methanol burner. The burner is weighed before and after heating the water.
The student obtains the following results: - mass of burner and methanol before combustion = 35.674 g - mass of burner and methanol after combustion = 34.396 g - temperature of water in can before heating = 16.3°C - temperature of water in can after heating = 28.1°C (a) Why was a metal can used rather than a glass container? (1 mark) (b) How many mol of methanol was burnt? (2 marks) (c) Calculate the heat energy given to the water. (1 mark) (d) From parts (b) and (c), calculate the heat of combustion of methanol in kJ mol−1.
(1 mark) (e) The accepted value for the heat of combustion of methanol is −725 kJ mol−1. Suggest two reasons why the value determined in part (d) is different from this value. (2 marks) (Total = 7 marks)
Question 6/ 29 Natural gas consists largely of methane, CH4, and is used as a source of energy in domestic gas supplies. In a laboratory using natural gas, a student uses a Bunsen burner to heat 300 g of water. The temperature rises from 16.7°C to 49.6°C. (a) Calculate the heat supplied to the water if the specific heat of water is 4.18 J°C−1 g−1. (1 mark) (b) If only 65% of the energy produced from the combustion of the gas is transmitted to the water, calculate the energy produced by the Bunsen burner. (1 mark) (c) Write the equation for the combustion of methane. (1 mark) (d) The student also measured the amount of gas used in the above experiment and found that 1.82 L at SLC were required. Calculate ΔH for the equation in part (c). (3 marks) (Total = 6 marks)
Question 7/ 29 Methylated spirits is mostly ethanol, C2H5OH, but also contains small amounts of methanol and water. The energy content of methylated spirits is found to be 28.5 MJ kg−1 and it has a density of 0.795 g mL−1. A camper uses methylated spirits as a source of energy to boil his drinking water. He heats 600 g of water from 15°C to boiling point. (a) Why is it not possible to express the energy content of methylated spirits in kJ mol−1?
(1 mark) (b) Write a balanced equation for the reaction of ethanol with oxygen. (1 mark) (c) Calculate the volume of methylated spirits that must be burnt to heat the water, if only 60% of the energy from burning the methylated spirits reaches the water. (4 marks) (Total = 6 marks)
Question 8/ 29 Copper forms two oxides, Cu2O and CuO. The energy change when each oxide is formed is given by the equations below. 2Cu(s) + O2(g) → 2CuO(s); ΔH = −310.4 kJ mol−1 4Cu(s) + O2(g) → 2Cu2O(s); ΔH = −338 kJ mol−1 Use this information to calculate ΔH for the reaction Cu2O(s) → Cu(s) + CuO(s) (Total = 3 marks)
Question 9/ 29 [Adapted VCAA 2014 SB Q3] The heat of combustion of ethanol is provided in the VCAA data book. This combustion of ethanol is represented by the following equation. C2H5OH(l) + 3O2(g) → 2CO2(g) + 3H2O(l) A spirit burner used 1.80 g of ethanol to raise the temperature of 100.0 g of water in a metal can from 25.0°C to 40.0°C (see diagram below). (a) Calculate the percentage of heat lost to the environment and to the apparatus. (5 marks)
(b) Identify one way to limit heat loss to the environment. (1 mark) (c) Biodiesel may be produced by reacting canola oil with methanol in the presence of a strong base. Since canola oil contains a mixture of triglycerides, the reaction produces glycerol and a mixture of biodiesel molecules. A typical biodiesel molecule derived from canola oil has the chemical formula C15H30O2. The heat content of canola oil can be determined by placing it in the spirit burner in place of ethanol. A typical result is 17 kJ g−1. Suggest why the heat content of fuels such as canola oil and biodiesel are measured in kJ g−1 and not kJ mol−1. (1 mark)
(Total = 7 marks)
Question 10/ 29 [Adapted VCAA 2017 SB Q2] A vehicle that is powered by a diesel engine is able to use either petrodiesel or biodiesel as a fuel. Petrodiesel and biodiesel are not pure substances but are a mixture of molecules. In general, petrodiesel consists of molecules that are shorter in length, on average, than those found in biodiesel. Biodiesel contains molecules that include functional groups. The table below lists some of the properties of the two fuels. Fuel
Major component
Energy content (MJ kg−1)
CO2 emission (kg CO2/kg of fuel)
petrodiesel
C12H26
43
3.17
biodiesel
C19H32O2
38
2.52
(a) Assume that combustion occurs in an unlimited supply of oxygen for each of the following calculations. Using the data from the table above: (i) calculate the number of litres of biodiesel that are required to be burnt to produce the same amount of energy as
2.5 kg of petrodiesel. [density (biodiesel) = 0.89 kg L−1] (3 marks) (ii) calculate the mass of carbon dioxide, CO2, that would be produced from 3.91 kg of biodiesel. (1 mark) (b) In some circumstances, there is a limited supply of oxygen. Write the balanced chemical equation for the combustion reaction of the major component of biodiesel, C19H32O2, where carbon monoxide, CO, is the only product containing carbon. (2 marks) (Total = 6 marks)
Question 11/ 29 [Adapted VCAA 2020 SB Q6] Methane gas, CH4, can be captured from the breakdown of waste in landfills. CH4 is also a primary component of natural gas. CH4 can be used to produce energy through combustion. (a) Write the equation for the incomplete combustion of CH4 to produce carbon monoxide, CO. (1 mark) (b) A Bunsen burner is used to heat a beaker containing 350.0 g of water. Complete combustion of 0.485 g of CH4 raises the temperature of the water from 20 °C to 32.3 °C. Calculate the percentage of the Bunsen burner's energy that is lost to the environment. (3 marks) (c) Compare the environmental impact of CH4 obtained from landfill to the environmental impact of CH4 obtained from natural gas. (2 marks) (Total = 6 marks)
Question 12/ 29
[VCAA 2021 SB Q1] Digesters use bacteria to convert organic waste into biogas, which contains mainly methane, CH4. Biogas can be used as a source of energy. (a) Both biogas and coal seam gas contain CH4 as their main component. Why is biogas considered a renewable energy source but coal seam gas is not? (1 mark) (b) A digester processed 1 kg of organic waste to produce 496.0 L of biogas at standard laboratory conditions (SLC). The biogas contained 60.0% CH4. (i) Write the thermochemical equation for the complete combustion of CH4 at SLC. (2 marks) (ii) Calculate the amount of energy that could be produced by CH4 from 1 kg of organic waste. (3 marks) (c) Biogas was combusted to release 1.63 x 103 kJ of energy. This energy was used to heat 100 kg of water in a tank. The initial temperature of the water was 25.0 °C. (i) What is the maximum temperature that the water in the tank could reach? (2 marks) (ii) State why this temperature may not be reached. (1 mark) (Total = 9 marks)
Question 13/ 29 Carbohydrates, vitamins, fats and proteins are all important components of a balanced diet. Carbohydrates are an immediate source of energy for most living things. Fats and proteins can also be used to provide energy but also have other important functions. (a) A bomb calorimeter is used to determine the energy content of a vegetable oil. 4.86 g of the vegetable oil was completely combusted in a calorimeter that contained 2.50 L of water. The temperature of the water rose from 19.5°C to 33.8°C. Calculate the energy content of the vegetable oil in kJ g−1. (3 marks) (b) Why is the energy content of the vegetable oil calculated in kJ g−1 and not kJ mol−1? (1 mark)
(Total = 4 marks)
Question 14/ 29 A breakfast food company has a new product, Breckyflakes, which it claims is less fattening than the product of its main rival, Iron-bran. To test the accuracy of these claims, the makers of Iron-bran employ a chemist to determine the heat content of each breakfast cereal. A 15.0 g sample of each cereal is placed in a calorimeter where it is burned in an excess of oxygen. The results shown below were obtained. Breckyflakes sample: • initial temperature of calorimeter and sample
= 18.417°C
• temperature after complete combustion
= 21.577°C
• temperature of calorimeter and combustion products after electric current is used to add 30.2 kJ
= 22.186°C
Iron-bran sample: (a) Determine the calibration factor of the calorimeter in kJ °C−1. (1 mark) (b) For each of the breakfast cereals, calculate the energy content in kJ g−1. (4 marks) (c) From these results can you decide which cereal is most fattening? If you cannot make a decision, what extra evidence might you need? (2 marks) (Total = 7 marks)
Question 15/ 29 Calorimeters are often calibrated by measuring the temperature change when a compound with a known heat of combustion is reacted. In a typical experiment 0.1049 g of benzoic acid, C6H5COOH, is completely burned in a calorimeter. The temperature of the calorimeter changes from 18.674°C to 21.905°C. The equation for the reaction is 2C6H5COOH(s) + 15O2(g) → 14CO2(g) + 6H2O(l); ΔH = −6526 kJ mol−1
(a) How many moles of benzoic acid reacted? (1 mark) (b) How much heat energy was released during the reaction? (2 marks) (c) Calculate a value for the calorimeter constant in J°C−1. (2 marks) Ethanol, C2H5OH, has been suggested as an alternative fuel to petrol. 0.545 mL of ethanol is burned in the same calorimeter and a temperature rise of 14.618°C is recorded. (d) How much energy was released by the burning ethanol? (1 mark) (e) Calculate the heat of combustion of ethanol in kJ mL−1. (1 mark) (Total = 7 marks)
Question 16/ 29 A middle-distance runner runs for 4 minutes 30 seconds and takes 70 breaths per minute. He has a lung capacity of 7.2 L and exchanges all of the air in his lungs with each breath. Air contains 20% oxygen, 25% of which is used in his cells for the reaction C6H12O6(aq) + 6O2(aq) → 6CO2(g) + 6H2O(l); ΔH = −2800 kJ mol−1 (a) What volume of oxygen is inhaled in 4.5 minutes? (1 mark) (b) What volume of oxygen reacts at the cells? (1 mark) (c) Assuming the oxygen was at SLC, calculate the minimum mass of glucose that the runner uses while running. (2 marks) (d) Calculate the energy the runner has obtained from the reaction of the glucose. (1 mark) (Total = 5 marks)
Question 17/ 29 [Adapted VCAA 2019 SB Q6] There are many varieties of bread available to consumers in Australia. The nutritional values for one type of wholemeal bread are given in the table below. • initial temperature of calorimeter and sample
= 18.961°C
• temperature after combustion of sample
= 22.384°C
Per 100 g Energy
1000 kJ
Protein
9.1 g
Fats and oils
2.5 g
Carbohydrates
41.5 g
Sugars
3.0 g
Fibre
6.4 g
(a) Calculate the energy, in kilojoules, provided by the protein and fats and oils in 100 g of this wholemeal bread. (1 mark) (b) The wholemeal bread undergoes complete combustion in a bomb calorimeter containing 200 g of water. Assume that all of the energy in the combustion is transferred to the water. (i) Calculate the mass of bread needed to raise the temperature of the water by 6°C. (2 marks) (ii) The combustion of the bread was investigated using a different method. The bread was ignited under a beaker containing 200 g of water, which was set on a tripod. The equipment used is shown below.
If 1.2 g of bread was needed to raise the temperature of the water by 6°C using this different method, calculate the efficiency of the energy transfer in this combustion. (1 mark) (Total = 4 marks)
Question 18/ 29 A chemist places tin rods in each of four 1.0 M aqueous solutions. The solutes are respectively AgNO3, CuSO4, FeSO4 and ZnCl2. Describe what you would expect to happen in each of these experiments. Give reasons for your answers. Give equations for any reactions that occur. (Total = 4 marks)
Question 19/ 29 The potential differences and electrode polarities of two standard electrochemical cells are shown below. (Note that not all of these half-cells are listed in the electrochemical series provided in the VCAA data book.)
(a) From the information given above, deduce which species in the two cells is the strongest oxidising agent. Explain your reasoning. (2 marks) (b) Give the equation for the reaction occurring at the anode in each cell. (2 marks) (c) If a cell was constructed from the Fe3+/Fe2+ and the Cd2+/Cd half-cells, what would be the value for the potential difference of the cell? (1 mark) (Total = 5 marks)
Question 20/ 29 A home chemistry kit contains solutions of Sn2+, Cu2+, Fe3+, a dilute acid and pieces of metallic copper, iron, lead and zinc. (a) Describe an experiment in which Sn2+(aq) would be oxidised to Sn4+(aq). Give a balanced equation for the reaction. (2 marks) (b) If a mixture of Cu2+(aq) and Fe3+(aq) was prepared, how could the Fe3+(aq) be reduced without the Cu2+(aq) reacting? Give a balanced equation for the reaction. (2 marks) (c) Give a balanced equation for a reaction that could be used to prepare a sample of hydrogen gas. (1 mark)
(Total = 5 marks)
Question 21/ 29 A chemist carried out reactions with three metals, X, Y and Z, and solutions of their nitrate salts. The observations below were made when clean metal surfaces were used. I Metal Z dissolved in a 1.0 M YNO3 solution, forming a deposit of metal Y. II Metal X did not react with a 1.0 M Z(NO3)3 solution. III Metal Y did not react with a 1.0 M X(NO3)2 solution. (a) Use this information to place the three metals in order of increasing strength as reducing agents (put the least reactive first). Give reasons for your answer. (3 marks) (b) Some methods for mining metals from metal ores utilise a reaction between the metal and a substance pumped into the ore, such as an acid. This means that more reactive metals are more easily extracted in this type of process as they more readily react and dissolve, as metal ions, into the solution. The liquid is then extracted from the ore with the dissolved ions. The naturally occurring ores of these metals are XS, Y2S and Z2O3. Which metal is likely to be the easiest to extract from its ore and which metal is likely to be the most difficult to extract? Give reasons for your answers. (2 marks) (Total = 5 marks)
Question 22/ 29 Three electrochemical cells are set up as shown below. The potential difference is shown on each voltmeter.
(a) From this information, deduce the order of the four half-cells Cu2+/Cu, X+/X, Y2+/Y and Z2+/Z in the electrochemical series. (List the one with the strongest oxidant first.) (3 marks) (b) If a cell was constructed from the Y2+/Y and Z2+/Z half-cells, deduce the polarity of the electrodes and the potential difference of the cell. (2 marks) (Total = 5 marks)
Question 23/ 29 Six experiments were carried out in which pairs of reagents were mixed. The pairs are indicated in the left-hand column of the table below. For those cases where the electrochemical series would predict that a reaction should occur, write a balanced chemical equation for the predicted reaction. Where you do not expect a reaction, write ‘no reaction’. Reactants Fe2+(aq)/Cl2(g) AgNO3(aq)/Sn(s) SnCl2(aq)/Cu(s) Cd2+(aq)/Ag(s) Ni2+(aq)/Cd(s) Cl−(aq)/I2(aq) (Total = 9 marks)
Predicted reaction Yes/No
Equation
Question 24/ 29 Copper plates were once attached to the hulls of wooden ships. In water, the copper corroded and produced Cu2+(aq) ions. These ions are poisonous to many marine organisms and so the formation of barnacles and other organisms on the ships’ hulls was prevented. In seawater, the copper corroded very rapidly. To slow down the removal of the copper, pieces of a reactive metal were attached to the copper plates. Zinc was often used as the reactive metal. The copper plates then lasted for a longer time, but the barnacles and other organisms quickly attached themselves to the hulls of the ships. Use the electrochemical series to answer the questions below. (a) Why do the copper plates corrode? Write a balanced equation for the reaction. (2 marks) (b) The corrosion is faster in seawater. Suggest a reason for this. (1 mark) (c) Why do pieces of a reactive metal prevent the copper from corroding? What happens to the reactive metal, such as zinc? Write the equation for any reaction that occurs. (3 marks) (d) When a piece of zinc is joined to the copper plates, barnacles rapidly become attached to the hull. Suggest a reason for this. (1 mark) (Total = 7 marks)
Question 25/ 29 Consider the following electrochemical series. Cu+(aq) + e− ⇌ Cu(s) E° = 0.52 V Cu2+(aq) + e− ⇌ Cu+(aq) E° = 0.16 V Many solid compounds of copper(I) are known (such as solid copper(I) oxide, Cu2O; solid copper(I) chloride, CuCl) and are quite stable. However, attempts to prepare solutions containing Cu+(aq) are always unsuccessful. Use the information provided above to explain why solutions of Cu+(aq) are unstable. (Total = 3 marks)
Question 26/ 29 [VCAA 2014 SB Q10] The diagram below shows a cross-section of a small zinc-air button cell, a button cell that is used in hearing aids. The zinc acts as the anode. It is in the form of a powder dispersed in a gel (a jelly-like substance) that also contains potassium hydroxide. The cathode consists of a carbon disc. Oxygen enters the cell via a porous Teflon membrane. This membrane also prevents any chemicals from leaking out.
The following reaction takes place as the cell discharges. 2Zn(s) + O2(g) + 2H2O(l) → 2Zn(OH)2(s) (a) Write a balanced half-equation for the reaction occurring at the anode. (1 mark) (b) Suggest one role of potassium hydroxide in this cell. (1 mark) (c) A zinc-air button cell is run for 10 hours at a steady current of 2.36 mA. What mass of zinc metal reacts to form zinc oxide during that time? (3 marks) (d) A hydrogen-oxygen fuel cell can operate with an alkaline electrolyte such as potassium hydroxide. In this cell, the reaction at the cathode is the same as that in the zinc-air cell. A porous carbon cathode is used. Write the halfequation for the reaction that occurs at the anode in a hydrogen-oxygen cell with an alkaline electrolyte. (1 mark) (Total = 6 marks)
Question 27/ 29 [VCAA 2018 SB Q6] Redox reactions occur in the human body as well as in electrochemical cells. (a) Nicotinamide adenine dinucleotide (NAD) is a vital coenzyme for energy production in the human body. It exists in two forms: an oxidised form, NAD+, and a reduced form, NADH. NAD is involved in the conversion of ethanol, CH3CH2OH, to ethanal, CH3CHO, in the human body. The overall equation for this redox reaction is CH3CH2OH + NAD+ → CH3CHO + NADH + H+ (i) Write the two half-equations for this redox reaction. States are not required. Oxidation half-equation: Reduction half-equation: (2 marks) (ii) Identify the reducing agent in this redox reaction. (1 mark) (b) The Daniell cell, a type of galvanic cell, was first constructed in the mid-1800s and this type of cell is still in use today. A diagram of the Daniell cell is shown below. (i) Label the polarity of the electrodes by placing a positive (+) or negative (−) sign in each of the circles next to the electrodes on the diagram. (1 mark) (ii) Use the electrochemical series to determine the theoretical voltage of this cell. (1 mark) (iii) In the diagram below, the electrolyte in the salt bridge is a potassium nitrate solution, KNO3(aq). In the box above the salt bridge, use an arrow to indicate the direction of flow of K+(aq) ions. (1 mark) (iv) List two visible changes that are likely to be observed when the Daniell cell has been operating for some time. (2 marks) (c) What design features of the Daniell cell structure would allow it to produce electrical energy? (2 marks)
Question 28/ 29 [VCAA 2019 SB Q4] Internal combustion engines are used in large numbers of motor vehicles. Historically, internal combustion engines have used fuels obtained from crude oil as a source of power. As concerns for the environment have grown, efforts have been made to obtain fuel for combustion engines from other sources. (a) One way of reducing the environmental effects of fossil fuels is to blend them with biofuels. A common method is to blend petrol with ethanol in varying ratios. A fuel can be obtained by blending 1 mole of octane, C8H18, and 1 mole of ethanol, C2H5OH. The chemical equation for the complete combustion of this fuel mixture is C8H18(l) + C2H5OH(l) + 15½O2(g) → 10CO2(g) + H2O(g) Calculate the energy released, in kilojoules, when 80 g of this fuel mixture undergoes complete combustion. Show your working. (3 marks) (b) Some car manufacturers are exploring the use of an acidic ethanol fuel cell to power vehicles. In this fuel cell, the ethanol at one electrode reacts with water that has been produced at the other electrode. A membrane is used to transport ions between the electrodes. A diagram of an acidic ethanol fuel cell is shown below.
(i) Identify the electrode as either the cathode or the anode in the box provided in the diagram above. (1 mark) (ii) Write the half-equation for the reaction occurring at the anode. (1 mark) (iii) The combustion of ethanol and the combustion of octane release about the same amount of energy per mole of carbon dioxide produced. Identify two advantages of powering a vehicle using an ethanol fuel cell instead of an internal combustion engine powered by octane. (2 marks) (Total = 7 marks)
Question 29/ 29 [VCAA 2021 SB Q4] (a) What is a fuel cell? (2 marks)
(b) The diagram below shows part of an ethanol fuel cell, which produces carbon dioxide and uses an acidic electrolyte.
(i) Name the species that crosses the membrane to enable fuel cell operation. (1 mark) (ii) In the box provided on the diagram above, indicate the direction of flow of the species named in part b.i. (1 mark) (c) Write the equation for the reaction that occurs at the anode of an ethanol fuel cell, which produces carbon dioxide and uses an acidic electrolyte. (1 mark) (d) If an ethanol fuel cell was operating at 25 °C and at 100% efficiency, how much electrical energy could be produced from 1.0 g of ethanol? (1 mark) (e) Identify two aspects of electrode design that can improve the efficiency of a fuel cell. (2 marks) (f) State how the environmental impact of using an ethanol fuel cell operating at 100% efficiency can be minimised. (1 mark) (Total = 9 marks)
Question 1/ 6 In the species ClO3− and H3PO3, the oxidation states of the underlined atoms are respectively
A. +5 and +3 B. +5 and 0 C. +6 and +3 D. −5 and −3
Question 2/ 6 The energy diagram shown below contains the information from the following two combustion reactions. CH4(g) + 2O2(g) → CO2(g) + 2H2O(l); ΔH = −890 kJ mol−1 CO(g) + ½O2(g) → CO2(g); ΔH = −282 kJ mol−1
From the information above, ΔH for the reaction 2CH4(g) + 3O2(g) → 2CO(g) + 4H2O(l) is most likely to be A. −608 kJ mol−1 B. −1172 kJ mol−1 C. −1216 kJ mol−1 D. −2344 kJ mol−1
Question 3/ 6 One of the reactions involved in the production of methanol, CH3OH, is CO2(g) + 3H2(g) → CH3OH(g) + H2O(g); ΔH = −48 kJ mol−1 From this information it can be concluded that A. formation of 1 mol of water releases 24 kJ. B. when 3.0 g of hydrogen reacts 48 kJ of energy are released. C. reaction of 1 mol of carbon dioxide absorbs 48 kJ of energy. D. production of 2 mol of methanol would release 96 kJ of energy.
Question 4/ 6 A recently developed fuel cell uses methanol and oxygen as the two reactants. In this cell, complete combustion of methanol takes place. The reaction occurring at the anode of this cell is A. 2CH3OH(aq) + 3O2(g) → 2CO2(g) + 4H2O(l) B. O2(g) + 4H+(aq) + 4e− → 2H2O(l) C. CH3OH(aq) → CO(g) + 4H+(aq) + 4e− D. CH3OH(aq) + H2O(l) → CO2(g) + 6H+(aq) + 6e−
Question 5/ 6 Using a data table, a student finds that the heat of combustion of propan-1-ol is 2021 kJ mol−1. What value would the student calculate for the heat of combustion of propan-1-ol in kJ g−1? A. 23.0 B. 27.3 C. 33.6
D. 43.9
Question 6/ 6 Silver oxide and zinc are used in some galvanic cells. When these cells produce an electric current, the following reaction occurs. Ag2O(s) + Zn(s) + H2O(l) → 2Ag(s) + Zn(OH)2(s) The reaction occurring at the positive electrode when cells of this type produce a current is A. Zn(s) + 2OH−(aq) → Zn(OH)2(s) + 2e− B. Ag2O(s) + H2O(l) + 2e− → 2Ag(s) + 2OH−(aq) C. Zn(OH)2(s) + 2e− → Zn(s) + 2OH−(aq) D. 2Ag(s) + 2OH−(aq) → Ag2O(s) + H2O(l) + 2e−
Question 7/ 6 The following information refers to Questions 8 and 9. Four metals, Cu, p, q and r, were each placed in a solution of their metal ions. The electrodes and solutions were then connected in pairs as shown in the diagram below and the voltage of each cell was recorded.
The table below shows the results obtained. Negative terminal
Positive terminal
Voltage (V)
Negative terminal
Positive terminal
Voltage (V)
Cu
p
0.45
Cu
q
1.29
r
Cu
0.75
Question 8/ 6 From this information, place the metals in order showing the increasing ease of oxidation (easiest to oxidise last). A. p < q < r < Cu B. Cu < r < q < p C. q < p < Cu < r D. r < Cu < p < q
Question 9/ 6 If the metals p and q were connected, then the results expected would be Negative terminal
Voltage (V)
p
0.84
p
1.74
q
0.84
q
1.74
Question 10/ 6 Students in a VCE Chemistry class were asked to determine the heat of combustion of an alcohol. Each pair of
students used a different alcohol. The alcohols studied were methanol, ethanol, propan-1-ol, butan-1-ol and pentan-1ol. All students used the equipment shown in the diagram below.
The results obtained by the students using propan-1-ol are shown below. Mass of water in can = 250 g Mass of propan-1-ol burned = 0.496 g Temperature rise of water = 7.2°C (a) (i) What value, in kJ mol−1, should the students calculate for the heat of combustion of propan-1-ol using their results? (2 marks) (ii) Write the thermochemical equation for the heat of combustion of propan-1-ol. (2 marks) The heats of combustion determined by some of the other groups of students are given in the table below. Alcohol
Heat of combustion (kJ mol−1)
Methanol
380
Butan-1-ol
1140
Pentan-1-ol
1330
(b) (i) Use the results in the table and the value calculated in part (a) to plot a graph of heat of combustion against the number of carbon atoms in the alcohol. (2 marks) (ii) From your graph, determine the heat of combustion obtained by the students who used ethanol. (1 mark) (c) The students using butan-1-ol noticed that the alcohol burned with a yellow flame and concluded that some of the alcohol was undergoing incomplete combustion and producing carbon rather than carbon dioxide. Write the equation for the incomplete combustion of butan-1-ol. (2 marks)
(Total = 9 marks)
Question 11/ 6 Methanol can be produced by the partial oxidation of methane in a two-step process. 2CH4(g) + O2(g) → 2CO(g) + 4H2(g); ΔH = −74 kJ mol−1 followed by 2CO(g) + 4H2(g) → 2CH3OH(g); ΔH = −180 kJ mol−1 (a) The methanol produced in this way can be described as a renewable fuel or as a non-renewable fuel. Explain why this is possible. (3 marks) (b) Calculate the amount of energy released (in MJ) when 1.00 kg of methane is converted into methanol. (3 marks) (Total = 6 marks)
Question 12/ 6 In recent years, solid oxide fuel cells have been developed that use methane as the fuel. The other reactant is oxygen from the air. The electrodes are often made from metals such as platinum or nickel. The fuel cell operates at high temperatures and the electrolyte is a solid ceramic oxide. At high temperatures, O2− ions are able to move through the electrolyte. (a) The half-equation for the reaction occurring at one of the electrodes is O2(g) + 4e− → 2O2−(s) Give the name of this electrode and state its polarity. (2 marks) (b) Give two properties of the electrode essential for the successful operation of the fuel cell. (2 marks) (c) At the other electrode, methane is consumed, and carbon dioxide and water are produced.
Write the half-equation for the reaction occurring at this electrode. (2 marks) (d) Give the overall cell reaction. (1 mark) (Total = 7 marks)
Question 13/ 6 (a) Sucrose is a sugar found in many foods. It has the formula C12H22O11 and can be oxidised to form carbon dioxide and water. Write an equation for the oxidation of sucrose. (1 mark) (b) A bomb calorimeter can be used to determine the energy released when sucrose is oxidised. Draw and label a bomb calorimeter suitable for measuring the energy released when sucrose is oxidised in oxygen. (3 marks) (c) 0.281 g of sucrose is burned in excess oxygen in a bomb calorimeter. The temperature is observed to rise from 294.156 K to 294.781 K. This bomb calorimeter has a calibration factor of 7380 J K−1. (i) How much heat is evolved by the combustion of 0.281 g of sucrose? (1 mark) (ii) Calculate the heat that would be evolved by burning 1 mol of sucrose. (1 mark) (Total = 6 marks)
Question 14/ 6 In acidic solution and in the presence of a suitable catalyst, the following reaction proceeds rapidly: 2H2O2(aq) + N2H4(aq) ⇌ N2(g) + 4H2O(l) A chemist wishes to use this reaction as the cell reaction in the galvanic cell shown below.
(a) What changes in oxidation number occur in the above equation? (2 marks) (b) The barrier prevents solutions A and B from directly reacting. It is made of a chemically inert material. Give another important property that the barrier must possess. (1 mark) (c) Identify the solutions, A and B. (2 marks) (d) Suggest two necessary properties of the electrode materials. (2 marks) (e) Assuming that solutions A and B are acidic, write the half-cell reactions when the cell is operating for (i) the reaction at the positive electrode (cathode). (ii) the reaction at the negative electrode (anode). (1 + 1 = 2 marks) (Total = 9 marks)
Question 15/ 6 (a) Why is glucose, C6H12O6, important to life? Give an equation to show how the body uses glucose. (2 marks) (b) Plants are able to synthesise glucose. Give an equation for the reaction in which glucose is synthesised and mention any conditions that are essential for the process to occur.
(2 marks) (c) Name the major food group to which glucose belongs. (1 mark) (Total = 5 marks) Total marks for test = 50 marks
Chapter 2: Unit 3 Area of Study 2 – How can the rate and yield of chemical reactions be optimised? Question 1/ 56 Acetone, CH3COCH3, and iodine, I2, react according to the equation given below. A small amount of sulfuric acid is needed to catalyse the reaction. CH3COCH3(l) + I2(aq) → CH3COCH2I(aq) + HI(aq) A student determines which factors will change the rate of this reaction. Four experiments are carried out with different initial concentrations of acetone, iodine and sulfuric acid. The time taken to form a small amount of product is measured. This amount of product is the same for each experiment. The results are listed in the table. [CH3COCH3]
[I2]
[H+]
Time taken
0.100 M
0.100 M
0.010 M
60 s
0.100 M
0.100 M
0.020 M
30 s
0.200 M
0.100 M
0.010 M
30 s
0.100 M
0.200 M
0.010 M
60 s
The student deduces that the rate of the reaction A. depends only on the concentration of acetone. B. is not affected by the concentration of sulfuric acid. C. depends on the concentrations of acetone, iodine and acid. D. is only affected by the concentrations of acetone and acid.
Question 2/ 56 [VCAA 2019 SA Q11] 5 mL of ethanol, CH3CH2OH, undergoes combustion in a test tube with a diameter of 1 cm. This experiment is performed in a fume cupboard. The temperature in the fume cupboard is 20 °C. Which one of the following actions will reduce the rate of reaction? A. Mix 2 mL of a dilute solution of sodium hydroxide, NaOH, with the ethanol. B. Perform the experiment in a test tube with a diameter of 2 cm. C. Increase the temperature in the fume cupboard to 25 °C. D. Increase the volume of the ethanol to 7 mL.
Question 3/ 56 Use the following information to answer Questions 4 and 5. Cu(s) + 4HNO3(aq) → Cu(NO3)2(aq) + 2NO2(g) + 2H2O(l)
Question 4/ 56 [VCAA 2013 SA Q14]
Which one of the following will not increase the rate of the above reaction? A. decreasing the size of the solid copper particles B. increasing the temperature of HNO3 by 20°C C. increasing the concentration of HNO3 D. allowing NO2 gas to escape
Question 5/ 56 [VCAA 2013 SA Q15] In the above reaction, the number of successful collisions per second is a small fraction of the total number of collisions. The major reason for this is that A. the nitric acid is ionised in solution. B. some reactant particles have too much kinetic energy. C. the kinetic energy of the particles is reduced when they collide with the container's walls. D. not all reactant particles have the minimum kinetic energy required to initiate the reaction.
Question 6/ 56 [VCAA 2018 SA Q13] The energy profile diagram below represents a particular reaction. One graph represents the uncatalysed reaction and the other graph represents the catalysed reaction.
Which of the following best matches the energy profile diagram? Ea uncatalysed reaction (kJ mol−1)
ΔH catalysed reaction (kJ mol−1)
40
−140
90
−140
40
−50
90
−50
Question 7/ 56 [Adapted VCAA 2015 SA Q17] The oxidation of sulfur dioxide is an exothermic reaction. The reaction is catalysed by vanadium(V) oxide. 2SO2(g) + O2(g) → 2SO3(g) Which one of the following energy profile diagrams correctly represents both the catalysed and the uncatalysed reaction?
A.
B.
C.
D.
Question 8/ 56 An important industrial process is the conversion of carbon monoxide into carbon dioxide using steam. CO(g) + H2O(g) ⇌ CO2(g) + H2(g); ΔH = −40 kJ mol−1 Which of the following would increase the percentage conversion of CO into CO2? A. increasing the pressure B. increasing the temperature
C. increasing the concentration of water D. increasing the volume of the container
Question 9/ 56 An important reaction in the production of ammonia, NH3, is given below. N2(g) + 3H2(g) ⇌ 2NH3(g); ΔH = −90 kJ mol−1 If the reaction takes place in a sealed container, which of the following procedures would not cause the rate of the forward reaction to increase? A. adding an inert gas B. increasing the pressure C. adding a suitable catalyst D. increasing the temperature
Question 10/ 56 In the commercial production of methanol, CH3OH, carbon monoxide and hydrogen are heated and passed over a catalyst. The following equilibrium is set up. CO(g) + 2H2(g) ⇌ CH3OH(g); ΔH = −95 kJ mol−1 The reaction does not go to completion and the conditions have to be carefully adjusted to produce a maximum yield. Which of the following would be expected to increase the yield of methanol? A. Condense the methanol and recycle the remaining gases. B. Lower the pressure in the reaction vessel. C. Use a more effective catalyst. D. Increase the temperature in the reaction vessel.
Question 11/ 56 When hydrogen (H2) and iodine (I2) react, hydrogen iodide (HI) is formed. H2(g) + I2(g) ⇌ 2HI(g) In one experiment in a 2.0 L vessel at a certain temperature, the equilibrium mixture contained 0.5 mol of HI, 0.25 mol of H2 and 0.1 mol of I2. The value for the equilibrium constant at this temperature is A. 0.05 B. 0.1 C. 10 D. 20
Question 12/ 56 In the production of nitric acid, an important step is the conversion of nitric oxide (NO) into nitrogen dioxide (NO2). 2NO(g) + O2(g) ⇌ 2NO2(g); ΔH = −114 kJ mol−1 Which of the following sets of conditions would be expected to give the best equilibrium yield of nitrogen dioxide? A. 500°C and 4 atm pressure B. 30°C and 4 atm pressure C. 500°C and 1 atm pressure D. 30°C and 1 atm pressure
Question 13/ 56 Aqueous solutions containing dichromate ions (Cr2O72−) are orange, while those containing chromate ions (CrO42−) are yellow. These two ions can be interconverted by the reaction below. 2CrO42−(aq) + 2H+(aq) ⇌ Cr2O72−(aq) + H2O(l)
A yellow solution of CrO42− will be converted into one containing orange Cr2O72− when A. HCl(aq) is added. B. NaOH(aq) is added. C. water is added. D. K2Cr2O7 is added.
Question 14/ 56 The following information is referred to in Questions 15 and 16. The equilibrium below is established when solutions containing Fe3+ and SCN− are mixed. $\begin{align} & \text{F}{{\text{e}}^{3+}}(\text{aq})\quad +\ \ \ \text{SC}{{\text{N}}^{-}}(\text{aq}) \rightleftharpoons \text{Fe}{{(\text{SCN})}^{2+}}(\text{aq}) \\ & (\text{colourless})\quad (\text{colourless})\quad \ \ (\text{deep}\ \text{red}) \\ \end{align}$
Question 15/ 56 When a small volume of a concentrated solution containing Fe(NO3)3 is added to this system, the colour changes, showing that more Fe(SCN)2+ has been formed. Which of the graphs shown below correctly shows the changes in Fe3+ concentration before and after the addition of Fe(NO3)3?
A.
B.
C.
D.
Question 16/ 56 The solution from Question 13 is diluted with an equal volume of water. The colour becomes a paler red. The addition of water has caused the concentration A. and the number of moles of Fe(SCN)2+ to decrease. B. and the number of moles of Fe(SCN)2+ to remain unchanged. C. of Fe(SCN)2+ to decrease but the number of moles of Fe(SCN)2+ to remain unchanged. D. of Fe(SCN)2+ to decrease but the number of moles of Fe(SCN)2+ to increase.
Question 17/ 56 [VCAA 2018 SA Q24] The four equations below represent different equilibrium systems. Equation 1 2SO2(g) + O2(g) ⇌ 2SO3(g) ΔH = −180 kJ mol−1 Equation 2 CO(g) + H2O(g) ⇌ CO2(g) + H2(g) ΔH = −46 kJ mol−1 Equation 3 PCl5(g) ⇌ PCl3(g) + Cl2(g) ΔH = +93 kJ mol−1 Equation 4 CH4(g) + H2O(g) ⇌ CO(g) + 3H2(g) ΔH = +205 kJ mol−1 After equilibrium was established in each system, the temperature was decreased and the pressure was increased. In which equilibrium system would both changes result in an increase in yield? A. Equation 1 B. Equation 2 C. Equation 3 D. Equation 4
Question 18/ 56 The reaction below is allowed to reach equilibrium at 500°C. 2H2O(g) + C2H6(g) ⇌ 2CO(g) + 5H2(g); ΔH = +347 kJ mol−1 The temperature is then lowered and the amount of H2O changes by 0.20 mol. The changes occurring would be H 2O increase by 0.20 mol increase by 0.20 mol decrease by 0.20 mol decrease by 0.20 mol
C2H6 increase by 0.40 mol increase by 0.10 mol decrease by 0.40 mol decrease by 0.10 mol
CO
H2
decrease by 0.20 mol
decrease by 0.040 mol
decrease by 0.20 mol increase by 0.20 mol increase by 0.20 mol
decrease by 0.50 mol increase by 0.040 mol increase by 0.50 mol
Question 19/ 56 [Adapted VCAA 2012 E2 SA Q8] The following equilibrium is established. 2+
Fe3+ (aq) + SCN− (aq) ⇌ Fe(SCN) (aq) yellow deepred Which one of the graphs below best represents the changes in concentration when the equilibrium mixture is diluted at time t2?
A.
B.
C.
D.
Question 20/ 56 [VCAA 2011 E2 SA Q1] Consider the following equilibrium expression. 4
] K= [[LJ][]6M [K]
The equation of the forward reaction for this equilibrium expression is A. 6J + K ⇌ L + 4M B. L + M4 ⇌ J6 + K C. J6 + K ⇌ L + M4 D. L + 4M ⇌ 6J + K
Question 21/ 56 [VCAA 2018 SA Q27] Br2(g) + I2(g) ⇌ 2IBr(g) K = 1.2 × 102 at 150°C Given the information above, what is K for the reaction 4IBr(g) ⇌ 2Br2(g) + 2I2(g) at 150°C? A. 1.6 × 10−2 B. 4.1 × 10−3
C. 6.9 × 10−5 D. 8.03 × 10−5
Question 22/ 56 [Adapted VCAA 2013 SA Q18] Use the following information to answer the question. 2NOCl(g) ⇌ 2NO(g) + Cl2(g); ΔH is positive. A concentration–time graph for this system is shown below.
What event occurred at time t to cause the change in equilibrium concentrations? A. The pressure was decreased at a constant temperature. B. The temperature was increased at a constant volume. C. A catalyst was added at a constant temperature and volume. D. Additional NO gas was added at a constant volume and temperature.
Question 23/ 56 [VCAA 2020 SA Q17] The following equation represents the reaction between chlorine gas, Cl2, and carbon monoxide gas, CO. Cl2(g) + CO(g) ⇌ COCl2(g) ΔH = −108 kJ mol−1 The concentration–time graph below represents changes to the system.
Which of the following identifies the changes to the system that took place at 1 minute and at 7 minutes? 1 minute
7 minutes
increase in temperature
increase in volume
decrease in temperature
decrease in volume
decrease in temperature
increase in volume
increase in temperature
decrease in volume
Question 24/ 56 [VCAA 2020 SA Q19] Nitrogen dioxide, NO2, and dinitrogen tetroxide, N2O4, form an equilibrium mixture represented by the following equation. 2NO2(g) ⇌ N2O4(g) ΔH = −57.2 kJ mol−1 brown colourless
A change was made at time t1 to an equilibrium mixture of NO2 and N2O4, which achieved a new equilibrium at time t2. A graph showing the rate of the forward reaction is shown below.
Which one of the following describes the change that was made to the initial equilibrium system and the colour change that occurred between t1 and t2? A. The temperature was increased and the colour lightened. B. The temperature was increased and the colour darkened. C. The temperature was decreased and the colour lightened. D. The temperature was decreased and the colour darkened.
Question 25/ 56 [VCAA 2019 SA Q28] The concentration of all of the gases in the equilibrium reactions below is 1.0 M. Reaction 1 CH4(g) + 2H2O(g) ⇌ CO2(g) + 4H2(g) Reaction 2 N2(g) + 3H2(g) ⇌ 2NH3(g) Reaction 3 H2(g) + I2(g) ⇌ 2HI(g) Reaction 4 2NO2(g) ⇌ N2O4(g) In which reaction does K = 1.0 M−2? A. Reaction 1 B. Reaction 2 C. Reaction 3
D. Reaction 4
Question 26/ 56 The following information is referred to in Questions 27 and 28. Hydrogen, H2, and iodine, I2, react to form hydrogen iodide, HI. 1 1 −1 2 H2(g) + 2 I2(g) ⇌ HI(g) ΔH = +25.9 kJ mo1
The graph below shows the concentrations of H2, I2 and HI in a sealed container. One change was made to the equilibrium system at time t2.
Question 27/ 56 [VCAA 2021 SA Q27] Which one of the following statements is correct? A. A catalyst was added at time t2. B. The amount of HI is greater at time t3 compared with time t1.
C. The rate of reaction producing HI is the same at time t1 and time t3. D. The rate of production of HI at time t3 is double the rate of production of H2 at time t3.
Question 28/ 56 [VCAA 2021 SA Q28] One change was made to the equilibrium system at time t4, which altered the equilibrium constant. Equilibrium was re-established at time t5. The rate of the reverse reaction at time t5 was higher than at time t3. Which of the following options correctly shows the change in the equilibrium system from time t3 to time t5? Changes from t3 to time t5 Equilibrium constant
Total chemical energy
increase
increase
increase
decrease
decrease
increase
decrease
decrease
Question 29/ 56 Which one of the statements below regarding galvanic and electrolytic cells is correct? A. Reduction occurs at the cathode in galvanic cells but at the anode in electrolytic cells. B. Oxidation occurs at the cathode in both cells. C. Reduction occurs at the cathode and oxidation occurs at the anode in both cells. D. Oxidation occurs at the anode in galvanic cells but at the cathode in electrolytic cells.
Question 30/ 56 A student sets up the circuit shown below to electrolyse solutions of copper nitrate and gold(III) chloride using inert electrodes.
The mass of gold to the mass of copper deposited at the two cathodes will be in the ratio A. 1.00 : 1.00 B. 2.07 : 1.00 C. 3.10 : 1.00 D. 4.65 : 1.00
Question 31/ 56 An aqueous solution of zinc nitrate is electrolysed for 75.0 minutes by a current of 4.50 A. The mass of zinc deposited, in grams, is closest to A. 0.23 B. 6.85 C. 13.70 D. 27.40
Question 32/ 56
In the electrolytic production of aluminium, the current, in amps, needed to deposit 5.0 kg of aluminium in 60.0 minutes is closest to A. 15 B. 5.0 × 103 C. 1.5 × 104 D. 8.9 × 105
Question 33/ 56 In the electrolysis of thallium nitrate solution, 0.168 g of thallium is deposited at the cathode in 144 seconds by a current of 1.65 A. The charge on the thallium ion in the solution of thallium nitrate is A. −3 B. −1 C. +1 D. +3
Question 34/ 56 A solution of tin(II) chloride was electrolysed using the circuit shown below.
The reaction that is most likely to occur at the positive electrode is A. Sn2+(aq) + 2e− → Sn(s)
B. 2Cl−(aq) → Cl (g) + 2e− C. 2H2O(l) → O2(g) + 4H+(aq) + 4e− D. Sn(s) → Sn2+(aq) + 2e−
Question 35/ 56 9650 C of electrical charge is used to electrolyse 1.00 L of a 0.50 M lead nitrate solution. If the volume of the solution remains unchanged, then the Pb2+(aq) concentration after electrolysis will be A. 0 M B. 0.30 M C. 0.40 M D. 0.45 M
Question 36/ 56 [VCAA 2018 SA Q9] When molten sodium chloride, NaCl, is electrolysed, the product formed at the cathode is A. sodium liquid, Na. B. hydrogen gas, H2. C. chlorine gas, Cl2. D. oxygen gas, O2.
Question 37/ 56
[VCAA 2011 E2 SA Q17] If we compare a galvanic cell with an electrolytic cell, it is true to state that A. in a galvanic cell reduction occurs at the negative electrode. B. in both cells the anode is positive and the cathode is negative. C. in an electrolytic cell oxidation occurs at the cathode. D. in both cells reduction occurs at the cathode.
Question 38/ 56 Use the following information to answer Questions 39 and 40. An electrolytic cell is set up to obtain pure copper from an impure piece of copper called ‘blister copper’. The electrolyte solution contains both copper(II) sulfate and sulfuric acid. The blister copper, Electrode I, contains impurities such as zinc, cobalt, silver, gold, nickel and iron. The cell voltage is adjusted so that only copper is deposited on Electrode II. Sludge, which contains some of the solid metal impurities present in the blister copper, forms beneath Electrode I. The other impurities remain in solution as ions. The diagram below represents the cell.
Question 39/ 56 [VCAA 2015 SA Q28] The solid metal impurities that are found in the sludge are A. gold, nickel and cobalt.
B. cobalt, nickel and iron. C. nickel and iron. D. silver and gold.
Question 40/ 56 [VCAA 2015 SA Q29] Which of the following correctly shows both the equation for the reaction occurring at the cathode and the polarity of Electrode I? Cathode reaction
Polarity of Electrode I
Cu2+(aq) + 2e− → Cu(s)
positive
Cu(s) → Cu2+(aq) + 2e−
negative
Cu2+(aq) + 2e− → Cu(s)
negative
Cu(s) → Cu2+(aq) + 2e−
positive
Question 41/ 56 [VCAA 2015 SA Q30] Which one of the following graphs best shows the change in mass of Electrode I over a period of time, starting from the moment the power supply is connected?
A.
B.
C.
D.
Question 42/ 56 [VCAA 2019 SA Q7] A molten mixture of equal parts aluminium fluoride, AlF3, and sodium chloride, NaCl, undergoes electrolysis. Which one of the following statements about this reaction is correct? A. Sodium metal will be produced at the cathode and fluorine gas will be produced at the anode. B. Sodium metal will be produced at the anode and chlorine gas will be produced at the cathode. C. Aluminium metal will be produced at the cathode and chlorine gas will be produced at the anode. D. Aluminium metal will be produced at the anode and fluorine gas will be produced at the cathode.
Question 43/ 56 [VCAA 2021 SA Q9] An electrolysis cell consumed a charge of 4.00 C in 5.00 minutes. This represents a consumption of A. 4.15 × 10−5 mol of electrons. B. 2.07 × 10−4 mol of electrons. C. 1.93 × 104 mol of electrons. D. 2.41 × 104 mol of electrons.
Question 44/ 56 [VCAA 2017 SA Q30] The diagram below shows the basic set-up of an electroplating cell.
Initially the cell is set up with a lead, Pb, electrode as Electrode Z and 1.0 mol L−1 lead nitrate, Pb(NO3)2, as the electroplating solution. The cell runs for a set time and current, with 1.0 g of Pb deposited onto Electrode Z. Four subsequent electroplating cells are set up, each containing a platinum, Pt, electrode, a different Electrode Z and an appropriate 1.0 mol L−1 electroplating solution. These four electroplating cells are operated for the same time and at the same current as the original Pb electroplating cell. Which combination of Electrode Z and electroplating solution would be expected to deposit more metal by mass onto Electrode Z than the original Pb electroplating cell? Electrode Z
Electroplating solution
chromium, Cr
1.0 mol L−1 Cr(NO3)3
silver, Ag
1.0 mol L−1 AgNO3
gold, Au
1.0 mol L−1 AuCl3
tin, Sn
1.0 mol L−1 SnSO4
Question 45/ 56 [VCAA 2019 SA Q24] The diagram below shows an electroplating cell.
The cell contains 1 L of an electroplating solution. The electroplating cell is run for one hour at 3 A. Which one of the following electroplating solutions will deposit the largest mass of metal onto the object? A. 1 M AgNO3 B. 1 M Cd(NO3)2 C. 1 M Pb(NO3)2 D. 1 M Al(NO3)3
Question 46/ 56 [VCAA 2021 SA Q7] Consider the following characteristics of electrolytic and galvanic cells.
Characteristic number
Electrolytic cells
Galvanic cells
1
cathode is negative
cathode is positive
2
have non-spontaneous reactions
have spontaneous reactions
3
reduction occurs at the anode
reduction occurs at the cathode
4
produce electricity
consume electricity
Which of the following combinations of characteristics of electrolytic cells and galvanic cells are correct? A. only 1 and 2 B. only 2 and 3 C. only 3 and 4 D. only 1, 2 and 4
Question 47/ 56 Use the following information to answer Questions 48 and 49. The lead-acid battery is made up of a series of secondary cells in which the following half-reactions are utilised. PbSO4(s) + 2e− ⇌ Pb(s) + SO42−(aq) E° = −0.36 V PbO2(s) + 4H+(aq) + SO42−(aq) + 2e− ⇌ PbSO4(s) + 2H2O(l) E° = 1.69 V
Question 48/ 56 [VCAA 2011 E2 SA Q13] When the battery is discharging the A. H+ concentration decreases resulting in a higher pH. B. H+ concentration increases resulting in a higher pH. C. H+ concentration decreases resulting in a lower pH.
D. H+ concentration increases resulting in a lower pH.
Question 49/ 56 [VCAA 2011 E2 SA Q15] The reaction which occurs at the anode when the battery is recharging is A. PbSO4(s) + 2e− → Pb(s) + SO42−(aq) B. Pb(s) + SO42−(aq) → PbSO4(s) + 2e− C. PbSO4(s) + 2H2O(l) → PbO2(s) + 4H+(aq) + SO42−(aq) + 2e− D. PbO2(s) + 4H+(aq) + SO42−(aq) + 2e− → PbSO4(s) + 2H2O(l)
Question 50/ 56 The following information is referred to in Questions 51 and 52. An electrolysis cell with a 5 V power supply is shown below.
Question 51/ 56 [VCAA 2021 SA Q20] l F is equivalent to the charge on 1 mol of electrons. The mass of nickel, Ni, that can be electroplated onto the platinum, Pt, electrode with 320 F of charge is A. 9.73 × 10−2 g B. 1.95 × 10−l g C. 9.39 × 103 g D. 1.88 × 104 g
Question 52/ 56 [VCAA 2021 SA Q21] Using the electrochemical series, which one of the following changes to the electrolysis cell may reduce the amount of Ni electroplated onto the Pt electrode? A. replacing the Ni electrode with a Cu electrode B. replacing Ni(NO3)2(l) with 1 M Ni(NO3)2(aq) C. replacing the Pt electrode with Pb(s) D. replacing Ni(NO3)2(l) with NiCl2(l)
Question 53/ 56 [VCAA 2017 SA Q20] The reaction below represents the discharge cycle of a standard lead–acid rechargeable car battery. Pb(s) + PbO2(s) + 4H+(aq) + 2SO42−(aq) → 2PbSO4(s) + 2H2O(l)
During the recharge cycle, the pH A. increases and solid Pb is a reactant. B. increases and solid PbO2 is produced. C. decreases and chemical energy is converted to electrical energy. D. decreases and electrical energy is converted to chemical energy.
Question 54/ 56 Use the following information to answer Questions 55 and 56. An increasingly popular battery for storing energy from solar panels is the vanadium redox battery. The battery takes advantage of the four oxidation states of vanadium that are stable in aqueous acidic solutions in the absence of oxygen. A schematic diagram of a vanadium redox battery is shown below.
The two relevant half-equations for the battery are as follows. VO2+(aq) + 2H+(aq) + e− → VO2+(aq) + H2O(l) E° = +1.00 V V3+(aq) + e− → V2+(aq) E° = −0.26 V
Question 55/ 56
[VCAA 2017 SA Q27] The overall reaction that occurs when the battery is discharging is A. VO2+(aq) + 2H+(aq) + V2+(aq) → VO2+(aq) + V3+(aq) + H2O(l) B. VO2+(aq) + H2O(l) + V3+(aq) → VO2+(aq) + V2+(aq) + 2H+(aq) C. VO2+(aq) + V2+(aq) + 2H+(aq) → 2V3+(aq) + H2O(l) D. VO2+(aq) + V3+(aq) → 2VO2+(aq)
Question 56/ 56 [VCAA 2017 SA Q28] If air is present, the following half-equations are also relevant. O2(g) + 4H+(aq) + 4e− → 2H2O(l) E° = +1.23 V VO2+(aq) + 2H+(aq) + e− → V3+(aq) + H2O(l) E° = +0.34 V If air is present, the A. VO2+(aq) ion is oxidised to the V2+(aq) ion. B. VO2+(aq) ion is reduced to the V3+(aq) ion. C. V2+(aq) ion is oxidised to the VO2+(aq) ion. D. VO2+(aq) ion is reduced to the VO2+(aq) ion.
Question 57/ 56 [VCAA 2018 SA Q16] The silver oxide-zinc battery is rechargeable and utilises sodium hydroxide, NaOH, solution as the electrolyte. The battery is used as a backup in spacecraft, if the primary energy supply fails. The overall reaction during discharge is Zn + Ag2O → ZnO + 2Ag
When the silver oxide-zinc battery is being recharged, the reaction at the anode is A. 2Ag + 2OH− → Ag2O + H2O + 2e− B. Ag2O + H2O + 2e− → 2Ag + 2OH− C. ZnO + H2O + 2e− → Zn + 2OH− D. Zn + 2OH− → ZnO + H2O + 2e−
Question 58/ 56 [VCAA 2021 SA Q13] Rechargeable batteries A. use reversible reactions. B. operate as galvanic cells during recharge. C. require a continuous flow of reactants to operate. D. have fewer side reactions as temperature increases.
Question 59/ 56 Use the following information to answer Questions 60 and 61. The overall discharge reaction for a lead-acid battery is Pb(s) + PbO2(s) + 2H2SO4(aq) → 2PbSO4(s) + 2H2O(l)
Question 60/ 56 During recharge, the reaction at the cathode is
A. Pb(s) + SO42−(aq) → PbSO4(s) + 2e− B. PbSO4(s) + 2e− → Pb(s) + SO42−(aq) C. PbO2(s) + SO42−(aq) + 4H+(aq) + 2e− → PbSO4(s) + 2H2O(1) D. PbSO4(s) + 2H2O(l) → PbO2(s) + SO42−(aq) + 4H+(aq) + 2e−
Question 61/ 56 [VCAA 2021 SA Q14] When the lead-acid battery is discharging, the oxidising agent is A. Pb B. PbO2 C. PbSO4 D. H2SO4
Question 62/ 56 [VCAA 2022 SA Q13] An electrolysis cell is set up with inert platinum, Pt, electrodes. Which one of the following will produce a gas at the cathode when undergoing electrolysis in the cell? A. potassium iodide, KI(aq) B. sodium chloride, NaCl(l) C. lead bromide, PbBr2(l) D. copper sulfate, CuSO4(aq)
Question 63/ 56 Use the following information to answer Questions 64 and 65. Lithium-ion batteries are used in a range of electronic devices, including mobile phones. The discharge reaction for this type of battery is LiC6(s) + CoO2(s) → C6(s) + LiCoO2(s)
Question 64/ 56 [VCAA 2022 SA Q22] Which of the following is correct about lithium-ion batteries? During discharge, reduction occurs at the
During recharge, reduction occurs at the
anode
cathode
cathode
anode
anode
anode
cathode
cathode
Question 65/ 56 [VCAA 2022 SA Q23] Which one of the following statements about lithium-ion batteries is correct? A. During recharge, LiCoO2 is formed at the negative electrode. B. During discharge, Li+ ions move towards the positive electrode. C. Raising the battery temperature increases the rate of reaction, thereby increasing the battery life. D. The battery operates as an electrolytic cell during discharge and as a galvanic cell during recharge.
Question 1/ 29 Under certain conditions of temperature and pressure, incomplete combustion of ethane can occur according to the equation C2H6(g) + O2(g) → 2CO(g) + 3H2(g) In one experiment 0.10 mol of ethane and 0.10 mol of oxygen are brought to equilibrium in a 1.0 L flask. 0.16 mol of carbon monoxide is formed. Calculate a value for the equilibrium constant for this reaction. (Total = 4 marks)
Question 2/ 29 A student added 0.260 g of zinc to 100 mL of 1.00 M hydrochloric acid in the equipment shown below. The temperature recorded was 25°C and the pressure was 100 kPa.
The student noted the volume of gas in the syringe at regular intervals and plotted the graph shown below.
(a) Write an equation for the reaction between hydrochloric acid and zinc. (1 mark) (b) Calculate the mass of hydrogen produced in the reaction. (2 marks) (c) What is the maximum volume of hydrogen that could be collected from this experiment? (1 mark) (d) How did the rate of evolution (production) of hydrogen change over the time taken for the reaction? (1 mark) (e) Give an explanation for your answer to part (d). (2 marks) (f) Suggest two changes to the experiment that would decrease the rate of evolution of hydrogen. (2 marks) (Total = 9 marks)
Question 3/ 29 [VCAA 2013 SB Q4] The industrial production of hydrogen involves the following two reactions. reaction I: CH4(g) + H2O(g) ⇌ CO(g) + 3H2(g); ΔH = +206 kJ mol−1 reaction II: CO(g) + H2O(g) ⇌ CO2(g) + H2(g); ΔH = −41 kJ mol−1
(a) (i) Write ‘increase’, ‘decrease’ or ‘no change’ in the table below to identify the expected effect of each change to reaction I and reaction II on the equilibrium yield of hydrogen. (3 marks) Change to reaction I and reaction II
Effect of the change on the hydrogen yield in reaction I
Effect of the change on the hydrogen yield in reaction II
addition of steam at a constant volume and temperature increase in temperature at a constant volume addition of a suitable catalyst at a constant volume and temperature (ii) Explain the effect of decreasing the volume, at constant temperature, on the hydrogen equilibrium yield in each reaction. (4 marks) (iii) What is the effect of an increase in temperature at constant volume on the rate of hydrogen production in each reaction? (2 marks) The reaction between hydrogen and oxygen is the basis of energy production in a number of fuel cells. 2H2(g) + O2(g) → 2H2O(l); ΔH = −571.6 kJ mol−1 (b) An alkaline electrolyte is used in a particular hydrogen/oxygen fuel cell. Write a balanced half-equation for the reaction occurring at the (i) cathode (ii) anode. (2 marks) (c) What is the maximum voltage predicted for one alkaline hydrogen/oxygen fuel cell under standard conditions? (1 mark) Much of the hydrogen used in fuel cells is produced from methane. CH4(g) + H2O(g) ⇌ CO(g) + 3H2(g) CO(g) + H2O(g) ⇌ CO2(g) + H2(g) (d) Explain why methane generated by biomass is a renewable fuel while methane derived from fossil fuels is not. (2 marks) (Total = 14 marks)
Question 4/ 29 [VCAA 2018 SB Q2] Hydrogen peroxide, H2O2, in aqueous solution at room temperature decomposes slowly and irreversibly to form water, H2O, and oxygen, O2, according to the following equation. 2H2O2(aq) → 2H2O(l) + O2(g); ΔH < 0 (a) What effect will increasing the temperature have on the rate of O2 production? Use collision theory to explain your answer. (3 marks) (b) When a small lump of manganese(IV) dioxide, MnO2, is added to the H2O2 solution, the rate of O2 production increases, but when powdered MnO2 is added instead, the rate of O2 production is greatly increased. The MnO2 is recovered at the end of the reaction. State the function of MnO2 in this reaction. (1 mark) (c) A solution of H2O2 is labelled ‘10 volume’ because 1.00 L of this solution produces 10.0 L of O2 measured at standard laboratory conditions (SLC) when the H2O2 in the solution is fully decomposed. Calculate the concentration of H2O2 in the ‘10 volume’ solution, in grams per litre, when this solution is first prepared. (2 marks) (d) Propose a method to determine how quickly a solution of H2O2 decomposes when stored at a particular temperature. (3 marks) (Total = 9 marks)
Question 5/ 29 [VCAA 2011 E2 SB Q7] Methanol is produced on an industrial scale by the catalytic conversion of a mixture of hydrogen and carbon monoxide gases at a temperature of 520 K and a pressure of 50 to 100 atmospheres. The reaction that occurs in the methanol converter is CO(g) + 2H2(g) ⇌ CH3OH(g)
(a) Carbon monoxide gas and hydrogen gas are mixed in a reaction vessel and equilibrium is established. The graph above shows how the concentration of methanol in this vessel changes with time at three different temperatures. The pressure is the same at each temperature. (i) Is the reaction exothermic or endothermic? Explain your answer. (2 marks) (ii) Explain why a moderately high temperature of 520 K is used although the equilibrium concentration of methanol is greater at a lower temperature. (1 mark) (iii) Explain why, at a given temperature, the use of high pressures results in a greater equilibrium concentration of methanol. (2 marks) (b) A catalyst consisting of a mixture of copper, zinc and aluminium is used to increase the rate of this reaction. Explain how a catalyst can increase reaction rate. (1 mark) (Total = 6 marks)
Question 6/ 29 [VCAA 2015 SB Q7] Consider the reaction shown in the following equation. 2NO(g) + Br2(g) ⇌ 2NOBr(g); ΔH = −16.1 kJ mol−1, K = 1.3 × 10−2 M−1 at 1000 K (a) Write an expression for the equilibrium constant for this reaction.
(1 mark) (b) 10.0 mol of NOBr, 10.0 mol of NO and 5.0 mol of Br2 are placed in a 1.0 L container at 1000 K. Predict in which direction the reaction will proceed. Justify your answer. (3 marks) (c) A mixture of NO, NOBr and Br2 is initially at equilibrium. The graph below shows how the rate of formation of NOBr in the mixture changes when the volume of the reaction vessel is decreased at time t1.
Use collision theory and factors that affect the rate of a reaction to explain the shape of the graph at the time intervals indicated in the table below. (3 marks) Time
Explanation
between t0 and t1 at t1 between t1 and t2 (Total = 7 marks)
Question 7/ 29 [VCAA 2017 SB Q4] Sulfur trioxide, SO3, is made by the reaction of sulfur dioxide, SO2, and oxygen, O2, in the presence of a catalyst, according to the equation below. 2SO2(g) + O2(g) ⇌ 2SO3(g); ΔH < 0 In a closed system in the presence of the catalyst, the reaction quickly achieves equilibrium at 1000 K.
(a) A mixture of 2.00 mol of SO2(g) and 2.00 mol of O2(g) was placed in a 4.00 L evacuated, sealed vessel and kept at 1000 K until equilibrium was reached. At equilibrium, the vessel was found to contain 1.66 mol of SO3(g). Calculate the equilibrium constant, K, at 1000 K. (4 marks) (b) A manufacturer of SO3 investigates changes to the reaction conditions used in part (a) in order to increase the percentage yield of the product in a closed system, where the volume may be changed, if required. What changes would the manufacturer make to the temperature and volume of the system in order to increase the percentage yield of SO3? Justify your answer. (4 marks) (Total = 8 marks)
Question 8/ 29 [VCAA 2019 SB Q3] The cobalt(II) tetrachloride ion, CoCl4−, dissociates into the cobalt(II) ion, Co2+, and chloride ions, Cl−, according to the following chemical equation. CoCl42−(aq) ⇌ Co2+(aq) + 4Cl−(aq) 20 mL samples of the equilibrium mixture were heated to two temperatures, 30°C and 80°C. The intensity of the pink colour of the Co2+ product was recorded every 30 seconds by measuring the absorbance of the solution. The higher the intensity of the pink colour, the higher the absorbance. The results of this experiment are shown in the graph below.
(a) State whether the forward reaction is exothermic or endothermic. Justify your answer by referring to the graph.
(2 marks) (b) When 5 mL of water was added to the equilibrium mixture, the colour of the solution immediately became lighter pink. Describe the final colour of the solution once equilibrium is re-established. Explain your answer. (2 marks) (c) Five drops of silver nitrate, AgNO3, solution are added to the equilibrium mixture at time t1. A concentration–time graph for this reaction is shown below for times between zero and t1.
Continue the graph to show the changes that occur to the system from t1 until equilibrium is re-established. (3 marks) (Total = 7 marks)
Question 9/ 29 [VCAA 2020 SB Q1]
Methanol is a very useful fuel. It can be manufactured from biogas. The main reaction in methanol production from biogas is represented by the following equation. CO(g) + 2H2(g) ⇌ CH3OH(g) ΔH < 0 This reaction requires the use of a catalyst to maximise the yield of methanol produced in optimum conditions. The energy profile diagram below represents the uncatalysed reaction.
(a) On the energy profile diagram, sketch how the catalyst would alter the reaction pathway. (1 mark) (b) (i) How does the reaction temperature affect the yield of methanol from biogas? In your answer, refer to Le Chatelier's principle. (2 marks) (ii) How does the reaction pressure affect the yield of methanol from biogas? In your answer, refer to Le Chatelier's principle. (2 marks) (c) Write the expression for the equilibrium constant, K, for this reaction. (1 mark) (d) 0.760 mol of carbon monoxide, CO, and 0.525 mol of hydrogen, H2, were allowed to reach equilibrium in a 500 mL container. At equilibrium the mixture contained 0.122 mol of methanol. Calculate the equilibrium constant, K. (3 marks) (Total = 9 marks)
Question 10/ 29 [VCAA 2021 SB Q8] The reaction for the oxidation of sulfur dioxide, SO2, is shown below. 2SO2(g) + O2(g) ⇌ 2SO3(g) ΔH = -197 kJ mol−1 (a) 1.00 mol of SO2 and 1.00 mol of oxygen, O2, are placed into an evacuated, sealed 3.00 L container at 100 °C. After the reaction reaches equilibrium, the container contains 20.0 g of sulfur trioxide, SO3. Calculate the equilibrium constant, K, for this reaction at 100 °C. (4 marks) (b) The volume of the closed container is doubled. Describe the effect that this has on the concentration of SO2 from the time just before the volume was changed until after the system re-established its equilibrium. (3 marks) (Total = 7 marks)
Question 11/ 29 An electrolysis cell is constructed from two pure nickel electrodes and an aqueous solution of NiSO4. The cell is used to measure the amount of electricity flowing in a circuit. The reaction at the negative electrode (cathode) is Ni2+(aq) + 2e− → Ni(s).
What current, in amps, is required to deposit 20 mg of nickel in 30 minutes?(Total = 4 marks)
Question 12/ 29 A piece of copper can be polished by making it the anode in an electrolysis cell. If it is assumed that the only reaction occurring at the anode is the conversion of copper metal into Cu2+ ions, calculate the mass of copper removed from the piece of copper by a current of 9.5 A passing for 4 minutes. (Total = 4 marks)
Question 13/ 29 Three cells are connected as shown in the diagram below, and a steady current is passed for a fixed time. The aqueous solutions contain Pb2+, Ag+ and Al3+ respectively, and Pt electrodes are used.
(a) Write the equations for the reactions occurring at the cathode in each of the three cells. (3 marks) (b) If 0.03 mol of silver is deposited at the cathode in the centre cell, how much material (in moles) would you expect to be produced in each of the other cells? Explain your answer. (2 marks) (Total = 5 marks)
Question 14/ 29 Two platinum electrodes were placed in 1.00 L of a 0.210 M AgNO3 solution. An electric current of 0.57 A was passed through the solution for some time, and silver metal formed on one of the electrodes. The volume of the solution was unchanged, and the final concentration of silver ion in the solution was 0.110 M. (a) At which electrode (anode or cathode) was the silver deposited?
(1 mark) (b) What is the polarity of this electrode? (1 mark) (c) Calculate the time taken to deposit the silver. (4 marks) (Total = 6 marks)
Question 15/ 29 0.75 L of an aqueous solution is prepared and contains 0.025 mol each of SnCl2, ZnCl2 and CuCl2. Two graphite rods are placed in the solution and an electric current is passed through. When the electrolysis is finished, all of the metal ions (Sn2+, Zn2+ and Cu2+) have been deposited onto one of the graphite rods. The metals form three successive coatings: A, B and C (see diagram below).
(a) Identify the three metals A, B and C. Explain your answer. (2 marks) (b) Calculate the amount of electricity, in coulombs, needed to deposit the zinc layer alone. (3 marks) (c) How many coulombs would be needed to deposit the other two metals? Explain your answer. (2 marks) (Total = 7 marks)
Question 16/ 29 A student sets up a circuit for electroplating copper, silver and gold in three separate cells as shown in the diagram below. The cells are connected in series. A current flows through the circuit for 1.0 hour and 1.30 g of copper is deposited.
(a) At which electrode was the copper deposited? (1 mark) (b) The student measures the masses of the three metals deposited in this experiment, and then calculates the moles of each metal produced. What result would you expect the student to find for the ratio ‘n(Cu) : n(Ag) : n(Au)’? Explain your answer. (2 marks) (c) Calculate the current, in amps, that flowed through the circuit. (3 marks) (d) What were the masses of silver and gold deposited in the other two cells? (4 marks) (Total = 10 marks)
Question 17/ 29 Electrolysis of aqueous solutions containing nickel ions, Ni2+(aq), leads to the formation of nickel metal on the cathode (or negative electrode). However, calcium metal cannot be produced in this way from the electrolysis of aqueous solution containing calcium ions, Ca2+(aq). (a) What would you expect to occur at the cathode when an aqueous solution of calcium chloride is electrolysed? Use an equation to illustrate your answer. (2 marks) (b) How can calcium metal be obtained from calcium chloride by electrolysis?
(1 mark) (Total = 3 marks)
Question 18/ 29 A student connects two cells in series and passes an electric current through both. The first cell contains 2.0 M hydrochloric acid and platinum electrodes. In the second cell, the student uses silver electrodes and silver nitrate solution. The student passes a current of 2.85 A through both cells. A gas is produced at the cathode in the first cell and 2.00 g of silver is deposited on the cathode of the second cell. (a) Draw a labelled diagram to show how the experiment described above would be set up. For each cell, indicate the polarity of the electrodes and label the cathode. (3 marks) (b) Calculate the time for which the current was passed. (2 marks) (c) Identify the gas formed at the cathode in the first cell and give the equation for the reaction that produces this gas. (2 marks) (d) What volume of the gas in part (c) would be formed at SLC? (2 marks) (Total = 9 marks)
Question 19/ 29 A metal ornament of total surface area 48 cm2 is to be completely covered with a nickel coating of 2.50 × 10−3 cm thickness. The nickel is deposited by electrolysis. The ornament is suspended in an aqueous solution containing nickel ions, Ni2+(aq), and is made one of the electrodes of an electrolysis cell. Ni2+(aq) + 2e− → Ni(s) (a) To which electrode (cathode or anode) should the ornament be connected? (1 mark) (b) What volume of nickel is needed to plate the ornament?
(volume (mL) ≈ surface area (cm2) × thickness (cm)) (1 mark) (c) What mass of nickel will be used? (Density of nickel = 8.90 g mL−1) (1 mark) (d) Calculate the time needed to deposit the nickel coating if a steady current of 0.750 A is passed through the cell. (4 marks) (Total = 7 marks)
Question 20/ 29 A student is asked to determine a value for the Faraday constant by electrolysis of a copper sulfate solution using copper electrodes. Copper is deposited at the cathode, which is washed and dried at the end of the experiment. 0.175 g of copper was deposited by a current of 0.863 A in 10.00 minutes. (a) Calculate a value for the Faraday constant from these results in C mol−1. (3 marks) (b) The data table gives the value of the Faraday constant as 96 500 C mol−1. Suggest a reason why the value determined from the student's results differs from the value in the data table. (1 mark) (c) The student repeats the experiment using a different solution of copper sulfate and this time obtains a value for the Faraday constant of 98 900 C mol−1. The student then discovers that the copper sulfate solution used contained small amounts of nickel sulfate and zinc sulfate. What effect would these impurities have (if any) on the result? (1 marks) (Total = 5 marks)
Question 21/ 29 When current is drawn from a lead-acid accumulator, the electrode reactions are Pb(s) + SO42−(aq) → PbSO4(s) + 2e−
PbO2(s) + 3H+(aq) + HSO4−(aq) + 2e− → PbSO4(s) + 2H2O(l) (a) As the accumulator discharges, describe what happens to the (i) sulfuric acid concentration (ii) number of ions in solution (iii) pH (1 + 1 + 1 = 3 marks) (b) In the overall cell reaction, what are the changes in oxidation number? (2 marks) (c) Give the equation of the reaction that occurs at the positive electrode during discharge. (1 mark) (d) Give the equation of the reaction that occurs at the negative electrode when the accumulator is being recharged. (1 mark) (Total = 7 marks)
Question 22/ 29 [Adapted VCAA 2013 SB Q7] An electrolytic process known as electrorefining is the final stage in producing highly purified copper. In a smallscale trial, a lump of impure copper is used as one electrode and a small plate of pure copper is used as the other electrode. The electrolyte is a mixture of aqueous sulfuric acid and copper sulfate. (a) Indicate in the box labelled ‘polarity’ on the diagram below, the polarity of the impure copper electrode. (1 mark)
In a trial experiment, the electrodes were weighed before and after electrolysis. The results are provided in the following table. Mass of lump of impure copper
Mass of pure copper
before electrolysis
10.30 kg
1.55 kg
after electrolysis
0.855 kg
9.80 kg
(b) On the basis of these results • calculate a percentage purity of the lump of impure copper • indicate one factor that may affect the accuracy of these results. (4 marks) (c) Conditions in the electrolytic cell shown in the diagram above are carefully controlled to ensure a high degree of copper purity and electrical efficiency. Use the mass of pure copper deposited that is given in the table in part (a) to determine the time, in days, taken for this electrolysis reaction to be completed. Assume the current was a constant 24 A. (5 marks) Lumps of impure copper typically contain impurities such as silver, gold, cobalt, nickel and zinc. Cobalt, nickel and zinc are oxidised from the copper lump and exist as ions in the electrolyte. Silver and gold are not oxidised and form part of an insoluble sludge at the base of the cell. (d) Why is it important that silver and gold are not present as cations in the electrolyte? (1 mark) (Total = 11 marks)
Question 23/ 29 [Adapted VCAA 2011 E2 SB Q8] A chemical engineer designs a pilot plant to determine the conditions that will give the best results for copper plating different objects. A range of experiments indicates that an electroplating cell with an aqueous electrolyte containing copper(I) cyanide, CuCN, potassium cyanide, KCN, and potassium hydroxide, KOH, will produce a uniform copper coating. (a) Write a balanced half-equation for the cathode reaction in this electrolytic cell. (1 mark) The quality of the copper coating depends on maintaining a low, constant concentration of copper(I) ions in the electrolyte. This is achieved by making use of the following reaction, which takes place in the electrolyte bath. In this reaction, copper(I) ions, Cu+, react with the cyanide ions, CN−, according to the equation Cu+(aq) + 4CN−(aq) ⇌ Cu(CN)43− K = 1 × 1028 (b) Refer to this information to explain how the presence of excess potassium cyanide in the electrolyte maintains a low concentration of Cu+(aq) ions in solution. (1 mark) The cyanide ion, CN−, is the conjugate base of the acid hydrogen cyanide, HCN. CN−(aq) + H2O(l) ⇌ HCN(aq) + OH−(aq); K = 10−4.8 Hydrogen cyanide is highly toxic and can bubble out of solution. (c) Explain how the presence of potassium hydroxide in the electrolyte is essential to the safe operation of this cell. (1 mark) Any gas produced at the cathode is found to damage the quality of the copper plate. This is avoided by maintaining a low current. (d) Write a balanced equation for the gas most likely to be produced at the cathode if the current is too high. (1 mark) (e) In one trial, a medal is copper plated in the cell. The experimental data is given below. Mass of medal before copper plating = 25.2 g Mass of medal after copper plating = 36.4 g Current = 0.900 A Calculate the time, in minutes, taken to copper plate the medal. (4 marks) (Total = 8 marks)
Question 24/ 29 [VCAA 2017 SB Q8] Fluorine, F2, gas is the most reactive of all non-metals. Anhydrous liquid hydrogen fluoride, HF, can be electrolysed to produce F2 and hydrogen, H2, gases. Potassium fluoride, KF, is added to the liquid HF to increase electrical conductivity. The equation for the reaction is 2HF(l) → F2(g) + H2(g) F2 is used to make a range of chemicals, including sulfur hexafluoride, SF6, an excellent electrical insulator, and xenon difluoride, XeF2, a strong fluorinating agent. The diagram below shows an electrolytic cell used to prepare F2 gas.
Liquid HF, like water, is an excellent solvent for ionic compounds. In the same way that water molecules in an aqueous solution form the ions K+(aq) and F−(aq), when KF is dissolved in HF, the K+ and F− ions form ions that are written as K+(HF) and F−(HF). (a) Label the polarities of each electrode in the circles provided on the diagram above. (1 mark) (b) Write the equation for the half-reaction occurring at the anode. (1 mark) (c) Suggest why the diaphragm, shown in the diagram above, is important for the safe operation of the electrolytic cell. (1 mark)
(d) Explain why the carbon electrode cannot be replaced with an iron electrode. (3 marks) (e) Calculate the volume of F2 gas, measured at standard laboratory conditions (SLC), that would be produced when a current of 1.50 A is passed through the cell for 2.00 hours. (3 marks) (Total = 9 marks)
Question 25/ 29 [VCAA 2014 SB Q9] Magnesium is one of the most abundant elements on Earth. It is used extensively in the production of magnesiumaluminium alloys. It is produced by the electrolysis of molten magnesium chloride. A schematic diagram of the electrolytic cell is shown below. The design of this cell takes into account the following properties of both magnesium metal and magnesium chloride: Molten magnesium reacts vigorously with oxygen. At the temperature of molten magnesium chloride, magnesium is a liquid. Molten magnesium has a lower density than molten magnesium chloride and forms a separate layer on the surface. (a) Write a balanced half-equation for the reaction occurring at each of the cathode and the anode. (2 marks)
(b) Explain why an inert gas is constantly blown through the cathode compartment. (1 mark) (c) The melting point of a compound can often be lowered by the addition of small amounts of other compounds. In an industrial process, this will save energy. In this cell, NaCl and CaCl2 are used to lower the melting point of MgCl2.
Why can NaCl and CaCl2 be used to lower the melting point of MgCl2 but ZnCl2 cannot be used? (2 marks) (d) What difference would it make to the half-cell reactions if the graphite anode were replaced with an iron anode? Write the half-equation for any different half-cell reaction. Justify your answer. (3 marks) (Total = 8 marks)
Question 26/ 29 [VCAA 2020 SB Q2] The electrolysis of carbon dioxide gas, CO2, in water is one way of making ethanol, C2H5OH. The diagram below shows a CO2-H2O electrolysis cell. The electrolyte used in the electrolysis cell is sodium bicarbonate solution, NaHCO3(aq).
The following half-cell reactions occur in the CO2–H2O electrolysis cell. O2(g) + 2H2O(l) + 4e− ⇌ 4OH−(aq) E° = +0.40 V 2CO2(g) + 9H2O(l) + 12e− ⇌ C2H5OH(l) + 12OH−(aq) E° = −0.33 V (a) Identify the Cu-Zn electrode as either the anode or the cathode in the box provided in the diagram above.
(1 mark) (b) Determine the applied voltage required for the electrolysis cell to operate. (1 mark) (c) Write the balanced equation for the overall electrolysis reaction. (1 mark) (d) Identify the oxidising agent in the electrolysis reaction. Give your reasoning using oxidation numbers. (2 marks) (e) A current of 2.70 A is passed through the CO2–H2O electrolysis cell. The cell has an efficiency of 58%. Calculate the time taken, in minutes, for this cell to consume 6.05 × 10−3 mol of CO2(g). (3 marks) (Total = 8 marks)
Question 27/ 29 [Adapted VCAA 2015 SB Q10] A car manufacturer is planning to sell hybrid cars powered by a type of hydrogen fuel cell connected to a nickel metal hydride, NiMH, battery. A representation of the hydrogen fuel cell is given below.
The overall cell reaction is
2H2(g) + O2(g) → 2H2O(g) (a) (i) On the diagram above, indicate the polarity of the anode and the cathode in circles A and B, and identify the product of the reaction in box C. (2 marks) (ii) Write an equation for the reaction that occurs at the cathode when the switch is closed. (1 mark) (iii) Identify one advantage and one disadvantage of using this fuel cell instead of a petrol engine to power the car. (2 marks) (b) The storage battery to be used in the hybrid cars is comprised of a series of nickel metal hydride, NiMH, cells. MH represents a metal hydride alloy that is used as one electrode. The other electrode contains nickel oxide hydroxide, NiOOH. The electrolyte is aqueous KOH. The simplified equation for the reaction at the anode while recharging is Ni(OH)2(s) + OH−(aq) → NiOOH(s) + H2O(l) + e− The simplified equation for the reaction at the cathode while recharging is M(s) + H2O(l) + e− → MH(s) + OH−(aq) (i) What is the overall equation for the discharging reaction? (1 mark)
(ii) In the boxes on the diagram above, indicate which is the MH electrode and which is the NiOOH electrode. (1 mark) (iii) In the box provided in the cell diagram, use an arrow, → or ←, to indicate the direction of the electron flow as the cell is discharging. (1 mark) (iv) The battery discharged for 60 minutes, producing a current of 1.15 A. What mass, in grams, of NiOOH would be used during this period? (3 marks)
(Total = 11 marks)
Question 28/ 29 [VCAA 2019 SB Q7] The zinc-cerium battery is a commercial rechargeable battery that comprises a series of cells. During recharging, the cells use energy from wind farms or solar cell panels. During discharging, energy is supplied to electric grids to power local factories and homes. The electrolytes are stored in separate storage tanks and are pumped into and out of each cell when in use. A membrane separates the two electrodes that are immersed in 1 M methanesulfonic acid, CH3SO3H. A diagram representing a zinc-cerium cell is shown below.
The following half-cell reactions occur in the zinc-cerium cell. Zn(CH3SO3)2(aq) + 2H+(aq) + 2e− ⇌ Zn(s) + 2CH3SO3H(aq) E° = −0.76 V Ce(CH3SO3)4(aq) + H+(aq) + e− ⇌ Ce(CH3SO3)3(aq) + CH3SO3H(aq) E° = 1.64 V (a) Write the equation for the overall discharge reaction. (1 mark) (b) Identify the oxidising agent during discharging and justify your answer using oxidation numbers. (2 marks) (c) Determine the theoretical voltage produced by a single cell as it discharges.
(1 mark) (d) Write the ionic equation for the reaction occurring at the positive electrode during recharging. (1 mark) (e) Other than transporting ions between the electrodes, describe one function of the membrane in the zinc-cerium cell. (1 mark) (f) Specify one factor that would limit the life of the zinc-cerium cell. (1 mark) (g) Experts have regarded the zinc-cerium cell as a hybrid of a fuel cell and a secondary cell. Why would this be the case? (1 mark) (Total = 8 marks)
Question 29/ 29 [VCAA 2021 SB Q2] Research scientists are developing a rechargeable magnesium-sodium, Mg-Na, hybrid cell for use in portable devices. The Mg-Na hybrid cell uses magnesium metal and sodium ion electrodes and a hybrid organic/salt electrolyte, X. A simplified diagram of the rechargeable Mg-Na hybrid cell is shown below.
(a) The equation for the overall reaction during recharge is 2NaX + Mg2+ →Mg + 2Na2+ + 2X
(i) Identify the polarity of the Mg electrode when the cell is discharging by placing a positive (+) or a negative (-) sign in the box provided in the diagram above. (1 mark) (ii) Write the half-cell equation of the reaction that occurs at the Mg electrode when the cell is discharging. (1 mark) (b) A pacemaker is a small electronic device that is implanted in the body to regulate a person's heart rate. If the MgNa hybrid cell were to be used to power pacemakers, what would be two potential safety hazards of having this cell in the body? (2 marks) (c) One source of Mg is magnesium chloride, MgCl2, which can be obtained from seawater. Explain how Mg can be produced from MgCl2 in an electrolytic cell. (3 marks) (Total = 7 marks)
Question 1/ 5 The following information is referred to in Questions 2 to 4. The important reaction in the Haber process for the production of ammonia, NH3, is N2(g) + 3H2(g) ⇌ 2NH3(g); ΔH = −91 kJ mol−1
Question 2/ 5 The highest yield of ammonia would be obtained using A. high temperatures and high pressures. B. low temperatures and high pressures. C. high temperatures and low pressures. D. low temperatures and low pressures.
Question 3/ 5 In the industrial process a catalyst is used. The catalyst A. increases the rates of the forward and back reactions but does not change the equilibrium constant. B. increases the rates of the forward and back reactions and increases the equilibrium constant. C. increases the rate of the forward reaction only but does not change the equilibrium constant. D. increases the rate of the forward reaction only and increases the equilibrium constant.
Question 4/ 5 In a certain equilibrium mixture [N2] = 0.100 M, [H2] = 0.200 M and [NH3] = 0.800 M. The value of the equilibrium constant is A. 1.00 × 10 B. 40.0 C. 800 D. 2.67
Question 5/ 5 An alloy of iridium and rhodium is used to catalyse the following reaction. 4NH3(g) + 5O2(g) ⇌ 4NO(g) + 6H2O(g); ΔH = −900 kJ mol−1 The purpose of the catalyst is to A. increase the equilibrium constant, K, of the reaction. B. increase the activation energy of the reaction.
C. decrease the equilibrium constant, K, of the reaction. D. decrease the activation energy of the reaction.
Question 6/ 5 Butane can be ‘cracked’ into two smaller molecules. C4H10(g) ⇌ C2H6(g) + C2H4(g); ΔH = +93 kJ mol−1 Which of the following sets of conditions would lead to the greatest amount of cracking? A. 280°C and 2 atmospheres pressure B. 280°C and 10 atmospheres pressure C. 350°C and 2 atmospheres pressure D. 350°C and 10 atmospheres pressure
Question 7/ 5 When limestone, CaCO3, reacts with hydrochloric acid, the following reaction occurs. CaCO3(s) + 2HCl(aq) → CaCl2(aq) + CO2(g) + H2O(l) Which of the following would not increase the rate of the reaction? A. Increasing the volume of the container B. Using finely powdered limestone C. Changing the temperature from 15°C to 25°C D. Using 2.0 M acid instead of 1.0 M acid
Question 8/ 5 In the conversion of carbon monoxide to carbon dioxide, the following reaction is used. CO(g) + H2O(g) ⇌ CO2(g) + H2(g); ΔH = −40 kJ mol−1 Which of the following would not increase the percentage conversion of CO into CO2? A. Decreasing the temperature B. Decreasing the pressure C. Adding more steam D. Removing CO2
Question 9/ 5 [VCAA 2020 SA Q6] Which one of the following pairs of statements is correct for both electrolysis cells and galvanic cells? Electrolysis cell Both electrodes are always inert.
Galvanic cell Both electrodes are always made of metal.
Electrical energy is converted to chemical energy.
The voltage of the cell is independent of the electrolyte concentration.
Chemical energy is converted to electrical energy.
The products are dependent on the half-cell components.
The products are dependent on the half-cell components.
Chemical energy is converted to electrical energy.
Question 10/ 5 [Adapted VCAA 2012 E2 SA Q11] The following reaction is used in some industries to produce hydrogen. CO(g) + H2O(g) ⇌ CO2(g) + H2(g); ΔH = −41 kJ mol−1
In trials, the reaction is carried out with and without a catalyst in the sealed container. All other conditions are unchanged. The change in hydrogen concentration with time between an uncatalysed and a catalysed reaction is represented by a graph. Which graph below is correct?
A.
B.
C.
D.
Question 11/ 5 The following information is referred to in Questions 12 and 13. The following reaction is allowed to come to equilibrium at 350°C. C2H6(g) ⇌ C2H4(g) + H2(g); ΔH = +137 kJ mol−1
Question 12/ 5 Which of the following will increase the yield of ethene, C2H4? A. Adding more hydrogen at constant pressure B. Increasing the overall pressure C. Lowering the temperature D. Removing hydrogen
Question 13/ 5 When the volume of the container is reduced A. there will be no change in the position of equilibrium. B. the equilibrium constant will decrease. C. more ethene, C2H4, and hydrogen will be produced. D. more ethane, C2H6, will be formed.
Question 14/ 5
When galvanic and electrolytic cells are compared A. the cathode is positive in galvanic cells but negative in electrolytic cells. B. the anode is positive in galvanic cells but negative in electrolytic cells. C. the cathode is negative in galvanic cells but positive in electrolytic cells. D. the anode is negative in both galvanic and electrolytic cells.
Question 15/ 5 The following information is referred to in Questions 16 and 17. A student wishes to plate a steel rod with copper. The steel rod is one electrode, a copper rod is the second electrode and the electrolyte is a solution of copper(II) sulfate. A battery is used to provide the electrical energy.
Question 16/ 5 Which one of the following is correct? Steel rod is connected to battery at
Reaction occurring at the steel rod is
positive terminal
an oxidation
positive terminal
a reduction
negative terminal
an oxidation
negative terminal
a reduction
Question 17/ 5 The mass of copper deposited on the steel rod is 0.247 g. If the current used in the experiment was 1.50 A, then the time, in seconds, needed for the experiment is closest to A. 250
B. 500 C. 750 D. 1000
Question 18/ 5 A student passed 750 C of electricity through an aqueous solution of an ionic salt, MCln 0.81 g of metal, M, is deposited at the cathode. The metal and the value of n are most likely to be Metal, M
n
lead
2
chromium
2
palladium
2
silver
1
Question 19/ 5 An important reaction in the production of nitric acid is the conversion of nitric oxide into nitrogen dioxide. 2NO(g) + O2(g) ⇌ 2NO2(g); ΔH = −114 kJ mol−1 For each of the actions (a) and (b), indicate what effect it would have on (i) the equilibrium constant, K, and (ii) the yield of nitrogen dioxide. Action (a) Changing the temperature from 400°C to 450°C (b) Adding more oxygen at constant temperature and pressure (Total = 4 marks)
(i) Effect on K
(ii) Effect on yield of NO2
Question 20/ 5 Hydrogen iodide will decompose when heated according to the following reaction: 2HI(g) ⇌ H2(g) + I2(g) 0.100 mol of hydrogen iodide was placed in a 1.00 L flask and heated to 350 K. When equilibrium had been established, 0.033 mol of HI remained. (a) How many moles of HI have been reacted at equilibrium? (1 mark) (b) How many moles of H2 have been formed at equilibrium? (2 marks) (c) Calculate the numerical value for the equilibrium constant for this reaction at 350 K. (2 marks) (Total = 5 marks)
Question 21/ 5 When steam and carbon monoxide are heated, the following reaction occurs CO(g) + H2O(g) ⇌ CO2(g) + H2(g); ΔH = −40 kJ mol−1 For each of the actions mentioned in the table below, state how it would affect the (a) yield of hydrogen. (2 marks) (b) equilibrium constant, K, for the reaction. (2 marks) (c) rate of reaction. (2 marks) Action Increasing the pressure Increasing the temperature
(a) Yield of hydrogen
(b) K
(c) Rate of reaction
(Total = 6 marks)
Question 22/ 5 When methane is heated with steam at 650°C, the following reaction occurs CH4(g) + H2O(g) ⇌ CO(g) + 3H2(g); ΔH = +220 kJ mol−1 In one equilibrium mixture, the following concentrations were measured. [CH4] = 0.15 M, [H2O] = 3.25 M, [CO] = 1.05 M, [H2] = 1.05 M (a) Write an expression for the equilibrium constant for this reaction. (1 mark) (b) Calculate a value for the equilibrium constant at 650°C. (3 marks) (c) How would you expect the value of the equilibrium constant at 400°C to differ from the value at 650°C? Give a reason for your answer. (2 marks) (Total = 6 marks)
Question 23/ 5 A student sets up the electrolysis cell shown below. Two graphite rods are placed in an aqueous solution that contains 0.40 mol of AgNO3 and 0.40 mol of Cu(NO3)2.
(a) If a current of 9.65 A is passed through the cell for 8000 seconds, describe what will happen at the negative electrode. (3 marks) (b) For how much longer must the electrolysis be continued to completely deposit all of the two metals? (2 marks) (Total = 5 marks) Total marks for test = 41 marks
Chapter 3: Unit 3 revision paper Question 1/ 20 [VCAA 2011 E2 SA Q7] Consider the following combustion reactions for graphite and diamond. C(graphite) + O2(g) → CO2(g); ΔH = −393 kJ mol−1 C(diamond) + O2(g) → CO2(g); ΔH = −395 kJ mol−1 The following diagram summarises this information.
From the data provided it can be determined that the enthalpy change, ΔH, for the conversion of graphite to diamond C(graphite) → C(diamond) is A. −2 kJ mol−1
B. +2 kJ mol−1 C. −788 kJ mol−1 D. +788 kJ mol−1
Question 2/ 20 VCAA 2011 E2 SA Q8] What mass of butane (M = 58.0 g mol−1) must undergo complete combustion to raise the temperature of 100.0 g of water by 1.00°C? Assume that there is no heat loss. A. 8.44 g B. 6.88 g C. 0.399 g D. 8.44 × 10−3 g
Question 3/ 20 [Adapted VCAA 2012 E2 SA Q2] Which one of the following fuels is the most sustainable? A. biodiesel B. petrol C. coal D. natural gas
Question 4/ 20
Consider the enthalpy changes for the decomposition of two oxides of nitrogen. 2NO2(g) → N2(g) + 2O2(g) ΔH = −66 kJ mol−1 (reaction 1) 2NO(g) → N2(g) + O2(g) ΔH = −180 kJ mol−1 (reaction 2) From this information, the enthalpy change for the reaction represented by the equation NO(g) + ½O2(g) → NO2(g) is A. −57 kJ mol−1 B. −114 kJ mol−1 C. −123 kJ mol−1 D. −246 kJ mol−1
Question 5/ 20 [Adapted VCAA 2012 E2 SA Q12] Consider the following energy profile diagram for a reaction represented by the equation X + Y → Z.
Which one of the following provides the correct values of the activation energy and enthalpy change for the reaction X + Y → Z? Activation energy (kJ mol−1)
Enthalpy change (kJ mol−1)
+75
+100
+100
+175
+175
+100
+200
−125
Question 6/ 20 One methanol oxygen fuel cell uses 2.00 × 10−7 mol of methanol per second. The current (in mA) produced by this cell is A. 3.22 B. 19.3 C. 77.2 D. 116
Question 7/ 20 [VCAA 2011 E2 SA Q10] Two galvanic cells were constructed under standard conditions in an experiment to determine the relative positions in the electrochemical series of the standard electrode potential, E°, for the following reactions. Both cells generate a potential difference.
Ag(NH3)2+(aq) + e− ⇌ Ag(s) + 2NH3(aq) E°1 Ag+(aq) + e− ⇌ Ag(s) E°2
Ag(CN)2−(aq) + e− ⇌ Ag(s) + 2CN−(aq) E°3 The values of the electrode potentials in order from highest to lowest would be A. E°1, E°2, E°3 B. E°1, E°3, E°2 C. E°2, E°1, E°3 D. E°3, E°2, E°1
Question 8/ 20 Use the following information to answer Questions 9 to 11. A galvanic cell set up under standard conditions is shown below.
Question 9/ 20 [Adapted VCAA 2012 E2 SA Q16] Which one of the following is correct as the cell discharges?
Electrons would flow from the
In the salt bridge
zinc electrode to the silver electrode.
anions migrate to the Ag+/Ag half-cell.
silver electrode to the zinc electrode.
cations migrate to the Zn2+/Zn half-cell.
silver electrode to the zinc electrode.
cations migrate to the Ag+/Ag half-cell.
zinc electrode to the silver electrode.
anions migrate to the Zn2+/Zn half-cell.
Question 10/ 20 [VCAA 2012 E2 SA Q17] In this cell A. Ag+(aq) is reduced and the Zn(s) is oxidised. B. Ag(s) is oxidised and the Zn2+(aq) is reduced. C. Ag(s) is reduced and the Zn2+(aq) is oxidised. D. Ag+(aq) is oxidised and the Zn(s) is reduced.
Question 11/ 20 [VCAA 2012 E2 SA Q18] The cathode in this cell and the maximum voltage produced by this cell, under standard conditions, are respectively A. Ag and 0.16 V B. Ag and 1.56 V C. Zn and 0.16 V D. Zn and 1.56 V
Question 12/ 20 [VCAA 2017 SA Q18] Ammonia, NH3, can be produced by the reaction of hydrogen, H2, and nitrogen, N2. When this reaction takes place in a sealed container of fixed volume, an equilibrium system is established. The equation for the reaction is shown below. N2(g) + 3H2(g) ⇌ 2NH3(g); ΔH = −92 kJ mol−1 If the pressure and volume remain constant when the temperature is increased, the forward reaction rate will A. increase and the [NH3] will increase. B. increase and the [NH3] will decrease. C. decrease and the [NH3] will decrease. D. decrease and the [NH3] will remain the same.
Question 13/ 20 [VCAA 2019 SA Q1] An understanding of Le Chatelier's principle is useful in the chemical industry. The prediction that can be made using this principle is the effect of A. catalysts on the rate of reaction. B. catalysts on the position of the equilibrium. C. changes in temperature on the rate of reaction. D. changes in the concentration of reactants on the position of the equilibrium.
Question 14/ 20 [VCAA 2019 SA Q25]
The following concentration–time graph refers to a mixture of three gases, P, Q and R, in an enclosed 5.0 L container. At time t1 the mixture is heated.
The equilibrium system that represents the graph is A. P(g) ⇌ 2Q(g) + R(g) and the forward reaction is exothermic. B. 2Q(g) ⇌ P(g) + R(g) and the forward reaction is endothermic. C. 2Q(g) + R(g) ⇌ P(g) and the forward reaction is exothermic. D. P(g) + 2Q(g) ⇌ R(g) and the forward reaction is endothermic.
Question 15/ 20 Use the following information to answer Questions 16 and 17. The magnitude of the equilibrium constant, K, at 25 °C for the following reaction is 640. N2(g) + 3H2(g) ⇌ NH3(g) ΔH = −92.3 kJ mol−1
Question 16/ 20 [VCAA 2020 SA Q14] For the reaction 13 N2(g) + H2(g) ⇌ 32 NH3(g), the magnitude of K at 25 °C is A. 9 and ΔH = −30.8 kJ mol−1 B. 213 and ΔH = −30.8 kJ mol−1 C. 640 and ΔH = −30.8 kJ mol−1 D. 640 and ΔH = −92.3 kJ mol−1
Question 17/ 20 [VCAA 2020 SA Q15] For the reaction N2(g) + 3H2(g) ⇌ 2NH3(g) A. a catalyst increases the number of collisions between the reactants. B. the rate of the forward reaction increases when the temperature increases. C. a catalyst reduces the activation energy of the forward and backward reactions by the same proportion. D. the activation energy of the forward reaction is greater than the activation energy of the reverse reaction.
Question 18/ 20 [VCAA 2011 E2 SA Q18] A series of electrolysis experiments is conducted using the apparatus shown below.
An electric charge of 0.030 faraday was passed through separate solutions of 1.0 M Cr(NO3)3, 1.0 M Cu(NO3)2 and 1.0 M AgNO3. In each case the corresponding metal was deposited on the negative electrode. The amount, in mol, of each metal deposited is Amount, in mol, of chromium deposited
Amount, in mol, of copper deposited
Amount, in mol, of silver deposited
0.030
0.030
0.030
0.010
0.015
0.030
0.090
0.060
0.030
0.030
0.020
0.010
Question 19/ 20 [VCAA 2011 E2 SA Q19] An ornament was coated with a metal, M, by electrolysis of a solution of the metal ion, Mx+. During the electrolysis, a current of 1.50 amperes was applied for 180 seconds. The ornament was coated in 0.0014 mol of metal. The value of x in Mx+ is A. 1 B. 2 C. 3 D. 4
Question 20/ 20 Use the following information to answer Questions 21 to 23. A solution contains an equilibrium mixture of two different cobalt(II) ions. Co(H2O)62+(aq) + 4Cl–(aq) ⇌
CoCl42–(aq) + 6H2O(l)
pink
blue
The solution contains pink Co(H2O)62− ions and blue CoCl42− ions, and the solution has a purple colour. 10 mL of the purple solution was poured into each of three test tubes labelled X, Y and Z.
Question 21/ 20 [VCAA 2015 SA Q19] The test tubes were placed in separate water baths, each having a different temperature. The resulting colour changes in the equilibrium mixtures were observed. The results are shown in the following table. Test tube
Water bath temperature
Observation
X
20°C
solution remained purple
Y
80°C
solution turned blue
Z
0°C
solution turned pink
Which one of the following conclusions can be drawn from these observations? A. Cooling significantly reduced the volume of the solution and this favoured the forward reaction. B. Heating caused some water to evaporate and this favoured the reverse reaction. C. Heating increased the value of the equilibrium constant for the reaction. D. The forward reaction must be exothermic.
Question 22/ 20
[VCAA 2015 SA Q20] Which one of the following changes would cause 10 mL of the purple cobalt(II) ion solution to turn blue? A. the addition of a few drops of 10 M hydrochloric acid at a constant temperature B. the addition of a few drops of 0.1 M silver nitrate at a constant temperature C. the addition of a few drops of a catalyst at a constant temperature D. the addition of a few drops of water at a constant temperature
Question 23/ 20 [VCAA 2015 SA Q21] When the equilibrium system was heated, the colour changed from purple to blue. Which one of the concentration– time graphs below best represents this change?
A.
B.
C.
D.
Question 1/ 10 [VCAA 2012 E2 SB Q8] Decisions about clean energy with reduced carbon dioxide emissions will have an impact on electricity generation from brown coal. However, there will be a much smaller impact on the use of black coal for electricity generation. The table below compares the energy and carbon content of three different coal samples. Percentage carbon* by mass
Energy content (kJ g−1)
Black coal
93
36.0
Brown coal (dried)
66
28.0
Brown coal (wet – as mined)
40
5.0
*Coal is not a pure substance and the composition of samples will vary even within one mine. From the data in this table, it can be deduced that the complete combustion of 1 tonne of black coal will generate 3.6 × 107 kJ of energy.
(a) (i) Calculate the mass, in tonne, of wet brown coal that is required to generate 3.6 × 107 kJ of energy. (1 mark) (ii) Calculate the mass, in tonne, of carbon dioxide that is produced from the complete combustion of this mass of wet brown coal. (2 marks) (b) What are the most likely reasons for the energy content of wet brown coal being so much lower than the energy content of dried brown coal? Justify your answer. (2 marks) (Total = 5 marks)
Question 2/ 10 A piece of jewellery was coated with gold by electrolysis in a cell containing an aqueous solution of gold ions. The electrolysis was carried out using a current of 5.25 A for 18.00 minutes. The volume of gold deposited was 0.200 mL. (a) To which electrode of the electrolytic cell should the piece of jewellery be attached? (1 mark) (b) Given that the density of gold is 19.3 g mL−1, what amount of gold, in mole, was deposited on the jewellery? (2 marks) (c) What number of electrons, in mole, was passed through the electrolytic cell? (2 marks) (d) Determine the charge on the gold ions in the solution used for the electrolysis. (2 marks) (Total = 7 marks)
Question 3/ 10 [Adapted VCAA 2018 SB Q8]
An energy company investigates the feasibility of supplying energy while reducing greenhouse gas emissions. Solar panels collect energy from the sun during daylight hours and this energy is used to electrolyse water, H2O, to produce oxygen gas, O2, and hydrogen gas, H2. These gases are stored separately and then used in a fuel cell to produce energy when required. The diagram below shows a simplified representation of the set-up used.
(a) (i) State the polarity of Electrode W in the electrolysis cell. (1 mark) (ii) The fuel cell operates in an alkaline environment. Write the half-equation for the reaction that takes place at Electrode Y. (1 mark) (b) Each of the four solar panels produces an average current of 5.20 A and operates over an eight-hour period. The electrical energy generated is used by the electrolysis cell to produce O2 and H2. Calculate the amount, in moles, of H2 produced by the electrolysis cell. (3 marks) (c) The fuel cell produces 3553 kJ when 20 mol of H2 is consumed. Another possible energy source is a generator using petrodiesel as a fuel. The generator operates with an efficiency of 35%. A particular petrodiesel containing a range of hydrocarbons has been found to have a heat content of 45 kJ g−1. The formula for this petrodiesel can be represented by C12H24 (M = 168 g mol−1). (i) Calculate the mass of petrodiesel required to produce 3553 kJ. (2 marks) (ii) Calculate the mass of CO2(g) released when 3553 kJ of energy is produced from petrodiesel. (2 marks)
(iii) How would the mass of CO2 produced from the combustion of this petrodiesel compare with the mass of CO2 produced by the fuel cell? (1 mark) (Total = 10 marks)
Question 4/ 10 Propan-1-ol was used to heat water in a can as shown in the diagram below.
The results obtained from the experiment were: Initial temperature of water in the can = 20.2°C Mass of water in the can = 500 g Mass of propan-1-ol burnt = 3.15 g Final temperature of water = 53.1°C (a) Write the equation for the complete combustion of propan-1-ol. (1 mark) (b) (i) From the results above, calculate the heat of combustion of propan-1-ol. (3 marks) (ii) What is ΔH for the equation given in part (a)? (1 mark) (c) The accepted value for the heat of combustion of propan-1-ol is 2021 kJ mol−1. Calculate the percentage heat lost in the above experiment.
(1 mark) (d) Calculate the expected temperature if no heat had been lost during the experiment. (2 marks) (e) Some of the expected heat energy is lost through incomplete combustion. Write an equation for the incomplete combustion of propan-1-ol. (1 mark) (Total = 9 marks)
Question 5/ 10 [VCAA 2012 E2 SB Q4] In an experiment, 1.0 mol of pure phosgene, COCl2, is placed in a 3.0 L flask where the following reaction takes place. COCl2(g) ⇌ CO(g) + Cl2(g) K = 2.1 × 10−8 M (a) It can be assumed that, at equilibrium, the amount of unreacted COCl2 is approximately equal to 1.0 mol. On the basis of the data provided, explain why this assumption is justified. (2 marks) (b) (i) Calculate the equilibrium concentration, in mol L−1, of carbon monoxide, CO. Assume that the amount of unreacted COCl2 is approximately equal to 1.0 mol. (3 marks) (ii) What is the equilibrium concentration of chlorine gas? (1 mark) (Total = 6 marks)
Question 6/ 10 A galvanic cell was constructed using the following two half-cells. Half-cell 1: A copper electrode in 200 mL of 1.00 mol L−1 Cu2+(aq).
Half-cell 2: An inert electrode in 200 mL of 1.00 mol L−1 Y+(aq). The cell is shown in the diagram below.
The cell is used to provide power to a device. After delivering 5790 C of electricity, the concentration of Y+(aq) in half-cell 2 was 0.850 mol L−1. The initial voltmeter reading is shown. The volume of the liquids in the two half-cells was unchanged. (a) Calculate the amount, in mol, of Y+(aq) that has reacted in half-cell 2. (1 mark) (b) Calculate the ratio of n(e−) delivered to n(Y+) reacted in this cell. (2 marks) (c) Determine the oxidation state of the product of the half-reaction in half-cell 2. (1 mark) (d) Write an equation for the half-reaction that occurred in half-cell 2. (1 mark) (e) Calculate the standard reduction potential for the species in half-cell 2. (1 mark) (Total = 6 marks)
Question 7/ 10 [VCAA 2012 E2 SB Q1] Two experiments were conducted to investigate various factors that affect the rate of reaction between calcium carbonate and dilute hydrochloric acid.
CaCO3(s) + 2HCl(aq) ⇌ CO2(g) + CaCl2(aq) + H2O(l) The two experiments are summarised in the diagrams below. Experiment 1
Experiment 2
(a) How could the rate of this reaction be measured in these experiments? (1 mark) (b) (i) Identify the rate determining factor that is investigated in experiment 1. (1 mark) (ii) In experiment 2, will the rate of reaction be faster in beaker A or beaker B? Explain your selection in terms of collision theory. (2 marks) (c) Why is the following statement incorrect? ‘Collision theory states that all collisions between reactant particles will result in a chemical reaction.’ (2 marks) (Total = 6 marks)
Question 8/ 10 [VCAA 2012 E2 SB Q2] The reaction between 2-bromo-2-methylpropane and hydroxide ions occurs in two steps. step 1: (CH3)3CBr(aq) → (CH3)3C+(aq) + Br−(aq)
step 2: (CH3)3C+(aq) + OH−(aq) → (CH3)3COH(aq) (a) Write an equation that represents the overall reaction between hydroxide ions and 2-bromo-2-methylpropane. (1 mark) The energy profile diagrams for step 1 and step 2 are shown below. Both are drawn to the same scale.
(b) (i) Which step involves an endothermic reaction? Provide a reason for your answer. (1 mark) The reaction at step 1 occurs at a different rate to the reaction at step 2. (ii) Which step is slower? Justify your answer. (2 marks) (Total = 4 marks)
Question 9/ 10 In the presence of a suitable catalyst, ammonia, NH3, will decompose into nitrogen, N2, and hydrogen, H2, to reach equilibrium at a fixed temperature. 2NH3(g) ⇌ N2(g) + 3H2(g) The graph below shows how the concentration of ammonia, the equilibrium constant, K, and the concentration fraction, CF, vary with time. At time t1, the concentration of ammonia is suddenly increased, but the temperature remains constant. (a) Complete the graph to show how these three factors will change to re-establish equilibrium. (3 marks)
(b) Give explanations for your answers. (2 marks) (Total = 5 marks)
Question 10/ 10 [VCAA 2022 SB Q2] A coal-fired power station is used to generate electricity. Carbon dioxide, CO2, gas is produced as part of the process. (a) Hydrogen, H2, can be produced using electricity generated by renewable sources. A simplified diagram of an acidic electrolyser used to produce hydrogen is shown below.
(i) Draw an arrow in the box provided on the diagram above to show the direction of flow of electrons through the wire. Justify your answer. (2 marks) (ii) State two functions of the membrane. (2 marks) (b) (i) Write the overall equation for the reaction that takes place in the acidic electrolyser shown in the diagram above when it is operating at 80 °C. (1 mark) (ii) How many moles of H2 could be produced by the acidic electrolyser using 1625.0 A in 1.25 hours, assuming 100% efficiency? (3 marks) (Total = 8 marks)
Chapter 4: Unit 4 Area of Study 1 – How are organic
compounds categorised and synthesised? Question 1/ 34 Which of the following pairs of compounds are not isomers? A. CH3CH2CH2CH3 and CH3CH(CH3)CH3 B. CH3OCH3 and CH3CH2OH C. CH3CHCl2 and CH2ClCH2Cl D. CH3CH2CH3 and CH3CH2CH2CH3
Question 2/ 34 A compound has the molecular formula C3H9X. The atom X is most likely to be A. chlorine. B. hydrogen. C. nitrogen. D. oxygen.
Question 3/ 34 A substance is in the same homologous series as chloroethane, CH3CH2Cl, is A. CH3CHCl2 B. CH2Cl2 C. CH3CH2OH D. CH3CH2CH2Cl
Question 4/ 34
The two compounds shown above are correctly named as Compound 1
Compound 2
2-methylpentane
2-methylpentan-1-ol
2-methylpentane
1-hydroxy-2-methylpentane
hexane
2-hexanol
2-methylhexane
1-hexanol
Question 5/ 34 A hydrocarbon has the molecular formula C6H10. If its structure does not contain any rings, how many carbon-tocarbon double bonds must be present? A. 0 B. 1 C. 2 D. 3
Question 6/ 34
The correct name for this compound is A. 4-chloro-3-methylbut-1-ene. B. 1-chloro-2-methylbut-3-ene. C. 4-chloropent-1-ene. D. 1-chloro-2-methylbutene.
Question 7/ 34 The compound 3-methylpentan-2-amine has the structure
A.
B.
C.
D.
Question 8/ 34 The number of chloroalkene isomers with the molecular formula C3H5Cl is A. 1 B. 2 C. 3 D. 4
Question 9/ 34 A compound has the empirical formula CH2Cl. What is a possible name for this compound? A. chloroethene B. 1,2-dichloroethene C. 1,2-dichloroethane D. chloroethane
Question 10/ 34 The ketone, butan-2-one, has the semi-structural formula CH3COCH2CH3. An isomer of this compound is most likely to be A. another ketone. B. an aldehyde. C. a carboxylic acid. D. an ester.
Question 11/ 34 [VCAA 2011 E1 SB Q4] The compound that is not an isomer of 2,2,4-trimethylpentane is A. octane. B. 3-ethylhexane. C. 2,4-dimethylpentane. D. 2,4-dimethylhexane.
Question 12/ 34 [VCAA 2013 SB Q9]
The systematic IUPAC name for the molecule shown above is A. ethyl ethanoate. B. ethyl propanoate. C. propyl ethanoate. D. methyl propanoate.
Question 13/ 34 [VCAA 2014 SA Q19]
What is the systematic name for the product of the reaction above? A. 2-methylpentanoic acid B. 4-methylpentanoic acid C. 2-methylbutanoic acid D. 3-methylbutanoic acid
Question 14/ 34 [VCAA 2015 SA Q13] What is the name of the product formed when chlorine, Cl2, reacts with but-1-ene? A. 1,2-dichlorobutane B. 1,4-dichlorobutane C. 2,2-dichlorobutane D. 2,3-dichlorobutane
Question 15/ 34 [VCAA 2019 SA Q3] A compound has the following skeletal formula.
The molar mass of the compound is A. 71 g mol−1 B. 74 g mol−1 C. 85 g mol−1 D. 86 g mol−1
Question 16/ 34 [VCAA 2020 SA Q4]
What is the IUPAC name of the molecule shown above? A. 3-hydroxy-3-ethyl-propan-1-amine B. 3-amino-l-methylpropan-1-ol C. 3-hydroxypentan-1-amine D. l-aminopentan-3-ol
Question 17/ 34 [VCAA 2020 SA Q7] How many structural isomers have the molecular formula C3H6BrCl? A. 4 B. 5 C. 6 D. 7
Question 18/ 34 [VCAA 2020 SA Q16] The following table provides information about three organic compounds, X, Y and Z. Molar mass (g mol−1)
Boiling point (°C)
X
60
97
Y
60
118
Z
60
?
Compound
Structural formula
Which one of the following is the best estimate for the boiling point of Compound Z?
A. 31 °C B. 101 °C C. 114 °C D. 156 °C
Question 19/ 34 [VCAA 2022 SA Q16] The correct IUPAC name for CH3CH2CHClCHOHCH3 is A. 3-chloropentan-4-ol B. 3-chloropentan-2-ol C. 2,3-chloro-pentanol D. 3,2-chloro-pentanol
Question 20/ 34 1 mol of propane, C3H8, is mixed with 8 mol of oxygen. The mixture is ignited so that complete combustion occurs. The number of mole of oxygen remaining will be A. 1.0 B. 3.0 C. 5.0 D. 7.0
Question 21/ 34
Propene, C3H6, undergoes an addition reaction with bromine, Br2. The molecular formula of the product is C3H6Br2. The semi-structural formula of this product is A. CH3CHBrCH2Br B. CH3CH2CHBr2 C. CH3CBr2CH3 D. BrCH2CH2CH2Br
Question 22/ 34 Polyenes are organic molecules that contain more than one carbon-to-carbon double bond. A particular polyene undergoes an addition reaction with bromine. The empirical formula of the product is C3H5Br2. The molecular formula of the polyene is most likely to be A. C3H4 B. C3H5 C. C6H8 D. C6H10
Question 23/ 34 1-butene and 2-butene are isomers and have the molecular formula C4H8. If both compounds are hydrogenated, in an addition reaction with hydrogen, in separate reactions, the products will A. have the same formula and be isomers. B. be the same compound. C. differ in formula by CH2 but be in the same homologous series. D. be alcohols.
Question 24/ 34 An alkene has the molecular formula C5H10. When it is reacted with hydrogen in the presence of a catalyst, 2-methylbutane is formed. Which one of the structures below could NOT be that of the alkene?
A.
B.
C.
D.
Question 25/ 34 Consider the following reactions CH3CH2CH2CH3 → CH4 + X; followed by X + H2O → Y; X and Y would be represented by X
Y
CH3CH2CH=CH2
CH3CH2CH2CH2OH
CH3CH2CH3
CH3CH(OH)CH3
CH3CH=CH2
CH3CH2COOH
CH3CH=CH2
CH3CH(OH)CH3
Question 26/ 34 The flow chart below refers to the preparation of ethyl ethanoate and is referred to in Questions 27 and 28.
Question 27/ 34 Step 4 is best described as A. oxidation. B. hydrogenation. C. condensation. D. addition.
Question 28/ 34 A substitution reaction occurs in A. step 1 only. B. steps 1 and 2. C. step 2 only. D. step 3 only.
Question 29/ 34 If the desired product in each case is the organic compound, which one of the reactions below has the lowest atom economy? A. CH3I + NaOH → CH3OH + NaI B. C2H5I + NaOH → C2H5OH + NaI C. CH3Br + NaOH → CH3OH + NaBr D. C2H5Br + NaOH → C2H5OH + NaBr
Question 30/ 34 When 1.50 g of propan-1-ol is heated with an excess of acidified potassium dichromate oxidation of the alcohol occurs. After removal of the other oxidation products, 0.78 g of pure propanoic acid is obtained. The percentage yield of propanoic acid is closest to A. 42% B. 44% C. 52% D. 64%
Question 31/ 34 Hex-3-ene can be converted into CH3CH2CHO in a two-step process as shown below.
If the percentage yield for the overall process is 80.0%, what mass of propanal, CH3CH2CHO, will be obtained from 2.00 g of hex-3-ene? A. 1.10 g B. 1.60 g C. 2.21 g D. 2.76 g
Question 32/ 34 A student performs two tests on an organic compound. In the first test, 3 mol of the compound was completely reacted with oxygen and 6 mol of carbon dioxide were produced. In the second test, a few drops of bromine were added to the compound. The compound did not react rapidly with bromine. The formula of the compound is likely to be A. C2H4 B. C2H6 C. C3H8 D. C6H14
Question 33/ 34 [VCAA 2011 E1 SA Q7] Halothane is a general anaesthetic. The following diagram represents the reaction pathway that produces halothane.
Which one of the following answers correctly identifies the type of reaction occurring in step 2 and correctly states the systematic name of molecule X?
Type of reaction in step 2
Systematic name of molecule X
substitution
1,2,2-trichloroethane
addition
1,1,2-trichloroethane
substitution
1,1,2-trichloroethene
addition
1,2,2-trichloroethene
Question 34/ 34 [VCAA 2013 SA Q10]
The systematic IUPAC name for the product of the above chemical reaction is A. 1-chlorobutane. B. 2-chlorobutane. C. 3-chlorobutane. D. 4-chlorobutane.
Question 35/ 34 [VCAA 2022 SA Q27] Which one of the following reactions has the highest atom economy in the production of an organic molecule? A. complete combustion of propyne, C3H4 B. reaction of iodine, I2, with propane, C3H8
C. reaction of bromine, Br2, and propene, C3H6 D. formation of a dipeptide from alanine, C3H7NO2
Question 1/ 11 Draw structural formulas for the following compounds. (a) 2,3-dimethylbutan-1-amine (b) 2,2-dimethylhex-3-yne (2 marks)
Question 2/ 11 Give the name for each of the structures shown below. (a)
(c)
(3 marks)
Question 3/ 11
(b)
There are a number of alcohols with the formula C4H10O. (a) Draw semi-structural formulae of four of these alcohols and give their names. (4 marks) (b) Can any of these alcohols exist as optical isomers? Explain your answer. (1 mark) (c) (i) Draw the semi-structural formula of one compound that is isomeric with these alcohols but contains a different functional group. (1 mark) (ii) The boiling temperatures of the four alcohols are in the range 80° to 120°C and their flash points range from +11°C to +30°C. How would you expect the boiling temperature and flash point of the isomer you drew in part (i) to compare with these values for the alcohols? Give a reason for your answer. (2 marks) (d) Four of the five alcohols are readily oxidised by acidified potassium permanganate solution. For each of these reactions, draw the semi-structural formula of the product. (3 marks) (Total = 11 marks)
Question 4/ 11 The flow chart below shows a sequence of reactions used to convert an alkene, A, into the ester, CH3CH(CH3)COOCH2CH3.
(a) Deduce the structures of the compounds A to E. (5 marks) (b) Give the formulae for the reagents labelled ‘X’, ‘Y’ and ‘Z’.
(3 marks) (c) Draw the structure of an isomer of A. (1 mark) (d) Name the type of reaction used to convert (i) A to C (ii) C to D. (2 marks) (Total = 11 marks)
Question 5/ 11 A compound of carbon, hydrogen and oxygen is found by analysis to contain 40.91% carbon and 4.55% hydrogen. (a) Deduce the empirical formula of the compound. (3 marks) The compound is a carboxylic acid but the molar ratio for reaction with sodium hydroxide is not known. 0.262 g of the compound reacts with 17.86 mL of 0.250 M sodium hydroxide. (b) How many moles of sodium hydroxide was used? (1 mark) (c) Deduce a possible molecular formula for the compound and give a possible structure. (4 marks) (Total = 8 marks)
Question 6/ 11 1,3-dihydroxypropane can be converted into 3-chloropropanoic acid in a two-step process as shown below.
(a) 2.50 g of 1,3-propanediol is reacted in the sequence shown above. Calculate the mass of 3-chloropropanoic acid produced. (2 marks) The balanced equation for the second step is ClC2H4CH2OH + 4HNO3 → ClC2H4CO2H + 4NO2 + 3H2O (b) Calculate the atom economy for this reaction. (2 marks) (Total = 4 marks)
Question 7/ 11 [VCAA 2014 SB Q2] Compounds B and F may be synthesised as follows.
(a) Draw the structural formulas of Compounds A, C, D and E in the boxes provided. (4 marks) (b) Write the systematic names of Compounds B and D in the appropriate boxes. (2 marks) (c) Insert the semi-structural formula and systematic name of Compound F in the box provided. (2 marks) (Total = 8 marks)
Question 8/ 11 [Adapted VCAA 2018 SB Q1] Organic compounds are numerous and diverse due to the nature of the carbon atom. There are international conventions for the naming and representation of organic compounds.
(a) (i) Draw the structural formula of 2-methylpropan-2-ol. (1 mark) (ii) Give the molecular formula of but-2-yne. (1 mark) (iii) Give the IUPAC name of the compound that has the structural formula shown below. (1 mark)
(b) The following diagram represents a reaction pathway for the synthesis of Compound P.
(i) Identify the starting substance, Compound M, by writing its semi-structural formula. (1 mark) (ii) Identify the reagent(s) needed to convert propan-1-ol to propanoic acid, C2H5COOH, by writing the chemical formula(e) of the reagent(s). (1 mark) (iii) When C2H5COOH is mixed with ethanamine, CH3CH2NH2, in an acidified high-temperature environment, Compound P is formed. Write the semi-structural formula of Compound P. (1 mark)
(Total = 6 marks)
Question 9/ 11 [VCAA 2013 SB Q6] The reaction pathway shown below represents the synthesis of compound C.
(a) Identify reagent X. (1 mark) (b) In the appropriate boxes above, write the semi-structural formulae for compounds A, B and C. (3 marks) (c) Give the systematic IUPAC names for compounds A and B. (2 marks) (d) Sketch the energy profile for the complete combustion of compound C, labelling the energy of the reactants, the products and the activation energy. (1 mark) (Total = 7 marks)
Question 10/ 11 [VCAA 2017 SB Q1] Industrially, ethanol, C2H5OH, is made by either of two methods. One method uses ethene, C2H4, which is derived from crude oil. The other method uses a sugar, such as sucrose, C12H22O11, and yeast, in aqueous solution. The production of C2H5OH from C12H22O11 and yeast proceeds according to the equation C12H22O11(aq) + H2O(l) → 4C2H5OH(aq) + 4CO2(g) (a) Determine the mass, in grams, of pure C2H5OH that would be produced from 1.250 kg of C12H22O11 dissolved in water. M(C12H22O11) = 342 g mol−1 (2 marks) (b) (i) Complete the reaction by writing the formula for the reactant in the box provided below. (1 mark)
(ii) Classify this type of reaction. (1 mark) (c) C2H5OH can be converted into ethanoic acid, CH3COOH, in the presence of Reagent X. Write the formula for Reagent X in the box provided below. (1 mark)
(d) CH3COOH can be used in the production of esters. (i) Write a balanced chemical equation for the reaction of CH3COOH with propan-1-ol using semi-structural formulas for all organic compounds. (2 marks) (ii) Write the IUPAC name for the ester product of the equation written in part (d)(i). (1 mark) (Total = 8 marks)
Question 11/ 11 [VCAA 2020 SB Q3] Below is a reaction pathway beginning with hex-3-ene.
(a) Write the IUPAC name of Compound J in the box provided. (1 mark) (b) State the reagent(s) required to convert hex-3-ene to hexan-3-ol in the box provided. (1 mark) (c) Draw the structural formula for a tertiary alcohol that is an isomer of hexan-3-ol. (1 mark) (d) Hexan-3-ol is reacted with Compound M under acidic conditions to produce Compound L. Draw the semi-structural formula for Compound M in the box provided.
(1 mark) (e) (i) Draw the semi-structural formula for Compound K in the box provided. (1 mark) (ii) Name the class of organic compound (homologous series) to which Compound K belongs. (1 mark) (f) What type of reaction produces Compound K from hexan-3-ol? (1 mark) (Total = 7 marks)
Question 1/ 4 Abscisic acid is a substance that regulates the growth of plants and has the structure shown below.
The correct names for the functional groups labelled X, Y and Z are X
Y
Z
ester
carboxylic acid
alkene
aldehyde
ester
ketone hydroxy
alkyne carboxylic acid
amide
alkane
alkene
Question 2/ 4 Molecules of vitamin A have the formula C20H30O and their structure contains one ring and one hydroxy group. The number of carbon-to-carbon double bonds present is A. 3 B. 4 C. 5 D. 6
Question 3/ 4 The correct names for the compounds CH3CH2CH2CH2CH=CH2 and CH3CH2CH2CH2CH2CH2CH3 are, respectively, A. 1–hexene and heptane. B. 1–heptene and hexane. C. hexane and 1–heptene. D. 1–heptene and octane.
Question 4/ 4 The sequence of reactions required to convert ethene, C2H4, into ethyl ethanoate, CH3COOCH2CH3, would be A. addition, oxidation, esterification. B. addition, substitution, oxidation. C. oxidation, esterification, substitution. D. esterification, oxidation, addition.
Question 5/ 4 Which of the lists below contains compounds that are isomers of each other? A. CH3CH(OH)CH3, CH3CH2CH2OH, CH3CH2OCH3 B. CH3OH, CH3CH2OH, CH3CH2CH2OH C. CH3CH2CH2OH, CH3CH(OH)CH2OH, CH2(OH)CH(OH)CH2OH D. CH3CH2CH3, CH3CH2CH2OH, CH3CH(OH)CH3
Question 6/ 4 When ethanol, CH3CH2OH, is oxidised by acidified potassium permanganate, the most likely product is A. CH2=CH2 B. CH2(OH)CH2OH C. HCOOH D. CH3COOH
Question 7/ 4 The reaction between methanol, CH3OH, and propanoic acid, CH3CH2COOH, is an example of A. alcoholysis. B. substitution. C. esterification. D. addition.
Question 8/ 4 Which of the substances below is in the same homologous series as CH3CH2COOH? A. butane B. ethanol C. butanoic acid D. propene
Question 9/ 4 Which of the following pairs of compounds will both undergo substitution reactions? A. CH3CH2CH3 and CH3CH2Cl B. CH2=CH2 and CH3CH=CH2 C. CH3CH2CH3 and CH3CH2COOH D. CH3CH2Cl and CH2=CH2
Question 10/ 4 To carry out the following sequence of reactions
the reagents X and Y are, respectively, A. ethanol and ethanoic acid. B. acidified KMnO4 and water/catalyst. C. HCl(aq) and acidified KMnO4.
D. water/catalyst and acidified KMnO4.
Question 11/ 4 The pair of compounds CH3CH2OH and CH3OCH3 are best described as A. alcohols. B. isomers. C. alkanes. D. isotopes.
Question 12/ 4 Alkanes and alkenes are two important classes of organic compounds. (a) Describe the difference in structure between alkanes and alkenes. (2 marks) (b) There are five isomers with the molecular formula C5H10 that are alkenes. Give the semi-structural formula and correct name for any three of these isomers. (3 marks) (Total = 5 marks)
Question 13/ 4 [Adapted VCAA 2020 SB Q10]
Analytical chemistry deals with methods for determining the chemical composition of samples of matter. A qualitative method yields information about the identity of atomic or molecular species or the functional groups in the sample ... Analytical methods are often classified as being either classical or instrumental. Source: DA Skoog, FJ Holler and SR Crouch, Principles of Instrumental Analysis, 6th edition, Thomson Brooks/Cole , Belmont (CA), 2007, p. 1 Classical methods include qualitative analysis, such as treating a compound with reagents to observe any reaction, and quantitative methods, such as volumetric analysis, where the amount of a compound is determined by its reaction with a standard reagent. Instrumental methods include a variety of spectroscopy, such as IR spectroscopy and NMR spectroscopy. (a) Explain how the classical methods of analytical chemistry can be used to determine information about alcohols. In your answer, refer to: • qualitative analysis and how it can be used to determine whether a compound is an alcohol and, if it is, the type of alcohol • quantitative analysis. (3 marks) (b) C3H6O can exist as a ketone or as a primary alcohol. Explain how IR spectroscopy and 1H NMR spectroscopy can be used to differentiate between the ketone and primary alcohol isomers of C3H6O. (2 marks) (Total = 5 marks)
Question 14/ 4 [VCAA 2022 SB Q1] A reaction pathway to produce a primary alcohol is shown below.
C4H8 reacts with HCl(g) to form two unbranched isomers – Compound A and Compound B. Only Compound A can react to produce a primary alcohol. (a) Identify the type of reaction that converts C4H8 into Compound A. (1 mark) (b) Write the semi-structural formula for Compound B in the box provided. (1 mark) (c) State the reagent(s) required to convert Compound A into a primary alcohol in the box provided. (1 mark) (d) Propan-1-ol can react with methanoic acid to produce an organic molecule. (i) Identify the catalyst for this reaction. (1 mark) (ii) Write a balanced chemical equation for the reaction. (2 marks) (iii)Write the systematic IUPAC name for the organic molecule produced. (1 mark) (Total = 7 marks)
Question 15/ 4 [Adapted VCAA 2021 SB Q6] A reaction pathway beginning with 1-bromopentane is shown below.
(a) (i) Write a balanced equation for the reaction that will produce pentan-1-ol from 1-bromopentane and a sodium salt. (2 marks) (ii) Calculate the atom economy in the production of pentan-1-ol from 1-bromopentane and a sodium salt. (3 marks) (b) Pentan-1-ol is fully oxidised to Compound S. Write the IUPAC name of Compound S in the box provided. (1 mark) (c) In an alternative reaction pathway, pentanamide can be formed from 1-bromopentane. Draw the skeletal formula for pentanamide. (1 mark) (Total = 7 marks) Total marks for test = 35 marks
Chapter 5: Unit 4 Area of Study 2 – How are organic compounds analysed and used? Question 1/ 68 A 0.0491 M solution of sodium carbonate was used to standardise a solution of ethanoic acid. A 20.00 mL aliquot of the sodium carbonate solution was placed in a conical flask and titrated with the ethanoic acid solution from a burette. The correct indicator for this reaction would be one that changes colour when the number of mole of hydrogen ions added A. results in the pH of the solution in the flask being 7. B. just exceeds the number of mole of CO32− ions present originally. C. just exceeds double the number of mole of CO32− ions present originally. D. equals the number of mole of CO32− ions present originally.
Question 2/ 68 200 mL of 0.10 mol L−1 hydrochloric acid, 200 mL of 0.20 mol L−1 hydrochloric acid and 100 mL of 0.40 mol L−1 hydrochloric acid are mixed together. The concentration of hydrochloric acid in the resulting solution, in mol L−1, is A. 0.10 B. 0.20 C. 0.70 D. 5.0
Question 3/ 68 Anhydrous sodium carbonate, Na2CO3, is a good primary standard. What mass of sodium carbonate, when dissolved in water in a 250 mL volumetric flask, is needed to make a 0.0650 mol L−1 solution? A. 0.01625 g B. 1.722 g C. 6.890 g D. 27.56 g
Question 4/ 68 The label on a 5.00 L container of ‘Pool Acid’ states that it contains 33% w/w of hydrochloric acid. Calculate the mass of acid present in the container, in kilograms, if the density of the acid is 1.17 g mL−1. A. 17.7 B. 1.93 C. 1.65 D. 1.41
Question 5/ 68 Lithium hydroxide can be used to remove carbon dioxide from gas mixtures. The equation for the reaction is 2LiOH(s) + CO2(g) → Li2CO3(s) + H2O(l) The volume of carbon dioxide, measured at SLC, that could be absorbed by 1.00 kg of LiOH is A. 0.511 L B. 1023 L C. 511 L D. 468 L
Question 6/ 68 0.1851 g of a pure dicarboxylic acid, Z(COOH)2, was added to approximately 20.00 mL of water and titrated with 0.136 M NaOH solution. To reach the endpoint, a titre of 20.62 mL was required. The identity of the dicarboxylic acid is most likely to be A. CH2(COOH)2 B. C2H4(COOH)2 C. C3H6(COOH)2 D. C4H8(COOH)2
Question 7/ 68 [VCAA 2021 SA Q4] A titration was performed to determine the concentration of an ethanoic acid, C2H4O2, solution using the following procedure: 1. 25.00 mL of the C2H4O2 solution was pipetted into a conical flask. 2. A few drops of indicator were added to the flask. 3. A burette was filled with standard sodium hydroxide, NaOH, solution. 4. The C2H4O2 solution was then titrated with the NaOH solution. 5. Steps 1−4 were repeated until three concordant titres were obtained. A systematic error could result if the A. burette tap leaked during one of the titrations. B. burette readings were recorded to the nearest 0.1 mL. C. number of drops of indicator was not consistent for each titration. D. actual concentration of the standard NaOH solution was lower than the stated concentration.
Question 8/ 68 The following information refers to Questions 9 and 10. Four students titrate 20.00 mL of 0.100 mol L−1 sodium hydroxide solution with a solution of ethanoic acid. The students used the same solutions of sodium hydroxide and ethanoic acid and delivered the ethanoic acid from different 50 mL burettes. Their results are given in the table below. Student I
Student II
Student III
Student IV
Titre 1 (mL)
21.47
22.63
22.57
22.86
Titre 2 (mL)
21.49
22.65
22.69
22.73
Titre 3 (mL)
21.39
22.58
22.46
22.62
Titre 4 (mL)
21.42
22.60
22.76
22.63
Average (mL)
21.44
22.62
22.62
22.71
Question 9/ 68 Which student is most likely to have made a systematic error? A. Student I B. Student II C. Student III D. Student IV
Question 10/ 68 Which student may have rinsed their burette incorrectly? A. Student I B. Student II
C. Student III D. Student IV
Question 11/ 68 0.153 g of an organic base is dissolved in ∼20 mL of water and titrated with 0.1051 mol L−1 hydrochloric acid. 24.56 mL of the acid is required to reach the end point. The formula of the organic base is most likely to be A. CH3CH2NH2 B. CH3CH2CH2NH2 C. H2NCH2CH2NH2 D. CH3CH2CH2CH2NH2
Question 12/ 68 [VCAA 2013 SA Q3] In a titration, a 25.00 mL titre of 1.00 M hydrochloric acid neutralised a 20.00 mL aliquot of sodium hydroxide solution. If, in repeating the titration, a student failed to rinse one of the pieces of glassware with the appropriate solution, the titre would be A. equal to 25.00 mL if water was left in the titration flask after final rinsing. B. less than 25.00 mL if the final rinsing of the burette is with water rather than the acid. C. greater than 25.00 mL if the final rinsing of the 20.00 mL pipette is with water rather than the base. D. greater than 25.00 mL if the titration flask had been rinsed with the acid prior to the addition of the aliquot.
Question 13/ 68 Use the following information to answer Questions 14 and 15.
A clear, colourless liquid extract of the rhubarb plant was analysed for the concentration of oxalic acid, H2C2O4, by direct titration with a recently standardised and acidified potassium permanganate solution, KMnO4(aq). The balanced equation for this titration is shown below. 2− + 2+ 2MnO− 4 (aq) + 5C2 O4 (aq) + 16H (aq) → 2Mn (aq) + 10CO2 ( g) + 8H2 O(l) purple colourless colourless
The steps in the titration were as follows: Step 1 – A 20.00 mL aliquot of the rhubarb extract was placed in a 200 mL conical flask. Step 2 – The burette was filled with acidified 0.0200 M KMnO4 solution. Step 3 – The acidified 0.0200 M KMnO4 solution was titrated into the rhubarb extract in the conical flask. The titration was considered to have reached the end point when the solution in the conical flask showed a permanent change in colour to pink. The volume of the titre was recorded. Step 4 – The titration was repeated until three concordant results were obtained. The average of the concordant titres was 21.7 mL.
Question 14/ 68 [VCAA 2018 SA Q17] The concentration of H2C2O4 in the rhubarb extract is closest to A. 5.43 × 10−2 M B. 5.00 × 10−2 M C. 2.17 × 10−2 M D. 7.40 × 10−4 M
Question 15/ 68 [VCAA 2018 SA Q18] Which of the following rinses is least likely to affect the accuracy of the results? Item
Rinse solution
Item
Rinse solution
burette
distilled water
burette
rhubarb extract
pipette
KMnO4(aq)
conical flask
distilled water
Question 16/ 68 To find the ethanol content of a low alcohol beer, a student reacts 20.00 mL of the beer with an acidified solution of potassium dichromate. 23.75 mL of 0.105 mol L−1 K2Cr2O7 is required for complete reaction. The equation for the reaction is 2Cr2O72−(aq) + 16H+(aq) + 3C2H5OH(aq) → 4Cr3+(aq) + 11H2O(l) + 3CH3CO2H(aq) The concentration of ethanol in the beer in g mL−1 is A. 0.172 B. 0.115 C. 8.62 × 10−3 D. 5.75 × 10−3
Question 17/ 68 Use the following information to answer Questions 18 and 19. The concentration of vitamin C in a filtered sample of grapefruit juice was determined by titrating the juice with 9.367 × 10−4 M iodine, I2, solution using starch solution as an indicator. The molar mass of vitamin C is 176.0 g mo1−1. The reaction can be represented by the following equation. C6H8O6(aq) + I2(aq) → C6H6O6(aq) + 2H+(aq) + 2I−(aq) The following method was used: 1. Weigh a clean 250 mL conical flask.
2. Use a 10 mL measuring cylinder to measure 5 mL of grapefruit juice into the conical flask and reweigh it. 3. Add 20 mL of deionised water to the conical flask. 4. Add a drop of starch solution to the conical flask. 5. Titrate the diluted grapefruit juice against the I2 solution.
Question 18/ 68 [VCAA 2019 SA Q29] Which one of the following errors would result in an underestimation of the concentration of vitamin C in grapefruit juice? A. 19 mL of deionised water was added to the conical flask. B. The concentration of the I2 solution was actually 9.178 × 10−4 M. C. The initial volume of the I2 solution in the burette was 1.50 mL, but it was read as 2.50 mL. D. The balance was faulty and the measured mass of grapefruit juice was lower than the actual mass.
Question 19/ 68 [VCAA 2019 SA Q30] If the measured mass of grapefruit juice was 4.90 g and the titre was 21.50 mL, what was the measured percentage mass/mass (% m/m) concentration of vitamin C in the grapefruit juice? A. 0.00987 B. 0.0723 C. 0.354 D. 3.36
Question 20/ 68 [VCAA 2015 SA Q3] In an experiment, 0.051 mol of sodium hydroxide, NaOH, reacted completely with 0.017 mol of citric acid, C6H8O7. Which one of the following equations correctly represents the reaction between citric acid and the sodium hydroxide solution? A. NaOH(aq) + C6H8O7(aq) → NaC6H7O7(aq) + H2O(l) B. 2NaOH(aq) + C6H8O7(aq) → Na2C6H6O7(aq) + 2H2O(l) C. 3NaOH(aq) + C6H8O7(aq) → Na3C6H5O7(aq) + 3H2O(l) D. 4NaOH(aq) + C6H8O7(aq) → Na4C6H4O7(aq) + 4H2O(l)
Question 21/ 68 Use the following information to answer Questions 22 and 23. A solution of citric acid, C3H5O(COOH)3, was analysed by titration. 25.0 mL aliquots of the C3H5O(COOH)3 solution were titrated against a standardised solution of 0.0250 M sodium hydroxide, NaOH. Phenolphthalein indicator was used and the average titre was found to be 24.0 mL.
Question 22/ 68 [VCAA 2020 SA Q23] Based on the titration, the concentration of C3H5O(COOH)3 in the solution was A. 8.0 × 10−3 M B. 8.7 × 10−3 M C. 2.6 × 10−2 M D. 7.2 × 10−2 M
Question 23/ 68 [VCAA 2020 SA Q24] Which one of the following would have resulted in a concentration that is higher than the actual concentration? A. The pipette was rinsed with NaOH solution. B. The pipette was rinsed with C3H5O(COOH)3 solution. C. The conical flask was rinsed with NaOH solution. D. The conical flask was rinsed with C3H5O(COOH)3 solution.
Question 24/ 68 [VCAA 2021 SA Q23] A student titrated 25 mL aliquots of three different concentrations of an organic acid against a standardised potassium hydroxide, KOH, solution. The student's results are shown in the table below. KOH titre for Sample 1 (mL)
KOH titre for Sample 2 (mL)
KOH titre for Sample 3 (mL)
Titration 1
20.35
19.85
21.55
Titration 2
20.45
19.65
21.45
Titration 3
20.30
20.45
21.65
Average Titre
20.37
19.98
21.55
Which one of the following statements is consistent with the results shown in the table? A. Sample 2 is the most concentrated acid. B. Sample 3 is the most concentrated acid. C. There is not enough information to draw a valid conclusion. D. The averages in the table are correct as the results are concordant.
Question 25/ 68
The mass spectrum of dimethyl ether is shown above. The parent molecular ion (m/e = 46.0) has the formula CH3OCH3+. When this ion breaks up, other particles are produced. Which species is most likely to have been lost from the parent ion to form the particle with m/e = X in the above spectrum? A. CH3 B. CH3+ C. CH3O D. CH3O+
Question 26/ 68 Which one of the compounds below will not have an absorption band between 1700 cm−1 and 1800 cm−1 in its infrared spectrum? A. CH3CH2COCH3 B. CH3CH2OCOCH3 C. CH3CH2OCH2CH3 D. CH3CH2NHCOCH3
Question 27/ 68 A hydrocarbon has the formula C6H14. Its 13C NMR spectrum consists of two lines at 33.89 ppm and 19.49 ppm. Which one of the structures below is consistent with this information? A. CH3CH2CH2CH2CH2CH3 B. CH3CH2CH2CH(CH3)2 C. CH3CH2CH(CH3)CH2CH3 D. (CH3)2CHCH(CH3)2
Question 28/ 68 There are two isomers with the molecular formula C2H4Cl2. The 13C NMR is measured for one of the isomers and consists of two singlets. If the 1H NMR spectrum of this isomer were measured it would consist of A. a singlet. B. two singlets. C. two triplets. D. a doublet and a quartet.
Question 29/ 68 The 1H NMR spectrum of a compound is represented in the sketch below. It consists of two signals, I and II.
The relative areas of the two signals I and II is 3:1. Which one of the following compounds is consistent with this spectrum? A. CH3CHCl2 B. ClCH2CH2Cl C. (CH3)3COCH3 D. CH3CH2OCH2CH3
Question 30/ 68 There are four different groups of protons in 1,1-dichlorobutane as shown in the diagram below.
In the 1H NMR spectrum the group of protons expected to have the largest chemical shift would be A. I B. II C. III D. IV
Question 31/ 68 There are four alcohols with the molecular formula C4H9OH. The one that has the least number of signals in its 13C NMR spectrum is A.
B.
C.
D.
Question 32/ 68 The instruments shown below are used in different techniques. I mass spectrometer II NMR spectrometer III HPLC IV IR spectrometer Which instruments make use of a magnetic field in their operation? A. I and II B. II and III C. III and IV D. I and IV
Question 33/ 68 [VCAA 2015 SA Q9] Which two isomers of C3H6Br2 have two peaks (other than the TMS peak) in their 13C NMR spectrum? A. CH3CBr2CH3 and CHBr2CH2CH3 B. CHBr2CH2CH3 and CH2BrCHBrCH3 C. CH2BrCHBrCH3 and CH2BrCH2CH2Br D. CH2BrCH2CH2Br and CH3CBr2CH3
Question 34/ 68 Use the following information to answer Questions 35 and 36. Four straight chain alcohols, S, T, U, V, with a general formula ROH, were analysed using a gas chromatograph combined with a mass spectrometer. The following chromatogram was produced.
Question 35/ 68 [VCAA 2014 SA Q15] The 13C NMR spectrum below corresponds to which one of the following compounds?
A. propane B. 2-methylbutane C. 2-methylpropan-1-ol D. 2-methylpropan-2-ol
Question 36/ 68 [VCAA 2015 SA Q10] The high-resolution proton NMR spectrum of chloroethane has two sets of peaks. Both peaks are split. Which of the following correctly describes the splitting pattern? A. a singlet and a doublet B. a doublet and a doublet C. a doublet and a triplet D. a triplet and a quartet
Question 37/ 68 [VCAA 2019 SA Q12] A compound has the molecular formula C4H9Cl. Which type of chemical analysis would be most useful in
determining whether this compound has a stereoisomer? A. mass spectrometry B. infra-red spectroscopy C. high-performance liquid chromatography D. nuclear magnetic resonance spectroscopy
Question 38/ 68 [VCAA 2019 SA Q27] An organic compound has a molar mass of 88 g mo1−1. The 13C NMR spectrum of the organic compound shows four distinct peaks. The organic compound is most likely A. butan-1-ol. B. 2-methyl-butan-1-ol. C. 2-methyl-butan-2-ol. D. 2,2-dimethyl-propan-1-ol.
Question 39/ 68 [VCAA 2020 SA Q21] The infra-red (IR) spectrum of an organic compound is shown below.
Data: SDBS Web www.sdbs.db.aist.go.jp, National Institute of Advanced Industrial Science and Technology Referring to the IR spectrum above, the compound could be A. CH3CH2COOCH3 B. CH3CH2CH2CHO C. NH2CH2CH2CONH2 D. NH2CH2CH2CHOHCH3
Question 40/ 68 [VCAA 2021 SA Q11] The spectroscopy information for an organic molecule is given below. number of peaks in 13C NMR
2
number of sets of peaks in 1H NMR
3
m/z of the last peak in the mass spectrum
60
infra-red (IR) spectrum
an absorption peak appears at 3350 cm−1
The organic molecule is
A.
B.
C.
D.
Question 41/ 68 [VCAA 2021 SA Q16] Which one of the following statements about IR spectroscopy is correct? A. IR radiation changes the spin state of electrons. B. Bond wavenumber is influenced only by bond strength. C. An IR spectrum can be used to determine the purity of a sample. D. In an IR spectrum, high transmittance corresponds to high absorption.
Question 42/ 68 [Adapted VCAA 2021 SA Q30] The 1H NMR spectrum of an organic compound has three unique sets of peaks: a single peak, seven peaks (septet) and two peaks (doublet). The compound is A. 3-methylbutanoic acid. B. 2-methylpropanoic acid. C. 2-chloro-2-methylpropane. D. 1,2-dichloro-2-methylpropane.
Question 43/ 68 A mixture of ethanol (C2H5OH), methanol (CH3OH) and 1-propanol (C3H7OH) was analysed by high performance liquid chromatography. The output from the chart recorder is shown below.
If the sensitivity of the detector is the same per mole for all three alcohols, the mole percentage of ethanol in the sample is closest to A. 25 B. 31 C. 44 D. 50
Question 44/ 68 [VCAA 2020 SA Q20] Consider the following changes that could be applied to the operating parameters for a chromatogram set up to carry out high-performance liquid chromatography (HPLC) with a polar stationary phase and a non-polar mobile phase: I decreasing the viscosity of the mobile phase II using a more tightly packed stationary phase III using a mobile phase that is more polar than the stationary phase A. I only B. I and III only C. III only D. II and III only
Question 45/ 68 Use the following information to answer Questions 46 and 47. The mass of caffeine in a particular coffee drink was determined by high-performance liquid chromatography (HPLC). The calibration curve produced from running standard solutions of caffeine through an HPLC column is shown below.
A 5.0 mL aliquot of the coffee drink was diluted to 50.0 mL with de-ionised water. A sample of the diluted coffee drink was run through the HPLC column under identical conditions to those used to obtain the calibration curve. The peak area obtained for this diluted sample was 2400 arbitrary units.
Question 46/ 68 [VCAA 2017 SA Q21] The HPLC column used has a non-polar stationary phase. The most suitable solvent for determining the concentration of caffeine in the sample is A. carbon tetrachloride, CCl4 B. methanol, CH3OH C. octanol, C8H17OH D. hexane, C6H14
Question 47/ 68 [VCAA 2017 SA Q22]
The mass of caffeine, in grams, in 350 mL of the undiluted coffee drink is closest to A. 0.014 B. 0.070 C. 0.14 D. 0.40
Question 48/ 68 Which one of the following molecules contains a chiral carbon atom?
A.
B.
C.
D.
Question 49/ 68 [VCAA 2018 SA Q19] Which one of the following molecules contains a chiral carbon? A. CH2CHCH2CH3
B. CH2FCH2CH2Cl C. CH3CHOHCH2CH3 D. CH3CH2CFClCH2CH3
Question 50/ 68 [VCAA 2017 SA Q4] Which of the following contains a chiral carbon? Name
Semi-structural formula
2-methylbut-1-ene
CH2C(CH3)CH2CH3
2-chlorobutane
CH3CHClCH2CH3
Propanoic acid
CH3CH2COOH
1,2-dichloroethene
ClCHCHCl
Question 51/ 68 Which two functional groups react to form the peptide link found in proteins? A. −NH2 and −OH B. −NH2 and −NH2 C. −OH and −COOH D. −COOH and −NH2
Question 52/ 68
One of the hormones produced in the adrenal gland is epinephrine, which has the structure shown below.
It is most likely that the amino acids used to make this hormone are A. phenylalanine or tyrosine. B. tyrosine or tryptophan. C. proline or phenylalanine. D. proline or tryptophan.
Question 53/ 68 Maltose is a naturally occurring disaccharide formed when two molecules of glucose, C6H12O6, react together. The most likely formula of maltose is A. C12H22O11 B. C12H24O12 C. C10H22O11 D. C12H20O10
Question 54/ 68 Part of the secondary structure of many proteins is a spiral shape, often called an α-helix. This shape is mostly maintained by A. hydrogen bonding between C=O and N–H groups on different parts of the protein chain. B. hydrogen bonding between C=O and N–H groups within each peptide linkage. C. covalent S–S bonds formed from S–H groups within the protein chain.
D. ionic bonds formed when −COOH and −NH2 groups react to make the protein chain.
Question 55/ 68 In living things, polypeptides and proteins can be converted into amino acids such as glycine and alanine. These reactions of polypeptides to produce amino acids are classified as A. denitrification. B. condensation. C. hydrogenation. D. hydrolysis.
Question 56/ 68 The number of different dipeptides that can be formed containing any two of the amino acids, alanine, glycine and serine, is A. 2 B. 3 C. 4 D. 6
Question 57/ 68 Most living things need a number of enzymes in order to function correctly. Which one of the following statements is correct concerning enzymes? A. Enzymes function well over a wide range of pH and temperature conditions. B. All enzymes catalyse a wide variety of chemical reactions.
C. Enzymes are more effective than other catalysts at increasing the rate of reaction. D. Many enzymes are consumed by the chemical reaction they help to catalyse.
Question 58/ 68 Which one of the substances below is most likely to be involved in the production of a protein? A. CH3(CH2)14COOH B. H2NCH2CH2COOH C. HOCH2CH(OH)CH2OH D. H2NCH(CH3)COOH
Question 59/ 68 Spiders spin their webs using a silky protein. This material contains ∼42% glycine (M = 75.0 g mol−1) and ∼25% alanine (M = 89.0 g mol−1). A strand of this protein is found to have a molar mass of ∼200 000 g mol−1. The number of glycine residues present in this protein is closest to A. 1120 B. 1475 C. 2670 D. 3510
Question 60/ 68 A pentapeptide used in the manufacture of anti-wrinkle creams has the amino acid sequence Lys–Thr–Thr–Lys–Ser.
The number of hydroxy, amide (peptide) and amine functional groups present in this pentapeptide is –OH
–CONH–
–NH2
3
5
3
2
4
2
2
5
2
3
4
3
Question 61/ 68 After digestion of proteins in the diet any unwanted amino acids are broken down in the liver and the nitrogen is converted into urea, CH4N2O (M = 60.0 g mol−1). The maximum mass of urea that could be obtained from 2.0 g of arginine (M = 174.0 g mol−1) is A. 0.345 g B. 0.690 g C. 1.38 g D. 5.80 g
Question 62/ 68 The hydrolysis of proteins in food produces amino acids. Which one of the following is most likely to be an amino acid obtained in this way? A. NH2CH2CH2COOH B. NH2CH(SH)COOH C. (CH3)2CHCH2CH(NH2)COOH D. C6H5CH(NH2)COOH
Question 63/ 68 The amino acids glycine, threonine and valine are reacted to produce a tripeptide. The number of different tripeptides that could be produced from these amino acids is A. 1 B. 3 C. 5 D. 6
Question 64/ 68 [VCAA 2018 SA Q4] At the molecular level, Protein P is shaped like a coil. When a solution of Protein P is mixed with citric acid, solid lumps form. The change in the structure of Protein P is due to A. hydrolysis. B. denaturation. C. polymerisation. D. the formation of peptide bonds.
Question 65/ 68 [VCAA 2013 SA Q11] Australian jellyfish venom is a mixture of proteins for which there is no antivenom. Jellyfish stings are painful, can leave scars and, in some circumstances, can cause death. Some commercially available remedies disrupt ionic interactions between the side chains on amino acid residues. These products most likely disrupt the protein's A. primary structure only. B. secondary structure only.
C. tertiary structure only. D. primary, secondary and tertiary structures.
Question 66/ 68 [VCAA 2015 SA Q14] Which one of the following is not true of protein denaturation? A. It could result from a temperature change. B. It may be caused by a pH change. C. It alters the primary structure. D. It results in a change in the shape of the protein.
Question 67/ 68 [VCAA 2015 SA Q14] An enzyme A. can distinguish between optical isomers. B. catalyses forward and reverse reactions. C. always needs a coenzyme to function. D. is not able to change shape.
Question 68/ 68 [VCAA 2017 SA Q10]
Which one of the following structures represents a zwitterion of a 2-amino acid?
A.
B.
C.
D.
Question 69/ 68 [VCAA 2017 SA Q15] Which one of the following is a correct statement about the denaturation of a protein? A. Denaturation is characterised by the release of peptides. B. Alcohol denatures proteins by disrupting the hydrogen bonding. C. Denaturation involves disruption of all bonds in the tertiary structure. D. The primary and secondary structures are disrupted when denaturation occurs.
Question 70/ 68 [VCAA 2018 SA Q15] The following table contains the percentage composition by mass of the nutritional value of some common foods.
Food
% Carbohydrates
% Fats and oils
% Protein
fish
0
8
29
bread
50
4
8
cheese
1
34
25
milk
5
4
3
Which one of the following servings has the highest energy content? A. 100 g of fish B. 80 g of bread C. 40 g of cheese D. 258 g (250 mL) of milk
Question 71/ 68 [VCAA 2018 SA Q28] Which one of the following is a dipeptide made from α-amino acids?
A.
B.
C.
D.
Question 72/ 68 [Adapted VCAA 2018 SA Q30] In the human body, not all energy available from the metabolism of food is dissipated as heat energy. A student carried out further research on this and found that some of the energy is used in the production of adenine triphosphate, ATP3−, from adenine diphosphate, ADP2−, and inorganic phosphate, PO43−, according to the following equation. ADP2− + PO43− + 2H+ → ATP3− + H2O The student also learnt that the overall equation for aerobic respiration can be represented as shown below. C6H12O6 + 6O2 + 32ADP2− + 32PO43− + 64H+ → 6CO2 + 32ATP3− + 38H2O It is reasonable to deduce that in aerobic respiration A. the formation of ATP3− is a hydrolysis reaction. B. for 3.3 g of CO2 to be produced, 0.40 mol of ADP2− is needed [M(CO2) = 44.0 g mol−1]. C. the production of ATP3− from ADP2− and PO3− is an exothermic reaction. D. 9.5 g of C2H12O6 will produce 2.0 mol of ATP3− [M(C6H12O6) = 180.0 g mol−1].
Question 73/ 68 [Adapted VCAA 2019 SA Q15] Aspartame is an artificial sweetener sometimes added to make foods taste sweeter while not adding much additional energy consumed.
Aspartame has only A. one chiral centre. B. two stereoisomers. C. four optical isomers. D. three structural isomers.
Question 74/ 68 [VCAA 2020 SA Q12] The diagram below represents a section of an enzyme.
The diagram can be described as a
A. secondary structure consisting of glutamine, glycine and lysine. B. primary structure consisting of asparagine, glycine and lysine. C. secondary structure consisting of asparagine, alanine and lysine. D. primary structure consisting of glutamine, alanine and lysine.
Question 1/ 35 A student determined the concentration of ethanoic acid in vinegar by the following method. Using a pipette, 25.00 mL of the vinegar were added to a 250 mL volumetric flask. Water was added until the solution reached the calibration mark. A 20.00 mL aliquot of 0.1152 mol L−1 hydroxide solution was added to a conical and the solution was titrated with the diluted vinegar solution from a burette. This part of the experiment was repeated three times. The following results were obtained. Titration
Titre (mL)
1
24.16
2
22.68
3
22.71
4
22.64
(a) (i) Calculate the amount of sodium hydroxide used in each titration. (1 mark) (ii) Write the equation for the reaction between sodium hydroxide and ethanoic acid. (1 mark) (iii) Calculate the molarity of the diluted vinegar solution. (2 marks) (iv) Calculate the concentration of the original vinegar solution in g L−1. (2 marks) (v) Why was the vinegar diluted before being used in the titrations? (1 mark) (b) The pieces of glassware used in the experiment were all rinsed before use. In the table below, indicate which liquid should be used to rinse each piece of glassware. The choices are: • original vinegar solution
• water • diluted vinegar solution • sodium hydroxide solution. Glassware
Solution used for rinsing
25.00 mL pipette volumetric flask 20.00 mL pipette conical flask burette (5 marks) (Total = 12 marks)
Question 2/ 35 Citric acid is found in many fruits and some vegetables and has the semi-structural formula shown below.
A student determines the concentration of citric acid in lemon juice by the following method. 25.00 mL of the lemon juice is accurately diluted to 250 mL in a volumetric flask. The diluted lemon juice solution was then used to titrate 20.00 mL aliquots of 0.0946 mol L−1 sodium hydroxide solution. The average of three concordant titres was 25.16 mL. (a) Write a balanced equation for the reaction between sodium hydroxide and citric acid. (1 mark) (b) (i) Calculate the amount of sodium hydroxide used in each titration. (1 mark) (ii) Calculate the concentration, in mol L−1, of citric acid in the volumetric flask. (2 marks)
(iii) Calculate the concentration, in g L−1, of the citric acid in lemon juice. (2 marks) (Total = 6 marks)
Question 3/ 35 Glucose tablets are used by people with diabetes and help to treat low levels of sugar in the blood. A student determines the percentage of glucose in a glucose tablet by the following procedure. Two glucose tablets are weighed, crushed and added to water to dissolve the glucose. The resulting solution is filtered into a 250 mL volumetric flask and the volume made up to the mark. A 20.00 mL aliquot of an alkaline copper sulfate solution (concentration 0.1362 mol L−1) is pipetted into a conical flask, heated to approximately 75°C and titrated with the glucose solution from a burette. When most of the blue Cu2+ ions have reacted, a few drops of methylene blue indicator are added and more glucose solution is added until the intense blue colour of the indicator vanishes. The process is repeated until three concordant results are obtained. The equation for the reaction is C6H12O6(aq) + 2Cu2+(aq) + 5OH−(aq) → C6H11O7−(aq) + Cu2O(s) + 3H2O(l) Results: Mass of two tablets = 2.986 g Average of concordant titres = 21.62 mL (a) Explain why the reaction above is classified as a redox reaction. (1 mark) (b) Calculate the amount of Cu2+(aq), in mol, used in each titration. (1 mark) (c) Calculate the amount of glucose, in mol, in the volumetric flask. (2 marks) (d) Calculate the percentage of glucose in the tablets. (2 marks) (e) Suggest a reason why the copper sulfate solution is heated. (1 mark) (f) Suggest a reason why an indicator is needed for this reaction. (1 mark) (g) Comment on any safety aspects of this procedure. (1 mark)
(Total = 9 marks)
Question 4/ 35 The stalks of the rhubarb plant are edible. They are cooked with sugar and used in desserts such as pies and crumbles. However, the leaves of the rhubarb plant are poisonous since they contain small amounts of oxalic acid, HOOCCOOH or H2C2O4. A student determined the amount of oxalic acid in rhubarb leaves by the following method. 95.0 g of rhubarb leaves were cut and crushed into small pieces and treated to extract the oxalic acid as an aqueous solution. The extract was concentrated and added to a 100 mL volumetric flask. The level was made up to the calibration mark with water and the mixture thoroughly shaken. 20.00 mL aliquots of the solution were heated to approximately 60°C and titrated with 0.01961 mol L−1 potassium permanganate solution until a pale pink colour just remained. The average of three concordant titres was 21.62 mL. The equation for the reaction is 2MnO4−(aq) + 5H2C2O4(aq) + 6H+(aq) → 2Mn2+(aq) + 10CO2(g) + 8H2O(l) (a) (i) Calculate the amount of potassium permanganate used in the titration. (1 mark) (ii) Calculate the amount of oxalic acid that reacted with the MnO4−. (1 mark) (iii) Calculate the mass of oxalic acid in the rhubarb leaves. (2 marks) (iv) Express the concentration of oxalic acid as a %(m/m). (1 mark) (b) Describe two possible sources of error in this procedure and explain how these errors would affect the final result. (2 marks) (Total = 7 marks)
Question 5/ 35 Vitamin C (ascorbic acid) is an essential nutrient in the human diet and is present in most fruits and vegetables. The formula of vitamin C is C6H8O6 and has the structure shown below.
(a) Circle any chiral carbon atoms in this structure. (1 mark) Vitamin C reacts readily with iodine. C6H8O6(aq) + I2(aq) → C6H6O6(aq) + 2H+(aq) + 2I−(aq) (b) Is vitamin C an oxidising agent or a reducing agent? Explain your answer. (1 mark) Iodine can be produced by reacting iodate ions, IO3−, in acidic solution with an excess of iodide ions, I−. IO3−(aq) + 5I−(aq) + 6H+(aq) → 3I2(aq) + 3H2O(l) Potassium iodate, KIO3, is a primary standard. 0.1085 g of potassium iodate is added to a 250 mL volumetric flask. Water is added to dissolve the solid and then the volume is made up to the mark. (c) Calculate the molarity of the potassium iodate solution. (1 mark) The concentration of vitamin C was determined by the following procedure. 50.00 mL of grapefruit juice was pipetted into a conical flask. 5 mL of 1.0 mol L−1 potassium iodide solution and 5 mL of 1.0 mol L−1 hydrochloric acid were added to the flask, followed by 2 mL of starch solution. The mixture in the flask was titrated with the potassium iodate solution from a burette. As the iodate solution was added, it reacted with the iodide and acid to produce I2, which then reacted with the vitamin C. When all of the vitamin C had reacted, a slight excess of I2 reacted with the starch to produce a blue-black colour. The average of three concordant titres was 17.31 mL. (d) (i) Calculate the amount, in mol, of iodate used in each titre. (1 mark) (ii) Calculate the amount, in mol, of vitamin C in the aliquot. (1 mark) (iii) Calculate the concentration of vitamin C in the grapefruit juice in mg L−1. (3 marks) (e) Apart from the equipment used, suggest a source of a systematic error in this experiment. (1 mark) (Total = 9 marks)
Question 6/ 35 The following compound has been found in some naturally occurring oils.
The compound has the molecular formula C57H100O6 (M = 880 g mol−1). (a) How many carbon-to-carbon double bonds are present in this compound? Explain your answer. (2 marks) The iodine number is often used to indicate the amount of unsaturation present in a fat or oil. The iodine number is defined as the number of grams of iodine (I2) that will react with 100 g of the fat or oil. Iodine will react with carbonto-carbon double bonds as shown in the equation below.
(b) Calculate the iodine number for the oil shown above. (2 marks) (c) Give the semi-structural formulae of the products formed when this substance undergoes hydrolysis. Identify any mono-unsaturated and/or any polyunsaturated products. (4 marks) (Total = 8 marks)
Question 7/ 35 There are a number of isomers with the molecular formula C2H4O2. One is a carboxylic acid and another is an ester. (a) Draw the structural formula and give the name of:
(i) the carboxylic acid with this formula (1 mark) (ii) the ester with this formula. (1 mark) (b) The mass spectra of the compounds in part (a) are shown below. (spectrum I and spectrum II). Assign a spectrum to each of the isomers you have drawn in part (a) and in each case give a reason for your choice.
(4 marks) (Total = 6 marks)
Question 8/ 35 The 1H NMR spectrum of 2,4,4-trimethylpentan-2-ol consists of four singlets, as shown below.
The chemical shifts and peak areas are shown in the table below. Chemical shift (ppm)
Relative peak area
1.03
125 units
1.26
14 units
1.29
85 units
1.53
29 units
(a) Draw the semi-structural formula of 2,4,4-trimethylpentan-2-ol. (1 mark) (b) Use the information in the table to assign the peaks in the spectrum to the hydrogen atoms in the compound. (3 marks) (c) How many lines will be present in the 13C NMR spectrum of this compound? (1 mark) (Total = 5 marks)
Question 9/ 35 Five of the peaks observed in the mass spectrum of 1-bromo-2-chloroethane, BrCH2CH2Cl (M = 143.5 g mol−1), are listed below, along with their relative areas. mass/charge
relative area
146
2.0
144
8.1
mass/charge
relative area
142
6.8
65
33
63
100
Both chlorine and bromine have two naturally occurring isotopes with significant relative abundances. This information is given below. Isotope
Relative isotopic mass
Relative abundance (%)
35Cl
34.97
75.5
37Cl
36.97
24.5
79Br
78.92
50.5
81Br
80.92
49.5
(a) Use the information given on the previous page to explain the observation of three peaks at 146, 144 and 142 but no peak at 143.5 in the mass spectrum of this compound. (Assume that carbon is 100% 12C and hydrogen is 100% 1H.) (3 marks) (b) The peak at 144 is more intense than the peaks at 146 and 142. Suggest a reason for this. (1 mark) (c) Give possible isotopic compositions for the peaks at 65 and 63 m/z and explain why their relative areas are approximately 1:3. (3 marks) (Total = 7 marks)
Question 10/ 35 A scientist prepares a compound with the following composition: 24.44% carbon, 3.42% hydrogen and 72.14% chlorine. (a) Deduce the empirical formula of the compound. (2 marks) In another experiment, the scientist finds that 0.025 mol of the compound has a mass of 3.69 g.
(b) Determine the molecular formula of the compound. (2 marks) (c) The scientist obtains the 1H NMR spectrum of the compound, which is shown below.
From this spectrum, the scientist suggests that the structure of the compound must be as shown below.
Assuming that the structure above is the correct one, explain how the scientist assigned the peaks in the spectrum to the H atoms in the structure. (4 marks) (d) Two other isomers with this formula have the structures shown below. For each of these structures sketch the 1H NMR spectrum you would expect to observe.
(4 marks) (Total = 12 marks)
Question 11/ 35
A compound of carbon, hydrogen and oxygen contains 63.16% carbon and 8.77% hydrogen. (a) Determine the empirical formula of the compound. (3 marks) The mass spectrum of the compound is shown below.
(b) Use the information in the mass spectrum to determine the molecular formula of the compound. (1 mark) The compound is only slightly soluble in water, is not easily oxidised by acidified potassium dichromate and does not react with sodium hydrogen carbonate. (c) From this information and the molecular formula, name two functional groups that are unlikely to be present in the compound. (2 marks) The infrared spectrum and the 1H and 13C NMR spectra of the compound are shown below and on the following page. (d) Use the IR and NMR spectra to deduce the most likely structure of the compound. (3 marks)
The areas of the two peaks in the 1H NMR spectrum at 2.71 and 2.19 are in the ratio 2:3, respectively.
(Total = 9 marks)
Question 12/ 35 [VCAA 2018 SB Q3] A chemical that contains carbon, C, nitrogen, N, and hydrogen, H, in the ratio 4:1:11 is analysed using spectroscopy. (a) The infra-red (IR) spectrum of the chemical is shown below.
Data: SDBS Web, www.sdbs.ds.aist.go.ip, National Institute of Advanced Industrial Science and Technology In the table below, write the bond responsible for the wave numbers given. (1 mark) Wavenumber (cm−1)
Bond
2956 3376 (b) The mass spectrum of the chemical is shown below.
Data: SDBS Web, www.sdbs.ds.aist.go.ip, National Institute of Advanced Industrial Science and Technology (i) What is the molecular formula for the parent molecule? Justify your answer using information from the mass spectrum. (2 marks) (ii) Identify the fragment that produces the base peak. (1 mark) (iii) Draw the structural formulas for two possible structural isomers of the chemical, which are consistent with the mass spectrum and the IR spectrum. (2 marks) (c) The 13C NMR spectrum of the chemical is shown below.
Data: SDBS Web, www.sdbs.ds.aist.go.ip, National Institute of Advanced Industrial Science and Technology (i) Complete the following table using the 13C NMR spectrum. (2 marks) Chemical shift
Type of carbon
20.0 50.2 (ii) Draw the skeletal formula for the chemical, which is consistent with the IR spectrum, mass spectrum and 13C
NMR spectrum. (2 marks) (Total = 10 marks)
Question 13/ 35 [Adapted VCAA 2011 E1 SB Q2] (a) Bromine exists as two isotopes, 79Br and 81Br. The mass spectrum of bromoethane, C2H5Br, with two molecular ion peaks at m/z 108 and 110, is shown below.
(i) Identify the species that produces the peak at m/z = 29. (ii) What do the two molecular ion peaks indicate about the relative abundance of 79Br and 81Br? Give a reason for your answer. (1 + 2 = 3 marks) (b) There are two compounds that have the molecular formula C2H4Br2. The 1H NMR spectrum of one of these compounds is provided below.
(i) Draw the structural formula of each of the two compounds that have the molecular formula C2H4Br2. (ii) Which structure in part (i) corresponds to the 1H NMR spectrum provided? Justify your selection by referring to both the 1H NMR spectrum and to the structure of the compound. (2 + 3 = 5 marks) (Total = 8 marks)
Question 14/ 35 [VCAA 2013 SB Q9] An unknown organic compound, molecular formula C4H8O2, was presented to a spectroscopy laboratory for identification. A mass spectrum, infrared spectrum, and both 1H NMR (proton NMR) and 13C NMR spectra were produced. These are shown below and following. The analytical chemist identified the compound as ethyl ethanoate. A report was submitted to justify the interpretation of the spectra. The chemist's report indicating information about the structure provided by the 13C NMR spectrum has been completed for you. (a) Complete the rest of the report by identifying one piece of information from each spectrum that can be used to identify the compound. Indicate how the interpretation of this information justifies the chemist's analysis. Spectroscopic technique
Information provided
13C
The four signals in the 13C NMR spectrum indicate four different carbon environments, CH3COOCH2CH3 has four different carbon environments.
NMR spectrum
Mass spectrum
Spectroscopic technique Infrared spectrum 1H
NMR spectrum
(6 marks)
Information provided
(b) Another compound has the same molecular formula as ethyl ethanoate. However, the carbon 13C NMR spectrum of this compound shows only three signals. Draw a possible structure of this compound. (1 mark) (Total = 7 marks)
Question 15/ 35 [VCAA 2013 SB Q9] A small organic molecule has the molecular formula of the form CxHyO2Cl. A pH probe was inserted into a dilute aqueous solution of this compound and the pH was 4.5. The infrared spectrum, mass spectrum, 1H NMR spectrum and 13C NMR spectrum of this compound are provided below and following.
(a) On the infrared spectrum, label the peaks that correspond to the presence of two functional groups in this compound. Note: The peak due to the C-Cl stretch has been labelled. (2 marks) (b) Use the data provided to determine the values of x and y in CxHyO2Cl. (2 marks) (c) (i) What specific information about the structure of the compound is provided by the splitting pattern in the 1H NMR spectrum? (1 mark) (ii) Draw the complete molecular structure for this molecule. (1 mark) (d) Give a reason why the mass spectrum shows two molecular ion peaks at m/z = 108 and 110, rather than just one. (1 mark)
1H
NMR data
Chemical shift (ppm)
Peak splitting
Relative peak area
1.7
doublet (2 peaks)
3
4.5
quartet (4 peaks)
1
11.2
singlet (1 peak)
1
(Total = 7 marks)
Question 16/ 35 [VCAA 2017 SA Q5] There are a number of structural isomers for the molecular formula C3H6O. Three of these are propanal, propanone and prop-2-en-1-ol. The skeletal structure for the aldehyde propanal is as follows.
(a) (i) Write the semi-structural formula for the ketone isomer propanone. (1 mark) (ii) Draw the structural formula for the isomer prop-2-en-1-ol. (1 mark) (b) The mass spectrum on the following page was produced by one of the three named isomers of C3H6O. (i) Identify the fragment at 29 m/z. (1 mark) (ii) Name the isomer of C3H6O that produced this spectrum and justify your answer. (3 marks)
Data: SDBS Web, www.sdbs.db.aist.go.jp, National Institute of Advanced Industrial Science and Technology (c) Consider the 13C NMR and 1H NMR spectra below.
Data: SDBS Web, www.sdbs.db.aist.go.jp, National Institute of Advanced Industrial Science and Technology
Data: SDBS National Institute of Advanced Industrial Science and Technology Identify which one of the three named isomers of C3H6O produced these NMR spectra. Justify your answer by referencing both spectra. (3 marks) (Total = 9 marks)
Question 17/ 35 [VCAA 2019 SB Q8] An unknown organic compound contains carbon, hydrogen and oxygen. It is known that: • the compound does not contain carbon-to-carbon double bonds (C=C) • the molecular ion peak is found at a mass-to-charge ratio (m/z) of 74 • the 13C NMR has three distinct peaks. (a) A small peak in the mass spectrum can be identified at m/z = 75. Explain the presence of this peak. (1 mark) (b) (i) Use the information provided to give two possible molecular formulas for this compound. (2 marks) (ii) The 1H NMR spectrum of the compound shows three sets of peaks with a peak area ratio of 3:2:1. What does this information tell you about the structure of the compound and its molecular formula? Justify your answer by referring
to the information given about the peaks in the 1H NMR spectrum. (2 marks) (c) There are many structural isomers of this compound. Draw the structural formulas of two possible isomers. (2 marks) (d) The infra-red (IR) spectrum of the compound is shown below.
Data: SDBS Web, www.sdbs.db.aist.go.jp, National Institute of Advanced Industrial Science and Technology (i) Identify the functional groups responsible for the absorption peaks labelled A and B in the IR spectrum. (1 mark) A _______ B _______ (ii) Using the 1H NMR information given in part (b)(ii) and the IR spectrum provided above, draw the structural formula of the compound. (1 mark) (Total = 9 marks)
Question 18/ 35 [VCAA 2020 SB Q8] An unknown organic compound has a molecular formula of C4H8O. The compound is non-cyclic and contains a double bond. The infra-red (IR) spectrum of the molecule is shown below.
Data: SDBS Web, www.sdbs.db.aist.go.jp, National Institute of Advanced Industrial Science and Technology (a) What does the region 3100−4000 cm−1 indicate about the bonds in C4H8O? Give your reasoning. (2 marks) (b) The 13C NMR spectrum of the unknown compound has four distinct peaks. Draw two possible structural formulas of the unknown compound using the information provided. (2 marks) (c) The high-resolution 1H NMR spectrum of the unknown compound has three single peaks, as shown below.
Data: SDBS Web, www.sdbs.db.aist.go.jp, National Institute of Advanced Industrial Science and Technology Chemical Shift (ppm)
Relative peak area
1.82
3
3.53
3
3.85
2
Refer to the 1H NMR spectrum and the table of spectrum information provided. Identify three pieces of information about the unknown compound and indicate how each would assist in determining its structure. (3 marks) (Total = 7 marks)
Question 19/ 35 A simplified high-performance liquid chromatogram (HPLC) of a sample of standard grade petrol is shown below.
Some of the components labelled ‘I’ to ‘VI’ have been identified, as shown in the table below. Component
Name
Formula
I
Butane
C4H10
II
Hexane
C6H14
III
Benzene
C6H6
V
Trimethylpentane
C8H18
VI
Methylheptane
C8H18
(a) Two of the identified compounds are isomers. Name the two compounds and explain your choice. (2 marks) (b) One of the above compounds is not an alkane. Identify this compound and give a reason for your choice. (2 marks) (c) Suggest a likely formula for the component labelled ‘IV’. (1 mark) (d) When these compounds burn in an engine, the products are carbon dioxide and water. Write a balanced equation for the combustion of methylheptane. (2 marks) (Total = 7 marks)
Question 20/ 35 [VCAA 2021 SB Q7] Two students are given a homework assignment that involves analysing a set of spectra and identifying an unknown
compound. The unknown compound is one of the molecules shown below.
The 13C NMR spectrum of the unknown compound is shown below.
Data: SDBS Web, , National Institute of Advanced Industrial Science and Technology
(a) Based on the number of peaks in the 13C NMR spectrum above, which compound- P, Q, R, S or T - could be eliminated as the unknown compound? (1 mark) (b) The infra-red (IR) spectrum of the unknown compound is shown below.
Data: SDBS Web, , National Institute of Advanced Industrial Science and Technology Identify which of the five compounds can be eliminated on the basis of the IR spectrum. Justify your answer using data from the IR spectrum. (3 marks) (c) The mass spectrum of the unknown compound is shown below.
Data: SDBS Web, , National Institute of Advanced Industrial Science and Technology (i) Write the chemical formula of the species that produces a peak at m/z = 43. (1 mark) (ii) Define m/z as used in mass spectroscopy. (1 mark) (iii) Explain why one molecule can produce multiple peaks on a mass spectrum. (2 marks) (Total = 8 marks)
Question 21/ 35 The diagram below represents the equipment used in high-performance liquid chromatography.
(a) What function does the liquid phase perform? (1 mark) (b) How would a sample consisting of a mixture of solids be introduced into the equipment? (1 mark) (c) The size of the particles of the solid in the column is normally very small. Give one advantage and one disadvantage of using very small particles. (2 marks) (d) A mixture of liquid hydrocarbons was introduced into the equipment and part of the chromatogram is shown below.
Four of the hydrocarbons present in the mixture are heptane C7H16, hexane C6H14, nonane C9H20 and pentane C5H12. If the strength of the interaction between the solid in the column and the hydrocarbon increases with increasing molar mass of the hydrocarbon, then give the name of the hydrocarbon that is most likely to give the peaks A, B, C and D. A ___________ B ___________ C ___________ D ___________
(2 marks) (e) If octane, C8H18, had been present in the mixture, how would you expect the chromatogram to differ from the one shown? (2 marks) (Total = 8 marks)
Question 22/ 35 High-performance liquid chromatography has been used to measure the amount of nicotine in biological fluids. In one experiment, a sample of a biological fluid was divided into four equal parts (A, B, C and D). Pure nicotine was added to parts B, C and D to increase their nicotine concentrations by 100 ng/mL, 200 ng/mL and 300 ng/mL, respectively. Part A was not modified. The high-performance liquid chromatogram of each part was measured using the same conditions each time. The results for each part are shown below.
(a) How does the experimenter know that the peak being observed is due to nicotine? (1 mark) (b) Use the information above to deduce the concentration of nicotine in the biological fluid. (2 marks) (Total = 3 marks)
Question 23/ 35
[VCAA 2011 E1 SB Q3] Caffeine is a stimulant drug that is found in coffee, tea, energy drinks and some soft drinks. The concentration of caffeine in drinks can be determined using HPLC. Four caffeine standard solutions containing 50 ppm, 100 ppm, 150 ppm and 200 ppm were prepared. 25μL of each sample was injected into the HPLC column. The peak areas for the standard solutions were measured and used to construct the calibration graph shown below. The chromatograms of the standard solutions each produced a single peak at a retention time of 96 seconds.
25μL samples of various drinks thought to contain caffeine were then separately passed through the HPLC column. The results are summarised below. Sample
Retention time of major peak (seconds)
Peak area of largest peak
Soft drink A
96
12 000
Soft drink B
32
8 500
Espresso coffee
96
211 000
(a) Determine the caffeine content, in ppm, of soft drink A. (1 mark) The chromatograms of the 50 ppm standard caffeine solution, soft drink A, soft drink B and espresso coffee are shown below.
(b) What evidence is presented in the chromatogram that supports the conclusion that soft drink B does not contain any caffeine? (1 mark) (c) (i) Explain why the caffeine content of the espresso coffee sample cannot be reliably determined using the information provided. (1 mark) (ii) Describe what could be done to the espresso coffee sample so that its caffeine content can be reliably determined using the information provided.
(1 mark) (Total = 4 marks)
Question 24/ 35 [VCAA 2013 SB Q1] High-performance liquid chromatography is used to determine the amount of caffeine in a sample of a soft drink. The chromatogram below shows the detector response when a standard solution of caffeine with a concentration of 200 mg L−1 is measured using the instrument.
(a) What is the retention time of caffeine in this experiment? (1 mark) (b) On the chromatogram above, sketch the detector response when a commercial soft drink with a caffeine content of 350 mg L−1 is measured using the same instrument. (1 mark) (Total = 2 marks)
Question 25/ 35 [VCAA 2021 SB Q9] Aspartame is an ingredient in some soft drinks. Aspartame is unstable in some conditions and reacts to form four main products. One of the products of aspartame breakdown is 5-benzyl-3,6-dioxo-2-piperazineacetic acid (DKP). It is thought that DKP may be harmful to humans. A student, Kim, investigates the effect of storage temperature on the rate of production of DKP from aspartame in lemonade. Experimental data is obtained using high-performance liquid chromatography (HPLC) to analyse the aspartame and DKP content in lemonade samples. HPLC calibration
Kim first calibrated the HPLC using the following method: 1. Prepare and refrigerate a standard solution of pure aspartame with a concentration of 1000 mg L−1. 2. Transfer a 10.00 mL aliquot of the pure aspartame solution into a 1.000 L volumetric flask. 3. Fill the volumetric flask up to the 1.000 L mark with deionised water and shake the flask. 4. Inject a sample of the diluted aspartame solution into the HPLC to obtain a chromatogram. 5. Repeat steps 1−4 with DKP. The following two calibration chromatograms were obtained.
Analysis of lemonade samples Kim then followed the method given in steps 6−14 to investigate the rate of production of DKP from aspartame in lemonade at different storage temperatures. 6. Open a can of lemonade.
7. Transfer a 10.00 mL aliquot of lemonade from the can into a 1.000 L volumetric flask. 8. Fill the volumetric flask up to the 1.000 L mark with de-ionised water and shake the flask. 9. Inject a sample of the diluted lemonade into the HPLC using the same operating conditions used during calibration. 10. Set up three water baths at temperatures of 15 °C, 25 °C and 35 °C. 11. Put three unopened cans of lemonade into each of the three water baths. 12. After one day, take one can from each water bath and follow steps 6−9. 13. After two days, take one can from each water bath and follow steps 6−9. 14. After three days, take one can from each water bath and follow steps 6−9. One of the chromatograms from the diluted lemonade is given below.
(a) Using your knowledge of food chemistry, explain why aspartame is sometimes added to lemonade. (2 marks) (b) (i) What is the dependent variable? (1 mark) (ii) What steps, in addition to steps 1−14, need to be taken to use the HPLC data to measure the dependent variable? (3 marks) (c) (i) State a change to the operating conditions of the HPLC that could be made to reduce the errors in measuring the concentrations of aspartame and DKP. (1 mark) (ii) State how this change would reduce the measurement errors. (1 mark) Kim found that the can of lemonade tested at the beginning of the experiment contained: • 0.00178 M aspartame
• 0.00045 M DKP. Kim quantified the remaining data from the HPLC and prepared the following table. Storage temperature
Concentration after one day (M)
Concentration after two days (M)
Concentration after three days (M)
Aspartame
DKP
Aspartame
DKP
Aspartame
DKP
15 °C
0.00179
0.000430
0.00175
0.00042
0.00176
0.00041
25 °C
0.00175
0.00044
0.00172
0.00046
0.00171
0.00063
35 °C
0.00160
0.00051
0.00155
0.00049
0.00154
0.00058
(d) Write a conclusion based on the results given in the table above. (1 mark) (e) (i) Identify a variable that has not been controlled. (1 mark) (ii) Explain how the variable identified in part e.i. affects the validity of the experiment. (1 mark) (Total marks = 11 marks)
Question 26/ 35 There are many alcohol isomers with the formula C5H12O. (a) Draw semi-structural formulae for two of the isomers that contain a chiral carbon atom. Identify the carbon atom with a ‘*’. (4 marks) (b) For one of the isomers given in part (a), draw the structural formulae to show how the two optical isomers are related to each other. (2 marks) (Total = 6 marks)
Question 27/ 35 Two closely related nonapeptides are oxytocin and vasopressin. They have many amino acid residues in common but have very different functions. The sequence of amino acid residues in the two peptides are given below.
Oxytocin regulates two female reproductive functions, childbirth and breast feeding. Vasopressin helps prevent loss of water by reducing urine output and helps the kidneys re-absorb water. (a) List the differences in amino residues between the two nonapeptides. (2 marks) (b) In each nonapeptide, how are the two cysteine residues bonded together? (1 mark) (c) How many amide functional groups are in each oxytocin molecule? (1 mark) (d) What changes have followed from the variation in amino acid sequence that have led to the different properties of the two nonapeptides? (2 marks) (Total = 6 marks)
Question 28/ 35 Glycine, lysine and glutamic acid are three amino acids found in proteins. (a) 0.05 M aqueous solutions of each of these amino acids are prepared. Place the three solutions in order of increasing pH. Give an explanation for your answer. (3 marks) (b) When glycine reacts with lysine, apart from water, there are three possible products. Give the structures of these
three products. (3 marks) (Total = 6 marks)
Question 29/ 35 The structure of part of a protein is shown below.
(a) Circle any peptide links in this structure. (1 mark) (b) Draw the structural formulae of the three amino acids from which this part of the protein has been made. (3 marks) (c) What type of reaction is needed to convert the protein into its constituent amino acids? (1 mark) (d) Large protein molecules are usually twisted and folded into a unique shape that determines the function of the protein. Describe two ways in which the protein structure is maintained. (2 marks) (e) An amino acid found in many proteins has the molecular formula C3H7O3N. Draw the structural formula of this amino acid and name it. (2 marks) (Total = 9 marks)
Question 30/ 35 Alanine and lactic acid are two molecules that are found in many living systems. The structural formulae of these
molecules are shown below.
(a) Name the functional group present in both compounds. (1 mark) (b) When alanine reacts with lactic acid two different organic products are formed. (i) What type of reaction is most likely to occur between alanine and lactic acid? (1 mark) (ii) Draw the semi-structural formulae of these two products. (2 marks) (iii) For one of the substances given in part (ii), name the new functional group formed. (1 mark) (Total = 5 marks)
Question 31/ 35 [VCAA 2011 E1 SB Q8] Bradykinin is a peptide that lowers blood pressure. Diagram I shows the amino acid sequence of bradykinin.
Diagram II below shows the structure of a section of the bradykinin molecule.
(a) On diagram I, circle the section of bradykinin that is represented in diagram II. (1 mark) (b) Peptides can be completely hydrolysed to their component amino acids by treatment with 6 M HCl. Identify the two functional groups that are formed as a result of the hydrolysis of the peptide link. (2 marks) (c) Draw the chemical structure, showing all bonds, of the amino acid glycine as it would exist in solution at pH = 1. (1 mark) (Total = 4 marks)
Question 32/ 35 [VCAA 2014 SB Q7] Amino acids can be classified according to the nature of their side chains (Z groups). These may be polar, non-polar, acidic or basic. (a) Referring to the data book, name one amino acid that has a non-polar side chain and one amino acid that has an acidic side chain. (2 marks) The table below provides examples of different categories of side chains at a pH of 7. Name of amino acid
Structure of side chain of pH 7
alanine (Ala)
–CH3
asparagine (Asn)
–CH2–CO–NH2
aspartic acid (Asp)
–CH2COO−
cysteine (Cys)
–CH2–SH
lysine (Lys)
–CH2–CH2–CH2–CH2–NH3+
serine (Ser)
–CH2OH
(b) The tertiary structure of proteins is a result of the bonding interactions between side chains of amino acid residues. Use the information provided in the table to (i) identify the amino acid that is involved in the formation of disulfide bonds (sulfur bridges). (1 mark)
(ii) give an example of two amino acid side chains that may form hydrogen bonds between each other. (1 mark) (iii) give an example of amino acid side chains that may form ionic bonds (salt bridges) between each other. (1 mark) (iv) identify the type of bonding that exists between the side chains of two alanine residues. (1 mark) (c) The enzyme trypsin catalyses the breaking of peptide bonds in proteins. Trypsin is active in the upper part of the small intestine, where the pH is between 7.5 and 8.5. Trypsin is not effective in the stomach, where the pH is 4. Suggest a reason why. (1 mark) (Total = 7 marks)
Question 33/ 35 [VCAA 2013 SB Q3] Spider webs are very strong and elastic. Spider web silk is a protein that mainly consists of glycine and alanine residues. (a) Assuming that these amino acid residues alternate in a spider web, draw a section of the spider web protein that contains at least three amino acid residues. (2 marks) (b) What is the name of the bond between each amino acid residue? (1 mark) (c) What type of polymerisation reaction occurs in the formation of spider web silk? (1 mark) Glycine forms an ion at a pH of 6 that has both a positive and negative charge. (d) Draw the structure of a glycine ion at a pH of less than 4. (1 mark) (e) Describe the bonds that contribute to the spiral secondary structure of this protein. (2 marks) (Total = 7 marks)
Question 34/ 35 [Adapted VCAA 2015 SB Q6] After a murder had been committed, a forensic chemist obtained crime scene blood samples and immediately placed them in two sterile containers labelled Sample I and Sample II. The chemist discovered that Sample I contained a particular protein, which was analysed to reveal the following sequence of amino acid residues. -ser-gly-tyr (a) Referring to the data book, draw the structure of this sequence of amino acid residues and circle one amide link/peptide bond in your drawing. (3 marks) (b) The protein was hydrolysed in the presence of a suitable enzyme and the amino acid glycine was isolated. The glycine sample was then dissolved in a 0.1 M solution of sodium hydroxide. Draw the structure of glycine in this solution. (1 mark) (Total = 4 marks)
Question 35/ 35 Amaryllidaceae is a family of plants that grow from bulbs and are generally found in tropical regions. Many plants from the Amaryllidaceae family contain an organic compound called galanthamine, the structure of which is shown below.
(a) Circle and name one functional group found in galanthamine. (1 mark) (b) Acetylcholinesterase is an enzyme found within human neural tissue. This enzyme helps produce choline, a neural transmitter, in the simplified reaction shown: acetylcholine + H2O → choline + acetate Galanthamine can be used as a treatment for Alzheimer's disease, a degenerate neurological disease that slowly impacts memory in humans. Galanthamine works by slowing the rate of the above reaction through interacting with acetylcholinesterase. Provide an explanation for how galanthamine might slow the rate of the reaction. (2 marks) (c) Galanthamine is extracted from the bulbs and flowers using ethanol. This leaves a 0.10 % mixture of galanthamine in ethanol. The galanthamine must be isolated from the ethanol. (i) Explain how mixing the galanthamine mixture with a significant volume of water can be used to separate the galanthamine from the ethanol. (ii) Explain how distillation can be used to separate the galanthamine from the ethanol. (2 + 2 = 4 marks) (Total = 7 marks)
Question 1/ 5 The most commonly found amino acids have the general formula H2N–CHZ–COOH. For an amino acid with the molecular formula C4H7O4N, the formula of the group Z will be A. –CH(OH)CH3 B. –CH2OCH3 C. –CH2COOH D. –CH2CH2COOH
Question 2/ 5
Three amino acids are glycine (relative molecular mass = 75), alanine (relative molecular mass = 89) and serine (relative molecular mass = 105). The molar mass of the tripeptide formed when one molecule of each react together is A. 269 B. 251 C. 233 D. 215
Question 3/ 5 The following statements concern the amino acids isoleucine and leucine. I They can both react with acids and bases. II They are soluble in water and are present as zwitterions. III They are isomers. IV They react with each other to form one dipeptide. Which of these statements are correct? A. I, III and IV B. II, III and IV C. I, II and IV D. I, II, and III
Question 4/ 5 Three functional groups that are found in many naturally occurring compounds are I hydroxy, –OH II carboxylic acid, –COOH III amino, –NH2
These functional groups can react either with themselves or with each other. Which combination of groups will not react? A. I and I B. I and II C. II and III D. III and III
Question 5/ 5 Consider the following statements about enzymes. I An enzyme will usually increase the rate of one reaction or a few closely related reactions. II The shape of the active site of an enzyme determines which molecule or molecules will undergo reaction. III Enzymes can function effectively over a wide range of temperatures. IV All proteins are enzymes but only some enzymes are proteins. V Enzymes are more effective than other catalysts at increasing the rate of a reaction. Which of the above statements are correct? A. I, II and V B. II, III and IV C. I, III and IV D. I, IV and V
Question 6/ 5 Fats, carbohydrates and proteins are important molecules for many living organisms. Moderate amounts of sulfur occur in A. fats. B. carbohydrates.
C. proteins. D. none of these substances.
Question 7/ 5 2.00 g of each of four carboxylic acids is added to four separate containers. Enough water is added to dissolve the four acids. The names, semi-structural formulas and molar masses of the four acids are given in the table below. Name
Semi-structural formula
Ethanoic acid
CH3COOH
60.1
Butanoic acid
CH3CH2CH2COOH
88.1
Oxalic acid
HOOC–COOH
90.0
Citric acid
HO–C(COOH)(CH2COOH)2
192.0
Molar mass (g mol−1)
The acid that requires the largest volume of 0.15 mol L−1 sodium hydroxide solution for complete reaction is A. ethanoic acid. B. butanoic acid. C. oxalic acid. D. citric acid.
Question 8/ 5 [VCAA 2022 SA Q7] In a protein, hydrogen bonding takes place during the formation of the A. secondary, tertiary and quaternary structures only. B. primary, secondary and tertiary structures only. C. tertiary and quaternary structures only. D. primary and tertiary structures only.
Question 9/ 5 [VCAA 2022 SB Q28] The 13C NMR spectrum of an organic compound is shown below.
Data: SDBS Web, , National Institute of Advanced Industrial Science and Technology The organic compound could be
A. B.
C.
D.
Question 10/ 5 (a) Name the five elements that are often found in proteins. (2 marks) (b) Part of a polypeptide chain is represented below.
Draw the structures of the amino acids that were used to make this part of the polypeptide. (2 marks) (Total = 4 marks)
Question 11/ 5 Part of the mass spectrum of bromoethane, CH3CH2Br, is shown in the sketch below.
There are two naturally occurring isotopes of bromine whose details are shown below. Isotope
Relative isotopic mass
Relative abundance (%)
79Br
78.92
50.5
81Br
80.92
49.5
(a) The relative molecular mass of bromoethane is 109 but there is no peak with this mass to charge ratio in the mass spectrum. Give an explanation for this observation. (Assume that carbon is 100% 12C and hydrogen is 100% 1H.) (2 marks) (b) Suggest possible formulas for the peaks observed at 93 and 95 m/z in the mass spectrum. How might these particles have been formed? (3 marks) (c) The mass spectrum of bromoethane also shows a strong peak at 29 m/z. Suggest a formula for the species responsible for this peak. (1 mark) (Total = 6 marks)
Question 12/ 5 White wines contain a number of different organic acids. Four of these acids are citric acid, C3H5O(COOH)3, tartaric acid, (CH(OH)COOH)2, lactic acid, CH3CH(OH)COOH and malic acid, HOOCCH2CH(OH)COOH. 25.00 mL of a particular wine is diluted to 50.00 mL in a volumetric flask. HPLC is used to examine the acids present in this solution of wine. The result is shown in the diagram below. Only two of the peaks have been labelled.
For tartaric acid, a calibration curve is obtained by recording the detector response for varying concentrations of tartaric acid. The calibration curve is shown below. (a) Use the graph to determine the concentration of tartaric acid in the wine sample. (2 marks)
After the primary fermentation, in which glucose is converted into ethanol, winemakers often use a secondary fermentation to convert most of the tart tasting malic acid into the softer tasting lactic acid. The reaction is shown below.
At the completion of this reaction, the winemaker takes another sample of the wine, treats it the same way as the first sample and examines it by HPLC. The result is shown below.
(b) Use the two HPLC results to identify peaks 3 and 4. (1 mark) (c) Calculate the percentage of malic acid that has been converted into lactic acid. (1 mark) (d) What effect will the malolactic fermentation have on the pH of the wine? Explain your answer. (2 marks) (Total = 6 marks)
Question 13/ 5 [VCAA 2022 SB Q5] A chemist uses spectroscopy to identify an unknown organic molecule, Molecule J, that contains chlorine. The 13C
NMR spectrum of Molecule J is shown below.
Data: SDBS Web, , National Institute of Advanced Industrial Science and Technology (a) There are two possible carbon environments that can produce the peak at 168 ppm. Identify one of the two possible carbon environments that can produce the peak at 168 ppm. (1 mark) The infra-red (IR) spectrum of Molecule J is shown below.
Data: SDBS Web, , National Institute of Advanced Industrial Science and Technology
(b) Name the functional group that produces the peak at 168 ppm in the 13C NMR spectrum above, which is consistent with the IR spectrum shown above. Justify your answer with reference to the IR spectrum. (2 marks) The mass spectrum of Molecule J is shown below.
Data: SDBS Web, , National Institute of Advanced Industrial Science and Technology (c) The molecular mass of Molecule J is 108.5 (i) Explain the presence of the peak at 110 rn/z. (1 mark) (ii) Explain how the peaks in the mass spectrum relate to the molecular mass of Molecule J. (2 marks) The 1H NMR spectrum of Molecule J is shown below.
Data: SDBS Web, , National Institute of Advanced Industrial Science and Technology (d) The 1H NMR spectrum consists of two singlet peaks. What information does this give about the molecule? (2 marks) (e) Draw a structural formula for Molecule J that is consistent with the information provided in parts (a)–(d). (2 marks) (Total = 10 marks)
Question 14/ 5 [Adapted VCAA 2017 SB Q3] Glucagon is a peptide hormone that works with insulin to help regulate blood glucose levels. Glucagon acts to increase blood glucose levels through targeted action on the polysaccharide stored in the liver. Glucagon consists of a chain of 29 amino acids, the sequence of which is given below, and folds to form a short alpha-helix.
(a) Draw a diagram of the structure of the section of the glucagon peptide shown in the box in the amino acid sequence above.
(3 marks) (b) Describe the bonding that is found in the primary and secondary structures of the glucagon molecule. (3 marks) (Total = 6 marks) Total marks for test = 41 marks
Chapter 6: Unit 4 Area of Study 3 – Practical investigation Question 1/ 10 [VCAA 2019 SA Q22] Which one of the following statements about conducting an experiment is the most correct? A. Precise results may be biased. B. Accuracy is assured if sensitive instruments are used. C. A method is valid if it identifies all controlled variables. D. Repeating a procedure will remove the uncertainty of the results.
Question 2/ 10 [VCAA 2020 SA Q2] Using large sample sizes in an experiment increases A. reliability. B. precision. C. validity.
D. uncertainty.
Question 3/ 10 [VCAA 2018 SA Q6] Ethoxyethane, C2H5OC2H5, is commonly used as a solvent in the purification of compounds. The boiling point of C2H5OC2H5 is 36°C. The safety data sheet for C2H5OC2H5 states: ‘Extremely flammable. Keep away from sources of ignition.’ During the purification process, a compound is dissolved in C2H5OC2H5 by heating it for an extended period of time. This is done using glassware that is open to the atmosphere. This step in the purification process should be carried out using a A. water bath in a fume cupboard. B. water bath on a laboratory bench. C. Bunsen burner in a fume cupboard. D. Bunsen burner on a laboratory bench.
Question 4/ 10 [VCAA 2017 SA Q23] The heat of combustion of a sample of crude oil is to be determined using a bomb calorimeter. All of the students in a class are given the same method to follow. The apparatus used by the students is shown below.
For this experiment, the students could maximise A. precision by using a digital thermometer ±0.2°C. B. validity by calculating the heat of combustion per mole. C. accuracy by taking samples from three different sources. D. uncertainty by having all students closely follow the same experimental procedure.
Question 5/ 10 [VCAA 2012 E2 SA Q1] A solvent has the following risk statement printed on its label. ‘Inhalation of fumes may cause dizziness.’ To minimise the risk associated with the effects of exposure when using this solvent, a student should A. use gloves. B. wear a laboratory coat. C. keep the solvent away from flames. D. use the solvent in a well-ventilated area.
Question 6/ 10 [VCAA 2013 SA Q1] Consider the following. ‘Calculate the pressure exerted by 6.9 g of argon in a 0.07500 L container at 11.5 °C.’ The number of significant figures that should be expressed in the answer is A. 2 B. 3 C. 4 D. 5
Question 7/ 10 [VCAA 2017 SA Q19] A Year 12 Chemistry assignment requires students to quantitatively and qualitatively compare fossil fuels and biofuels. Which one of the following investigations would be most appropriate for this comparison? A. Use a bomb calorimeter to determine the heat of combustion for both fossil fuels and biofuels. B. Interview car owners to determine what petrol price would make them consider using biofuels. C. Produce biodiesel from vegetable oil and compare the viscosity of the biodiesel produced with that of a range of fossil fuels. D. Find reliable information about the environmental impacts of producing fossil fuels and biofuels, and the amount of carbon dioxide produced per litre from the combustion of these fuels.
Question 8/ 10
[VCAA 2021 SA Q10] A student hypothesised that polishing the zinc, Zn, electrode in an Fe-Zn galvanic cell would increase the current produced by the cell. What would be the most valid method of testing this hypothesis? A. researching the scientific literature to determine how polishing changes the structure of Zn B. measuring the conductivity of a Zn electrode after polishing it C. measuring the change in mass per unit time of the Fe electrode in the same Fe-Zn galvanic cell before and after the Zn electrode was polished D. measuring the current produced by two different Fe-Zn galvanic cells, one using a polished Zn electrode and the other using an unpolished Zn electrode
Question 9/ 10 [VCAA 2022 SA Q1] Scientific posters communicate the findings of scientific investigations. Which section of a scientific poster should explain the reason for undertaking an investigation? A. discussion B. conclusion C. introduction D. methodology
Question 10/ 10 [VCAA 2022 SA Q5] Scientists often repeat trials of an experiment using the same experimental method and the same equipment. Which one attribute of experimental data will be improved when there is an increase in the number of times that a trial is repeated? A. bias B. validity
C. accuracy D. reliability
Question 1/ 7 [VCAA 2020 SB Q9] A student decided to investigate the effect of temperature on the rate of the following reaction. 2HCl(aq) + CaCO3(aq) → CaCl2(aq) + H2O(l) + CO2(g) Part of the student's experimental report is provided below.
Effect of temperature on the rate of production of carbon dioxide gas
Aim
To find out how temperature affects the rate of production of carbon dioxide gas, CO2, when a solution of hydrochloric acid, HCl, is added to chips of calcium carbonate, CaCO3
Method
1. Put 0.6 g of CaCO3 chips into a conical flask. 2. Put a reagent bottle containing 2 M HCl into a water bath at 5 °C. 3. When the temperature of the HCl solution has stabilised at 5 °C, use a pipette to put 10.0 mL of the HCl solution into the conical flask containing the CaCO3 chips. 4. Put a balloon over the conical flask and begin timing. 5. When the top of the balloon has inflated so that it is 10 cm over the conical flask, stop timing and record the time. 6. Repeat steps 1−5 using temperatures of 15 °C, 25 °C, 35 °C and 45 °C.
Results
(a) What does the student need to do to ensure that they comply with all applicable safety guidelines during the investigation? (2 marks) (b) What is the independent variable? (1 mark) (c) What is the dependent variable and how is it measured? (2 marks) (d) (i) Predict the relationship between the independent variable and the dependent variable. Explain your prediction. (3 marks) (ii) Is the graph of the student's results consistent with your prediction? Give your reasoning. (1 mark) (e) Identify two ways in which the graph could have been presented differently to better illustrate the relationship between the independent variable and the dependent variable. (2 marks) (f) Identify two changes that could be made to the experimental method to improve the precision of the results if the
experiment was repeated. For each change, explain how it would improve precision. (2 marks) (Total = 13 marks)
Question 2/ 7 [VCAA 2019 SB Q9] A student designed an experiment to investigate current efficiency during the electrolysis of a sodium chloride, NaCl, solution. Current efficiency is the amount of product produced, expressed as a percentage of the theoretical amount of product, calculated using Faraday's law. When the products of an electrolysis are gases, current efficiency can be calculated using the following.
current efficiency =
volume of gas produced
volume of gas expected based on Faradays law
× 100
All experimental work was carried out under standard laboratory conditions (SLC). The experiment involved the use of a Hoffman electrolysis apparatus. The following is the first section of the student's report.
What is the effect on current efficiency during electrolysis when the concentration of a sodium chloride, NaCl, solution is changed? Aim To investigate the effect on current efficiency during electrolysis when the concentration of a sodium chloride, NaCl, solution is changed Procedure Step 1: Rinse the Hoffman electrolysis apparatus with distilled water. Step 2: Fill the Hoffman electrolysis apparatus with distilled water so that the bottom of the meniscus in both tubes is level with the 170 mL mark. Step 3: Connect the power supply and ammeter to the electrodes of the Hoffman electrolysis apparatus. Step 4: Turn on the power supply and start timing. Record the current displayed on the ammeter. Step 5: After five minutes turn off the power supply and record the volume level on each of the tubes. Step 6: Repeat steps 2−5 four times. Step 7: Average the readings of the initial and final volumes at each electrode and current readings.
Step 8: Repeat steps 1−7 using 1.5 M NaCl solution instead of distilled water. Step 9: Repeat steps 1−7 using 4 M NaCl solution instead of distilled water.
(a) Identify the dependent variable. (1 mark) (b) (i) Identify a safety risk associated with the chemicals produced during the experiment. (1 mark) (ii) What are the safety measures required to reduce the safety risk identified in part b.i.? (1 mark) A diagram of the Hoffman electrolysis apparatus, correctly filled as required in Step 2, is shown below.
The results for steps 1−7 of the procedure are given in Part 1 below. Part 1 – Distilled water
Trial
Initial volume (mL)
Final volume (mL)
Current (A)
Negative electrode
Positive electrode
Negative electrode
Positive electrode
1
170.0
170.0
100.2
135.3
2.0
2
170.0
170.0
100.3
135.3
2.0
3
170.0
170.0
99.9
135.0
2.0
4
170.0
170.0
99.8
134.8
2.0
5
170.0
170.0
100.1
135.1
2.0
Average
170.0
170.0
100.1
135.1
2.0
(c) Are the results in Part 1 precise? Justify your answer. (1 mark) (d) Write the half-equation for the reaction that would be expected to be observed at the negative electrode. (1 mark) (e) (i) Calculate the volume of gas expected at the negative electrode for Part 1 of the experiment using Faraday's law. (3 marks) (ii) Calculate the current efficiency for Part 1 of the experiment. (1 mark) The results for steps 8 and 9 of the procedure are given in Part 2 and Part 3. Part 2 – 1.5 M NaCl (Step 8 of the procedure) Trial
Average
Initial volume (mL)
Final volume (mL)
Negative electrode
Positive electrode
Negative electrode
Positive electrode
170.0
170.0
98.0
133.2
Current (A)
2.0
Part 3 – 4 M NaCl (Step 9 of the procedure) Trial
Average
Initial volume (mL)
Final volume (mL)
Negative electrode
Positive electrode
Negative electrode
Positive electrode
170.0
170.0
95.2
100.0
(f) What conclusion can be drawn from the results for parts 1, 2 and 3? Give your reasoning. (2 marks)
Current (A)
2.0
(g) State the change the student should make to their experimental design to ensure they achieve their aim. Justify your answer. (2 marks) (h) Scientists may use scientific posters to convey their research results to other scientists. State two different aspects of the electrolysis experiment that the student should include in the discussion section of their scientific poster. (2 marks) (Total = 15 marks)
Question 3/ 7 [VCAA 2019 SB Q9] A group of students designed and carried out an experiment to investigate if tartaric acid, C4H6O6, that was bought commercially is 99% pure, as claimed by the manufacturer. The experiment involved titrating C4H6O6 with sodium hydroxide, NaOH, solution, calculating the percentage purity of C4H6O6 and comparing the experimental value to the manufacturer's stated value. Part of the report submitted by one of the students is shown below.
Research Tartaric acid is a diprotic acid that occurs naturally in grapes and other fruit.
Equation for reaction C4H6O6(aq) + 2NaOH(aq) → Na2C4H4O6(aq) + 2H2O(l) Aim To determine the percentage purity of the commercial sample of tartaric acid by titration to verify the stated value of 99.0% Calculations of predicted titre, in mL 30 [C4H6O6] solution = 150
×
1 −1 0.50 = 0.40 mol L
n(C4H6O6) in 10.00 mL = 0.40×10 1000 = 0.0040 mol
n(NaOH) = 2 × n(C4H6O6) = 0.0080 mol V(NaOH) titre = 0.0080 0.5 = 0.016 L = 16.00 mL Method Part A – Preparation of tartaric acid solution 1. Purchase tartaric acid, C4H6O6, powder. 2. Prepare a solution of C4H6O6 by accurately measuring 30.0 g of the powder, placing it in a 500.00 mL volumetric flask and then making it up to 500.00 mL with de-ionised water. Part B – Titration 1. Collect stock solution of 0.5 M sodium hydroxide, NaOH, and use this to fill a burette. 2. Deliver a 10.00 mL aliquot of C4H6O6 solution into a conical flask. Add four drops of phenolphthalein indicator. 3. Carefully titrate 0.5 M NaOH into the C4H6O6 solution until a permanent pink colour remains. 4. Record the volume of the titre. 5. Repeat the titration until concordant titres are obtained. Results Trial number
Volume of aliquot of C4H6O6 (mL)
Volume of titre of NaOH (mL)
1
10.00
14.96
2
10.00
14.81
3
10.00
14.70
4
10.00
14.76
5
10.00
14.79
Calculations Average titre = 14.81+14.76+14.79 = 14.79 mL 3 n(NaOH) = 0.5 × 0.01479 mol = 0.00749 n(C4H6O6) = 12 × n(NaOH) = 0.00749 2 = 0.00370 mol in 10.00 mL of C4H6O6 solution Percentage purity actual n % purity of C4H6O6 = predicted n
Conclusion
× 100 =
0.0037 0.0040
× 100 = 92.5%
Through direct titration of tartaric acid with sodium hydroxide solution, the percentage purity of the commercial supply of tartaric acid was found to be 92.5%. This is less than the stated value of 99% purity. Consequently, the manufacturer's claim is wrong.
(a) Name the independent variable in this experiment. (1 mark) (b) Identify a controlled variable in this experiment and state why it is important for this variable to be controlled. (2 marks) (c) Is the value the student used for the average titre in the ‘Calculations’ section above appropriate? Explain your reasoning. (2 marks) (d) Consider the method undertaken by the student in this experiment to determine the percentage purity of C4H6O6 powder. Identify how specific steps in the method affect the accuracy and reliability of the data. (4 marks) (e) Identify a limitation of the student's conclusion. How could this limitation be addressed? (2 marks) (f) The material safety data sheet (MSDS) for C4H6O6 powder includes the statement below: ‘Warning! This product causes eye, skin and respiratory tract irritation.’ Apart from a laboratory coat, what personal protective equipment (PPE) should be used by the students in each of the following situations? (i) Preparing the C4H6O6 solution (ii) Conducting the titration (2 marks) (Total = 13 marks)
Question 4/ 7 [VCAA 2014 SB Q12] A student investigated the effect of different catalysts on the molar enthalpy of the decomposition reaction of hydrogen peroxide. The student's report is provided below.
Report – Effect of different catalysts on the enthalpy of a reaction Background Different catalysts, such as manganese dioxide, MnO2, and iron(III) nitrate solution, Fe(NO3)3, will increase the rate of decomposition of hydrogen peroxide. 2H2O2(aq) → 2H2O(l) + O2(g) Purpose This experiment investigated the effect of using different catalysts on the molar enthalpy of the decomposition of hydrogen peroxide. Procedure The temperature change was measured when MnO2 catalyst was added to a volume of hydrogen peroxide in a beaker. The procedure was repeated using Fe(NO3)3 solution as a catalyst. Results
Volume H2O2 Concentration H2O2 Catalyst Temperature change °C
Trial 1
Trial 2
100 mL
200 mL
2.0 M
4.0 M
0.5 g MnO2
50 mL 0.1 M Fe(NO3)3
3.0
10.1
Conclusion The change in temperature using the Fe(NO3)3 catalyst was greater than the change in temperature using the MnO2 catalyst. This demonstrates that the molar enthalpy for the decomposition reaction depends on the catalyst used.
The student’s conclusion is not valid because the experimental design is flawed. Critically review the student’s experimental design. In your response, you should: • identify and explain three improvements or modifications that you would make to the experimental design • discuss the experimental outcomes you would expect regarding the effect of different catalysts on molar heats of reaction. Justify your expectations in terms of chemical ideas you have studied this year. (Total = 5 marks)
Question 5/ 7 [VCAA 2016 SB Q11] A student investigated the electroplating of a metal with nickel. The following is her report.
Aim To investigate whether Faraday’s laws apply to the electroplating of a brass key with nickel Procedure Step 1 – The apparatus was set up as in the diagram below. The electrolyte solution was supplied. The brass key was sanded, weighed and placed in the solution, as shown below.
Step 2 – The current was turned on for exactly 20 minutes. The current and voltage were measured when the power was turned on. Step 3 – The key was removed from the solution, patted dry with a paper towel and weighed. Steps 1−3 were repeated for two more keys. Results Three trials of the experiment were conducted, X, Y and Z. Trial
Initial mass of brass key (g)
Final mass of brass key (g)
X
2.774
2.907
0.133
0.52
2.4
Y
3.068
3.269
0.201
0.54
2.2
Z
3.122
3.310
0.188
0.50
1.9
Predicted mass for Trial X using Faraday’s laws
m(Ni) = Conclusion
0.52×20×60 96500
×
58.7 2
= 0.19 g
Mass of nickel deposit (g)
Current (A)
Voltage (V)
Faraday’s laws apply to the electroplating of a brass key with nickel.
Evaluate the student’s experimental design and report. In your response: • identify and explain one strength of the experimental design • suggest two improvements or modifications that you would make to the experimental design and justify your suggestions • comment on the validity of the conclusion based on the results obtained. (Total = 7 marks)
Question 6/ 7 [VCAA 2018 SB Q9] A Chemistry class conducted a practical investigation to determine the calibration factor of a calorimeter using two different methods: electrical and chemical. Each student compared the results from the two different methods and presented the investigation as a scientific poster. The materials, set-up and methods used by the students are shown below. Materials calorimeter
ammeter
DC power supply
voltmeter
5 × wire leads
3 g potassium nitrate (KNO3)
thermometer
electronic balance
stopwatch
measuring cylinder
Methods Electrical method for collecting calibration data 1. Add 100 mL of water to the calorimeter. Stir the water and record its temperature every 30 seconds for several minutes. 2. Apply a voltage of 6 V for three minutes. Stir throughout and record the temperature every 30 seconds. 3. Record the voltage and the current while the water is heating. 4. Once the power is turned off, continue to stir the water and record the temperature every 30 seconds for a further three minutes. Chemical method for collecting calibration data 1. Measure 3.0 g of KNO3 accurately. 2. After completing the electrical calibration, add the KNO3 to the calorimeter. 3. Stir and record the temperature every 30 seconds. Student A wrote the following aim.
Student A Aim To compare the calibration factors obtained from two different methods The calibration factors were found by recording the temperature change of a solution resulting from the addition of a measured electrical input and from potassium nitrate dissolving in water.
(a) The dependent variable in this investigation is the calibration factor. Identify the independent variable from Student A’s aim.
(1 mark) (b) Identify one systematic error that applies only to the electrical method of calibration. (1 mark) (c) Identify one limitation of the chemical method of calibration, given on the previous page. Explain how it could affect the reliability of the results. (2 marks) (d) Examine the graphs below prepared by Student A and Student B for the temperature change during electrical calibration.
Student A Results – Electrical method of calibration voltage = 5.8 V current = 1.6 A
Student B Results – Electrical method of calibration voltage = 5.8 V current = 1.6 A
Identify one difference in the results between the students’ graphs and suggest what variation in the students’ experiments might account for this difference. (2 marks) Student B’s data for the chemical method of calibration is shown in the graph below.
Student B Results – Chemical method of calibration Below is the chemical equation and enthalpy used to calculate the calibration factor for the chemical method. H2O KNO3(s) → K+(aq) + NO3−(aq) ΔH = 35 kJ mol−1
Use this data to calculate the calibration factor, in J °C−1, for the chemical method of calibration. (3 marks) (Total = 9 marks)
Question 7/ 7 [VCAA 2022 SB Q8] A student wrote the following partial experimental report. Experimental report
Introduction Wine is made from grapes containing sugars that are fermented by bacteria to produce ethanol. If a bottle of wine is left open, the ethanol will oxidise. Aim To investigate how the oxidation rate of ethanol in white wine from a freshly opened bottle is affected by the concentration of ethanol in the wine Method
Open a bottle of white wine and prepare samples in four beakers according to Part I below. Then, determine the acidity of the samples in each beaker after two weeks using the method described in Part II. Part I – Beaker preparation Prepare four different beakers. 1. Put a clean and dry 250 mL beaker on a balance. 2. Zero the balance and add 250.00 g of wine to the beaker. 3. Remove the first beaker from the balance and put a second 250 mL beaker on the balance. 4. Zero the balance and add 245.00 g of wine to the beaker. 5. Zero the balance and add 5.00 g of pure ethanol to the beaker. 6. Repeat steps 4 and 5 with different amounts of wine and ethanol for Beaker 3 and Beaker 4, as shown in Table 1. Table 1 Mass of wine added to beaker (g)
Mass of pure ethanol added to beaker (g)
Total mass of contents (g)
Beaker 1
250.00
0.00
250.00
Beaker 2
245.00
5.00
250.00
Beaker 3
240.00
10.00
250.00
Beaker 4
235.00
15.00
250.00
7. Cover each of the four beakers with a watch glass and leave the covered beakers on a bench in an unused corner of the laboratory for two weeks. Part II – Acid–base titrations 1. Rinse a clean and dry burette with a freshly standardised solution of 0.0100 M sodium hydroxide, NaOH. 2. Fill the burette with more of the freshly standardised solution of NaOH. 3. Flush about 5 mL of the NaOH through the burette and into a waste beaker to remove any air bubbles. 4. Rinse a clean conical flask with distilled water. 5. Rinse a 25.00 mL pipette using a small amount of the contents of Beaker 1. 6. Use the rinsed pipette to transfer 25.00 mL of the contents of Beaker 1 to the rinsed conical flask. 7. Add two drops of phenolphthalein indicator to the conical flask. 8. Note the initial volume reading on the burette.
9. Slowly add the NaOH from the burette to the conical flask, swirling to mix. As soon as the colour permanently changes, stop adding NaOH and note the final volume reading on the burette. 10. Calculate the titre. 11. Repeat steps 4 to 10 to obtain three concordant titres for Beaker 1. Refill the burette as necessary. 12. Repeat steps 2 to 11 for Beaker 2, Beaker 3 and Beaker 4.
(a) State how the precision of the experimental data will be affected by the acid–base titration method specified in Part II. (1 mark) Immediately after the bottle was opened, an experienced and qualified laboratory technician analysed a sample of the wine and found that: • the wine contained 8.12% m/m ethanol • the concentration of acid in the sample was 9.45 × 10−4 M (assuming a monoprotic acid). (b) Use the laboratory technician’s results and the information given in Table 1 above to calculate the initial ethanol concentration of the ethanol–wine mixture in Beaker 2 in % m/m. (3 marks) (c) What is the independent variable in the student’s investigation? (1 mark) (d) At Step 5 of Part II above, the student mistakenly rinsed the pipette with distilled water instead of a small amount of the contents of the beaker. Explain how this change would affect the student’s calculated value for the concentration of a monoprotic acid in the sample. (2 marks) (e) State why analysing the acidity of the wine in beakers 1, 2, 3 and 4 can be related to the oxidation of ethanol in the wine in each beaker. (1 mark) The student obtained the following results. Table 2 Titre 1 (mL)
Titre 2 (mL)
Titre 3 (mL)
Titre 4 (mL)
Titre 5 (mL)
Beaker 1
23.65
24.54
24.64
24.59
Beaker 2
21.32
24.55
22.25
21.25
21.30
Beaker 3
3.55
2.60
4.45
2.65
2.58
Beaker 4
1.80
2.45
2.75
2.65
2.85
Titre 6 (mL)
2.72
(f) (i) Write a conclusion relating to the oxidation rate of ethanol, which is consistent with the student’s results in Table 2. (1 mark) (ii) Discuss your conclusion in relation to the white wine tested in this experiment. In your answer, make two points relating to one or both of the following: • the limitations of your conclusion • an explanation for the student’s findings. (2 marks) (Total = 11 marks)
Chapter 7: End of Year trial paper Question 1/ 30 [VCAA 2020 SA Q8] Which one of the following is the most correct statement about fuel cells and secondary cells? A. Fuel cells can be recharged like secondary cells. B. Fuel cells produce thermal energy, whereas secondary cells do not produce thermal energy. C. The anode in a fuel cell is positive, whereas the anode in a secondary cell is negative. D. Fuel cells deliver a constant voltage during their operation, whereas secondary cells reduce in voltage as they discharge.
Question 2/ 30 [VCAA 2012 E2 SA Q13] 1.30 g of glucose (Mr = 180 g mol−1 and ΔH = −2816 kJ mol−1) underwent complete combustion. The energy released was used to heat an unknown mass of water. If the temperature of the water increased by 24.3°C and it is
assumed no heat was lost, the mass of the water heated was A. 2.00 × 10−1 g B. 1.02 × 102 g C. 2.00 × 102 g D. 3.84 × 103 g
Question 3/ 30 Use the following information to answer Questions 4 and 5. The following reaction is used in some industries to produce hydrogen. CO(g) + H2O(g) ⇌ CO2(g) + H2(g); ΔH = −41 kJ mol−1
Question 4/ 30 [VCAA 2012 E2 SA Q9] Carbon monoxide, water vapour, carbon dioxide and hydrogen were pumped into a sealed container that was maintained at a constant temperature of 200°C. After 30 seconds, the concentration of gases in the sealed container was found to be [CO] = 0.1 M, [H2O] = 0.1 M, [H2] = 2.0 M, [CO2] = 2.0 M. The equilibrium constant at 200°C for the above reaction is K = 210. Which one of the following statements about the relative rates of the forward reaction and the reverse reaction at 30 seconds is true? A. The rate of the forward reaction is greater than the rate of the reverse reaction. B. The rate of the forward reaction is equal to the rate of the reverse reaction. C. The rate of the forward reaction is less than the rate of the reverse reaction. D. There is insufficient information to allow a statement to be made about the relative rates of the forward and reverse reactions.
Question 5/ 30 [VCAA 2012 E2 SA Q10] The reaction between carbon monoxide and water vapour is carried out in a sealed container. The equilibrium yield of hydrogen will be increased by A. an increase in pressure at constant temperature. B. a decrease in temperature. C. the addition of an inert gas at constant temperature. D. the use of a suitable catalyst at constant temperature.
Question 6/ 30 [VCAA 2012 E2 SA Q19] Which one of the following statements is true for both galvanic cells and electrolytic cells? A. Reduction occurs at the negative electrode in both cells. B. Reduction occurs at the cathode in both cells. C. Anions migrate to the cathode in both cells. D. The anode is positive in both cells.
Question 7/ 30 [VCAA 2011 E1 SA Q10] Biogas can be generated as a by-product of many farming activities. Waste waters often contain sugars, such as glucose, which can be converted to methane. A simplified reaction sequence is given below. Step 1 fermentation: C6H12O6(aq) → 2CH3CH2OH(aq) + 2CO2(g) Step 2 oxidation:
CH3CH2OH(aq) + O2(aq) → CH3COOH(aq) + H2O(l) Step 3 neutralisation: 2CH3COOH(aq) + CaCO3(s) → Ca(CH3COO)2(aq) + CO2(g) + H2O(l) Step 4 bacterial conversion: Ca(CH3COO)2(aq) + H2O(l) → 2CH4(g) + CO2(g) + CaCO3(s) The ratio of the volume of methane produced to volume of carbon dioxide produced in the overall process is A. 1:1 B. 1:2 C. 2:1 D. 2:3
Question 8/ 30 [VCAA 2015 SA Q16] Consider the following energy profile for a particular chemical reaction, where I, II and III represent enthalpy changes during the reaction.
Which one of the following statements is correct? A. The activation energy for the reverse reaction is (III–II). B. The net energy released for the forward reaction is represented by II. C. The energy required to break the reactant bonds is represented by II. D. The energy released by the formation of new bonds is represented by I.
Question 9/ 30 [VCAA 2015 SA Q6] In which one of the following compounds is sulfur in its lowest oxidation state? A. SO3 B. HSO4− C. SO2 D. Al2S3
Question 10/ 30 [VCAA 2015 SA Q27] Which one of the following classes of electrochemical cells involves only a non-spontaneous redox reaction? A. fuel cells B. electroplating cells C. primary galvanic cells D. secondary galvanic cells
Question 11/ 30 [Adapted VCAA 2019 SA Q5] At the start of the day, a student set up a galvanic cell using two electrodes: nickel, Ni, and metal X. This set-up is shown in the diagram below.
Consider the following alternative metals that could be used to replace metal X: 1. zinc, Zn 2. lead, Pb 3. cadmium, Cd 4. copper, Cu At the end of the day, the student checked the colour of the solution in Half-cell 1 and observed that the solution was a darker green. Which of the alternative metals could cause the colour of Half-cell 1 to become a darker green? A. metals 1 and 3 B. metals 2 and 4 C. metals 1, 2 and 3 D. metals 3 and 4
Question 12/ 30 [VCAA 2021 SA Q18] Consider the following equations. 2NO2(g) → 2NO(g) + O2(g) ΔH = +14 kJ mol−1 NO2(g) + CO(g) → CO2(g) + NO(g) ΔH = −226 kJ mol−1 2NO2(g) ⇌ N2O4(g) ΔH = −57 kJ mol−1 N2(g) + O2(g) ⇌ 2NO(g) ΔH = +181 kJ mol−1
Which one of the following graphs is consistent with the chemical equations above? A.
B.
C.
D.
Question 13/ 30 [VCAA 2017 SA Q1] A catalyst A. slows the rate of reaction.
B. ensures that a reaction is exothermic. C. moves the chemical equilibrium of a reaction in the forward direction. D. provides an alternative pathway for the reaction with a lower activation energy.
Question 14/ 30 Use the following information to answer Questions 15 and 16. Hydrogen is produced on an industrial scale from methane. The equation for the reaction is 2H2O(g) + CH4(g) ⇌ CO2(g) + 4H2(g)
Question 15/ 30 [VCAA 2014 SA Q1] The expression for the equilibrium constant for the reverse reaction is A. K
=
[H2 O]2 [CH4 ] [H2 ]4 [CO2 ]
B. K
=
[H2 ]4 [CO2 ] [H2 O]2 [CH4 ]
C. K
=
[H2 O][CH4 ] [H2 ][CO2 ]
D. K
=
4[H2 ][CO2 ] 2[H2 O][CH4 ]
Question 16/ 30 [VCAA 2014 SA Q2] If an inert gas is added to the equilibrium system at a constant temperature and a constant volume, the concentration
of hydrogen will A. increase. B. decrease. C. not change. D. decrease then increase.
Question 17/ 30 [VCAA 2019 SA Q20] The oxidation of sulfur dioxide, SO2, to sulfur trioxide, SO3, can be represented by the following equation. 2SO2(g) + O2(g) ⇌ 2SO3(g) K = 1.75 M−1 at 1000°C An equilibrium mixture has a concentration of 0.12 M SO2 and 0.16 M oxygen gas, O2. The temperature of the container is 1000°C. The equilibrium concentration of SO3 at 1000°C is A. 1.5 × 10−4 M B. 4.0 × 10−3 M C. 1.2 × 10−2 M D. 6.3 × 10−2 M
Question 18/ 30 [VCAA 2021 SA Q25] An equilibrium mixture of four gases is represented by the following equation. A(g) + 2B(g) ⇌ C(g) + D(g) ΔH > 0
Which one of the following is consistent with the information given? A. Argon is added to the equilibrium mixture at time t1. B. At time t1 reactants are removed from the equilibrium mixture. C. The amount of products is higher at time t2 compared to just before time t1. D. The change made at time t1 results in an increase in the equilibrium constant at time t2.
Question 19/ 30 [VCAA 2013 SA Q30] A student prepares 1.0 M aqueous solutions of AgNO3, Fe(NO3)2 and KNO3. Equal volumes of each solution are placed in separate beakers, identical platinum electrodes are placed in each beaker and each solution undergoes electrolysis with the same current applied for 5.0 minutes under SLC. Each cathode is then dried and weighed to determine mass change. Assume that the concentrations of the solutions have decreased only slightly. In order of increasing mass, the metals deposited on the three cathodes are likely to be A. potassium, silver, iron. B. silver, iron, potassium. C. iron, potassium, silver. D. potassium, iron, silver.
Question 20/ 30 [VCAA 2019 SA Q17] The tradition of bronzing baby shoes dates back for generations. Before electroplating, the shoe is painted with a conductive material. The copper, Cu, electrode and copper sulfate, CuSO4, solution cell used for electroplating a shoe is shown below.
During the electroplating process A. the copper electrode is oxidised and its mass is unchanged. B. the shoe is coated with copper metal at the cathode. C. the copper electrode is the oxidising agent. D. oxygen is produced at the cathode.
Question 21/ 30 [VCAA 2021 SA Q29] The following diagram shows two connected electrochemical cells.
Which of the following gives the energy transformations that occur in Cell 1 and in Cell 2? Cell 1
Cell 2
chemical → electrical
chemical → electrical
electrical → chemical
chemical → electrical
chemical → electrical
electrical → chemical
electrical → chemical
electrical → chemical
Question 22/ 30 [VCAA 2017 SA Q17] Shown below is the infra-red spectrum of an organic compound.
Data: SDBS web, , National Institute of Advanced Science and Technology The organic compound that produces this spectrum is an A. aldehyde. B. alcohol. C. amide. D. ester.
Question 23/ 30 [VCAA 2015 SA Q8] Consider the following statements about a high-performance liquid chromatography (HPLC) column that uses a polar solvent and a non-polar stationary phase to analyse a solution: Statement I – Polar molecules in the solution will be attracted to the solvent particles by dipole-dipole attraction. Statement II – Non-polar molecules in the solution will be attracted to the stationary phase by dispersion forces. Statement III – Polar molecules in the solution will travel through the HPLC column more rapidly than non-polar molecules. Which of these statements are true? A. I and II only
B. I and III only C. II and III only D. I, II and III
Question 24/ 30 The following information refers to Questions 25 and 26. A student wishes to determine the concentration of ethanoic (acetic) acid in vinegar. The student titrates a 20.00 mL sample of a standard sodium hydroxide solution with a diluted vinegar solution from a burette. Five experiments were carried out and the following titration results were obtained: 22.55 mL, 23.35 mL, 23.30 mL, 23.27 mL and 23.32 mL.
Question 25/ 30 The discrepancy in the first titration could be due to the student initially washing A. the conical flask with sodium hydroxide solution only. B. the pipette with water only. C. the burette with water only. D. the pipette with sodium hydroxide solution only.
Question 26/ 30 The best estimates of the average titre and its uncertainty are Average titre (mL)
Uncertainty (mL) 23.16
±0.61
23.31
±0.04
23.3
±0.03
23.2
±0.6
Question 27/ 30 Which one of the substances below will not react with dilute sulfuric acid? A. CH3COOH B. CH3CONH2 C. CH3COOCH2CH3 D. CH3CH2NH2
Question 28/ 30 [VCAA 2018 SA Q21] A student wants to use a physical property to distinguish between two alcohols, octan-1-ol and propan-1-ol. Both alcohols are colourless liquids at standard laboratory conditions (SLC). The student should use A. density because propan-1-ol has a much higher density than octan-1-ol. B. boiling point because octan-1-ol has a higher boiling point than propan-1-ol. C. electrical conductivity because octan-1-ol has a higher conductivity than propan-1-ol. D. spectroscopy because it is not possible to distinguish between the alcohols using their physical properties.
Question 29/ 30 [VCAA 2022 SA Q11] The graphs shown below are energy profiles for the following reaction.
A + B ⇌ C ΔH < 0 The graphs represent the forward reaction, with and without a catalyst, and the reverse reaction, with and without a catalyst. All graphs are drawn to the same scale.
Which energy profile represents the reverse reaction without a catalyst? A. Graph 1 B. Graph 2 C. Graph 3 D. Graph 4
Question 30/ 30 [VCAA 2022 SA Q15] The molar heat of combustion of glucose, C6H12O6, in the cellular respiration equation is 2805 kJ mol−1 at standard laboratory conditions (SLC). Which one of the following statements about cellular respiration is correct? A. Cellular respiration is an endothermic reaction. B. The products of cellular respiration are carbon and carbon dioxide. C. Cellular respiration is a redox reaction because C6H12O6 accepts electrons from oxygen. D. When one mole of oxygen is consumed in the reaction, 467.5 kJ of energy is released.
Question 31/ 30 [VCAA 2022 SA Q20] The equipment below was set up by a student.
Which one of the following is correct? A. In the beaker, the reaction between Zn(s) and Co2+(aq) produces 0.48 V. B. In the beaker, chemical energy stored in the reactants is converted to heat energy. C. In the beaker, the concentration of ions increases because Zn(s) loses 2e−. D. In the beaker, a voltage of greater than 0.42 V must be applied to Zn(s) so that it reacts with Mn2+(aq).
Question 32/ 30 [VCAA 2022 SA Q24] A high-performance liquid chromatography (HPLC) instrument is set up with a polar mobile phase and a non-polar stationary phase. Three amino acids – leucine, Leu, alanine, Ala, and asparagine, Asn – are added to the mobile phase and are run through the HPLC. The order of the retention times, from shortest to longest, for these three amino acids is A. Leu, Ala, Asn B. Leu, Asn, Ala C. Ala, Asn, Leu D. Asn, Ala, Leu
Question 33/ 30 Enzymes are commonly not effective in acidic conditions because acids A. change the charges on the enzymes. B. react with the enzymes to form zwitterions. C. esterify the enzymes into smaller molecules. D. react with the carboxyl groups on the enzymes’ amino acid residues.
Question 1/ 11 [VCAA 2022 SB Q7] Liquefied petroleum gas (LPG) is a type of fuel currently used in some cars. (a) The main component of LPG is propane, C3H8 gas. Write a thermochemical equation for the complete combustion of propane gas. (2 marks) (b) An LPG-powered car uses 33.7 L of C3H8 to travel 270 km. Calculate the amount of energy released when 33.7 L of C3H8 undergoes complete combustion. The density of C3H8 is 0.510 kg L−1.
(2 marks) A diagram of an acidic LPG fuel cell is shown below.
(c) State the polarity of Electrode P. (1 mark) (d) Write a balanced half-equation for the reaction at Electrode Q. (2 marks) (e) Identify one difference between an acidic LPG fuel cell and a secondary cell during discharge. (1 mark) (Total = 8 marks)
Question 2/ 11 [VCAA 2011 E1 SB Q7] Banana oil, 3-methylbutylethanoate, CH3COOCH2CH2CH(CH3)2, is a sweet-smelling liquid that gives bananas their characteristic odour. (a) A chemist working for Go Bananas Pty Ltd has proposed the following reaction pathway for the synthesis of banana oil.
(i) Identify reagent A. (ii) Compound B is an alcohol. Draw a structure of compound B. (iii) Give the systematic name of compound B. (iv) Give the systematic name of compound C. (v) Identify reagent D. (vi) Of the reactions in the flow chart (reaction I, reaction II or reaction III), which reaction is an oxidation reaction? (1 + 1 + 1 + 1 + 1 + 1 = 6 marks) (b) The chemist decided to use fractional distillation to separate the final product from the reaction mixture. Describe the principles of fraction distillation. (2 marks) The chemist compared the IR spectrum of the banana oil after distillation with the IR spectrum of a pure sample of compound B. These are shown below and on the following page. The chemist claimed that these IR spectra indicate that a complete separation of the banana oil from the reaction mixture has been achieved.
(c) Explain how the evidence provided by these spectra supports the chemist’s claim. (2 marks) (Total = 10 marks)
Question 3/ 11 Chemical reactions in biological systems are catalysed by enzymes. In humans the enzyme salivary amylase catalyses the hydrolysis (breakdown) of starch to glucose. Students studied the effects of temperature and pH on the rate of hydrolysis of starch using salivary amylase in the laboratory obtained the following results.
(a) At what pH does salivary amylase operate most effectively? (1 mark) (b) Changes in temperature change the activity of an enzyme. Explain why the rate of hydrolysis of starch increases as the temperature increases from 5°C to 35°C. (1 mark) (c) The rate of hydrolysis of starch decreases markedly after 40°C. Explain what has happened to the salivary amylase to cause this fall in the rate of reaction. (2 marks) (Total = 4 marks)
Question 4/ 11 [Adapted VCAA 2022 SB Q7] The nutritional information for one medium serving (124 g) of sweet potato is provided in the table below. Nutrient
Per 124 g
Nutrient
Per 124 g
protein
2.0 g
fat
3.0 g
carbohydrates
18.7 g
vitamin C
3.0 mg
vitamin D
Less than 0.2 mg
(a) Calculate the energy contained in one medium serving of sweet potato. (1 mark) (b) The structure of vitamin D is shown below.
Explain, with reference to the chemistry, how boiling sweet potato in water may affect its level of vitamin D. (3 marks) (c) The loss of vitamin C, C6H8O6, in sweet potato after heating can be determined in a titration by reacting vitamin C with iodine, I2, solution. The balanced titration equation is shown below. C6H8O6(aq) + I2(aq) → 2HI(aq) + C6H6O6(aq) A sample of sweet potato was blended with water and filtered. The filtrate was titrated against 0.0500 M of I2(aq). The average of three concordant titres was 21.81 mL. Calculate the mass of vitamin C in the sweet potato sample. (2 marks) (Total = 6 marks)
Question 5/ 11 [VCAA 2017 SB Q6] Submarines operate both on the surface and underwater. When operating underwater, the submarine acts as a closed system, where there is no interaction with the atmosphere. Most types of submarines use both batteries and diesel engines to provide their energy requirements. A new type of submarine uses proton exchange membrane (PEM) fuel cells and diesel engines. Below is a diagram of a PEM fuel cell.
(a) (i) State the function of the electrolyte in a fuel cell. (1 mark) (ii) Write the balanced overall redox reaction that occurs in this PEM fuel cell. (1 mark) (iii) Give two safety considerations for the safe storage of hydrogen, H2, gas on a submarine. (2 marks) (b) (i) State two advantages of using a PEM fuel cell compared to a diesel engine when a submarine is underwater. (2 marks) (ii) Most submarines generate more H2 gas for their fuel cells when travelling on the surface. Explain how the H2 gas could be generated. (2 marks) (Total = 8 marks)
Question 6/ 11 [VCAA 2014 SB Q1] The decomposition of ammonia is represented by the following equation. 2NH3(g) ⇌ N2(g) + 3H2(g); ΔH = 92.4 kJ mol−1 (a) The activation energy for the uncatalysed reaction is 335 kJ mol−1. The activation energy for the reaction when tungsten is used as a catalyst is 163 kJ mol−1. On the grid provided below, draw a labelled energy profile diagram for the uncatalysed and catalysed reactions. (3 marks)
(b) When osmium is used as a catalyst, the activation energy is 197 kJ mol−1. Which catalyst, osmium or tungsten, will cause ammonia to decompose at a faster rate? Justify your answer in terms of the chemical principles you have studied this year. (2 marks) (Total = 5 marks)
Question 7/ 11 [VCAA 2018 SB Q7] A student is investigating the following reaction system. 2NO2(g) ⇌ N2O4(g) ΔH < 0 brown colourless (a) The reaction system can be observed in a sealed test tube, which allows the student to investigate the impact of temperature on the equilibrium position of the reaction. State the colour change expected when the student places the sealed test tube of the gas mixture in a beaker of hot water. Explain why this colour change occurs. (3 marks) (b) The concentration versus time graph for the reaction system is shown below. The graph was produced using secondary data at a temperature of 22°C.
(i) Time t1 is shown on the graph above. Calculate the equilibrium constant at time t1. (2 marks) (ii) At time t2 the volume of the system was halved, keeping the temperature at 22°C. Continue the graph to show how this change would affect the reaction system and how the system would respond to this change until equilibrium is restored. (3 marks) (Total = 8 marks)
Question 8/ 11 [VCAA 2012 E2 SB Q9] A teacher demonstrated the process of electrolysis of a molten salt using an unknown metal salt, XBr2. The apparatus was set up as shown below. At the conclusion of the demonstration, the students were provided with the following information. • A current of 1.50 amperes was applied for 30.0 minutes. • 2.90 g of metal X was produced.
(a) Write a balanced half-equation for the anode reaction in this electrolytic cell. (1 mark) (b) (i) Determine the amount, in mol, of metal X that was deposited on the cathode. (3 marks) (ii) Identify metal X. (2 marks) (Total = 6 marks)
Question 9/ 11 [VCAA 2020 SB Q4] Research scientists are developing a rechargeable lithium–carbon dioxide, Li–CO2, battery. The rechargeable Li–CO2 battery is made of lithium metal, carbon in the form of graphite (coated with a catalyst) and a non-aqueous electrolyte that absorbs CO2.
A diagram of the rechargeable Li–CO2 cell is shown below. One Li–CO2 cell generates 4.5 V.
(a) When the Li–CO2 cell generates electricity, the two half-cell reactions are 4Li+ +3CO2 + 4e− → 2Li2CO3 + C Li → Li+ + e− Write the equation for the overall recharge reaction. (1 mark) (b) During discharge, lithium carbonate, Li2CO3, deposits break away from the electrode. Describe how this might affect the performance of the battery. (2 marks) (c) Explain why it is unsafe to use an aqueous electrolyte in the design of the Li–CO2 battery. Include appropriate equations in your answer. (3 marks) (d) Could the Li–CO2 battery be used to reduce the amount of CO2(g) in the atmosphere? Give your reasoning. (1 mark) (Total = 7 marks)
Question 10/ 11 [VCAA 2019 SB Q2] (a) The following diagram represents a reaction pathway for the synthesis of Compound Q from pent-2-ene.
(i) Draw the skeletal formula for pent-2-ene in the box provided. (1 mark) Two structural isomers are possible when pent-2-ene is hydrolysed at a high temperature in the presence of an acid catalyst. Compounds M and N are formed. Compound M has a chiral carbon, but Compound N does not. (ii) Give the IUPAC name of Compound M in the box provided. (1 mark)
(iii) When Compound M is reacted with acidified dichromate ions, Cr2O72−, Compound Q is formed. Draw the semi-structural formula of Compound Q in the box provided. (1 mark) (b) 2-chloropropane can be reacted with ammonia to produce an uncharged organic molecule, Compound R. (i) Write the equation for the reaction that occurs. (1 mark) (ii) Give the IUPAC name of Compound R. (1 mark) (iii) Name the type of reaction that produces Compound R. (1 mark) (iv) Calculate the percentage atom economy for the production of Compound R. (2 marks) (Total = 8 marks)
Question 11/ 11 [Adapted VCAA 2022 SB Q6] Corn makes up a large proportion of people’s diet in some parts of the world. Air-popped popcorn is made from whole corn kernels. The nutrition content of a particular type of air-popped popcorn is provided in Table 1. Table 1 Average quantity per 100 g Protein
10.7 g
Fat
5.0 g
Carbohydrate
78.7 g
(a) Using the information provided in Table 1, calculate the energy content of air-popped popcorn in kilojoules per gram. (2 marks)
The energy content of food can be determined experimentally using a bomb calorimeter similar to the one shown in the diagram below.
A 1.50 g sample of air-popped popcorn is placed in the bomb calorimeter. The initial temperature of the water is 22.2°C and the final temperature is 25.7°C. Assume that the air-popped popcorn is fully combusted. The calibration factor for the bomb calorimeter is 6.54 kJ °C−1. (b) Using the calibration factor provided, calculate the energy released by the air-popped popcorn in kilojoules per gram. (2 marks) (c) Assume that the calorimeter was accurately calibrated so that heat loss from the calorimeter was accounted for in the calibration factor. State two factors that may contribute to a difference in the energy content that was calculated using the methods in part a. and part b. (2 marks) (Total = 6 marks)
Solutions
Chapter 1: Unit 3 Area of Study 1 – What are the current and future options for supplying energy?
Question 1/ 82 Which one of the following statements about fuels is correct? A. When fuels react, they all produce carbon dioxide. B. Heat energy is always released when fuels are burnt. C. All fuels are hydrocarbons. D. Fuels need pure oxygen to produce energy.
Solution
B. Fuels undergo an exothermic reaction when they react. H2 is a fuel and produces H2O when burnt. Alcohols are an example of a non-hydrocarbon fuel.
Question 2/ 82 Which one of the following lists contains only fossil fuels? A. biogas, bioethanol, biodiesel B. coal seam gas, biogas, natural gas C. coal, petrol, diesel D. peat, wood, charcoal
Solution
C. These fuels are produced from the fossilised remains of plants and animals over millions of years.
Question 3/ 82 Propane is often used as a fuel in portable barbecues. The equation for the combustion of propane is: C3H8(g) + 5O2(g) → 3CO2(g) + 4H2O(g) For this reaction, the sign of ΔH is A. negative and the total chemical energy of the products is less than that of the reactants. B. positive and the total chemical energy of the products is less than that of the reactants. C. negative and the total chemical energy of the products is greater than that of the reactants. D. positive and the total chemical energy of the products is greater than that of the reactants.
Solution
A. A fuel is a substance that releases energy when it reacts with oxygen, i.e. the reaction is exothermic. In exothermic reactions the energy of the products is less than that of the reactants.
Question 4/ 82 Which one of the following is not likely to be a biofuel? A. a gas mixture containing ∼96% methane and 4% carbon dioxide B. ethanol, C2H5OH C. methyl stearate, CH3(CH2)16COOCH3 D. a gas mixture containing approximately equal amounts of methane and carbon dioxide
Solution
A. This mixture is most likely to be coal seam gas. C is a component of biodiesel and D is biogas.
Question 5/ 82 Below are four molecules that have been found in fuels. I cyclohexane, C6H12 II octane, C8H18 III methyl palmitate, CH3OOC(CH2)14CH3 IV ethanol, C2H5OH Which of these is/are not likely to be found in crude oil? A. I and II B. I, III and IV C. III and IV D. II only
Solution
C. Only cyclohexane and octane are found in crude oil.
Question 6/ 82 The following is a list of fuels. I coal II biogas III natural gas IV biodiesel V bioethanol VI petrol
Which of these are renewable fuels? A. II, IV and VI B. I, III and VI C. I, III and V D. II, IV and V
Solution
D. Biogas, biodiesel and bioethanol are renewable, the rest are non-renewable fuels.
Question 7/ 82 [VCAA 2018 SA Q3] Which one of the following statements about fuels is correct? A. Petroleum gas is a form of renewable energy. B. Electricity can only be generated by burning coal. C. Carbon dioxide is not produced when biogas is burnt. D. Biodiesel can be derived from both plant and animal material.
Solution
D. Petroleum is a non-renewable form of energy. Many different substances can be burnt to produce electricity. CO2 is one of the products from the combustion of biogas. Biodiesel can be produced from vegetable oils or animal fats.
Question 8/ 82 [VCAA 2015 SA Q5] Which one of the following statements best defines a renewable energy resource? A. an energy resource that will not be consumed within our lifetime B. an energy resource that does not produce greenhouse gases when consumed C. an energy resource derived from plants that are grown for the production of liquid biofuels D. an energy resource that can be replaced by natural processes within a relatively short time
Solution
D. Definition.
Question 9/ 82 [VCAA 2014 SA Q24] Methane gas may be obtained from a number of different sources. It is a major component of natural gas. Methane trapped in coal is called coal seam gas and can be extracted by a process known as fracking. Methane is also produced by the microbial decomposition of plant and animal materials. In addition, large reserves of methane were trapped in ice as methane hydrate in the ocean depths long ago. Methane is a renewable energy source when it is obtained from A. natural gas. B. coal seam gas. C. methane hydrate. D. microbial decomposition.
Solution
D. Plant and animal materials can be easily replenished in a relatively short time (< human lifetime). The time scale to produce methane from the other sources is very long (millions of years).
Question 10/ 82 [Adapted VCAA 2017 SA Q5] Which one of the following is a biofuel? A. ethanol produced from crude oil B. ethanol produced from plant material C. propane produced from natural gas D. electricity produced by hydropower
Solution
B. Plant material can be obtained from natural sources, i.e. it is a renewable resource. Fermentation of plant material to produce ethanol is therefore a biofuel (renewable fuel).
Question 11/ 82 [VCAA 2020 SA Q11] Which one of the following statements is correct? A. Crude oil can be classified as a biofuel because it originally comes from plants. B. Methane, CH4, can be classified as a fossil fuel because it has major environmental impacts. C. Ethanol, CH3CH2OH, can be classified as a fossil fuel because it can be produced from crude oil. D. Hydrogen, H2, can be classified as a biofuel because, when it combusts, it does not produce carbon dioxide, CO2.
Solution
C. Any fuel sourced from crude oil is a fossil fuel. Ethanol can be produced through the addition reaction between water and ethene. The ethene is typically sourced from crude oil.
Question 12/ 82 [VCAA 2018 SA Q14] An equation for the complete combustion of methanol is 2CH3OH(l) + 3O2(g) → 2CO2(g) + 4H2O(g) ΔH for this equation would be A. +726 kJ mol−1 B. −726 kJ mol−1 C. +1452 kJ mol−1 D. −1452 kJ mol−1
Solution
D. Combustion of 1 mole of CH3OH will release 726 kJ. Hence, combustion of 2 moles will release 1452 kJ and ΔH is negative.
Question 13/ 82 Methane reacts with oxygen according to the following equation: CH4(g) + 2O2(g) → CO2(g) + 2H2O(l); ΔH = −890 kJ mol−1 The energy change for this reaction is best described as A. exothermic, because the net strength of the bonds in the products is greater than the net strength of the bonds in
the reactants. B. endothermic, because the net strength of the bonds in the products is greater than the net strength of the bonds in the reactants. C. exothermic, because the net strength of the bonds in the products is less than the net strength of the bonds in the reactants. D. endothermic, because the net strength of the bonds in the products is less than the net strength of the bonds in the reactants.
Solution
A. Exothermic reactions have a negative ΔH. The products are more stable than the reactants and thus at a lower energy. Hence the products have stronger bonds.
Question 14/ 82 Which of the following equations best represents the incomplete combustion of ethanol? A. C2H5OH(l) + 3O2(g) → 2CO2(g) + 3H2O(g) B. C2H5OH(l) → C2H4(g) + H2O(g) C. C2H5OH(l) + 2O2(g) → CO2(g) + C(s) + 3H2O(g) D. 2C2H5OH(l) + O2(g) → 2C2H4O(g) + 2H2O(g)
Solution
C. For complete combustion, all the C and H atoms are converted into CO2 and H2O, i.e. A. B. In incomplete combustion, carbon and/or carbon monoxide, CO, is produced. This occurs only in C.
Question 15/ 82 The partial oxidation of methane is one step in the production of methanol. 2CH4(g) + O2(g) → 2CO(g) + 4H2(g); ΔH = −74 kJ mol−1 The activation energy for this reaction is 32 kJ mol−1. The energy profile for this reaction is best represented by
A.
B.
C.
D.
Solution
D. Since the reaction is exothermic, the energy of the products must be lower than that of the reactants by 74 kJ
mol−1. The top of the curve must be 32 kJ mol−1 higher than the energy of the reactants.
Question 16/ 82 [VCAA 2017 SA Q29] The following energy profile shows the results obtained during an enzyme-catalysed reaction. Each stage of the reaction is labelled: M represents the initial reactants, N represents a stable intermediate and P represents the final products.
Which one of the following statements is correct? A. The energy change from M to N is exothermic and the energy change from N to P is exothermic. B. The energy change from M to P is exothermic and the energy change from N to P is endothermic. C. The energy change from M to N is endothermic and the energy change from N to P is endothermic. D. The energy change from M to N is endothermic and the energy change from M to P is endothermic.
Solution
D. Both N and P are at higher energy than M.
Question 17/ 82
When propane is used as a fuel (for example, as portable camping gas), it reacts with oxygen according to the equation C3H8(g) + 5O2(g) → 3CO2(g) + 4H2O(l) Compared with the energy of the reactants, the chemical energy of the combustion products will be A. higher and the reaction is endothermic. B. lower and the reaction is exothermic. C. higher and the reaction is exothermic. D. lower and the reaction is endothermic.
Solution
B. When a fuel burns, the reaction releases energy. Hence this is an exothermic reaction. In exothermic reactions the products have less energy than the reactants.
Question 18/ 82 [VCAA 2011 E2 SA Q6] In an endothermic reaction the A. reaction system loses energy to the surroundings. B. addition of a catalyst increases the activation energy. C. activation energy is greater than the enthalpy of reaction. D. energy required to break bonds in the reactants is less than the energy released when bonds are formed in the products.
Solution
C. For any endothermic reaction, the enthalpy change (ΔH) will always be less than the activation energy. Catalysts decrease the activation energy of reactions (both endothermic and exothermic). A and D are true for exothermic reactions.
Question 19/ 82 [VCAA 2020 SA Q27] The heat of combustion of ethanoic acid, C2H4O2 is −876 kJ mo1−1 and the heat of combustion of methyl methanoate, C2H4O2, is −973 kJ mo1−1. The auto-ignition temperature (the temperature at which a substance will combust in air without a source of ignition) of ethanoic acid is 485 °C and the auto-ignition temperature of methyl methanoate is 449 °C. Which one of the following pairs is correct? Compound with the lower chemical energy per mole ethanoic acid
Compound with the lower activation energy of combustion per mole methyl methanoate
ethanoic acid
ethanoic acid
methyl methanoate
methyl methanoate
methyl methanoate
ethanoic acid
Solution
A. Both fuels would combust to form the same products and therefore given the heat of combustion for ethanoic acid was lower, so was its chemical energy per mole. The auto-ignition temperature of methyl methanoate was lower, this indicated that the activation energy for methyl methanoate was also lower.
Question 20/ 82 [VCAA 2021 SA Q24] Which one of the following statements describes the effect that adding a catalyst will have on the energy profile diagram for an exothermic reaction? A. The energy of the products will remain the same.
B. The shape of the energy profile diagram will remain the same. C. The peak of the energy profile will move to the left as the reaction rate increases. D. The activation energy will be lowered by the same proportion in the forward and reverse reactions.
Solution
A. When a catalyst is added, the energy of the reactants and products remains the same but the energy of the transition state (activated complex) is reduced. Only A is consistent with this.
Question 21/ 82 Detonators often contain lead azide, Pb(N3)2, because when heated or struck, lead azide decomposes very rapidly, according to the equation Pb(N3)2(s) → Pb(s) + 3N2(g); ΔH = −440 kJ mol−1 Compared with the total chemical energy of the products, the chemical energy of the lead azide will be A. higher because the reaction is endothermic. B. higher because the reaction is exothermic. C. lower because the reaction is endothermic. D. lower because the reaction is exothermic.
Solution
B. In exothermic reactions, the energy of the reactants is higher than that of the products.
Question 22/ 82 [VCAA 2017 SA Q9] The nutrition information panel on a packet of muesli includes the information shown below. Nutrition information Average serving size = 45 g Average quantity per 100 g protein
13.2 g
fat, total
16.3 g
– saturated
2.9 g
carbohydrate, total
48.2 g
– sugars
17.4 g
dietary fibre
4.9 g
sodium
10.5 mg
Using the information above, the percentage energy content due to protein in an average serving size of this muesli is A. 31.2% B. 29.3% C. 14.0% D. 13.2%
Solution
C. Energy from protein = 0.45 × 13.2 × 17 = 100.98 kJ. Energy from fat = 16.3 × 0.45 × 37 = 271.4 kJ. Energy from carbohydrate = 16 × 0.45 × 38.2 = 347.0 kJ. % energy from protein = (100.98 ÷ 719.4) × 100 = 14.0%.
Question 23/ 82 [VCAA 2022 SA Q3] The correct equation for the incomplete combustion of ethanol is A. C2H5OH(l) + 12 O2(g) → 2CO(g) + 3H2(g) B. C2H5OH(l) + 23 O2(g) → 2CO2(g) + 3H2(g) C. C2H5OH(l) + 2O2(g) → 2CO(g) + 3H2O(l) D. C2H5OH(l) + 3O2(g) → 2CO2(g) + 3H2O(l)
Solution
C. The product of incomplete combustion reactions are carbon monoxide and water, only C has this in the reaction.
Question 24/ 82 In a laboratory experiment, 100 mL of ethane gas was mixed with 500 mL of oxygen gas at SLC and sparked. The reaction shown by the following equation occurred: 2C2H6(g) + 7O2(g) → 4CO2(g) + 6H2O(l) What would be the total volume of gas present when the reaction had cooled back to SLC? A. 200 mL B. 350 mL C. 550 mL D. 650 mL
Solution
B. The initial temperature and pressure are the same as the final, thus volume-volume stoichiometry can be applied to the gases.
Mole ratio of ethane : oxygen = 2 : 7 V(O2)reacting = 72 × V(C2H6) = 350 mL V(O2)remaining/excess = initial-reacting = 500 – 350 mL = 150 mL Mol ratio of C2H6 : CO2 = 2 : 4 V(CO2) = 24 × V(C2H6) = 200 mL Total volume of gas = V(O2)remaining + V(CO2) = 150 + 200 = 350 mL
Question 25/ 82 [Adapted VCAA 2014 SA Q8] When hydrochloric acid, HCl, is added to aluminium sulfide, Al2S3, the highly toxic gas hydrogen sulfide, H2S, is evolved. The equation for this reaction is Al2S3(s) + 6HCl(aq) → 2AlCl3(aq) + 3H2S(g) If excess hydrochloric acid is added to 0.200 mol of aluminium sulfide, then the volume of hydrogen sulfide produced at standard laboratory conditions (SLC) will be A. 1.63 L B. 4.90 L C. 7.44 L D. 14.9 L
Solution
D. n(H2S) = 3 × 0.200 = 0.600 mol; V(H2S) = 0.600 × 24.8 L
Question 26/ 82 Methane, CH4, ethane, C2H6, ethyne, C2H2, and propane, C3H8, have all been used as fuels. The enthalpy change for the balanced complete combustion reactions of these fuels is given by the following equations: CH4(g) + 2O2(g) → CO2(g) + 2H2O(l); ΔH = −890 kJ mol−1 2C2H6(g) + 7O2(g) → 4CO2(g) + 6H2O(l); ΔH = −3120 kJ mol−1 2C2H2(g) + 5O2(g) → 4CO2(g) + 2H2O(l); ΔH = −2600 kJ mol−1 C3H8(g) + 5O2(g) → 3CO2(g) + 4H2O(l); ΔH = −2208 kJ mol−1 When 1.0 g of each fuel is burned, then the fuel releasing the greatest amount of energy would be A. CH4 B. C2H6 C. C2H2 D. C3H8
Solution
A. Heat released for 1 g of each gas is CH4 = 890 ÷ 16 = 55.6 kJ; C2H6 = 1560 ÷ 30 = 52 kJ C2H2 = 1300 ÷ 26 = 50 kJ; C3H8 = 2208 ÷ 44 = 50.2 kJ
Question 27/ 82 Both ethanol, C2H5OH, and methanol, CH3OH, have been suggested as alternative fuels for transport vehicles. The equations describing the complete combustion of ethanol and methanol are given below. C2H5OH(g) + 3O2(g) → 2CO2(g) + 3H2O(l); ΔH = −1368 kJ mol−1 CH3OH(g) + 32 O2(g) → CO2(g) + 2H2O(l); ΔH = −726 kJ mol−1 Separate experiments are conducted in which 1 mol of ethanol and 2 mol of methanol undergo complete combustion. In these experiments
A. the combustion of methanol produces more carbon dioxide. B. more heat energy is released from the combustion of ethanol. C. more water is formed in the combustion of ethanol. D. the two experiments consume the same amount of oxygen.
Solution
D. Combustion of 1 mol of C2H5OH consumes 3 mol of O2 and produces 2 mol of CO2, 3 mol of H2O and 1368 kJ. The values for 2 mol of CH3OH are 3 mol of O2, 2 mol of CO2, 4 mol of H2O and 1452 kJ.
Question 28/ 82 The heat of combustion for three methyl esters is given in the table below. Name
Formula
Methyl pentanoate
C4H9COOCH3
−3558
Methyl hexanoate
C5H11COOCH3
−4211
Methyl heptanoate
C6H13COOCH3
−4863
ΔH (kJ mol−1)
One of the molecules found in biodiesel is methyl stearate, C17H35COOCH3. The best estimate for the molar enthalpy change (in kJ mol−1) of methyl stearate is A. −7178 B. −12 040 C. −12 632 D. −13 937
Solution
B. The three esters given in the table differ in formula by a CH2 group. The differences in ΔH are 653 and 652 kJ mol−1. The difference in formulae between methyl heptanoate and methyl stearate is 11 × (CH2). Hence, ΔH should decrease by approximately 11 × 652.5, i.e. ∼−7178 kJ mol−1. ΔH for methyl stearate is ∼(−7178) + (−4863) = ∼−12 040 kJ mol−1.
Question 29/ 82 [VCAA 2013 SA Q16] C(s) + O2(g) → CO2(g); ΔH = −393.5 kJ mol−1 2H2(g) + O2(g) → 2H2O(l); ΔH = −571.6 kJ mol−1 Given the information above, what is the enthalpy change for the following reaction? C(s) + 2H2O(l) → CO2(g) + 2H2(g) A. −965.1 kJ mol−1 B. −107.7 kJ mol−1 C. +178.1 kJ mol−1 D. +679.3 kJ mol−1
Solution
C. To produce the reaction shown, the second equation must be reversed and added to the first equation. Hence, ΔH for the reaction will be +571.6 – 393.5 kJ.
Question 30/ 82 [VCAA 2018 SA Q10] Bioethanol, C2H5OH, is produced by the fermentation of glucose, C6H12O6, according to the following equation.
C6H12O6(aq) → 2C2H5OH(aq) + 2CO2(g) The mass of C2H5OH obtained when 5.68 g of carbon dioxide, CO2, is produced is A. 0.168 g B. 0.337 g C. 2.97 g D. 5.94 g
Solution
D. n(CO2) = 5.68 44 = 0.129 mol; n(C2H5OH) = n(CO2) since in the equation the ratio is 2 : 2. Mass C2H5OH = 0.129 × 46.0.
Question 31/ 82 [VCAA 2014 SA Q23] Large deposits of methane hydrate have been discovered deep under the sediment on the ocean floor. It has been suggested that methane hydrate deposits could be commercially mined to provide a clean fuel once the trapped methane is extracted. Methane hydrate has a complex structure. The simplified formula for methane hydrate is CH4.6H2O. The amount of energy released by the complete combustion of methane extracted from a 1.00 kg sample of methane hydrate at SLC is A. 8.89 × 102 kJ B. 7.17 × 103 kJ C. 4.30 × 104 kJ D. 5.56 × 104 kJ
Solution
B. n(CH4) = n(CH4.6H2O) = 1000 124 = 8.06 mol
Energy released = 8.06 × 889 = 7169 kJ.
Question 32/ 82 [VCAA 2018 SA Q22] Four fuels undergo complete combustion in excess oxygen, O2, and the energy released is used to heat 1000 g of water. Assuming there is no energy lost to the environment, which one of these fuels will increase the temperature of the water from 25.0°C to 85.0°C? A. 0.889 g of hydrogen, H2 B. 3.95 g of propane, C3H8 C. 0.282 mol of methane, CH4 D. 0.301 mol of methanol, CH3OH
Solution
C. Energy needed = 4.18 × (85.0 – 25.0) × 1.0 = 250.8 kJ Energy released by H2 = 0.889 × 141 = 125.3 kJ Energy released by C3H8 = 3.95 × 50.5 = 199.5 kJ Energy released by CH4 = 0.282 × 890 = 250.98 kJ Energy released by CH3OH = 0.306 × 726 = 218.5 kJ
Question 33/ 82 [VCAA 2017 SA Q7] What is the total energy released, in kilojoules, when 100 g of butane and 200 g of octane undergo combustion in the presence of excess oxygen?
A. 9760 B. 14 600 C. 17 300 D. 19 500
Solution
B. The heats of combustion of butane and octane are 49.7 kJ g−1 and 47.9 kJ g−1, respectively. Total energy released is (100 × 49.7) + (200 × 47.9) = 14 550 kJ.
Question 35/ 82 [VCAA 2017 SA Q13] Using the information in the table above, which one of the following statements about petrodiesel is correct? A. It has the highest energy content. B. It has the poorest fuel efficiency. C. It is a renewable energy source. D. It has the lowest CO2 emissions when burnt.
Solution
A. Petrodiesel has the lowest fuel consumption of the four fuels and thus has the best fuel efficiency. Since the four cars are the same model, it is expected that the same energy will be required to cover 100 km. Less volume of petrodiesel is used hence it will release more energy per litre. Petrodiesel is obtained from a non-renewable source.
Question 36/ 82 [VCAA 2017 SA Q14] The use of which vehicle has the smallest impact on the environment, in terms of the grams of CO2 produced per 100 km? A. Vehicle model 1 B. Vehicle model 2 C. Vehicle model 3 D. Vehicle model 4
Solution
D. When each car has covered 100 km, the mass of CO2 produced is: A = 32.8 kg; B = 34.7 kg; C = 32.7 kg; D = 24.3 kg.
Question 37/ 82 [Adapted VCAA 2018 SA Q25] The molar enthalpy change for the combustion of pentan-1-ol, C5H11OH, is −3329 kJ mol−1. M(C5H11OH) = 88.0 g mol−1 The mass of C5H11OH, in tonnes, required to produce 10 800 MJ of energy is closest to A. 0.0286 B. 0.286 C. 2.86 D. 286
Solution
B. n(pentan-1-ol) = 10800×1000 = 3244.2 mol mass (pentan-1-ol) = 3244.2 × 88.0 = 286 000 g This is 286 kg or 3329 0.286 tonne.
Question 38/ 82 100 mL of a gaseous hydrocarbon is mixed with 500 mL of oxygen at SLC At the end of the reaction, the gaseous mixture is returned to its original temperature and pressure. The final mixture consists of 300 mL of carbon dioxide and 100 mL of oxygen. The molecular formula of the hydrocarbon is A. C2H4 B. C3H4 C. C3H6 D. C3H8
Solution
B. The equation for the combustion of a hydrocarbon is x+y
CxHy + ( 4
)O2 → xCO2 + ( y2 )H2O
Since p and T are the same before and after reaction, n(gas) ∝ V(gas). 100 mL of hydrocarbon produces 300 mL of CO2, hence x = 3. V(O2) consumed = 400 mL hence
( x+y 4 ) 1
=
3+y 400 100 and ( 4 ) = 4 and y = 4.
Question 39/ 82 [VCAA 2020 SA Q18] An experiment was carried out to determine the enthalpy of combustion of propan-1-ol. Combustion of 557 mg of propan-1-ol increased the temperature of 150 g of water from 22.1 °C to 40.6 °C. The molar enthalpy of combustion is closest to
A. −2742 kJ mo1−1 B. −1208 kJ mo1−1 C. −1250 kJ mo1−1 D. −1540 kJ mol−1
Solution
C. q = mcΔT = 150 × 4.18 × 18.5 = 11.6 × 103 J = 11.6 kJ m n(propan-1-ol) = M q
ΔH = n
=
=
0.557 3 60.0 = 9.29 × 10 mol
11.6 3 −1 9.29×103 = −1.25 × 10 kJ mol
Question 40/ 82 [VCAA 2020 SA Q22] The combustion of which fuel provides the most energy per 100 g? A. pentane (M = 72 g mol−1), which releases 49 097 MJ tonne−1 B. nitromethane (M = 61 g mol−1), which releases 11.63 kJ g−1 C. butanol (M = 74 g mol−1), which releases 2670 kJ mo1−1 D. ethyne (M = 26 g mol−1), which releases 1300 kJ mo1−1
Solution
D. A. q = 49 097 MJ tonne−1 × 1.00 × 10−4 tonne = 4.910 MJ = 4910 kJ B. q = 11.63 kJ g−1 × 100 g = 1163 kJ C. q = 2670 kJ mol−1 × 100 74 = 3605 kJ
D. q = 1300 kJ mol−1 × 100 26 = 5005 kJ
Question 41/ 82 [VCAA 2021 SA Q12] Butane, C4H10, undergoes complete combustion according to the following equation. 2C4H10(g) + 13O2(g) → 8CO2(g) + 10H2O(g) 67.0 g of C4H10 released 3330 kJ of energy during complete combustion at standard laboratory conditions (SLC). The mass of carbon dioxide, CO2, produced was A. 0.105 g B. 3.18 g C. 50.9 g D. 204 g
Solution
D. n(C4H10) = m ÷ M = 67.0 ÷ 58.0 = 1.16 mol n(CO2) = n(C4H10) × = 4.62 mol m(CO2) = n × M = 4.62 × 44.0 = 203 g
Question 42/ 82 [VCAA 2021 SA Q22] 1 L of octane has a mass of 703 g at SLC. The efficiency of the reaction when octane undergoes combustion in the petrol engine of a car is 25.0%.
What volume of octane stored in a petrol tank at SLC is required to produce 528 MJ of usable energy in a combustion engine? A. 3.92 L B. 11.8 L C. 15.7 L D. 62.7 L
Solution
D. To 83 produce 528 MJ of usable energy, enough octane to produce 100 25 × 528 MJ must be burned (to account for the efficiency). This means 2112 MJ (2.112 × 106 kJ) of heat energy must be released. q
m(octane) = ΔH
=
2.112×106 kJ 4 47.9 kJ g−1 = 4.41 × 10 g
m V(octane) = 703 (from the ratio provided in the question)
=
4.41×104 g = 62.7 L 703
Question 43/ 82 For each mole of oxygen consumed, which one of the following fuels produces the largest amount of carbon dioxide? A. methane, CH4 B. ethyne, C2H2 C. ethene, C2H4 D. propane, C3H8
Solution
B. The equations for the combustion of these fuels are:
1 1 2 CH4 + O2 → 2 CO2 + H2O 2 4 2 5 C2H2 + O2 → 5 CO2 + 5 H2O 1 2 2 3 C2H4 + O2 → 3 CO2 + 5 H2O 1 3 4 5 C3H8 + O2 → 5 CO2 + 5 H2O
Question 44/ 82 [VCAA 2019 SA Q26] The calibration factor of a bomb calorimeter was determined by connecting the calorimeter to a power supply. The calibration was done using 100 mL of water, 6.5 V and a current of 3.6 A for 4.0 minutes. The temperature of the water increased by 0.48°C during the calibration. 4.20 g of sucrose underwent complete combustion in the bomb calorimeter. The temperature of the 100 mL of water increased from 19.6°C to 25.8°C. M(C12H22O11) = 342 g mo1−1 The experimental heat of combustion of pure sucrose, in joules per gram, is A. 5.9 × 106 B. 7.3 × 104 C. 1.7 × 104 D. 1.2 × 104
Solution
C. Calibration factor = 6.5×3.6×240 = 1.17 × 104 J °C−1 0.48 q = 1.17 × 104 × (25.8 – 19.6) = 7.25 × 104 J 4 ΔH = 7.25×10 = 1.7 × 104 J g−1 4.2
Question 46/ 82 [VCAA 2020 SA Q9] What is the calibration factor for this calorimeter? A. 125 J °C−1 B. 820 J °C−1 C. 847 J °C−1 D. 875 J °C−1
Solution
B. The temperature change is 3.2°C (21.2 – 18.0) as the maximum temperature must be used to calculate temperature It change. CF = VΔT = 5.4×2.7×180 = 820 J ∘ C−1 3.2
Question 47/ 82 [VCAA 2020 SA Q10] This type of calorimeter A. has no heat loss. B. can be used for bomb calorimetry. C. requires electrical calibration in order to determine the calibration factor. D. measures energy changes that can be measured in a bomb calorimeter.
Solution
D. C is not correct as a solution calorimeter can also be calibrated by delivering energy to the system through a chemical reaction with a known enthalpy change. D is the most correct answer as bomb calorimeters and solution
calorimeters both measure energy changes.
Question 48/ 82 [VCAA 2021 SA Q19] A food chemist conducted an experiment in a bomb calorimeter to determine the energy content, in joules per gram, of a muesli bar. A 3.95 g sample of the muesli bar was combusted in the calorimeter and the temperature of the water rose by 16.7 °C. The calibration factor of the calorimeter was previously determined to be 4780 J °C−1. The energy content of the muesli bar is A. 3.51 × 105 J g−1 B. 2.02 × 104 J g−1 C. 1.13 × 103 J g−1 D. 7.25 × 10 J g−1
Solution
B. q = calibration factor × ΔT = 4780 × 16.7 = 7.98 × 104 J q
Energy content = m
=
7.98×104 J = 2.02 × 104 g−1 3.95
Question 49/ 82 [VCAA 2022 SA Q2] A fuel undergoes combustion to heat water. Which of the following descriptions of the energy and enthalpy of combustion, ΔH, of the reaction is correct? Energy absorbed by water
ΔH negative
released by water
negative
absorbed by water
positive
released by water
positive
Solution
A. All combustion reactions are exothermic and therefore have a negative enthalpy change. To heat the water, the water must absorb energy.
Question 50/ 82 [VCAA 2022 SA Q26] Calorimeter 1 and Calorimeter 2 were each electrically calibrated. The same current, voltage and time were used to calibrate each calorimeter. A reaction was undertaken in Calorimeter 1 and Calorimeter 2. The same amount and type of each reactant was used in both calorimeters. The following temperature versus time graphs were produced for the reaction in each calorimeter.
Which one of the following statements is correct? A. Only Calorimeter 1 can be used to calculate m. B. Calorimeter 2 has better insulation than Calorimeter 1.
C. The calibration factor for Calorimeter 2 is higher than the calibration factor for Calorimeter 1. D. During the calibration, the temperature increase of Calorimeter 2 was greater than the temperature increase of Calorimeter 1.
Solution
C. The graphs show that Calorimeter 2 has poorer insulation as over time the temperature drops (after heating). So while both can be used, the calibration factor will be higher for Calorimeter 2.
Question 51/ 82 For which of the following species is the oxidation number of oxygen the lowest? A. Na2O2 B. H2O2 C. O2 D. H2SO4
Solution
D. The oxidation number of oxygen in each of these species is A = −1; B = −1; C = 0; D = −2.
Question 52/ 82 In which of the following reactions is nitrous acid, HNO2, behaving solely as an oxidising agent? A. 2H+(aq) + Zn(s) + 2HNO2(aq) → Zn2+(aq) + 2NO(g) + 2H2O(l)
B. MnO2(s) + HNO2(aq) + H+(aq) → Mn2+(aq) + NO3−(aq) + H2O(l) C. 3HNO2(aq) → HNO3(aq) + H2O(l) + 2NO(g) D. 2Fe3+(aq) + HNO2(aq) + H+(aq) → 2Fe2+(aq) + NO3−(aq) + H2O(l)
Solution
A. Oxidants oxidise other substances (increase the oxidation number of other atoms) and are themselves reduced. In A, Zn is oxidised (0 to +2). In B, manganese is reduced (+4 to +2). In C, the oxidation number of N is both increased and reduced. In D, iron is reduced (+3 to +2).
Question 53/ 82 In which one of the following reactions does sulfur have the largest change in oxidation number? A. 2S2O32−(aq) + I2(aq) → S4O62−(aq) + 2I−(aq) B. 2SO2(g) + O2(g) → 2SO3(g) C. H2SO4(l) + 8HI(g) → H2S(g) + 4H2O(l) + 4I2(s) D. S(l) + O2(g) → SO2(g)
Solution
C. The changes in oxidation number are in A +2 to +2.5, in B +4 to +6, in C +6 to −2 and in D 0 to +4.
Question 54/ 82 A galvanic cell is set up as shown in the diagram below.
In this cell, the aluminium electrode will be the A. anode and negatively charged. B. anode and positively charged. C. cathode and negatively charged. D. cathode and positively charged.
Solution
A. Al is lower in the reactivity series than Cu (i.e. Al is a more reactive metal) and will oxidise. Oxidation occurs at the anode. The oxidation process will produce electrons and so the Al will be negative.
Question 55/ 82 A Cu/Cu2+ half-cell and a Zn/Zn2+ half-cell are connected using a salt bridge and the system is used to produce an electric current. The purpose of the salt bridge is to A. allow the reactants to make contact with each other. B. allow cations and anions to flow in and out of the two half-cells. C. provide essential reactants for the overall reaction. D. provide electrons to complete the circuit in the cell.
Solution
B. The salt bridge prevents the reactants from making direct contact. Anions flow into the anode compartment and out of the cathode compartment. Cations go in the opposite direction.
Question 57/ 82 The strongest reducing agent present is A. Co B. Cu C. V D. Cu2+
Solution
C. The copper half-cell is positive in both cells. The Co and V electrodes are the two reductants. Since the voltage is larger in the Cu/V cell, the vanadium electrode must be at a lower (more negative) potential than the Co half-cell.
Question 58/ 82 The voltage of a cell using the Co/Co2+ and V/V2+ half-cells would be A. 0.90 V with the V electrode negative. B. 0.90 V with the Co electrode negative. C. 2.14 V with the V electrode negative. D. 2.14 V with the Co electrode negative.
Solution
A. The Co half-cell is more negative than Cu by 0.62 V, and the V half-cell is more negative than Cu by 1.52 V. Hence V will be more negative than Co by 1.52 – 0.62 = 0.90 V.
Question 59/ 82 A piece of steel plate is placed in each of four separate containers, each containing a different 0.50 M aqueous solution. The four solutions are Pb(NO3)2(aq), Zn(NO3)2(aq), AgNO3(aq) and Cu(NO3)2(aq). It is expected that the piece of steel will be coated with another metal in the solutions of A. Pb(NO3)2, AgNO3 and Cu(NO3)2. B. Pb(NO3)2 and AgNO3. C. AgNO3 and Cu(NO3)2. D. Zn(NO3)2 only.
Solution
A. The Fe in the steel will react with those cations that are higher in the reactivity series, i.e. Pb2+, Ag+ and Cu2+.
Question 60/ 82 Three metals, R, S and T, have the following properties: • Metal R does not react with 1.0 M H2SO4 • Metal S will react with 1.0 M H2SO4 to produce H2, and also reacts with 1.0 M RCl2 solution to produce R • Metal T will react with 1.0 M H2SO4 to produce H2 but does not react with 1.0 M SCl2 solution. From this information the order of reactivity of the metals and H2, from the highest to the lowest, is A. R > H2 > T > S
B. H2 > R > T > S C. S > H2 > T > R D. S > T > H2 > R
Solution
D. From the information, H2 is more reactive than R; S is more reactive than H2 and also R. T is more reactive than H2 but less reactive than S.
Question 61/ 82 [VCAA 2013 SA Q24] Three beakers, each containing an iron strip and a 1.0 mol L−1 solution of a metal salt, were set up as shown below.
A reaction will occur in beaker(s) A. I and II only. B. I and III only. C. II and III only. D. III only.
Solution
A. Fe is a stronger reductant than Pb and Ni but is weaker than Zn.
Question 62/ 82 [VCAA 2018 SA Q1] Which one of the following statements is the most accurate? A. All fuel cells are galvanic cells. B. All galvanic cells are primary cells. C. All secondary cells have porous electrodes. D. All fuel cells are more efficient than all secondary cells.
Solution
A. In a galvanic cell, chemical energy is converted into electrical energy. This occurs in all fuel cells.
Question 63/ 82 [VCAA 2018 SA Q11] A galvanic cell is set up as shown in the diagram below.
When this cell is operating A. a gas forms at the Ag electrode. B. the mass of the Ag electrode increases. C. Ag+ ions move towards the Fe electrode. D. electrons move from the Ag electrode to the Fe electrode.
Solution
B. When this cell is operating Fe will be oxidised. Electrons will move from the Fe electrode to the Ag electrode. Ag+ ions will be attracted to this electrode and reduced. Hence, Ag will be deposited on the Ag electrode.
Question 64/ 82 [VCAA 2013 SA Q25] A student constructs the following galvanic cell.
The student predicts that the following overall reaction will occur. 2H2O2(aq) → 2H2O(l) + O2(g) However, no reaction is observed. This is most likely because A. the difference between the E° values is too small for a reaction to occur. B. hydrogen peroxide will oxidise water in preference to itself. C. the student did not construct standard half-cells. D. the rate of the reaction is extremely slow.
Solution
D. The reaction can be predicted from the electrochemical series but this information gives no information on the speed of a reaction. Presumably the activation energy for this reaction is very large.
Question 65/ 82 [VCAA 2018 SA Q12] The overall reaction for an acidic fuel cell is shown below. 2H2(g) + O2(g) → 2H2O(l) Porous electrodes are often used in acidic fuel cells because they A. are highly reactive. B. are cheap to produce and readily available.
C. are more efficient than solid electrodes at moving charges and reactants. D. provide a surface for the hydrogen and oxygen to directly react together.
Solution
C. Porous electrodes have a greater surface area than solid electrodes and can thus interact with gases and liquids more efficiently. Porous electrodes often contain expensive catalysts, such as platinum, to increase the rate of reaction.
Question 66/ 82 [VCAA 2014 SA Q25] Consider the information below about the reaction of Ru2+ with various reagents. Ru2+(aq) + Fe2+(aq) → no observed reaction Ru2+(aq) + Ni(s) → Ru(s) + Ni2+(aq) Ru2+(aq) + Ag(s) → no observed reaction Ru2+(aq) + Cu(s) → Ru(s) + Cu2+(aq) Where would the following reaction be placed in the electrochemical series if the above tests were carried out under standard conditions? Ru2+(aq) + 2e− ⇌ Ru(s) A. below −0.23 V B. between −0.44 V and −0.23 V C. between 0.77 V and 0.34 V D. above 0.77 V
Solution
C. Ru2+ is reduced by Cu but not by Fe2+. Hence E° (Ru2+/Ru) must be greater than 0.34 V but less than 0.77 V.
Question 67/ 82 [VCAA 2014 SA Q26] Consider the following experiments that are carried out under standard conditions. Beaker I A strip of nickel metal is placed into a 1.0 M silver nitrate solution. Beaker II A 1.0 M copper(II) sulfate solution is added to a 1.0 M sodium iodide solution. Beaker III Chlorine gas is bubbled through a 1.0 M potassium iodide solution. It would be predicted that a reaction will occur in A. Beaker I only. B. Beaker II only. C. Beakers I and III only. D. Beakers II and III only.
Solution
C. From the information in the VCAA data book, only reactions I and III would occur. (However, Cu2+ + I− + e− ⇌ CuI is not listed and has an E° of 0.87 V, hence 2Cu2+ + 4I− → 2CuI + I2 would occur!)
Question 68/ 82 [VCAA 2015 SA Q24] The reaction between hydrogen peroxide and ammonium ions is represented by the following equation. 3H2O2(aq) + 2NH4+(aq) → N2(g) + 2H+(aq) + 6H2O(l)
Which one of the following is the correct half-equation for the reduction reaction? A. H2O2(aq) + 2H+(aq) + 2e− → 2H2O(l) B. 2NH4+(aq) → N2(g) + 8H+(aq) + 6e− C. 2NH4+(aq) + 2e− → N2(g) + 4H2(g) D. H2O2(aq) + 2H2O(l) → 2O2(g) + 6H+(aq) + 6e−
Solution
A. Oxygen is reduced from −1 in H2O2 to −2 in H2O. Nitrogen is oxidised from −3 in NH4+ to 0 in N2.
Question 69/ 82 [VCAA 2015 SA Q25] Solution I – 1.0 M NaCl Solution II – 1.0 M CuCl2 Solution III – 1.0 M MgCl2. Which solution or solutions above will react with Zn powder? A. Solution I only B. Solution II only C. Solutions I and III only D. Solutions I, II and III
Solution
B. Zn will reduce an oxidant that is higher in the electrochemical series, i.e. Cu2+. Both Na+ and Mg2+ are lower in the series and do not react with Zn.
Question 70/ 82 [VCAA 2017 SA Q6] The overall equation for a particular methanol fuel cell is shown below. 2CH3OH(g) + 3O2(g) → 2CO2(g) + 4H2O(l) The equation for the reaction that occurs at the cathode in this fuel cell is A. CO2(g) + 5H2O(l) + 6e− → CH3OH(g) + 6OH−(aq) B. CH3OH(g) + 6OH−(aq) → CO2(g) + 5H2O(l) + 6e− C. O2(g) + 2H2O(l) + 4e− → 4OH−(aq) D. 4OH−(aq) → O2(g) + 2H2O(l) + 4e−
Solution
C. In a fuel cell, oxygen is always reduced at the cathode. C is the only one that has O2 as a reactant and therefore it must be this option.
Question 71/ 82 [VCAA 2018 SA Q29] The diagrams below represent combinations of four galvanic half-cells (G/G2+, J/J2+, Q/Q2+ and R/R2+) that were investigated under standard conditions. Each half-cell consisted of a metal electrode placed in a 1.0 M nitrate solution of the respective metal ion. The diagrams show the polarity of the electrodes in each half-cell, as determined using an ammeter. The results were then used to determine the order of the E° values of the half-reactions.
Which of the following indicates the order of the half-cell reactions, from the lowest E° value to the highest? A. J/J2+, R/R2+, G/G2+, Q/Q2+ B. Q/Q2+, G/G2+, R/R2+, J/J2+ C. R/R2+, J/J2+, Q/Q2+, G/G2+ D. G/G2+, Q/Q2+, J/J2+, R/R2+
Solution
C. From the first cell, Q is a more reactive metal than G and the Q/Q2+ half-cell will thus have a lower E°. Similarly, from the second cell, J/J2+ has a lower E° than Q/Q2+ and from the last cell, R/R2+ has a lower E° than J/J2+.
Question 72/ 82
[VCAA 2017 SA Q11] A galvanic cell consists of two connected half-cells that can produce an electron flow. Which combination of standard half-cell pairs would be expected to result in a cell potential of 1.41 V? Al electrode with Al(NO3)3
Ag electrode with AgNO3
Zn electrode with Zn(NO3)2
Ni electrode with Ni(NO3)2
Ni electrode with Ni(NO3)2
Al electrode with Al(NO3)3
Ag electrode with AgNO3
Zn electrode with Zn(NO3)2
Solution
C. E°(cell) = E°(oxidant) – E°(reductant). Hence for C, E°(cell) is −0.25 – (−1.66) = 1.41 V. The other values are A = 2.46 V, B = 0.51 V and D = 1.56 V.
Question 73/ 82 [VCAA 2019 SA Q8] Consider the following statements about galvanic and fuel cells. Statement number
Statement
1
The overall reaction is exothermic.
2
Electrons are consumed at the negative electrode.
3
Both the reducing agent and oxidising agent are stored in each half-cell.
4
The electrodes are in contact with the reactants and the electrolyte.
5
The production of electricity requires the electrodes to be replaced regularly.
Which one of the following sets of statements is correct for both galvanic cells and fuel cells? A. statement numbers 2 and 3 B. statement numbers 1 and 4 C. statement numbers 2, 4 and 5 D. statement numbers 1, 3 and 5
Solution
B. Both galvanic cells and fuel cells utilise spontaneous redox reactions. This means that chemical energy is going to be lower in the products and therefore the reaction is exothermic. In all cells, the electrodes are in contact with both the electrolyte and reactants as the cell wouldn’t operate otherwise.
Question 74/ 82 [VCAA 2020 SA Q13] Hydrogen, H2, fuel cells and H2-powered combustion engines can both be used to power cars. Three statements about H2 fuel cells and H2-powered combustion engines are given below: I Neither H2 fuel cells nor H2-powered combustion engines produce greenhouse gases. II Less H2 is required per kilometre travelled when using an H2-powered combustion engine than when using H2 fuel cells. III More heat per kilogram of H2 is generated in an H2-powered combustion engine than in H2 fuel cells. A. II only B. I and II only C. III only D. I and III only
Solution
C. I is not correct as water is a greenhouse gas and both H2 fuel cells and combustion engines would produce water. II and III can be addressed through knowing that a fuel cell is much more efficient than a combustion engine. Therefore, II is incorrect as more H2 would be required and III is correct as more heat is generated, which is wasted energy, by the combustion engine.
Question 75/ 82 [VCAA 2019 SA Q18] Which one of the following galvanic cells will produce the largest cell voltage under standard laboratory conditions (SLC)?
A.
B.
C.
D.
Solution
A. The cell in A produces 0.51 V, which is higher than the other cells.
Question 76/ 82 [VCAA 2020 SA Q3] A diagram of an electrochemical cell is shown below.
Which of the following gives the correct combination of the electrode in the oxidation half-cell and the electrolyte in the reduction half-cell? Electrode (oxidation half-cell)
Electrolyte (reduction half-cell)
S
P
S
R
Q
R
Q
P
Solution
C. Electrons always move from the anode (location of oxidation) to the cathode (location of reduction). This means that the left side of the cell is the oxidation half-cell, and the right side is the reduction half-cell.
Question 77/ 82 [VCAA 2020 SA Q26] The following reactions occur in a primary cell battery. Zn + 2OH− → ZnO + H2O + 2e− 2MnO2 + 2e− + H2O → Mn2O3 + 2OH− Which one of the following statements about the battery is correct? A. The reaction produces heat and Zn reacts directly with MnO2. B. The reaction produces heat and Zn does not react directly with MnO2. C. The reaction does not produce heat and Zn reacts directly with MnO2. D. The reaction does not produce heat and Zn does not react directly with MnO2.
Solution
B. In any battery, the reactants do not react directly. No battery is 100% efficient and thus produces some waste heat energy.
Question 78/ 82 [VCAA 2020 SA Q30] Consider the following half-equation. ClO2(g) + e− ⇌ ClO2−(aq) It is also known that: • ClO2(g) will oxidise HI(aq), but not HCl(aq) • Fe3+(aq) will oxidise Hl(aq), but not NaClO2(aq). Based on this information, Fe2+(aq) can be oxidised by A. Cl2(g) and I2(aq). B. Cl2(g), but not ClO2(g). C. ClO2(g) and Cl2(g), but not I2(aq). D. Cl2(g), ClO2(g) and I2(aq).
Solution
C. From the information provided, an electrochemical series can be constructed. A substance that can oxidise another substance must be a relatively strong oxidising agent (higher on the left in an electrochemical series): Cl2 + 2H+ + 2e− ⇌ 2HCl ClO2 + 2e− ⇌ ClO22− Fe3+ + e− ⇌ Fe2+ I2 + 2H+ + 2e− ⇌ 2HI Therefore Fe2+ can be oxidised by Cl2 and ClO2 but not by I2.
Question 79/ 82
[VCAA 2021 SA Q26] Different metal ion (aq)/metal (s) half-cells are combined with an In3+(aq)/In(s) half-cell to create a galvanic cell at SLC, as shown in the diagram below. The equation for the In3+(aq)/In(s) half-cell is In3+(aq) + 3e− ⇌ In(s)
Which of the following shows the half-cells in decreasing order of voltage produced when combined with the In3+(aq)/In(s) half-cell and In(s) is the negative electrode? A. Mn2+(aq)/Mn(s), Al3+(aq)/Al(s), Mg2+(aq)/Mg(s) B. Mg2+(aq)/Mg(s), A13+(aq)/Al(s), Mn2+(aq)/Mn(s) C. Cu2+(aq)/Cu(s), Pb2+(aq)/Pb(s), Ni2+(aq)/Ni(s) D. Ni2+(aq)/Ni(s), Pb2+(aq)/Pb(s), Cu2+(aq)/Cu(s)
Solution
C. With In as the negative electrode, this would make it the anode, the site of oxidation. Therefore, the overall reaction must be between In and relative strong oxidising agents (found high on the left in the electrochemical series). C has chemicals present that fulfill this requirement in the set of half-cells and also lists the half-cells in order of decreasing potential difference with the In3+/In half-cell.
Question 80/ 82 [VCAA 2022 SA Q4] Which one of the following diagrams shows the common design features of a fuel cell?
A.
B.
C.
D.
Solution
A. The fuel always reacts at the anode in a fuel cell as it is being oxidised. No power source is required for a fuel cell to function as it is a type of galvanic cell. This leaves only A.
Question 81/ 82 [VCAA 2022 SA Q6 Galvanic cells and fuel cells have A. the same energy transformations and both are reversible. B. the same energy transformations and both produce heat. C. different energy transformations but galvanic cells produce electricity. D. different energy transformations but fuel cells use porous electrodes.
Solution
B. Fuel cells are a type of galvanic cell; therefore, the energy transformations are the same. All cells produce heat and therefore B is correct.
Question 82/ 82 [VCAA 2022 SA Q8] Unlike direct combustion of fuel, fuel cells A. can be recharged. B. do not produce greenhouse gases. C. require electrical energy to overcome the activation energy barrier. D. do not have direct contact between the oxidising and reducing agents.
Solution
D. D is true of all cells when compared to the direct redox reaction.
Question 83/ 82 [VCAA 2022 SA Q14] The discharge reaction in a vanadium redox battery is represented by the following equation. VO2+(aq) + 2H+(aq) + V2+(aq) → V3+(aq) + VO2+(aq) + H2O(l) When the vanadium redox battery is recharging A. H+ is the reducing agent. B. H2O is the oxidising agent. C. VO2+ is the reducing agent. D. VO2+ is the oxidising agent.
Solution
C. H+ and VO2+ are not reactants for the recharge reaction eliminating A and D. The oxygen and hydrogen in water do not change oxidation state through the reaction, meaning B is not possible. In the recharge reaction, VO2+ is converted into VO2+, the oxidation state of vanadium changes from 4+ to 5+, meaning that the vanadium is oxidised (and VO2+ is the reducing agent).
Question 84/ 82 [VCAA 2022 SA Q18] A student wants to investigate a galvanic cell consisting of Sn4+/Sn2+ and Ag+/Ag half-cells. Which one of the following combinations of electrodes and solutions will produce an operational galvanic cell? Sn4+/Sn2+ half-cell Electrode Sn
Solution(s) 1 M Sn(NO3)2
Ag+/Ag half-cell Electrode graphite
Solution 1 M AgNO3
Sn
1 M Sn(NO3)4, 1 M Sn(NO3)2
graphite
1 M AgNO3
graphite
1 M Sn(NO3)4, 1 M Sn(NO3)2
Ag
1 M AgNO3
graphite
1 M Sn(NO3)4
Ag
1 M AgNO3
Solution
C. The reaction that should take place in a galvanic cell containing the Sn4+/Sn2+ and Ag+/Ag half–cells is between Sn2+ and Ag+. Sn cannot be present as it would react preferentially to Sn2+ so A and B aren’t possible. D doesn’t have an option with Sn2+ present and thus C is correct.
Question 85/ 82
[VCAA 2022 SA Q30] Consider the following half-equations, which are not in standard electrode potential order. HCrO4−(aq) + 7H+(aq) + 3e− ⇌ Cr3+(aq) + 4H2O(l) HBrO(aq) + H+(aq) + e− ⇌ 12 Br2(aq) + H2O(l) 2IO3−(aq) + 12H+(aq) + 10e− ⇌ I2(aq) + 6H2O(l) BrO3−(aq) + 6H+(aq) + 6e− ⇌ Br−(aq) + 3H2O(l) The following is also known: • I2 reacts with BrO3− and HBrO but not with HCrO4−. • Br− reacts with HBrO but not with IO3−. Platinum electrodes were used in each half-cell. Which one of the following galvanic cells will produce the highest potential difference?
A.
B.
C.
D.
Solution
A. The first dot point of information in the question means that the order of strength of reducing is from weakest to strongest: Cr3+, I2, Br− & H2O or Br2 & H2O. The second dot point enables you to determine that Br2 & H2O is the strongest reducing agent. This means that the highest potential difference is going to occur in A.
Question 1/ 29 Methane and methanol will both burn in air. The reactions are described by the equations
CH4(g) + 2O2(g) → CO2(g) + 2H2O(l); ΔH = −890 kJ mol−1 2CH3OH(g) + 3O2(g) → 2CO2(g) + 4H2O(l); ΔH = −1452 kJ mol−1 (a) If 2 mol of methane and 2 mol of methanol are completely burned in separate experiments, which experiment will release the most energy? (1 mark) (b) If each of the above reactions is used to produce 1000 kJ of energy, which one will release the most carbon dioxide? (2 marks) (Total = 3 marks)
Solution
(a) Complete combustion of 2 mol of CH4 would release 2 × 890 = 1780 kJ. Complete combustion of 2 mol of methanol releases 1452 kJ. The first experiment would release the most energy. (1 mark) (b) For the first reaction:
energy released ΔH
=
n(CO2 ) 1
Hence n(CO2) = 1000 ÷ 890 = 1.12 mol In the second reaction:
energy released ΔH
=
n(CO2 ) 2
Hence n(CO2) = 1000 × 2 ÷ 1452 = 1.38 mol The combustion of methanol will release more CO2 to produce the same amount of energy as methane. (2 marks) (Total = 3 marks)
Question 2/ 29 The reaction between hydrogen and oxygen is described by the equation 2H2(g) + O2(g) → 2H2O(g); ΔH = −484 kJ mol−1
(a) Draw an energy level diagram showing how the energy of the reactants is related to that of the products. Your diagram should also show ΔH and an activation energy. (3 marks) (b) Describe how the strength of the bonds in the reactants is related to the strength of the bonds in the products. (1 mark) (c) Would you expect the magnitude of the enthalpy change for the reaction 2H2(g) + O2(g) → 2H2O(l) to be greater than, less than or the same as the heat change in the first reaction? Explain your answer. (2 marks) (Total = 6 marks)
Solution
(a)
(3 marks) (b) In an exothermic reaction, the products are at lower energy and have stronger bonds than the reactants. (1 mark) (c) When steam is converted into water, H2O(g) → H2O(l), energy is released. Hence the reaction H2(g)+ O2(g) → 2H2O(l) will release more energy than the reaction 2H2(g) + O2(g) → 2H2O(g) meaning that the magnitude of the enthalpy change will be greater. (2 marks) (Total = 6 marks)
Question 3/ 29 Glucose is a very important energy source and is present in many foods. It is oxidised according to the equation below. C6H12O6(s) + 6O2(aq) → 6CO2(g) + 6H2O(l); ΔH = −2803 kJ mol−1 (a) The energy required by a typical VCE chemistry student is about 13 500 kJ per day. If all of the student's energy is derived from the oxidation of glucose, as shown above, calculate the mass of glucose required each day. (2 marks) (b) The label on a bottle of fruit juice cordial indicates that 50.00 mL of the cordial yields 350 kJ of energy. If glucose is the only source of energy in the cordial, calculate the concentration of glucose in g L−1. (3 marks) (c) (i) According to the label on a packet of breakfast bars, each breakfast bar weighs 36.7 g, of which 66.7% is carbohydrate. If all of the carbohydrate is present as glucose, calculate the amount of energy that could be obtained from the combustion of the glucose in the breakfast bar. (3 marks) (ii) If the breakfast bar yields a total of 615 kJ, what percentage of the energy comes from the combustion of the carbohydrate? (1 mark) (Total = 9 marks)
Solution
(a) The oxidation of 1 mol of glucose releases 2803 kJ. n(C 6 H 12 O6 ) 1
=
13 500 2800
Hence n(C6H12O6) needed = 4.816 mol Mass of C6H12O6 required = 4.816 × 180 = 867 g (2 marks) (b) 1 L of fruit juice cordial will release 350×1000 50.00 = 7000 kJ
n(C6H12O6) = 7000 2810 = 2.49 mol and mass C6H12O6 = 2.49 × 180 = 448 g Hence concentration of glucose = 448 g L−1 (3 marks) (c) (i) Mass glucose = 36.7 × 0.667 = 24.5 g n(C6H12O6) = 24.5 180 = 0.136 mol Heat released = 0.136 × 2810 = 382 kJ (3 marks) (ii) % energy from carbohydrate = 382×100 = 62.2% 615 (1 mark) (Total = 9 marks)
Question 4/ 29 One substance used in detonators is lead azide, Pb(N3), because when given a shock (either thermal or mechanical), it decomposes rapidly according to the equation: Pb(N3)2(s) → Pb(s) + 3N2(g); ΔH = −436 kJ mol−1 (a) Would you expect the bonds in Pb and N2 to be stronger than those in Pb(N3)2 or weaker? Explain your answer. (2 marks) (b) Draw an energy level diagram showing how the energy of the reactants is related to that of the products. Your diagram should also show ΔH and an activation energy. (3 marks) (c) 10.0 g of lead azide rapidly decomposes in a volume of 5.00 mL. (i) Calculate the amount of energy released by this decomposition. (1 mark) (ii) Calculate the mass of the gas product. (2 marks) (Total = 8 marks)
Solution
(a) The bonds in Pb and N2 will be stronger than those in Pb(N3)2. The products (Pb and N2) are at a lower energy (are more stable) than the reactants. Hence, it will take more energy to pull apart the atoms of the products than those of the reactants. (2 marks) (b)
(c) (i) n(Pb(N3)2) = 10.0 ÷ 291.2 = 0.03434 mol (3 marks) Energy released = 0.03434 × 436 = 14.97 = 15.0 kJ (1 mark) (ii) n(N2) = 3 × 0.03434 = 0.103 mol; m(N2) = n × M = 0.103 × 28.0 = 2.88 g (3 significant figures) (2 marks) (Total = 8 marks)
Question 5/ 29 A student is asked to determine the heat of combustion of methanol, CH3OH, using the apparatus shown below. 300 g of water is placed in a metal can. The can is clamped above the flame from a spirit burner. The temperature of the water is measured before and after heating by the methanol burner. The burner is weighed before and after heating the water.
The student obtains the following results: - mass of burner and methanol before combustion = 35.674 g - mass of burner and methanol after combustion = 34.396 g - temperature of water in can before heating = 16.3°C - temperature of water in can after heating = 28.1°C (a) Why was a metal can used rather than a glass container? (1 mark) (b) How many mol of methanol was burnt? (2 marks) (c) Calculate the heat energy given to the water. (1 mark) (d) From parts (b) and (c), calculate the heat of combustion of methanol in kJ mol−1. (1 mark) (e) The accepted value for the heat of combustion of methanol is −725 kJ mol−1. Suggest two reasons why the value determined in part (d) is different from this value. (2 marks) (Total = 7 marks)
Solution
(a) Metals are better conductors of heat than glass. Less heat will be wasted heating the container.
(1 mark) (b) Mass methanol used = 35.674 – 34.396 = 1.278 n(methanol) = 1.278 ÷ 32.0 = 0.0399 (2 marks) (c) Heat given to water = 4.18 × 300 × 11.8 = 14.80 kJ (1 mark) (d) Heat of combustion = (–)14.80 ÷ 0.0399 = −371 kJ mol−1 (1 mark) (e) Any two of: • incomplete combustion of methanol • heat lost to the air • heat lost in heating the container • heat lost from the container. (2 marks) (Total = 7 marks)
Question 6/ 29 Natural gas consists largely of methane, CH4, and is used as a source of energy in domestic gas supplies. In a laboratory using natural gas, a student uses a Bunsen burner to heat 300 g of water. The temperature rises from 16.7°C to 49.6°C. (a) Calculate the heat supplied to the water if the specific heat of water is 4.18 J°C−1 g−1. (1 mark) (b) If only 65% of the energy produced from the combustion of the gas is transmitted to the water, calculate the energy produced by the Bunsen burner. (1 mark) (c) Write the equation for the combustion of methane. (1 mark) (d) The student also measured the amount of gas used in the above experiment and found that 1.82 L at SLC were required. Calculate ΔH for the equation in part (c).
(3 marks) (Total = 6 marks)
Solution
(a) Heat supplied to water = 4.18 × 300 × (49.6 – 16.7) = 41 256.6 J = 41.3 kJ (1 mark) (b) Heat produced by Bunsen = 41.3×100 kJ = 63.5 kJ 65 (1 mark) (c) CH4(g) + 2O2(g) → CO2(g) + 2H2O(g) (1 mark) (d) n(CH4) burned = 1.54 24.8 = 0.07334 (1 mark) This amount of gas released 63.5 kJ 63.5 1 mol of gas should release 0.07334 = 865.8 kJ
(1 mark) ΔH for reaction is −866 kJ mol−1 (1 mark) (Total = 6 marks)
Question 7/ 29 Methylated spirits is mostly ethanol, C2H5OH, but also contains small amounts of methanol and water. The energy content of methylated spirits is found to be 28.5 MJ kg−1 and it has a density of 0.795 g mL−1. A camper uses methylated spirits as a source of energy to boil his drinking water. He heats 600 g of water from 15°C to boiling point. (a) Why is it not possible to express the energy content of methylated spirits in kJ mol−1? (1 mark)
(b) Write a balanced equation for the reaction of ethanol with oxygen. (1 mark) (c) Calculate the volume of methylated spirits that must be burnt to heat the water, if only 60% of the energy from burning the methylated spirits reaches the water. (4 marks) (Total = 6 marks)
Solution
(a) Methylated spirits is not a pure substance and thus the molar mass cannot be calculated. (1 mark) (b) C2H5OH(l) + 3O2(g) → 2CO2(g) + 3H2O(g) (1 mark) (c) Energy needed =
4.18×600×(100−15) = 213.2 kJ 1000
(1 mark) Mass(methylated spirits) = 213.2 ÷ 28.5 = 7.48 g (1 g releases 28.5 kJ) (1 mark) Volume(methylated spirits) = 7.48 ÷ 0.795 = 9.41 mL (1 mark) However, only 60% of the energy reaches the water. Volume(methylated spirits) needed = 9.41 ÷ 0.60 = 15.7 mL (1 mark) (Total = 6 marks)
Question 8/ 29 Copper forms two oxides, Cu2O and CuO. The energy change when each oxide is formed is given by the equations below.
2Cu(s) + O2(g) → 2CuO(s); ΔH = −310.4 kJ mol−1 4Cu(s) + O2(g) → 2Cu2O(s); ΔH = −338 kJ mol−1 Use this information to calculate ΔH for the reaction Cu2O(s) → Cu(s) + CuO(s) (Total = 3 marks)
Solution
If the second equation is reversed and halved, then Cu2O(s) → 2Cu(s) + ½O2(g); ΔH = +169 kJ mol−1 Reacting half of the Cu with the O2 would give Cu(s) + ½O2(g) → CuO(s); ΔH = −155.2 kJ mol−1 Combining these two equations would give Cu2O(s) → Cu(s) + CuO(s) and ΔH = +169 + (−155.2) = +13.8 kJ mol−1 (Total = 3 marks)
Question 9/ 29 [Adapted VCAA 2014 SB Q3] The heat of combustion of ethanol is provided in the VCAA data book. This combustion of ethanol is represented by the following equation. C2H5OH(l) + 3O2(g) → 2CO2(g) + 3H2O(l) A spirit burner used 1.80 g of ethanol to raise the temperature of 100.0 g of water in a metal can from 25.0°C to 40.0°C (see diagram below). (a) Calculate the percentage of heat lost to the environment and to the apparatus. (5 marks) (b) Identify one way to limit heat loss to the environment.
(1 mark) (c) Biodiesel may be produced by reacting canola oil with methanol in the presence of a strong base. Since canola oil contains a mixture of triglycerides, the reaction produces glycerol and a mixture of biodiesel molecules. A typical biodiesel molecule derived from canola oil has the chemical formula C15H30O2. The heat content of canola oil can be determined by placing it in the spirit burner in place of ethanol. A typical result is 17 kJ g−1. Suggest why the heat content of fuels such as canola oil and biodiesel are measured in kJ g−1 and not kJ mol−1. (1 mark)
(Total = 7 marks)
Solution
(a) Energy given to water = 100.0 × 4.18 × (40.0 – 25.0) = 6270 J; i.e. 6.27 kJ Energy released by burning ethanol = 1364 × 1.80 46.0 = 53.37 kJ Energy not given to water = 53.37 – 6.27 = 47.10 kJ % energy lost to the environment = 47.10 53.37
× 100 = 88.26
= 88.3% (5 marks) (b) Place a lid on the can or insulate the heat transfer area between the flame and the can, e.g. with foil. (1 mark) (c) Canola oil is a mixture of triglycerides and thus the biodiesel produced from it will be a mixture of methyl esters. Each methyl ester will have a different formula and a different molar mass. Hence it is not possible to calculate the number of moles in a sample. (1 mark)
(Total = 7 marks)
Question 10/ 29 [Adapted VCAA 2017 SB Q2] A vehicle that is powered by a diesel engine is able to use either petrodiesel or biodiesel as a fuel. Petrodiesel and biodiesel are not pure substances but are a mixture of molecules. In general, petrodiesel consists of molecules that are shorter in length, on average, than those found in biodiesel. Biodiesel contains molecules that include functional groups. The table below lists some of the properties of the two fuels. Fuel
Major component
Energy content (MJ kg−1)
CO2 emission (kg CO2/kg of fuel)
petrodiesel
C12H26
43
3.17
biodiesel
C19H32O2
38
2.52
(a) Assume that combustion occurs in an unlimited supply of oxygen for each of the following calculations. Using the data from the table above: (i) calculate the number of litres of biodiesel that are required to be burnt to produce the same amount of energy as 2.5 kg of petrodiesel. [density (biodiesel) = 0.89 kg L−1] (3 marks) (ii) calculate the mass of carbon dioxide, CO2, that would be produced from 3.91 kg of biodiesel. (1 mark) (b) In some circumstances, there is a limited supply of oxygen. Write the balanced chemical equation for the combustion reaction of the major component of biodiesel, C19H32O2, where carbon monoxide, CO, is the only product containing carbon. (2 marks) (Total = 6 marks)
Solution
(a) (i) Energy from the petrodiesel = 2.5 × 43 = 107.5 MJ Mass of biodiesel needed to produce this energy = 107.5 ÷ 38 = 2.829 kg Volume of biodiesel needed = 2.829 ÷ 0.89 = 3.179, i.e. 3.2 L
(3 marks) (ii) Combustion of 3.91 kg of biodiesel will produce 3.91 × 2.52 = 9.853 kg, i.e. 9.85 kg (or 9850 g) (1 mark) (b) 2C19H32O2(l) + 33O2(g) → 38CO(g) + 32H2O(l) (2 marks) (Total = 6 marks)
Question 11/ 29 [Adapted VCAA 2020 SB Q6] Methane gas, CH4, can be captured from the breakdown of waste in landfills. CH4 is also a primary component of natural gas. CH4 can be used to produce energy through combustion. (a) Write the equation for the incomplete combustion of CH4 to produce carbon monoxide, CO. (1 mark) (b) A Bunsen burner is used to heat a beaker containing 350.0 g of water. Complete combustion of 0.485 g of CH4 raises the temperature of the water from 20 °C to 32.3 °C. Calculate the percentage of the Bunsen burner's energy that is lost to the environment. (3 marks) (c) Compare the environmental impact of CH4 obtained from landfill to the environmental impact of CH4 obtained from natural gas. (2 marks) (Total = 6 marks)
Solution
(a) 2CH4(g) + 3O2(g) → 2CO(g) + 4H2O(g or l) (1 mark)
(b) Energy from CH4 = 0.485 × 55.6 = 26.97 kJ Energy absorbed by water = mcΔT = 350.0 × 4.18 × (32.3 – 20) = 18.0 kJ Energy lost to the environment = 26.97 – 18.0 = 9.03 kJ 9.03 Percentage energy lost = 26.97
× 100= 33.3%
(3 marks) (c) Two marks for two valid comparison points from any of the following: • Methane produced from landfills is more carbon neutral than as it doesn’t add as much additional CO2 to the atmosphere. • Methane is a more potent greenhouse gas than carbon dioxide, by burning the methane from landfill there is a reduction in the amount of methane in the atmosphere. This would have a more positive impact than burning methane from natural gas. The methane in natural gas wouldn’t have made it into the atmosphere. • Methane from landfill is more easily collected compared to the methods used for natural gas extraction. • Natural gas can be sourced through fracking which can cause environmental damage. • Both sources of methane produce carbon dioxide when combusted. (2 marks) (Total = 6 marks)
Question 12/ 29 [VCAA 2021 SB Q1] Digesters use bacteria to convert organic waste into biogas, which contains mainly methane, CH4. Biogas can be used as a source of energy. (a) Both biogas and coal seam gas contain CH4 as their main component. Why is biogas considered a renewable energy source but coal seam gas is not? (1 mark) (b) A digester processed 1 kg of organic waste to produce 496.0 L of biogas at standard laboratory conditions (SLC). The biogas contained 60.0% CH4. (i) Write the thermochemical equation for the complete combustion of CH4 at SLC. (2 marks) (ii) Calculate the amount of energy that could be produced by CH4 from 1 kg of organic waste.
(3 marks) (c) Biogas was combusted to release 1.63 x 103 kJ of energy. This energy was used to heat 100 kg of water in a tank. The initial temperature of the water was 25.0 °C. (i) What is the maximum temperature that the water in the tank could reach? (2 marks) (ii) State why this temperature may not be reached. (1 mark) (Total = 9 marks)
Solution
(a) Coal seam gas is a fossil fuel while biogas is a biofuel this means that coal seam gas cannot be regenerated at the rate it is consumed while biogas can be, making it renewable. (1 mark) (b) (i) One mark each for: the correct equation (including states) and correct enthalpy change. CH4(g) + 2O2(g) → CO2(g) + 2H2O(l) ΔH = −890 kJ mol−1 (2 marks) 60 (ii) One mark: V(CH4) = 496 × 100 = 298 L
One mark: n(CH4) = VV
m
=
298 24.8 = 12.0 mol
One mark: q = ΔH × n = 890 × 12.0 = 10680 = 1.07 × 104 kJ (3 marks) (c) (i) 1.63 × 103 kJ = 1.63 × 106 J and 100 kg = 1.00 × 105 g q
One mark: ΔT = Cm
=
1.63×106 4.18×1.00×105 = 3.90°C
One mark: Max temperature = 25.0 + 3.90 = 28.9°C (2 marks) (ii) Not all of the energy released through the combustion of biogas would be used to heat the water, it would also heat the surroundings and other equipment in the environment. Therefore, less than the maximum amount of energy would go into the water and thus the temperature increase would be less than the maximum. (1 mark) (Total = 9 marks)
Question 13/ 29 Carbohydrates, vitamins, fats and proteins are all important components of a balanced diet. Carbohydrates are an immediate source of energy for most living things. Fats and proteins can also be used to provide energy but also have other important functions. (a) A bomb calorimeter is used to determine the energy content of a vegetable oil. 4.86 g of the vegetable oil was completely combusted in a calorimeter that contained 2.50 L of water. The temperature of the water rose from 19.5°C to 33.8°C. Calculate the energy content of the vegetable oil in kJ g−1. (3 marks) (b) Why is the energy content of the vegetable oil calculated in kJ g−1 and not kJ mol−1? (1 mark) (Total = 4 marks)
Solution
(a) Temperature rise = 33.8 – 19.5 = 14.3°C (1 mark) Energy given to water = 14.3 × 4.18 × 2.5 = 149.4 kJ (1 mark) Energy content of vegetable oil = 149.4 ÷ 4.86 = 30.7 kJ g−1 (1 mark) (b) The vegetable oil will be a mixture and hence is not a pure substance. Only pure substances have a chemical formula and thus a molar mass so that moles of substance can be calculated. (1 mark) (Total = 4 marks)
Question 14/ 29 A breakfast food company has a new product, Breckyflakes, which it claims is less fattening than the product of its main rival, Iron-bran. To test the accuracy of these claims, the makers of Iron-bran employ a chemist to determine the heat content of each breakfast cereal. A 15.0 g sample of each cereal is placed in a calorimeter where it is burned in an excess of oxygen. The results shown below were obtained. Breckyflakes sample: • initial temperature of calorimeter and sample
= 18.417°C
• temperature after complete combustion
= 21.577°C
• temperature of calorimeter and combustion products after electric current is used to add 30.2 kJ
= 22.186°C
Iron-bran sample: (a) Determine the calibration factor of the calorimeter in kJ °C−1. (1 mark) (b) For each of the breakfast cereals, calculate the energy content in kJ g−1. (4 marks) (c) From these results can you decide which cereal is most fattening? If you cannot make a decision, what extra evidence might you need? (2 marks) (Total = 7 marks)
Solution
(a) Calibration factor = 30.2 ÷ (22.186 – 21.577) = 49.59 kJ °C−1 (1 mark) (b) Breckyflakes: Heat released = 49.59 × (21.577 – 18.417) = 156.7 kJ Heat released per gram = 156.7 ÷ 15.0 = 10.45 kJ g−1 (2 marks) Iron-bran: Heat released = 49.59 × (22.384 – 18.961) = 169.8 kJ Heat released per gram = 169.8 ÷ 15.0 = 11.32 kJ g−1
(2 marks) (c) No. Some of the energy released may have resulted from the oxidation of cellulose or other indigestible material. (1 mark) Analyse the two breakfast cereals to determine the amount of indigestible material that may have contributed to the heat released when the food was burnt. or Determine the fattening capabilities of the two breakfast foods by studying their effect on suitable animals. (1 mark) (Total = 7 marks)
Question 15/ 29 Calorimeters are often calibrated by measuring the temperature change when a compound with a known heat of combustion is reacted. In a typical experiment 0.1049 g of benzoic acid, C6H5COOH, is completely burned in a calorimeter. The temperature of the calorimeter changes from 18.674°C to 21.905°C. The equation for the reaction is 2C6H5COOH(s) + 15O2(g) → 14CO2(g) + 6H2O(l); ΔH = −6526 kJ mol−1 (a) How many moles of benzoic acid reacted? (1 mark) (b) How much heat energy was released during the reaction? (2 marks) (c) Calculate a value for the calorimeter constant in J°C−1. (2 marks) Ethanol, C2H5OH, has been suggested as an alternative fuel to petrol. 0.545 mL of ethanol is burned in the same calorimeter and a temperature rise of 14.618°C is recorded. (d) How much energy was released by the burning ethanol? (1 mark) (e) Calculate the heat of combustion of ethanol in kJ mL−1. (1 mark) (Total = 7 marks)
Solution
(a) n(benzoic acid) = 0.1049 ÷ 122.0 = 8.598 × 10−4 mol (1 mark) 4 (b) Heat released = 6526×8.598×10 = 2.806 kJ 2
(2 marks) (c) Temperature rise = 3.231°C Calibration factor = 2.806×1000 3.231
= 868.5 J ∘ C −1
(2 marks) (d) Heat released = 868.5 × 14.618 = 12.70 kJ (1 mark) (e) Heat of combustion = 12.70 ÷ 0.545 = 23.29 kJ mL−1 (1 mark) (Total = 7 marks)
Question 16/ 29 A middle-distance runner runs for 4 minutes 30 seconds and takes 70 breaths per minute. He has a lung capacity of 7.2 L and exchanges all of the air in his lungs with each breath. Air contains 20% oxygen, 25% of which is used in his cells for the reaction C6H12O6(aq) + 6O2(aq) → 6CO2(g) + 6H2O(l); ΔH = −2800 kJ mol−1 (a) What volume of oxygen is inhaled in 4.5 minutes? (1 mark) (b) What volume of oxygen reacts at the cells? (1 mark) (c) Assuming the oxygen was at SLC, calculate the minimum mass of glucose that the runner uses while running. (2 marks) (d) Calculate the energy the runner has obtained from the reaction of the glucose.
(1 mark) (Total = 5 marks)
Solution
(a) Volume of O2 = 4.5 × 70 × 7.2 × 0.20 L = 453.6 L (1 mark) (b) Volume of O2 reacting at cells = 453.6 × 0.25 = 113.4 L (1 mark) (c) n(O2) = 113.4 ÷ 24.8 = 4.573 mol n(C6H12O6) = 4.573 ÷ 6 = 0.7620 mol Mass C6H12O6 = 0.7620 × 180 = 137.1 = 137 g (3 significant figures) (2 marks) (d) Energy supplied by glucose = 0.7620 × 2800 = 2134 kJ (1 mark) (Total = 5 marks)
Question 17/ 29 [Adapted VCAA 2019 SB Q6] There are many varieties of bread available to consumers in Australia. The nutritional values for one type of wholemeal bread are given in the table below. • initial temperature of calorimeter and sample
= 18.961°C
• temperature after combustion of sample
= 22.384°C
Per 100 g Energy
1000 kJ
Protein
9.1 g
Per 100 g Fats and oils
2.5 g
Carbohydrates
41.5 g
Sugars
3.0 g
Fibre
6.4 g
(a) Calculate the energy, in kilojoules, provided by the protein and fats and oils in 100 g of this wholemeal bread. (1 mark) (b) The wholemeal bread undergoes complete combustion in a bomb calorimeter containing 200 g of water. Assume that all of the energy in the combustion is transferred to the water. (i) Calculate the mass of bread needed to raise the temperature of the water by 6°C. (2 marks) (ii) The combustion of the bread was investigated using a different method. The bread was ignited under a beaker containing 200 g of water, which was set on a tripod. The equipment used is shown below.
If 1.2 g of bread was needed to raise the temperature of the water by 6°C using this different method, calculate the efficiency of the energy transfer in this combustion. (1 mark) (Total = 4 marks)
Solution
(a) E = 9.1 × 17 + 2.5 × 37 = 2.5 × 102 kJ (1 mark) (b) (i) q = 200 × 4.18 × 6 = 5 × 103 J = 5 kJ Energy content of bread = 1000 kJ ÷ 100 g = 10.0 kJ g−1 5 m(bread) = 10 = 0.5 g
(2 marks) (ii) Efficiency = 0.5 1.2
× 100 = 41.8 % = 4 × 10%
(1 mark) (Total = 4 marks)
Question 18/ 29 A chemist places tin rods in each of four 1.0 M aqueous solutions. The solutes are respectively AgNO3, CuSO4, FeSO4 and ZnCl2. Describe what you would expect to happen in each of these experiments. Give reasons for your answers. Give equations for any reactions that occur. (Total = 4 marks)
Solution
The relevant equations from the electrochemical series are Ag+(aq) + e− ⇌ Ag(s) Cu2+(aq) + 2e− ⇌ Cu(s) Sn2+(aq) + 2e− ⇌ Sn(s) Fe2+(aq) + 2e− ⇌ Fe(s) Zn2+(aq) + 2e− ⇌ Zn(s) Hence, the tin will react with the AgNO3 and CuSO4 solutions because Sn is a better reductant than Ag or Cu. However, Fe and Zn are better reductants than Sn. Hence no reaction will occur when pieces of tin are placed in solutions of FeSO4 and ZnCl2.
The equations for the reactions occurring in the other solutions are 2AgNO3(aq) + Sn(s) → 2Ag(s) + Sn(NO3)2(aq) CuSO4(aq) + Sn(s) → Cu(s) + SnSO4(aq) (Total = 4 marks)
Question 19/ 29 The potential differences and electrode polarities of two standard electrochemical cells are shown below. (Note that not all of these half-cells are listed in the electrochemical series provided in the VCAA data book.)
(a) From the information given above, deduce which species in the two cells is the strongest oxidising agent. Explain your reasoning. (2 marks) (b) Give the equation for the reaction occurring at the anode in each cell. (2 marks) (c) If a cell was constructed from the Fe3+/Fe2+ and the Cd2+/Cd half-cells, what would be the value for the potential difference of the cell? (1 mark) (Total = 5 marks)
Solution
(a) The strongest oxidant will be highest in the electrochemical series and will be the positive electrode (the oxidant will undergo reduction, i.e. it will consume electrons). The Sn4+/Sn2+ half-cell is common to both galvanic cells. While the Sn4+/Sn2+ half-cell is positive with respect to the Cd2+/Cd half-cell, it is negative when compared with Fe3+/Fe2+. Thus, the best oxidant must be in the Fe3+/Fe2+ half-cell. The best oxidant is Fe3+. (2 marks) (b) Oxidation occurs at the anode. In galvanic cells the anode is negative. Hence the equations for the reactions occurring are Cd(s) → Cd2+(aq) + 2e− Sn2+(aq) → Sn4+(aq) + 2e− (2 marks) (c) Of the three half-cells the Cd2+/Cd half-cell will be the lowest on the electrochemical series and the Fe3+/Fe2+ half-cell will be the highest. The likely voltage of a cell constructed from these two half-cells is 0.55 + 0.62 = 1.17 V. (1 mark) (Total = 5 marks)
Question 20/ 29 A home chemistry kit contains solutions of Sn2+, Cu2+, Fe3+, a dilute acid and pieces of metallic copper, iron, lead and zinc. (a) Describe an experiment in which Sn2+(aq) would be oxidised to Sn4+(aq). Give a balanced equation for the reaction. (2 marks) (b) If a mixture of Cu2+(aq) and Fe3+(aq) was prepared, how could the Fe3+(aq) be reduced without the Cu2+(aq) reacting? Give a balanced equation for the reaction. (2 marks) (c) Give a balanced equation for a reaction that could be used to prepare a sample of hydrogen gas. (1 mark) (Total = 5 marks)
Solution
The relevant equations from the electrochemical series are given below. The chemicals present in the chemistry kit are in bold. Fe3+(aq) + e− ⇌ Fe2+(aq) Cu2+(aq) + 2e− ⇌ Cu(s) Sn4+(aq) + 2e− ⇌ Sn2+(aq) 2H+(aq) + 2e− ⇌ H2(g) Pb2+(aq) + 2e− ⇌ Pb(s) Sn2+(aq) + 2e− ⇌ Sn(s) Fe2+(aq) + 2e− ⇌ Fe(s) Zn2+(aq) + 2e− ⇌ Zn(s) (a) Either the Cu2+ or the Fe3+ could be used to oxidise the Sn2+. Sn2+(aq) + Cu2+(aq) → Sn4+(aq) + Cu(s) or Sn2+(aq) + 2Fe3+(aq) → Sn4+(aq) + 2Fe2+(aq) (2 marks) (b) The only reagent that could reduce the Fe3+ without reducing the Cu2+ is copper metal. Cu(s) + 2Fe3+(aq) → 2Fe2+(aq) + Cu2+(aq) (2 marks) (c) In theory any of the metals Zn, Fe, Sn or Pb could be used to prepare a sample of hydrogen. However, in practice only Zn or Fe would give a fast enough reaction to produce the hydrogen in a reasonable time. Zn(s) + 2H+(aq) → Zn2+(aq) + H2(g) or Fe(s) + 2H+(aq) → 2Fe2+(aq) + H2(g) (1 mark) (Total = 5 marks)
Question 21/ 29 A chemist carried out reactions with three metals, X, Y and Z, and solutions of their nitrate salts. The observations below were made when clean metal surfaces were used. I Metal Z dissolved in a 1.0 M YNO3 solution, forming a deposit of metal Y. II Metal X did not react with a 1.0 M Z(NO3)3 solution. III Metal Y did not react with a 1.0 M X(NO3)2 solution. (a) Use this information to place the three metals in order of increasing strength as reducing agents (put the least reactive first). Give reasons for your answer. (3 marks) (b) Some methods for mining metals from metal ores utilise a reaction between the metal and a substance pumped into the ore, such as an acid. This means that more reactive metals are more easily extracted in this type of process as they more readily react and dissolve, as metal ions, into the solution. The liquid is then extracted from the ore with the dissolved ions. The naturally occurring ores of these metals are XS, Y2S and Z2O3. Which metal is likely to be the easiest to extract from its ore and which metal is likely to be the most difficult to extract? Give reasons for your answers. (2 marks) (Total = 5 marks)
Solution
(a) Z is more reactive (better reductant) than Y and is also more reactive than X. X is more reactive (better reducing agent) than Y. The order of reactivity (decreasing reducing strength) of metals is Z > X > Y and hence the ease of production from the ores will be the reverse of this order. (3 marks) (b) Y will be the easiest metal to extract (from Y2S) and Z will be the most difficult metal to extract. (2 marks) (Total = 5 marks)
Question 22/ 29 Three electrochemical cells are set up as shown below. The potential difference is shown on each voltmeter.
(a) From this information, deduce the order of the four half-cells Cu2+/Cu, X+/X, Y2+/Y and Z2+/Z in the electrochemical series. (List the one with the strongest oxidant first.) (3 marks) (b) If a cell was constructed from the Y2+/Y and Z2+/Z half-cells, deduce the polarity of the electrodes and the potential difference of the cell. (2 marks) (Total = 5 marks)
Solution
(a) Y is a stronger reductant than Cu by 0.45 V. Z is a stronger reductant than Cu by 1.10 V. Hence, Z is a stronger reductant than Y. Cu is a stronger reductant than X. Hence, the order of half-cells is X+/X > Cu2+/Cu > Y2+/Y > Z2+/Z (3 marks) (b) Since Y2+ is a stronger oxidant than Z2+, the Y2+/Y will be the positive half-cell. The potential difference will be the difference between the voltages that the half-cells produce with the Cu2+/Cu half-cell, i.e. 1.10 – 0.45 = 0.65 V (2 marks) (Total = 5 marks)
Question 23/ 29 Six experiments were carried out in which pairs of reagents were mixed. The pairs are indicated in the left-hand
column of the table below. For those cases where the electrochemical series would predict that a reaction should occur, write a balanced chemical equation for the predicted reaction. Where you do not expect a reaction, write ‘no reaction’. Reactants
Predicted reaction Yes/No
Equation
Fe2+(aq)/Cl2(g) AgNO3(aq)/Sn(s) SnCl2(aq)/Cu(s) Cd2+(aq)/Ag(s) Ni2+(aq)/Cd(s) Cl−(aq)/I2(aq) (Total = 9 marks)
Solution Reactants
Predicted reaction Yes/No
Equation
Fe2+(aq)/Cl2(g)
yes
2Fe2+(aq) + Cl2(g) → 2Fe3+(aq) + 2Cl−(aq)
AgNO3(aq)/Sn
yes
2Ag+(aq) + Sn(s) → 2Ag(s) + Sn2+(aq)
SnCl2(aq)/Cu
no
Cd2+(aq)/Ag(s)
no
Ni2+(aq)/Cd(s)
yes
Cl−(aq)/I2(aq)
no
Ni2+(aq) + Cd(s) → Ni(s) + Cd2+(aq)
(Total = 9 marks)
Question 24/ 29 Copper plates were once attached to the hulls of wooden ships. In water, the copper corroded and produced Cu2+(aq) ions. These ions are poisonous to many marine organisms and so the formation of barnacles and other organisms on the ships’ hulls was prevented. In seawater, the copper corroded very rapidly. To slow down the removal of the
copper, pieces of a reactive metal were attached to the copper plates. Zinc was often used as the reactive metal. The copper plates then lasted for a longer time, but the barnacles and other organisms quickly attached themselves to the hulls of the ships. Use the electrochemical series to answer the questions below. (a) Why do the copper plates corrode? Write a balanced equation for the reaction. (2 marks) (b) The corrosion is faster in seawater. Suggest a reason for this. (1 mark) (c) Why do pieces of a reactive metal prevent the copper from corroding? What happens to the reactive metal, such as zinc? Write the equation for any reaction that occurs. (3 marks) (d) When a piece of zinc is joined to the copper plates, barnacles rapidly become attached to the hull. Suggest a reason for this. (1 mark) (Total = 7 marks)
Solution
(a) The copper metal will react with oxygen and water (O2 is higher in the reactivity series as an oxidant than is Cu as a reductant). Hence 2Cu(s) + O2(g) + 2H2O(l) → 2Cu(OH)2(s) (2 marks) (b) The seawater contains dissolved ionic salts. Hence it is a better electrolyte than fresh water. (1 mark) (c) The reactive metal is more easily oxidised than the copper and thus supplies electrons to the copper. This prevents the copper from oxidising. The reactive metal is oxidised instead of the copper. The piece of reactive metal will eventually dissolve. Zn(s) → Zn2+(aq) + 2e− (3 marks) (d) Copper ions are needed to poison the barnacles. Since attaching a piece of zinc to the copper hull slows down the corrosion of the copper, the concentration of the copper ions near the hull is reduced and the concentration will not be high enough to poison the barnacles.
(1 mark) (Total = 7 marks)
Question 25/ 29 Consider the following electrochemical series. Cu+(aq) + e− ⇌ Cu(s) E° = 0.52 V Cu2+(aq) + e− ⇌ Cu+(aq) E° = 0.16 V Many solid compounds of copper(I) are known (such as solid copper(I) oxide, Cu2O; solid copper(I) chloride, CuCl) and are quite stable. However, attempts to prepare solutions containing Cu+(aq) are always unsuccessful. Use the information provided above to explain why solutions of Cu+(aq) are unstable. (Total = 3 marks)
Solution
In the electrochemical series given, Cu+ is present as both an oxidant and a reductant. In particular, Cu+ is the best reductant and also the best oxidant. Hence the following reaction should proceed: Cu+(aq) + Cu+(aq) → Cu2+(aq) + Cu(s) This process would be extremely slow in any solid because the Cu+ ions would only move very slowly, if at all. However, in solution the Cu+ ions are more mobile and a reaction occurs. (Total = 3 marks)
Question 26/ 29 [VCAA 2014 SB Q10] The diagram below shows a cross-section of a small zinc-air button cell, a button cell that is used in hearing aids. The zinc acts as the anode. It is in the form of a powder dispersed in a gel (a jelly-like substance) that also contains
potassium hydroxide. The cathode consists of a carbon disc. Oxygen enters the cell via a porous Teflon membrane. This membrane also prevents any chemicals from leaking out.
The following reaction takes place as the cell discharges. 2Zn(s) + O2(g) + 2H2O(l) → 2Zn(OH)2(s) (a) Write a balanced half-equation for the reaction occurring at the anode. (1 mark) (b) Suggest one role of potassium hydroxide in this cell. (1 mark) (c) A zinc-air button cell is run for 10 hours at a steady current of 2.36 mA. What mass of zinc metal reacts to form zinc oxide during that time? (3 marks) (d) A hydrogen-oxygen fuel cell can operate with an alkaline electrolyte such as potassium hydroxide. In this cell, the reaction at the cathode is the same as that in the zinc-air cell. A porous carbon cathode is used. Write the halfequation for the reaction that occurs at the anode in a hydrogen-oxygen cell with an alkaline electrolyte. (1 mark) (Total = 6 marks)
Solution
(a) Zn(s) + 2OH−(aq) → Zn(OH)2 + 2e− (1 mark) (b) Potassium hydroxide acts as the electrolyte. K+ and OH− ions can move through the gel to the cathode and anode respectively. At the electrodes these ions can balance the charges. OH− ions react with Zn at the anode and are formed at the cathode.
(1 mark) (c) t = 10 × 60 × 60 = 3600 s Q = It = 2.36 × 10−3 × 3600 = 85 C Q
n(e−) = F
=
85 −4 96500 = 8.8 × 10
n(Zn) = 12 × n(e−) = 12 × 8.8 × 10−4 = 4.4 × 10−4 m(Zn) = n × M = 4.4 × 10−4 × 65.4 = 0.029 g (3 marks) (d) Oxidation of H2 occurs at the anode. H2(g) + 2OH−(aq) → 2H2O(l) + 2e− (1 mark) (Total = 6 marks)
Question 27/ 29 [VCAA 2018 SB Q6] Redox reactions occur in the human body as well as in electrochemical cells. (a) Nicotinamide adenine dinucleotide (NAD) is a vital coenzyme for energy production in the human body. It exists in two forms: an oxidised form, NAD+, and a reduced form, NADH. NAD is involved in the conversion of ethanol, CH3CH2OH, to ethanal, CH3CHO, in the human body. The overall equation for this redox reaction is CH3CH2OH + NAD+ → CH3CHO + NADH + H+ (i) Write the two half-equations for this redox reaction. States are not required. Oxidation half-equation: Reduction half-equation: (2 marks) (ii) Identify the reducing agent in this redox reaction. (1 mark) (b) The Daniell cell, a type of galvanic cell, was first constructed in the mid-1800s and this type of cell is still in use today. A diagram of the Daniell cell is shown below.
(i) Label the polarity of the electrodes by placing a positive (+) or negative (−) sign in each of the circles next to the electrodes on the diagram. (1 mark) (ii) Use the electrochemical series to determine the theoretical voltage of this cell. (1 mark) (iii) In the diagram below, the electrolyte in the salt bridge is a potassium nitrate solution, KNO3(aq). In the box above the salt bridge, use an arrow to indicate the direction of flow of K+(aq) ions. (1 mark) (iv) List two visible changes that are likely to be observed when the Daniell cell has been operating for some time. (2 marks) (c) What design features of the Daniell cell structure would allow it to produce electrical energy? (2 marks)
Solution
(a) (i) Oxidation half-reaction: CH3CH2OH → CH3CHO + 2H++ 2e− Reduction half-equation: NAD+ + H+ + 2e− → NADH (2 marks)
(ii) The reducing agent is ethanol, CH3CH2OH. (1 mark) (b) (i) The zinc electrode is –ve and the copper electrode is +ve. (1 mark) (ii) E°(cell) = E°(oxidant) – E°(reductant) = 0.34 – (−0.76) = 1.10 V (1 mark) (iii) In the salt bridge, the K+ ions flow towards the Cu/Cu2+ half-cell. (1 mark) (iv) The changes that would be visible after the cell has been operated for some time are: • the Cu electrode would be coated with more Cu. • the Zn electrode would have decreased in size. • the blue colour of the Cu2+ solution would have faded. • the voltage would have fallen. (Any two for 2 marks) (c) To produce a flow of electrons in the external circuit, the oxidant and the reductant must be kept apart. This is achieved by having separate compartments (half-cells) for the two chemicals. A complete circuit is achieved by connecting the two half-cells with a salt bridge. (2 marks) (Total = 10 marks)
Question 28/ 29 [VCAA 2019 SB Q4] Internal combustion engines are used in large numbers of motor vehicles. Historically, internal combustion engines have used fuels obtained from crude oil as a source of power. As concerns for the environment have grown, efforts have been made to obtain fuel for combustion engines from other sources. (a) One way of reducing the environmental effects of fossil fuels is to blend them with biofuels. A common method is to blend petrol with ethanol in varying ratios. A fuel can be obtained by blending 1 mole of octane, C8H18, and 1 mole of ethanol, C2H5OH. The chemical equation for the complete combustion of this fuel mixture is
C8H18(l) + C2H5OH(l) + 15½O2(g) → 10CO2(g) + H2O(g) Calculate the energy released, in kilojoules, when 80 g of this fuel mixture undergoes complete combustion. Show your working. (3 marks) (b) Some car manufacturers are exploring the use of an acidic ethanol fuel cell to power vehicles. In this fuel cell, the ethanol at one electrode reacts with water that has been produced at the other electrode. A membrane is used to transport ions between the electrodes. A diagram of an acidic ethanol fuel cell is shown below.
(i) Identify the electrode as either the cathode or the anode in the box provided in the diagram above. (1 mark) (ii) Write the half-equation for the reaction occurring at the anode. (1 mark) (iii) The combustion of ethanol and the combustion of octane release about the same amount of energy per mole of carbon dioxide produced. Identify two advantages of powering a vehicle using an ethanol fuel cell instead of an internal combustion engine powered by octane. (2 marks) (Total = 7 marks)
Solution
(a) M(C8H18+C2H5OH) = 160.0 g mol−1 n(C8H18 + C2H5OH) = 80 ÷ 160 = 0.50 mol of each fuel q = 5460 × 0.50 + 1360 × 0.50 = 3.4 × 103 kJ (3 marks) (b) (i) Anode (1 mark) (ii) CH3CHOH(g) + 3H2O(l) → 2CO2(g) + 12H+(aq) + 12e− (1 mark) (iii) Ethanol is a renewable fuel as it can be produced through fermentation of feedstock. This means that when using ethanol, the net addition of carbon dioxide to the atmosphere is less than octane. A fuel cell is significantly more energy efficient than a combustion engine. This means to deliver the same amount of energy, less fuel is required and therefore less carbon dioxide is added to the atmosphere. (2 marks) (Total = 7 marks)
Question 29/ 29 [VCAA 2021 SB Q4] (a) What is a fuel cell? (2 marks) (b) The diagram below shows part of an ethanol fuel cell, which produces carbon dioxide and uses an acidic electrolyte.
(i) Name the species that crosses the membrane to enable fuel cell operation. (1 mark) (ii) In the box provided on the diagram above, indicate the direction of flow of the species named in part b.i. (1 mark) (c) Write the equation for the reaction that occurs at the anode of an ethanol fuel cell, which produces carbon dioxide and uses an acidic electrolyte. (1 mark) (d) If an ethanol fuel cell was operating at 25 °C and at 100% efficiency, how much electrical energy could be produced from 1.0 g of ethanol? (1 mark) (e) Identify two aspects of electrode design that can improve the efficiency of a fuel cell. (2 marks) (f) State how the environmental impact of using an ethanol fuel cell operating at 100% efficiency can be minimised. (1 mark) (Total = 9 marks)
Solution
(a) One mark for each of: • a type of galvanic cell or a cell that converts chemical energy into electrical energy • a cell where reactants are continuously supplied to the cell or reactants are not stored within the cell (2 marks)
(b) (i) Hydrogen ion or hydronium ion or proton (1 mark) (ii) → (cations always flow to the cathode) (1 mark) (c) CH3CH2OH(g) + 3H2O(l) → 2CO2(g) + 12H+(aq) + 12e− (1 mark) (d) Equal to the heat energy produced by burning. q = m × ΔH = 1.0 × 29.6 = 30 kJ (1 mark) (e) Any two of: • Increased surface area of the electrode through being porous or a mesh • Using electrodes that are catalytic • Using electrodes that are very good conductors to decrease heat lost through resistance of the electrodes. (2 marks) (f) Either of: • The CO2 produced by the cell could be captured and sequestered. • Use bioethanol as the source of ethanol for the cell. (1 mark) (Total = 9 marks)
Question 1/ 6 In the species ClO3− and H3PO3, the oxidation states of the underlined atoms are respectively A. +5 and +3 B. +5 and 0 C. +6 and +3 D. −5 and −3
Solution
A. The oxidation number of Cl in ClO3− is +5 and the oxidation number of P in H3PO3 is +3.
Question 2/ 6 The energy diagram shown below contains the information from the following two combustion reactions. CH4(g) + 2O2(g) → CO2(g) + 2H2O(l); ΔH = −890 kJ mol−1 CO(g) + ½O2(g) → CO2(g); ΔH = −282 kJ mol−1
From the information above, ΔH for the reaction 2CH4(g) + 3O2(g) → 2CO(g) + 4H2O(l) is most likely to be A. −608 kJ mol−1 B. −1172 kJ mol−1 C. −1216 kJ mol−1 D. −2344 kJ mol−1
Solution
C. Equation is obtained if the second equation provided is reversed, doubled and added to the first equation doubled. Hence ΔH = 2 × (−890) + 2 × 282 = −1216 kJ mol
Question 3/ 6 One of the reactions involved in the production of methanol, CH3OH, is CO2(g) + 3H2(g) → CH3OH(g) + H2O(g); ΔH = −48 kJ mol−1 From this information it can be concluded that A. formation of 1 mol of water releases 24 kJ. B. when 3.0 g of hydrogen reacts 48 kJ of energy are released. C. reaction of 1 mol of carbon dioxide absorbs 48 kJ of energy. D. production of 2 mol of methanol would release 96 kJ of energy.
Solution
D. The formation of 1 mol of methanol and 1 mol of water will release 48 kJ. The reaction of 3.0 g of hydrogen would release 24 kJ.
Question 4/ 6 A recently developed fuel cell uses methanol and oxygen as the two reactants. In this cell, complete combustion of methanol takes place. The reaction occurring at the anode of this cell is A. 2CH3OH(aq) + 3O2(g) → 2CO2(g) + 4H2O(l) B. O2(g) + 4H+(aq) + 4e− → 2H2O(l) C. CH3OH(aq) → CO(g) + 4H+(aq) + 4e− D. CH3OH(aq) + H2O(l) → CO2(g) + 6H+(aq) + 6e−
Solution
D. By definition, oxidation occurs at the anode. Option C is incomplete combustion.
Question 5/ 6 Using a data table, a student finds that the heat of combustion of propan-1-ol is 2021 kJ mol−1. What value would the student calculate for the heat of combustion of propan-1-ol in kJ g−1? A. 23.0 B. 27.3 C. 33.6 D. 43.9
Solution
C. Molar mass of 1-propanol = 60 g mol−1 ΔH(C3H7OH) = 2021 ÷ 60 = 33.68 kJ g−1
Question 6/ 6 Silver oxide and zinc are used in some galvanic cells. When these cells produce an electric current, the following reaction occurs. Ag2O(s) + Zn(s) + H2O(l) → 2Ag(s) + Zn(OH)2(s) The reaction occurring at the positive electrode when cells of this type produce a current is
A. Zn(s) + 2OH−(aq) → Zn(OH)2(s) + 2e− B. Ag2O(s) + H2O(l) + 2e− → 2Ag(s) + 2OH−(aq) C. Zn(OH)2(s) + 2e− → Zn(s) + 2OH−(aq) D. 2Ag(s) + 2OH−(aq) → Ag2O(s) + H2O(l) + 2e−
Solution
B. At the positive electrode, electrons are consumed. The reaction in A. occurs at the negative electrode and that in C. would occur during recharging of the cell.
Question 8/ 6 From this information, place the metals in order showing the increasing ease of oxidation (easiest to oxidise last). A. p < q < r < Cu B. Cu < r < q < p C. q < p < Cu < r D. r < Cu < p < q
Solution
C. In galvanic cells, electrons are produced at the negative electrode. Oxidation occurs at this electrode. From these results Cu is more easily oxidised than p and q but r is more easily oxidised than Cu. Since the voltage from the Cu/q cell is greater than that from the Cu/p cell p is more easily oxidised than q.
Question 9/ 6
If the metals p and q were connected, then the results expected would be Negative terminal
Voltage (V)
p
0.84
p
1.74
q
0.84
q
1.74
Solution
A. Since the voltage from the Cu/q cell is greater than that from the Cu/p cell, p is more easily oxidised than q and p will be the negative electrode. The cell voltage will be 1.29 – 0.45 V.
Question 10/ 6 Students in a VCE Chemistry class were asked to determine the heat of combustion of an alcohol. Each pair of students used a different alcohol. The alcohols studied were methanol, ethanol, propan-1-ol, butan-1-ol and pentan-1ol. All students used the equipment shown in the diagram below.
The results obtained by the students using propan-1-ol are shown below. Mass of water in can = 250 g Mass of propan-1-ol burned = 0.496 g Temperature rise of water = 7.2°C (a) (i) What value, in kJ mol−1, should the students calculate for the heat of combustion of propan-1-ol using their
results? (2 marks) (ii) Write the thermochemical equation for the heat of combustion of propan-1-ol. (2 marks) The heats of combustion determined by some of the other groups of students are given in the table below. Alcohol
Heat of combustion (kJ mol−1)
Methanol
380
Butan-1-ol
1140
Pentan-1-ol
1330
(b) (i) Use the results in the table and the value calculated in part (a) to plot a graph of heat of combustion against the number of carbon atoms in the alcohol. (2 marks) (ii) From your graph, determine the heat of combustion obtained by the students who used ethanol. (1 mark) (c) The students using butan-1-ol noticed that the alcohol burned with a yellow flame and concluded that some of the alcohol was undergoing incomplete combustion and producing carbon rather than carbon dioxide. Write the equation for the incomplete combustion of butan-1-ol. (2 marks) (Total = 9 marks)
Solution
(a) (i) Energy given to water = 4.18 × 0.250 × 7.2 = −7.524 kJ n(propan-1-ol) = 0.496 ÷ 60.1 = 0.008253 mol Heat of combustion = 7.524 ÷ 0.008253 = 911.6 = −910 kJ mol−1 (2 marks) (ii) 2C3H8O(l) + 9O2(g) → 6CO2(g) + 8H2O(l); ΔH = −1820 kJ mol−1 (2 marks) (b) (i)
(2 marks) (ii) The students who used ethanol determined a value of ∼660 kJ mol−1 for the heat of combustion. (1 mark) (c) C4H10O(l) + 2O2(g) → 4C(s) + 5H2O(l) (2 marks) (Total = 9 marks)
Question 11/ 6 Methanol can be produced by the partial oxidation of methane in a two-step process. 2CH4(g) + O2(g) → 2CO(g) + 4H2(g); ΔH = −74 kJ mol−1 followed by 2CO(g) + 4H2(g) → 2CH3OH(g); ΔH = −180 kJ mol−1 (a) The methanol produced in this way can be described as a renewable fuel or as a non-renewable fuel. Explain why this is possible. (3 marks) (b) Calculate the amount of energy released (in MJ) when 1.00 kg of methane is converted into methanol. (3 marks) (Total = 6 marks)
Solution
(a) To be classified as a renewable fuel the methanol must be produced from a source (or sources) that is renewable, i.e. produced by natural processes in a relatively short time. The methane obtained from crude oil or by the gasification of coal or from natural gas is not from a renewable source. The anaerobic decomposition of plant and animal waste produces biogas, a mixture of methane and carbon dioxide. If the methane is obtained in this way, it is from a renewable source. (3 marks) (b) From the two reactions, when 2 moles of methane are converted into 2 moles of methanol, 74 + 180 = 254 kJ of energy are released. = 62.5 mol n(CH4) = 1.00×1000 16 Energy released = 254×62.5 = 7937.5 kJ or 7.9 MJ. 2 (3 marks) (Total = 6 marks)
Question 12/ 6 In recent years, solid oxide fuel cells have been developed that use methane as the fuel. The other reactant is oxygen from the air. The electrodes are often made from metals such as platinum or nickel. The fuel cell operates at high temperatures and the electrolyte is a solid ceramic oxide. At high temperatures, O2− ions are able to move through the electrolyte. (a) The half-equation for the reaction occurring at one of the electrodes is O2(g) + 4e− → 2O2−(s) Give the name of this electrode and state its polarity. (2 marks) (b) Give two properties of the electrode essential for the successful operation of the fuel cell. (2 marks) (c) At the other electrode, methane is consumed, and carbon dioxide and water are produced. Write the half-equation for the reaction occurring at this electrode.
(2 marks) (d) Give the overall cell reaction. (1 mark) (Total = 7 marks)
Solution
(a) This reaction is a reduction and occurs at the cathode. Since electrons are absorbed, the electrode will be positive. (2 marks) (b) Electrodes must be good electrical conductors, porous (to increase the surface area so that gases can make good contact) and be able to catalyse the electrode reactions. (2 marks) (c) CH4(g) + 4O2− → CO2(g) + 2H2O(l) + 8e− (2 marks) (d) CH4(g) + 2O2(g) → CO2(g) + 2H2O(l) (1 mark) (Total = 7 marks)
Question 13/ 6 (a) Sucrose is a sugar found in many foods. It has the formula C12H22O11 and can be oxidised to form carbon dioxide and water. Write an equation for the oxidation of sucrose. (1 mark) (b) A bomb calorimeter can be used to determine the energy released when sucrose is oxidised. Draw and label a bomb calorimeter suitable for measuring the energy released when sucrose is oxidised in oxygen. (3 marks) (c) 0.281 g of sucrose is burned in excess oxygen in a bomb calorimeter. The temperature is observed to rise from 294.156 K to 294.781 K. This bomb calorimeter has a calibration factor of 7380 J K−1.
(i) How much heat is evolved by the combustion of 0.281 g of sucrose? (1 mark) (ii) Calculate the heat that would be evolved by burning 1 mol of sucrose. (1 mark) (Total = 6 marks)
Solution
(a) C12H22O11(s) + 12O2(g) → 12CO2(g) + 11H2O(l) (1 mark)
(b) The following should be correctly labelled features of the bomb calorimeter: • electrical heater for calibration • stopcock for admission of oxygen • ignition circuit to start reaction • stirrer in water bath • water bath surrounding the bomb (pressurised container) • thermometer for measuring temperature changes.
(3 marks) (c) (i) Heat evolved = temp. rise × calibration factor = (294.781 – 294.156) × 7380 = 0.625 × 7380 = 4612.5 J (1 mark) (ii) n(sucrose)= 0.281 ÷ 342 = 0.0008216 mol Heat evolved when 1 mol burns = 4612.5 ÷ 0.0008216 = 5 614 000 J = 5610 kJ mol−1 (1 mark) (Total = 6 marks)
Question 14/ 6 In acidic solution and in the presence of a suitable catalyst, the following reaction proceeds rapidly: 2H2O2(aq) + N2H4(aq) ⇌ N2(g) + 4H2O(l) A chemist wishes to use this reaction as the cell reaction in the galvanic cell shown below.
(a) What changes in oxidation number occur in the above equation? (2 marks) (b) The barrier prevents solutions A and B from directly reacting. It is made of a chemically inert material. Give another important property that the barrier must possess.
(1 mark) (c) Identify the solutions, A and B. (2 marks) (d) Suggest two necessary properties of the electrode materials. (2 marks) (e) Assuming that solutions A and B are acidic, write the half-cell reactions when the cell is operating for (i) the reaction at the positive electrode (cathode). (ii) the reaction at the negative electrode (anode). (1 + 1 = 2 marks) (Total = 9 marks)
Solution
(a) Oxygen changes from −1 (in H2O2) to −2 (in H2O). Nitrogen changes from −2 (in N2H4) to 0 (in N2). (2 marks) (b) The barrier must also be porous so that ions can flow in either direction. (1 mark) (c) Solution A is N2H4(aq) (since N2H4 will be oxidised and thus release electrons to the anode). Solution B is H2O2(aq) (H2O2 is reduced). (2 marks) (d) Electrode materials must be • good electrical conductors • chemically inert • good catalysts for the half-cell reactions. (Two of these properties for one mark each) (2 marks) (e) (i) Cathode reaction: H2O2(aq) + 2H+(aq) + 2e− → 2H2O(l)
(1 mark) (ii) Anode reaction: N2H4(aq) → N2(g) + 4H+(aq) + 4e− (1 mark) (Total = 9 marks)
Question 15/ 6 (a) Why is glucose, C6H12O6, important to life? Give an equation to show how the body uses glucose. (2 marks) (b) Plants are able to synthesise glucose. Give an equation for the reaction in which glucose is synthesised and mention any conditions that are essential for the process to occur. (2 marks) (c) Name the major food group to which glucose belongs. (1 mark) (Total = 5 marks) Total marks for test = 50 marks
Solution
(a) Glucose acts as the main energy source for most living tissue. (1 mark) Its most significant reaction is that involved in respiration to give CO2, H2O and energy. C6H12O6(aq) + 6O2(g) → 6CO2(g) + 6H2O(l) (1 mark) (b) 6CO2(g) + 6H2O(l) → C6H12O6(aq) + 6O2(g) (1 mark) Sunlight supplies the energy needed for this process. Chlorophyll is also essential.
(1 mark) (c) Carbohydrates. (1 mark) (Total = 5 marks)
Chapter 2: Unit 3 Area of Study 2 – How can the rate and yield of chemical reactions be optimised? Question 1/ 56 Acetone, CH3COCH3, and iodine, I2, react according to the equation given below. A small amount of sulfuric acid is needed to catalyse the reaction. CH3COCH3(l) + I2(aq) → CH3COCH2I(aq) + HI(aq) A student determines which factors will change the rate of this reaction. Four experiments are carried out with different initial concentrations of acetone, iodine and sulfuric acid. The time taken to form a small amount of product is measured. This amount of product is the same for each experiment. The results are listed in the table. [CH3COCH3]
[I2]
[H+]
Time taken
0.100 M
0.100 M
0.010 M
60 s
0.100 M
0.100 M
0.020 M
30 s
0.200 M
0.100 M
0.010 M
30 s
0.100 M
0.200 M
0.010 M
60 s
The student deduces that the rate of the reaction A. depends only on the concentration of acetone. B. is not affected by the concentration of sulfuric acid. C. depends on the concentrations of acetone, iodine and acid. D. is only affected by the concentrations of acetone and acid.
Solution
D. The first and last experiments require the same amount of time despite the concentration of I2 being doubled.
Question 2/ 56 [VCAA 2019 SA Q11] 5 mL of ethanol, CH3CH2OH, undergoes combustion in a test tube with a diameter of 1 cm. This experiment is performed in a fume cupboard. The temperature in the fume cupboard is 20 °C. Which one of the following actions will reduce the rate of reaction? A. Mix 2 mL of a dilute solution of sodium hydroxide, NaOH, with the ethanol. B. Perform the experiment in a test tube with a diameter of 2 cm. C. Increase the temperature in the fume cupboard to 25 °C. D. Increase the volume of the ethanol to 7 mL.
Solution
A. The addition of any solution will lower the concentration of ethanol and therefore reduce the reaction rate.
Question 4/ 56 [VCAA 2013 SA Q14] Which one of the following will not increase the rate of the above reaction? A. decreasing the size of the solid copper particles B. increasing the temperature of HNO3 by 20°C
C. increasing the concentration of HNO3 D. allowing NO2 gas to escape
Solution
D. The rate of the reaction will be determined by the collisions between atoms of Cu and molecules of HNO3, not by the presence of NO2 gas.
Question 5/ 56 [VCAA 2013 SA Q15] In the above reaction, the number of successful collisions per second is a small fraction of the total number of collisions. The major reason for this is that A. the nitric acid is ionised in solution. B. some reactant particles have too much kinetic energy. C. the kinetic energy of the particles is reduced when they collide with the container's walls. D. not all reactant particles have the minimum kinetic energy required to initiate the reaction.
Solution
D. For a reaction to occur the particles must possess the minimum amount of energy, i.e. the activation energy.
Question 6/ 56 [VCAA 2018 SA Q13]
The energy profile diagram below represents a particular reaction. One graph represents the uncatalysed reaction and the other graph represents the catalysed reaction.
Which of the following best matches the energy profile diagram? Ea uncatalysed reaction (kJ mol−1)
ΔH catalysed reaction (kJ mol−1)
40
−140
90
−140
40
−50
90
−50
Solution
D. Ea for the uncatalysed reaction is 90 – 0, whereas ΔH for the reaction is 0 – 50 = −50 kJ mol−1. ΔH is the same whether or not a catalyst is used.
Question 7/ 56 [Adapted VCAA 2015 SA Q17] The oxidation of sulfur dioxide is an exothermic reaction. The reaction is catalysed by vanadium(V) oxide. 2SO2(g) + O2(g) → 2SO3(g)
Which one of the following energy profile diagrams correctly represents both the catalysed and the uncatalysed reaction?
A.
B.
C.
D.
Solution
B. For an exothermic reaction, the enthalpy of the products is lower than that of the reactants. A catalyst lowers the peak of the energy profile but neither the enthalpy of the reactants nor that of the products is changed.
Question 8/ 56 An important industrial process is the conversion of carbon monoxide into carbon dioxide using steam. CO(g) + H2O(g) ⇌ CO2(g) + H2(g); ΔH = −40 kJ mol−1 Which of the following would increase the percentage conversion of CO into CO2? A. increasing the pressure B. increasing the temperature C. increasing the concentration of water D. increasing the volume of the container
Solution
C. Increasing the concentration of one of the reactants leads to the formation of more products. A and D would have no effect on the position of equilibrium because the number of moles on each side of the equation are equal. B would result in less CO2 being formed.
Question 9/ 56 An important reaction in the production of ammonia, NH3, is given below. N2(g) + 3H2(g) ⇌ 2NH3(g); ΔH = −90 kJ mol−1 If the reaction takes place in a sealed container, which of the following procedures would not cause the rate of the forward reaction to increase? A. adding an inert gas B. increasing the pressure C. adding a suitable catalyst D. increasing the temperature
Solution
A. Adding an inert gas will decrease the number of collisions per second between the reactant molecules, thus slowing the rate. B and D will increase the number of collisions per second. C would lower the activation energy.
Question 10/ 56 In the commercial production of methanol, CH3OH, carbon monoxide and hydrogen are heated and passed over a catalyst. The following equilibrium is set up. CO(g) + 2H2(g) ⇌ CH3OH(g); ΔH = −95 kJ mol−1 The reaction does not go to completion and the conditions have to be carefully adjusted to produce a maximum yield. Which of the following would be expected to increase the yield of methanol? A. Condense the methanol and recycle the remaining gases. B. Lower the pressure in the reaction vessel. C. Use a more effective catalyst. D. Increase the temperature in the reaction vessel.
Solution
A. Condensing the methanol would remove it from the mixture of gases present at equilibrium. Only CO and H2 would remain. If these gases were passed over the catalyst again, a new equilibrium would be established. B and D would result in less methanol being produced. C would not affect the position of equilibrium but would change the speed at which equilibrium is achieved.
Question 11/ 56
When hydrogen (H2) and iodine (I2) react, hydrogen iodide (HI) is formed. H2(g) + I2(g) ⇌ 2HI(g) In one experiment in a 2.0 L vessel at a certain temperature, the equilibrium mixture contained 0.5 mol of HI, 0.25 mol of H2 and 0.1 mol of I2. The value for the equilibrium constant at this temperature is A. 0.05 B. 0.1 C. 10 D. 20
Solution
C. K
=
[HI]2 [H 2 ][I 2 ]
=
0.25×0.25 0.125×0.05
= 10
Question 12/ 56 In the production of nitric acid, an important step is the conversion of nitric oxide (NO) into nitrogen dioxide (NO2). 2NO(g) + O2(g) ⇌ 2NO2(g); ΔH = −114 kJ mol−1 Which of the following sets of conditions would be expected to give the best equilibrium yield of nitrogen dioxide? A. 500°C and 4 atm pressure B. 30°C and 4 atm pressure C. 500°C and 1 atm pressure D. 30°C and 1 atm pressure
Solution
B. For an exothermic reaction, the lower temperature will give the best yield. Since 2 mol of products are formed
from 3 mol of reactants, increasing the pressure will result in more products being formed.
Question 13/ 56 Aqueous solutions containing dichromate ions (Cr2O72−) are orange, while those containing chromate ions (CrO42−) are yellow. These two ions can be interconverted by the reaction below. 2CrO42−(aq) + 2H+(aq) ⇌ Cr2O72−(aq) + H2O(l) A yellow solution of CrO42− will be converted into one containing orange Cr2O72− when A. HCl(aq) is added. B. NaOH(aq) is added. C. water is added. D. K2Cr2O7 is added.
Solution
A. HCl(aq) will contain large amounts of H+(aq), one of the reactants. This will push the equilibrium to the right. B, C and D will result in the equilibrium moving to the left.
Question 15/ 56 When a small volume of a concentrated solution containing Fe(NO3)3 is added to this system, the colour changes, showing that more Fe(SCN)2+ has been formed. Which of the graphs shown below correctly shows the changes in Fe3+ concentration before and after the addition of Fe(NO3)3?
A.
B.
C.
D.
Solution
B. Addition of a small amount of Fe(NO3)3 initially causes an increase in [Fe3+]. The reaction then moves to the right to re-establish equilibrium. This causes [Fe3+] to fall slightly.
Question 16/ 56 The solution from Question 13 is diluted with an equal volume of water. The colour becomes a paler red. The addition of water has caused the concentration A. and the number of moles of Fe(SCN)2+ to decrease. B. and the number of moles of Fe(SCN)2+ to remain unchanged. C. of Fe(SCN)2+ to decrease but the number of moles of Fe(SCN)2+ to remain unchanged. D. of Fe(SCN)2+ to decrease but the number of moles of Fe(SCN)2+ to increase.
Solution
A. Adding water initially decreases [FeSCN2+]. To regain equilibrium the system then moves to the left (Le Chatelier’s principle). Hence, [FeSCN2+] falls again and n(FeSCN2+) also decreases.
Question 17/ 56 [VCAA 2018 SA Q24] The four equations below represent different equilibrium systems. Equation 1 2SO2(g) + O2(g) ⇌ 2SO3(g) ΔH = −180 kJ mol−1 Equation 2 CO(g) + H2O(g) ⇌ CO2(g) + H2(g) ΔH = −46 kJ mol−1 Equation 3 PCl5(g) ⇌ PCl3(g) + Cl2(g) ΔH = +93 kJ mol−1 Equation 4 CH4(g) + H2O(g) ⇌ CO(g) + 3H2(g) ΔH = +205 kJ mol−1 After equilibrium was established in each system, the temperature was decreased and the pressure was increased. In which equilibrium system would both changes result in an increase in yield? A. Equation 1 B. Equation 2
C. Equation 3 D. Equation 4
Solution
A. Decreasing the temperature favours left to right reactions that are exothermic. Increasing the pressure will increase the yield of reactions with fewer particles on the right-hand side.
Question 18/ 56 The reaction below is allowed to reach equilibrium at 500°C. 2H2O(g) + C2H6(g) ⇌ 2CO(g) + 5H2(g); ΔH = +347 kJ mol−1 The temperature is then lowered and the amount of H2O changes by 0.20 mol. The changes occurring would be H 2O increase by 0.20 mol increase by 0.20 mol decrease by 0.20 mol decrease by 0.20 mol
C2H6 increase by 0.40 mol increase by 0.10 mol decrease by 0.40 mol decrease by 0.10 mol
CO
H2
decrease by 0.20 mol
decrease by 0.040 mol
decrease by 0.20 mol increase by 0.20 mol increase by 0.20 mol
decrease by 0.50 mol increase by 0.040 mol increase by 0.50 mol
Solution
B. The L to R reaction is endothermic, thus lowering the temperature will cause the position of equilibrium to move to the left. The amount of H2O will increase by 0.20 mol. The amount of C2H6 will increase by half this value.
Question 19/ 56 [Adapted VCAA 2012 E2 SA Q8] The following equilibrium is established. 2+
Fe3+ (aq) + SCN− (aq) ⇌ Fe(SCN) (aq) yellow deepred Which one of the graphs below best represents the changes in concentration when the equilibrium mixture is diluted at time t2?
A.
B.
C.
D.
Solution
B. When the mixture is diluted all of the concentrations fall and the system is no longer in equilibrium. The system responds by moving to the side with the most particles. Hence [Fe(SCN)2+] falls further and [Fe3+] and [SCN−] increase.
Question 20/ 56 [VCAA 2011 E2 SA Q1] Consider the following equilibrium expression. 4
] K= [[LJ][]6M [K]
The equation of the forward reaction for this equilibrium expression is A. 6J + K ⇌ L + 4M B. L + M4 ⇌ J6 + K C. J6 + K ⇌ L + M4 D. L + 4M ⇌ 6J + K
Solution
A. The products from the left to right reaction of this equilibrium are L and M, since these are in the numerator. J and K will be the reactants. The powers (M4 and J6) show there are 4 molecules of M and 6 of J in the equation.
Question 21/ 56 [VCAA 2018 SA Q27] Br2(g) + I2(g) ⇌ 2IBr(g) K = 1.2 × 102 at 150°C Given the information above, what is K for the reaction 4IBr(g) ⇌ 2Br2(g) + 2I2(g) at 150°C? A. 1.6 × 10−2 B. 4.1 × 10−3 C. 6.9 × 10−5 D. 8.03 × 10−5
Solution
1 C. For the second reaction, K = (1.2×10 2 )2
=
1 14400 .
Question 22/ 56 [Adapted VCAA 2013 SA Q18] Use the following information to answer the question. 2NOCl(g) ⇌ 2NO(g) + Cl2(g); ΔH is positive. A concentration–time graph for this system is shown below.
What event occurred at time t to cause the change in equilibrium concentrations? A. The pressure was decreased at a constant temperature. B. The temperature was increased at a constant volume. C. A catalyst was added at a constant temperature and volume. D. Additional NO gas was added at a constant volume and temperature.
Solution
D. Only the concentration of NO was increased at time t. Increasing the temperature would cause the equilibrium to move to the right, hence both [NO] and [Cl2] would increase. Decreasing the pressure would reduce all three concentrations. There would be no change if a catalyst was added since the system is already at equilibrium.
Question 23/ 56 [VCAA 2020 SA Q17] The following equation represents the reaction between chlorine gas, Cl2, and carbon monoxide gas, CO. Cl2(g) + CO(g) ⇌ COCl2(g) ΔH = −108 kJ mol−1 The concentration–time graph below represents changes to the system.
Which of the following identifies the changes to the system that took place at 1 minute and at 7 minutes? 1 minute
7 minutes
increase in temperature
increase in volume
decrease in temperature
decrease in volume
decrease in temperature
increase in volume
increase in temperature
decrease in volume
Solution
A. The change at 1 minute has to be a temperature change as there is no immediate change in the concentration of any compound. It is an increase in temperature as the back reaction is favoured (endothermic reaction). The change at 7 minutes has to be an increase in volume as all compounds decrease in concentration at the time of the change.
Question 24/ 56 [VCAA 2020 SA Q19] Nitrogen dioxide, NO2, and dinitrogen tetroxide, N2O4, form an equilibrium mixture represented by the following equation. 2NO2(g) ⇌ N2O4(g) ΔH = −57.2 kJ mol−1
brown colourless A change was made at time t1 to an equilibrium mixture of NO2 and N2O4, which achieved a new equilibrium at time t2. A graph showing the rate of the forward reaction is shown below.
Which one of the following describes the change that was made to the initial equilibrium system and the colour change that occurred between t1 and t2? A. The temperature was increased and the colour lightened. B. The temperature was increased and the colour darkened. C. The temperature was decreased and the colour lightened. D. The temperature was decreased and the colour darkened.
Solution
B. The rate of the forward reaction increased. This has to be caused by an increase in temperature as a decrease in temperature would decrease rate. The increase in temperature will favour the endothermic back reaction and cause the system to appear a darker brown as NO2 increases in concentration.
Question 25/ 56 [VCAA 2019 SA Q28] The concentration of all of the gases in the equilibrium reactions below is 1.0 M. Reaction 1 CH4(g) + 2H2O(g) ⇌ CO2(g) + 4H2(g)
Reaction 2 N2(g) + 3H2(g) ⇌ 2NH3(g) Reaction 3 H2(g) + I2(g) ⇌ 2HI(g) Reaction 4 2NO2(g) ⇌ N2O4(g) In which reaction does K = 1.0 M−2? A. Reaction 1 B. Reaction 2 C. Reaction 3 D. Reaction 4
Solution
B. Only B has a K with the units M−2. This is because the equilibrium reaction has two more reactant particles than product particles.
Question 27/ 56 [VCAA 2021 SA Q27] Which one of the following statements is correct? A. A catalyst was added at time t2. B. The amount of HI is greater at time t3 compared with time t1. C. The rate of reaction producing HI is the same at time t1 and time t3. D. The rate of production of HI at time t3 is double the rate of production of H2 at time t3.
Solution
D. The rate of a chemical reaction is measured as mol per volume per unit of time. Given the stoichiometric ratios in
the equation, HI must be produced at double the rate that H2 or I2 when the system is at equilibrium.
Question 28/ 56 [VCAA 2021 SA Q28] One change was made to the equilibrium system at time t4, which altered the equilibrium constant. Equilibrium was re-established at time t5. The rate of the reverse reaction at time t5 was higher than at time t3. Which of the following options correctly shows the change in the equilibrium system from time t3 to time t5? Changes from t3 to time t5 Equilibrium constant
Total chemical energy
increase
increase
increase
decrease
decrease
increase
decrease
decrease
Solution
A. The change at t4 is a temperature change as that is the only change that could alter the equilibrium constant. Given that the rate of the reverse reaction was higher at t5, the temperature must have been increased as this would raise the rate of both the forward and reverse reaction. Additionally, increasing the temperature would shift the system to the right and then there would be a higher concentration of the product and therefore the rate of the reverse reaction would be increased. A higher temperature when the forward reaction is endothermic means that the equilibrium constant will increase in value. The shift right means that the forward reaction is favoured, this is an endothermic reaction which would convert heat energy into chemical energy meaning more chemical energy is present.
Question 29/ 56 Which one of the statements below regarding galvanic and electrolytic cells is correct? A. Reduction occurs at the cathode in galvanic cells but at the anode in electrolytic cells.
B. Oxidation occurs at the cathode in both cells. C. Reduction occurs at the cathode and oxidation occurs at the anode in both cells. D. Oxidation occurs at the anode in galvanic cells but at the cathode in electrolytic cells.
Solution
C. This is the definition of cathode and anode.
Question 30/ 56 A student sets up the circuit shown below to electrolyse solutions of copper nitrate and gold(III) chloride using inert electrodes.
The mass of gold to the mass of copper deposited at the two cathodes will be in the ratio A. 1.00 : 1.00 B. 2.07 : 1.00 C. 3.10 : 1.00 D. 4.65 : 1.00
Solution
B. The same amount of current will flow through both cells. The cathode reactions will be Cu2+ + 2e− → Cu and Au3+ + 3e− → Au. Hence 6 mol of electrons would deposit 3 mol of Cu and 2 mol of Au. In this case, the mass of Cu = 3 × 63.5 g and the mass of Au would be 2 × 197 g. Ratio mass Au ÷ mass Cu = 394 ÷ 190.5 = 2.07.
Question 31/ 56 An aqueous solution of zinc nitrate is electrolysed for 75.0 minutes by a current of 4.50 A. The mass of zinc deposited, in grams, is closest to A. 0.23 B. 6.85 C. 13.70 D. 27.40
Solution
B. No. of coulombs = 75 × 60 × 4.5 = 20 250 C n(e−) = 20 250 ÷ 96 500 = 0.2098 n(Zn) = 0.2098 ÷ 2 = 0.1049 Mass Zn = 0.1049 × 65.3 g
Question 32/ 56 In the electrolytic production of aluminium, the current, in amps, needed to deposit 5.0 kg of aluminium in 60.0 minutes is closest to
A. 15 B. 5.0 × 103 C. 1.5 × 104 D. 8.9 × 105
Solution
C. n(Al) = 5.0 × 1000 ÷ 27.0 = 185.2 mol n(e−) = n(Al) × 3 = 555.6 mol No. of coulombs = 555.6 × 96 500 = 5.361 × 107 C 7 4 Current = 5.361×10 3600 = 1.5 × 10 A
Question 33/ 56 In the electrolysis of thallium nitrate solution, 0.168 g of thallium is deposited at the cathode in 144 seconds by a current of 1.65 A. The charge on the thallium ion in the solution of thallium nitrate is A. −3 B. −1 C. +1 D. +3
Solution
−3 D. n(e−) = 144×1.65 96500 = 2.46 × 10
n(Tl) = 0.168 ÷ 204.4 = 8.22 × 10−4 Charge = n(e) ÷ n(Tl) = 3
Must be +3 since Tl is deposited at the cathode.
Question 34/ 56 A solution of tin(II) chloride was electrolysed using the circuit shown below.
The reaction that is most likely to occur at the positive electrode is A. Sn2+(aq) + 2e− → Sn(s) B. 2Cl−(aq) → Cl (g) + 2e− C. 2H2O(l) → O2(g) + 4H+(aq) + 4e− D. Sn(s) → Sn2+(aq) + 2e−
Solution
D. In an electrolytic cell, oxidation occurs at the positive electrode (electrons are removed from this electrode). The substance most easily oxidised is Sn.
Question 35/ 56 9650 C of electrical charge is used to electrolyse 1.00 L of a 0.50 M lead nitrate solution. If the volume of the solution remains unchanged, then the Pb2+(aq) concentration after electrolysis will be
A. 0 M B. 0.30 M C. 0.40 M D. 0.45 M
Solution
9650 D. n(Pb) deposited = 96500
÷ 2 = 0.05 mol
n(Pb2+) remaining = (1.00 × 0.50) – 0.05 = 0.45 mol
Question 36/ 56 [VCAA 2018 SA Q9] When molten sodium chloride, NaCl, is electrolysed, the product formed at the cathode is A. sodium liquid, Na. B. hydrogen gas, H2. C. chlorine gas, Cl2. D. oxygen gas, O2.
Solution
A. Reduction occurs at the cathode and molten NaCl the reaction is Na+ + e− → Na. There is no water in the molten salt to produce H2 or O2.
Question 37/ 56 [VCAA 2011 E2 SA Q17] If we compare a galvanic cell with an electrolytic cell, it is true to state that A. in a galvanic cell reduction occurs at the negative electrode. B. in both cells the anode is positive and the cathode is negative. C. in an electrolytic cell oxidation occurs at the cathode. D. in both cells reduction occurs at the cathode.
Solution
D. Reduction always occurs at the cathode, irrespective of the type of cell. Reduction occurs at the negative electrode only in an electrolytic cell. The anode is positive in an electrolytic cell but negative in a galvanic cell.
Question 39/ 56 [VCAA 2015 SA Q28] The solid metal impurities that are found in the sludge are A. gold, nickel and cobalt. B. cobalt, nickel and iron. C. nickel and iron. D. silver and gold.
Solution
D. Electrode I is the positive electrode and oxidation reactions occur there. The most reactive metals will be oxidised first, e.g. Zn, Fe, Co, Ni and Cu. Ag and Au atoms will fall off the electrode before they can be oxidised.
Question 40/ 56 [VCAA 2015 SA Q29] Which of the following correctly shows both the equation for the reaction occurring at the cathode and the polarity of Electrode I? Cathode reaction
Polarity of Electrode I
Cu2+(aq) + 2e− → Cu(s)
positive
Cu(s) → Cu2+(aq) + 2e−
negative
Cu2+(aq) + 2e− → Cu(s)
negative
Cu(s) → Cu2+(aq) + 2e−
positive
Solution
A. Reduction occurs at the cathode (definition). Copper is deposited at this electrode, i.e. electrode II. Electrode I has a positive charge.
Question 41/ 56 [VCAA 2015 SA Q30] Which one of the following graphs best shows the change in mass of Electrode I over a period of time, starting from the moment the power supply is connected?
A.
B.
C.
D.
Solution
B. Oxidation of metal atoms occurs at electrode I, e.g. Cu → Cu2+ + 2e−. It will steadily lose mass as the electrolysis proceeds.
Question 42/ 56 [VCAA 2019 SA Q7] A molten mixture of equal parts aluminium fluoride, AlF3, and sodium chloride, NaCl, undergoes electrolysis. Which one of the following statements about this reaction is correct?
A. Sodium metal will be produced at the cathode and fluorine gas will be produced at the anode. B. Sodium metal will be produced at the anode and chlorine gas will be produced at the cathode. C. Aluminium metal will be produced at the cathode and chlorine gas will be produced at the anode. D. Aluminium metal will be produced at the anode and fluorine gas will be produced at the cathode.
Solution
C. Al3+ is the strongest reducing agent present in the molten mixture and so will react at the anode and undergo oxidation to produce Al. Cl− is the strongest reducing agent in the mixture and will undergo oxidation to produce Cl2.
Question 43/ 56 [VCAA 2021 SA Q9] An electrolysis cell consumed a charge of 4.00 C in 5.00 minutes. This represents a consumption of A. 4.15 × 10−5 mol of electrons. B. 2.07 × 10−4 mol of electrons. C. 1.93 × 104 mol of electrons. D. 2.41 × 104 mol of electrons.
Solution
A. n(e−) = Q ÷ F = 4.00 C ÷ 96500 C mol−1 = 4.15 × 10−5
Question 44/ 56 [VCAA 2017 SA Q30] The diagram below shows the basic set-up of an electroplating cell.
Initially the cell is set up with a lead, Pb, electrode as Electrode Z and 1.0 mol L−1 lead nitrate, Pb(NO3)2, as the electroplating solution. The cell runs for a set time and current, with 1.0 g of Pb deposited onto Electrode Z. Four subsequent electroplating cells are set up, each containing a platinum, Pt, electrode, a different Electrode Z and an appropriate 1.0 mol L−1 electroplating solution. These four electroplating cells are operated for the same time and at the same current as the original Pb electroplating cell. Which combination of Electrode Z and electroplating solution would be expected to deposit more metal by mass onto Electrode Z than the original Pb electroplating cell? Electrode Z
Electroplating solution
chromium, Cr
1.0 mol L−1 Cr(NO3)3
silver, Ag
1.0 mol L−1 AgNO3
gold, Au
1.0 mol L−1 AuCl3
tin, Sn
1.0 mol L−1 SnSO4
Solution
n(e− )
Q
B. F = constant = n(e−) and n(metal) = charge on ion . n(e−) = . Hence for B, Mass Ag = 2×1.0×107.9 207.9×1 = 1.04 g The masses for the other meta
mass×charge on ion ls are Cr = 0.17 g, Au = 0.63 g and Sn = 0.57 g Ar
Question 45/ 56 [VCAA 2019 SA Q24] The diagram below shows an electroplating cell.
The cell contains 1 L of an electroplating solution. The electroplating cell is run for one hour at 3 A. Which one of the following electroplating solutions will deposit the largest mass of metal onto the object? A. 1 M AgNO3 B. 1 M Cd(NO3)2 C. 1 M Pb(NO3)2 D. 1 M Al(NO3)3
Solution
A. The mass of a metal produced in electrolysis is determined by the molar mass of the metal and the charge of the ion as this determines the ratio with e− in the reduction half-equation. While Pb and Cd both have higher molar masses than Ag, they require twice the number of electrons to produce the same moles of metal. Since neither Pb nor Cd have twice the molar mass of Ag, the AgNO3 solution would deposit the largest mass of metal. Al3+ isn’t a strong enough oxidising agent to be reduced in this cell.
Question 46/ 56 [VCAA 2021 SA Q7] Consider the following characteristics of electrolytic and galvanic cells. Characteristic number
Electrolytic cells
Galvanic cells
1
cathode is negative
cathode is positive
2
have non-spontaneous reactions
have spontaneous reactions
3
reduction occurs at the anode
reduction occurs at the cathode
4
produce electricity
consume electricity
Which of the following combinations of characteristics of electrolytic cells and galvanic cells are correct? A. only 1 and 2 B. only 2 and 3 C. only 3 and 4 D. only 1, 2 and 4
Solution
A. Characteristics 1 and 2 are both correct. Characteristic 3 is wrong as reduction always occurs at the cathode and 4 is incorrect as the characteristics are the wrong way around.
Question 48/ 56 [VCAA 2011 E2 SA Q13] When the battery is discharging the A. H+ concentration decreases resulting in a higher pH. B. H+ concentration increases resulting in a higher pH. C. H+ concentration decreases resulting in a lower pH. D. H+ concentration increases resulting in a lower pH.
Solution
A. When a lead-acid battery discharges, the equation is Pb + PbO2 + 4H+ + 2SO42−→ 2PbSO4 + 2H2O. Thus [H+] falls and the pH rises.
Question 49/ 56 [VCAA 2011 E2 SA Q15] The reaction which occurs at the anode when the battery is recharging is A. PbSO4(s) + 2e− → Pb(s) + SO42−(aq) B. Pb(s) + SO42−(aq) → PbSO4(s) + 2e− C. PbSO4(s) + 2H2O(l) → PbO2(s) + 4H+(aq) + SO42−(aq) + 2e− D. PbO2(s) + 4H+(aq) + SO42−(aq) + 2e− → PbSO4(s) + 2H2O(l)
Solution
C. Oxidation always occurs at the anode. In C PbSO4 is oxidised to PbO2. B is the anode reaction that occurs during the discharge of the battery.
Question 51/ 56 [VCAA 2021 SA Q20] l F is equivalent to the charge on 1 mol of electrons.
The mass of nickel, Ni, that can be electroplated onto the platinum, Pt, electrode with 320 F of charge is A. 9.73 × 10−2 g B. 1.95 × 10−l g C. 9.39 × 103 g D. 1.88 × 104 g
Solution
C. 1 F = 1 mol of e−, therefore 320 F = 320 mol of e− The equation is Ni2+ + 2e− → Ni n(Ni) = n(e−) × 12 = 320 × 12 = 160 mol m(Ni) = n × M = 160 × 58.7 = 9.39 × 103 g
Question 52/ 56 [VCAA 2021 SA Q21] Using the electrochemical series, which one of the following changes to the electrolysis cell may reduce the amount of Ni electroplated onto the Pt electrode? A. replacing the Ni electrode with a Cu electrode B. replacing Ni(NO3)2(l) with 1 M Ni(NO3)2(aq) C. replacing the Pt electrode with Pb(s) D. replacing Ni(NO3)2(l) with NiCl2(l)
Solution
A. If the nickel electrode were replaced with copper this would change the reaction at the electrode to Cu → Cu2+ +
2e−. While this wouldn’t have an impact initially at the other electrode, the Cu2+ would migrate to the cathode over time and start being reduced preferentially to Ni2+. After some time, this would prevent any Nickel from being able to be plated onto the platinum.
Question 53/ 56 [VCAA 2017 SA Q20] The reaction below represents the discharge cycle of a standard lead–acid rechargeable car battery. Pb(s) + PbO2(s) + 4H+(aq) + 2SO42−(aq) → 2PbSO4(s) + 2H2O(l) During the recharge cycle, the pH A. increases and solid Pb is a reactant. B. increases and solid PbO2 is produced. C. decreases and chemical energy is converted to electrical energy. D. decreases and electrical energy is converted to chemical energy.
Solution
D. During the recharge cycle the equation is reversed, i.e. H+ is produced and the pH falls. During recharging, electrical energy is converted to chemical energy, which is stored.
Question 55/ 56 [VCAA 2017 SA Q27] The overall reaction that occurs when the battery is discharging is A. VO2+(aq) + 2H+(aq) + V2+(aq) → VO2+(aq) + V3+(aq) + H2O(l) B. VO2+(aq) + H2O(l) + V3+(aq) → VO2+(aq) + V2+(aq) + 2H+(aq)
C. VO2+(aq) + V2+(aq) + 2H+(aq) → 2V3+(aq) + H2O(l) D. VO2+(aq) + V3+(aq) → 2VO2+(aq)
Solution
A. V2+ is the strongest reductant present and VO2+ is the strongest oxidant.
Question 56/ 56 [VCAA 2017 SA Q28] If air is present, the following half-equations are also relevant. O2(g) + 4H+(aq) + 4e− → 2H2O(l) E° = +1.23 V VO2+(aq) + 2H+(aq) + e− → V3+(aq) + H2O(l) E° = +0.34 V If air is present, the A. VO2+(aq) ion is oxidised to the V2+(aq) ion. B. VO2+(aq) ion is reduced to the V3+(aq) ion. C. V2+(aq) ion is oxidised to the VO2+(aq) ion. D. VO2+(aq) ion is reduced to the VO2+(aq) ion.
Solution
C. When the battery is discharging V2+ is converted into V3+. If O2 is present, further oxidation of V3+ to VO2+ can occur.
Question 57/ 56 [VCAA 2018 SA Q16] The silver oxide-zinc battery is rechargeable and utilises sodium hydroxide, NaOH, solution as the electrolyte. The battery is used as a backup in spacecraft, if the primary energy supply fails. The overall reaction during discharge is Zn + Ag2O → ZnO + 2Ag When the silver oxide-zinc battery is being recharged, the reaction at the anode is A. 2Ag + 2OH− → Ag2O + H2O + 2e− B. Ag2O + H2O + 2e− → 2Ag + 2OH− C. ZnO + H2O + 2e− → Zn + 2OH− D. Zn + 2OH− → ZnO + H2O + 2e−
Solution
A. Oxidation always occurs at the anode. Recharging the battery converts Ag to Ag2O (i.e. the oxidation number changes from 0 to +1).
Question 58/ 56 [VCAA 2021 SA Q13] Rechargeable batteries A. use reversible reactions. B. operate as galvanic cells during recharge. C. require a continuous flow of reactants to operate. D. have fewer side reactions as temperature increases.
Solution
A. The reactions in rechargeable cells must be reversible.
Question 60/ 56 During recharge, the reaction at the cathode is A. Pb(s) + SO42−(aq) → PbSO4(s) + 2e− B. PbSO4(s) + 2e− → Pb(s) + SO42−(aq) C. PbO2(s) + SO42−(aq) + 4H+(aq) + 2e− → PbSO4(s) + 2H2O(1) D. PbSO4(s) + 2H2O(l) → PbO2(s) + SO42−(aq) + 4H+(aq) + 2e−
Solution
B. In recharge, PbSO4 is the reactant (determined by reversing the discharge reaction), this means A and C are incorrect. D is incorrect as it is an oxidation reaction, but reduction happens at the cathode.
Question 61/ 56 [VCAA 2021 SA Q14] When the lead-acid battery is discharging, the oxidising agent is A. Pb B. PbO2 C. PbSO4 D. H2SO4
Solution
B. During discharge the Pb in PbO2 is going from an oxidation state of +4 to +2, and is therefore gaining two electrons. This means it is being reduced which makes it the oxidising agent.
Question 62/ 56 [VCAA 2022 SA Q13] An electrolysis cell is set up with inert platinum, Pt, electrodes. Which one of the following will produce a gas at the cathode when undergoing electrolysis in the cell? A. potassium iodide, KI(aq) B. sodium chloride, NaCl(l) C. lead bromide, PbBr2(l) D. copper sulfate, CuSO4(aq)
Solution
A. KI(aq) solution in an electrolytic cell would mean that water is the strongest oxidant present at the cathode and would produce hydrogen and hydroxide ions. In D, the Cu2+(aq) is a stronger oxidant than water and in A and C, no water is present (as the mixtures are molten/liquid) or other chemicals capable of being converted into a gas in this manner.
Question 64/ 56 [VCAA 2022 SA Q22] Which of the following is correct about lithium-ion batteries?
During discharge, reduction occurs at the
During recharge, reduction occurs at the
anode
cathode
cathode
anode
anode
anode
cathode
cathode
Solution
D. Reduction always occurs at the cathode, in all cells at all times.
Question 65/ 56 [VCAA 2022 SA Q23] Which one of the following statements about lithium-ion batteries is correct? A. During recharge, LiCoO2 is formed at the negative electrode. B. During discharge, Li+ ions move towards the positive electrode. C. Raising the battery temperature increases the rate of reaction, thereby increasing the battery life. D. The battery operates as an electrolytic cell during discharge and as a galvanic cell during recharge.
Solution
B. Cations will always migrate to the cathode. In discharge, this is the positive electrode and therefore Li+ will migrate towards this electrode.
Question 1/ 29 Under certain conditions of temperature and pressure, incomplete combustion of ethane can occur according to the equation C2H6(g) + O2(g) → 2CO(g) + 3H2(g) In one experiment 0.10 mol of ethane and 0.10 mol of oxygen are brought to equilibrium in a 1.0 L flask. 0.16 mol of carbon monoxide is formed. Calculate a value for the equilibrium constant for this reaction. (Total = 4 marks)
Solution C2H6
O2
CO
H2
No. of mol at start
0.10
0.10
0
0
No. of mol at equilibrium
x
x
0.16
y
= 0.24 mol n(H2) = y = 3×0.16 2 (1 mark) At equilibrium n(C2H6) = x = 0.10 – amount C2H6 reacted = 0.10 – 0.08 = 0.02 mol (1 mark) n(O2) = n(C2H6) = 0.02 mol (1 mark)
K=
(0.16)2 ×(0.24)3 3 0.02×0.02 = 0.89 M
(1 mark) (Total = 4 marks)
Question 2/ 29 A student added 0.260 g of zinc to 100 mL of 1.00 M hydrochloric acid in the equipment shown below. The temperature recorded was 25°C and the pressure was 100 kPa.
The student noted the volume of gas in the syringe at regular intervals and plotted the graph shown below.
(a) Write an equation for the reaction between hydrochloric acid and zinc. (1 mark) (b) Calculate the mass of hydrogen produced in the reaction. (2 marks) (c) What is the maximum volume of hydrogen that could be collected from this experiment? (1 mark) (d) How did the rate of evolution (production) of hydrogen change over the time taken for the reaction? (1 mark) (e) Give an explanation for your answer to part (d). (2 marks) (f) Suggest two changes to the experiment that would decrease the rate of evolution of hydrogen. (2 marks) (Total = 9 marks)
Solution
(a) Zn(s) + 2HCl(aq) → ZnCl2(aq) + H2(g) (1 mark) (b) n(Zn) = 0.26 ÷ 65.4 = 3.98 × 10−3 (n(HCl) = 0.1, which is an excess) n(H2) = n(Zn) since it is a 1:1 reaction hence mass H2 = 3.98 × 10−3 × 2 = 7.95 × 10−3 g (2 marks) (c) V(H2) = n × Vm = 3.98 × 10−3 × 24.8 = 0.0987 L or 98.7 mL (1 mark) (d) The rate decreased over the time of the reaction. (1 mark) (e) As the Zn is consumed by the reaction the surface area of the Zn decreases. Reducing the surface area will decrease the rate of the reaction. The HCl is also used up during the reaction and its concentration will also fall. (2 marks) (f) There are three ways to reduce the speed of this reaction: • lower the temperature, i.e. cool the HCl solution before adding the Zn. • use a HCl solution with a lower concentration. • use larger lumps of Zn. (Any two for 2 marks) (Total = 9 marks)
Question 3/ 29 [VCAA 2013 SB Q4]
The industrial production of hydrogen involves the following two reactions. reaction I: CH4(g) + H2O(g) ⇌ CO(g) + 3H2(g); ΔH = +206 kJ mol−1 reaction II: CO(g) + H2O(g) ⇌ CO2(g) + H2(g); ΔH = −41 kJ mol−1 (a) (i) Write ‘increase’, ‘decrease’ or ‘no change’ in the table below to identify the expected effect of each change to reaction I and reaction II on the equilibrium yield of hydrogen. (3 marks) Change to reaction I and reaction II
Effect of the change on the hydrogen yield in reaction I
Effect of the change on the hydrogen yield in reaction II
addition of steam at a constant volume and temperature increase in temperature at a constant volume addition of a suitable catalyst at a constant volume and temperature (ii) Explain the effect of decreasing the volume, at constant temperature, on the hydrogen equilibrium yield in each reaction. (4 marks) (iii) What is the effect of an increase in temperature at constant volume on the rate of hydrogen production in each reaction? (2 marks) The reaction between hydrogen and oxygen is the basis of energy production in a number of fuel cells. 2H2(g) + O2(g) → 2H2O(l); ΔH = −571.6 kJ mol−1 (b) An alkaline electrolyte is used in a particular hydrogen/oxygen fuel cell. Write a balanced half-equation for the reaction occurring at the (i) cathode (ii) anode. (2 marks) (c) What is the maximum voltage predicted for one alkaline hydrogen/oxygen fuel cell under standard conditions? (1 mark) Much of the hydrogen used in fuel cells is produced from methane. CH4(g) + H2O(g) ⇌ CO(g) + 3H2(g) CO(g) + H2O(g) ⇌ CO2(g) + H2(g) (d) Explain why methane generated by biomass is a renewable fuel while methane derived from fossil fuels is not.
(2 marks) (Total = 14 marks)
Solution
(a) (i) Change to reaction I and reaction II
Effect of the change on the hydrogen yield in reaction I
Effect of the change on the hydrogen yield in reaction II
addition of steam at a constant volume and temperature
increase
increase
increase in temperature at a constant volume
increase
decrease
no change
no change
addition of a suitable catalyst at a constant volume and temperature (3 marks) (ii) Reaction 1
Decreasing the volume at constant temperature increases the pressure. The system responds and partially reduces the pressure by moving to the side of the equation with the smallest number of particles (Le Chatelier’s principle). In this reaction there are 2 molecules on the left and 4 on the right. Hence, the back reaction is favoured and the yield of H2 decreases. Reaction 2 In this reaction, there are 2 molecules on each side of the equation. Hence when the volume is reduced (and the pressure increased) neither the forward nor the back reaction is favoured and the system cannot respond to this change. The yield of hydrogen does not change. (4 marks) (iii) Increasing the temperature at constant volume will increase the rate of reaction 1 and increase the rate of reaction 2. (2 marks) (b) (i) O2(g) + 2H2O(l) + 4e− → 4OH−(aq) (ii) H2(g) + 2OH−(aq) → 2H2O(l) + 2e− (2 marks) (Note: equations involving H+ ions are not acceptable since this fuel cell has an alkaline electrolyte.) (c) E°(cell) = E°(oxidant) – E°(reductant)
E°(cell) = 0.40 – (−0.83) = 1.23 V (1 mark) (d) Biomass (animal waste and plant material) can be readily replaced, i.e. the time needed to produce this material is short. Hence methane from this source is renewable. Fossil fuels have been produced over very long periods of time (millions of years) and these fuels are non-renewable and methane from these sources is also non-renewable. (2 marks) (Total = 14 marks)
Question 4/ 29 [VCAA 2018 SB Q2] Hydrogen peroxide, H2O2, in aqueous solution at room temperature decomposes slowly and irreversibly to form water, H2O, and oxygen, O2, according to the following equation. 2H2O2(aq) → 2H2O(l) + O2(g); ΔH < 0 (a) What effect will increasing the temperature have on the rate of O2 production? Use collision theory to explain your answer. (3 marks) (b) When a small lump of manganese(IV) dioxide, MnO2, is added to the H2O2 solution, the rate of O2 production increases, but when powdered MnO2 is added instead, the rate of O2 production is greatly increased. The MnO2 is recovered at the end of the reaction. State the function of MnO2 in this reaction. (1 mark) (c) A solution of H2O2 is labelled ‘10 volume’ because 1.00 L of this solution produces 10.0 L of O2 measured at standard laboratory conditions (SLC) when the H2O2 in the solution is fully decomposed. Calculate the concentration of H2O2 in the ‘10 volume’ solution, in grams per litre, when this solution is first prepared. (2 marks) (d) Propose a method to determine how quickly a solution of H2O2 decomposes when stored at a particular temperature. (3 marks) (Total = 9 marks)
Solution
(a) Increasing the temperature will increase the rate of production of O2. When the temperature is increased, the average kinetic energy of the particles increases. This leads to more collisions per second and more energetic collisions. There is also an increase in the number of collisions whose energy is equal to or greater than the activation energy. Hence the proportion of successful collisions has increased. (3 marks) (b) MnO2 provides an alternative pathway for the reaction with a lower activation energy, i.e. it is a catalyst for this reaction. (1 mark) (c) n(O2) from 1.0 L of solution = 10.0 24.8 = 0.4032 mol and from the equation n(H2O2) = 2 × n(O2) = 0.8064 mol Mass H2O2 = 0.8064 × 34.0 = 27.42, i.e. 27.4 g L−1 (2 marks) (d) To determine how rapidly a H2O2 solution is decomposing a property of the solution must be measured over time (several days, weeks). When H2O2 decomposes, O2 gas will escape from the solution and the mass of the solution will decrease. Hence a small sample of H2O2 solution (e.g. ∼20 g) is weighed and then reweighed sometime later. An alternative method is to measure the volume of O2 gas (using a gas syringe) that is obtained from a known volume of the solution (e.g. 10.0 mL). Some MnO2 catalyst is used to rapidly produce all of the O2. This measurement could be repeated each day (or week). (3 marks) (Total = 9 marks)
Question 5/ 29 [VCAA 2011 E2 SB Q7] Methanol is produced on an industrial scale by the catalytic conversion of a mixture of hydrogen and carbon monoxide gases at a temperature of 520 K and a pressure of 50 to 100 atmospheres. The reaction that occurs in the methanol converter is CO(g) + 2H2(g) ⇌ CH3OH(g)
(a) Carbon monoxide gas and hydrogen gas are mixed in a reaction vessel and equilibrium is established. The graph above shows how the concentration of methanol in this vessel changes with time at three different temperatures. The pressure is the same at each temperature. (i) Is the reaction exothermic or endothermic? Explain your answer. (2 marks) (ii) Explain why a moderately high temperature of 520 K is used although the equilibrium concentration of methanol is greater at a lower temperature. (1 mark) (iii) Explain why, at a given temperature, the use of high pressures results in a greater equilibrium concentration of methanol. (2 marks) (b) A catalyst consisting of a mixture of copper, zinc and aluminium is used to increase the rate of this reaction. Explain how a catalyst can increase reaction rate. (1 mark) (Total = 6 marks)
Solution
(a) (i) The reaction is exothermic since the equilibrium concentration of methanol falls as the temperature increases. (2 marks) (ii) When the temperature of the process is increased, the yield of methanol falls but the rate of reaction increases. A temperature of 520 K is a compromise between the factors of yield and rate. At lower temperatures the rate of reaction is too slow but at higher temperatures the yield is too low. (1 mark)
(iii) According to Le Chatelier’s principle when a change is applied to a system at equilibrium the system will respond and partially oppose the change. Thus, if the pressure of the system is increased then the position of equilibrium will move to the side with the fewest particles to reduce the pressure. In this reaction the left-hand side has 3 particles and the right-hand side 1. Increasing the pressure will push the equilibrium to the right and more methanol will be formed. (2 marks) (b) A catalyst lowers the activation energy of a reaction by providing an alternative reaction pathway. Thus a greater proportion of collisions will be successful. (1 mark) (Total = 6 marks)
Question 6/ 29 [VCAA 2015 SB Q7] Consider the reaction shown in the following equation. 2NO(g) + Br2(g) ⇌ 2NOBr(g); ΔH = −16.1 kJ mol−1, K = 1.3 × 10−2 M−1 at 1000 K (a) Write an expression for the equilibrium constant for this reaction. (1 mark) (b) 10.0 mol of NOBr, 10.0 mol of NO and 5.0 mol of Br2 are placed in a 1.0 L container at 1000 K. Predict in which direction the reaction will proceed. Justify your answer. (3 marks) (c) A mixture of NO, NOBr and Br2 is initially at equilibrium. The graph below shows how the rate of formation of NOBr in the mixture changes when the volume of the reaction vessel is decreased at time t1.
Use collision theory and factors that affect the rate of a reaction to explain the shape of the graph at the time intervals
indicated in the table below. (3 marks) Time
Explanation
between t0 and t1 at t1 between t1 and t2 (Total = 7 marks)
Solution
(a) K
=
[NOBr]2 [NO]2 [Br2 ]
= 1.3 × 10−2 M −1 = 1.3 × 10−2 M−1
(1 mark) 10×10 (b) Concentration fraction (CF or Q) = 10×10×5 = 0.2
(3 marks) This is larger than the equilibrium constant K and the system is not at equilibrium. The reverse reaction will be favoured and the system will move to the left to decrease CF and thus reach equilibrium. (c) Between t0 and t1: Since the system is at equilibrium the rate of the forward reaction is equal to the rate of the back reaction. NO and Br2 will be formed as fast as they are consumed, and their concentrations are constant. Hence the rate of formation of NOBr is constant. (3 marks) At t1: The decrease in volume immediately increases all of the concentrations. This increases the number of collisions. Hence the rate of formation of NOBr increases. (Total = 7 marks) Between t1 and t2: The forward reaction is favoured and as NO and Br2 are converted into NOBr their concentrations fall. Hence the number of collisions between NO and Br2 decreases and the rate of formation of NOBr falls.
Question 7/ 29
[VCAA 2017 SB Q4] Sulfur trioxide, SO3, is made by the reaction of sulfur dioxide, SO2, and oxygen, O2, in the presence of a catalyst, according to the equation below. 2SO2(g) + O2(g) ⇌ 2SO3(g); ΔH < 0 In a closed system in the presence of the catalyst, the reaction quickly achieves equilibrium at 1000 K. (a) A mixture of 2.00 mol of SO2(g) and 2.00 mol of O2(g) was placed in a 4.00 L evacuated, sealed vessel and kept at 1000 K until equilibrium was reached. At equilibrium, the vessel was found to contain 1.66 mol of SO3(g). Calculate the equilibrium constant, K, at 1000 K. (4 marks) (b) A manufacturer of SO3 investigates changes to the reaction conditions used in part (a) in order to increase the percentage yield of the product in a closed system, where the volume may be changed, if required. What changes would the manufacturer make to the temperature and volume of the system in order to increase the percentage yield of SO3? Justify your answer. (4 marks) (Total = 8 marks)
Solution
(a) SO2
O2
SO3
Initial amount (mol)
2.00
2.00
0.0
Change (mol)
−1.66
−0.83
+1.66
Equilibrium (mol)
0.34
1.17
1.66
Concentration (mol L−1)
0.085
0.2925
0.415
K=
[SO3 ]2 [SO2 ]2 [O2 ]
=
[0.415]2 [0.085]2 [0.2925]
= 81.495, i.e. = 81 L mol−1
(4 marks) (b) The manufacturer should decrease the temperature. ΔH < 0 means that ΔH is negative and the L to R reaction is exothermic. When the temperature is reduced, the system responds by favouring the process that releases heat, i.e. the production of more SO3. The manufacturer should also decrease the volume. Decreasing the volume will increase the pressure. The system will respond by favouring the side of the reaction that has the smallest number of particles, i.e. the L to R process will be favoured and more SO3 will be produced. (4 marks)
(Total = 8 marks)
Question 8/ 29 [VCAA 2019 SB Q3] The cobalt(II) tetrachloride ion, CoCl4−, dissociates into the cobalt(II) ion, Co2+, and chloride ions, Cl−, according to the following chemical equation. CoCl42−(aq) ⇌ Co2+(aq) + 4Cl−(aq) 20 mL samples of the equilibrium mixture were heated to two temperatures, 30°C and 80°C. The intensity of the pink colour of the Co2+ product was recorded every 30 seconds by measuring the absorbance of the solution. The higher the intensity of the pink colour, the higher the absorbance. The results of this experiment are shown in the graph below.
(a) State whether the forward reaction is exothermic or endothermic. Justify your answer by referring to the graph. (2 marks) (b) When 5 mL of water was added to the equilibrium mixture, the colour of the solution immediately became lighter pink. Describe the final colour of the solution once equilibrium is re-established. Explain your answer. (2 marks) (c) Five drops of silver nitrate, AgNO3, solution are added to the equilibrium mixture at time t1. A concentration–time graph for this reaction is shown below for times between zero and t1.
Continue the graph to show the changes that occur to the system from t1 until equilibrium is re-established. (3 marks) (Total = 7 marks)
Solution
(a) When the temperature of the mixture is 30°C, the relative absorbance, at equilibrium, is higher. This means that there was a higher intensity of pink colour and [Co2+] at the lower temperature, indicating the net production of Co2+ (shift right). Given that a decrease in temperature favours an exothermic reaction, and there was a net forward reaction with the decrease in temperature, the forward reaction is exothermic. (2 marks) (b) The increase in volume will decrease the concentration of aqueous particles in the solution. According to Le Chatelier’s principle, the system will shift to partially oppose this change by favouring the reaction that produces more aqueous particles. In this equilibrium, this is the forward reaction. As the forward reaction produces Co2+, the colour of the solution will become more pink as equilibrium is re-established. The final pink colour of the solution won’t be as intense as the colour of the original equilibrium due to the initial decrease in concentration from the volume increase.
(2 marks) (c) The Ag+ in AgNO3 forms a precipitate with Cl−, removing it from the aqueous equilibrium. One mark for [Cl−] initially decreasing. One mark for [Cl−] and [Co2+] increasing while [CoCl42−] decreases. One mark for the change in concentration after t1 being the same as the stoichiometric ratio, 4 : 1 : 1, from the equilibrium equation.
(3 marks) (Total = 7 marks)
Question 9/ 29 [VCAA 2020 SB Q1] Methanol is a very useful fuel. It can be manufactured from biogas. The main reaction in methanol production from
biogas is represented by the following equation. CO(g) + 2H2(g) ⇌ CH3OH(g) ΔH < 0 This reaction requires the use of a catalyst to maximise the yield of methanol produced in optimum conditions. The energy profile diagram below represents the uncatalysed reaction.
(a) On the energy profile diagram, sketch how the catalyst would alter the reaction pathway. (1 mark) (b) (i) How does the reaction temperature affect the yield of methanol from biogas? In your answer, refer to Le Chatelier's principle. (2 marks) (ii) How does the reaction pressure affect the yield of methanol from biogas? In your answer, refer to Le Chatelier's principle. (2 marks) (c) Write the expression for the equilibrium constant, K, for this reaction. (1 mark) (d) 0.760 mol of carbon monoxide, CO, and 0.525 mol of hydrogen, H2, were allowed to reach equilibrium in a 500 mL container. At equilibrium the mixture contained 0.122 mol of methanol. Calculate the equilibrium constant, K. (3 marks) (Total = 9 marks)
Solution
(a) One mark for an unlabelled or labelled line inside the original curve and connecting the enthalpy of the reactants and products (see graph below).
(1 mark) (b) (i) One mark allocated to correct effect on yield for a particular temperature change and one mark for explanation using Le Chatelier’s principle including reference to exothermic or endothermic reaction: As the temperature of the reaction is increased, according to Le Chatelier’s principle, the system will partially oppose this change by shifting to decrease the temperature. This means that the endothermic back reaction is favoured. As a back reaction is favoured, a lower yield of methanol is obtained. (2 marks) (ii) One mark for the effect on the yield for a particular pressure change and one mark for explanation using Le Chatelier’s principle. For example, If the pressure of the system were increased, according to Le Chatelier’s principle, the system would shift to partially oppose the change by favouring the reaction, which decreases pressure. As the forward reaction converts three particles into one, this will be favoured by an increased pressure, which will also increase the yield of methanol. (2 marks) [ CH OH ]
3 (c) [ CO ][H 2]
(1 mark) (d) One mark for calculating correct moles at equilibrium One mark for correct concentrations and one mark for correct value, significant figures and units for K.
Initial moles
CO
H2
CH3OH
0.760
0.525
0
CO
H2
CH3OH
Change in moles
−0.122
−0.244
+0.122
Equilibrium moles
0.638
0.281
0.122
Equilibrium concentration (÷ 0.500)
1.276
0.562
0.244
0.244 −2 K = 1.276×0.562 2 = 0.605 M
(3 marks) (Total = 9 marks)
Question 10/ 29 [VCAA 2021 SB Q8] The reaction for the oxidation of sulfur dioxide, SO2, is shown below. 2SO2(g) + O2(g) ⇌ 2SO3(g) ΔH = -197 kJ mol−1 (a) 1.00 mol of SO2 and 1.00 mol of oxygen, O2, are placed into an evacuated, sealed 3.00 L container at 100 °C. After the reaction reaches equilibrium, the container contains 20.0 g of sulfur trioxide, SO3. Calculate the equilibrium constant, K, for this reaction at 100 °C. (4 marks) (b) The volume of the closed container is doubled. Describe the effect that this has on the concentration of SO2 from the time just before the volume was changed until after the system re-established its equilibrium. (3 marks) (Total = 7 marks)
Solution
m (a) One mark: neq(SO3) = M
One mark: ICE table
=
20.0 80.1 = 0.250 mol
SO2
O2
SO3
ni
1.00
1.00
0.00
nc
−0.250
−0.125
+0.250
neq
0.75
0.875
0.250
One mark: converting mol to concentration [SO3]eq = Vn
=
0.250 3 = 0.0833 M
[SO2]eq = Vn
=
0.750 3 = 0.25 M
[O2]eq = Vn
=
0.875 3 = 0.292 M [SO ]2
3 One mark: K = [SO ]2 × [O2 ] 2
=
0.09332 0.252 ×0.292
= 0.38 M−1 (4 marks) (b) One mark: When the volume of the container is doubled, the concentration of SO2 is halved initially. One mark: The volume increase is also a decrease in pressure, according to LCP the system will shift to partially oppose this change by increasing pressure. It does this by favouring the reaction that coverts less gaseous particles into more gaseous particles which is the reverse reaction. This will increase the concentration of SO2. One mark: Given the initial change halves the concentration and the system coming to equilibrium increases the concentration to partially oppose this, the concentration of SO2 will be between half its original concentration and the original concentration. (3 marks) (Total = 7 marks)
Question 11/ 29 An electrolysis cell is constructed from two pure nickel electrodes and an aqueous solution of NiSO4. The cell is used to measure the amount of electricity flowing in a circuit. The reaction at the negative electrode (cathode) is Ni2+(aq) + 2e− → Ni(s).
What current, in amps, is required to deposit 20 mg of nickel in 30 minutes?(Total = 4 marks)
Solution
−3 −4 n(Ni) = 20×10 58.71 = 3.41 × 10 mol
(1 mark) n(e−) = 2 × n(Ni) = 2 × 3.41 × 10−4 = 6.82 × 10−4 mol (1 mark) No. of coulombs required = 6.82 × 10−4 × 96 500 = 65.75 C (1 mark) 65.75 Current required = 30×60 = 0.0365 = 0.037 A
(1 mark) (Total = 4 marks)
Question 12/ 29 A piece of copper can be polished by making it the anode in an electrolysis cell. If it is assumed that the only reaction occurring at the anode is the conversion of copper metal into Cu2+ ions, calculate the mass of copper removed from the piece of copper by a current of 9.5 A passing for 4 minutes. (Total = 4 marks)
Solution
No. of coulombs = 9.5 × 4 × 60 (It) = 2280 C (1 mark) 2280 No. of faradays = 96 500 = 0.0236
(1 mark) n(Cu) = 0.5 × 0.0236 = 0.0118 (1 mark) Mass of Cu = 0.0118 × 63.5 = 0.75 g (1 mark) (Total = 4 marks)
Question 13/ 29 Three cells are connected as shown in the diagram below, and a steady current is passed for a fixed time. The aqueous solutions contain Pb2+, Ag+ and Al3+ respectively, and Pt electrodes are used.
(a) Write the equations for the reactions occurring at the cathode in each of the three cells. (3 marks) (b) If 0.03 mol of silver is deposited at the cathode in the centre cell, how much material (in moles) would you expect to be produced in each of the other cells? Explain your answer. (2 marks) (Total = 5 marks)
Solution
(a) Reduction occurs at the cathode in each of the cells. Pb2+(aq) + 2e− → Pb(s) Ag+(aq) + e− → Ag(s) 2H2O(l) + 2e− → H2(g) + 2OH−(aq) (Al cannot be deposited from aqueous solutions of Al3+) (3 marks) (b) n(e−) used in each cells = 0.03 mol; [since n(Ag) : n(e−) = 1 : 1] − n(Pb) = 0.03 2 = 0.015; [since n(Pb) : n(e ) = 1 : 2]
n(H2) = 0.015; [since n(H2) : n(e−) = 1 : 2] (2 marks) (Total = 5 marks)
Question 14/ 29 Two platinum electrodes were placed in 1.00 L of a 0.210 M AgNO3 solution. An electric current of 0.57 A was passed through the solution for some time, and silver metal formed on one of the electrodes. The volume of the solution was unchanged, and the final concentration of silver ion in the solution was 0.110 M. (a) At which electrode (anode or cathode) was the silver deposited? (1 mark) (b) What is the polarity of this electrode? (1 mark) (c) Calculate the time taken to deposit the silver. (4 marks) (Total = 6 marks)
Solution
(a) Cathode (1 mark) (b) Negative (1 mark) (c) n(Ag+) that reacted = 1.00 × (0.210 – 0.110) = 0.100 mol. (1 mark) n(e−) = n(Ag) = n(Ag+) = 0.100; (since the ratios are 1 : 1 : 1) (1 mark) No. of coulombs = 0.100 × 96 500 = 9650 (1 mark) Time taken = 9650 0.57 = 16 930 s or 4.7 h (1 mark) (Total = 6 marks)
Question 15/ 29 0.75 L of an aqueous solution is prepared and contains 0.025 mol each of SnCl2, ZnCl2 and CuCl2. Two graphite rods are placed in the solution and an electric current is passed through. When the electrolysis is finished, all of the metal ions (Sn2+, Zn2+ and Cu2+) have been deposited onto one of the graphite rods. The metals form three successive coatings: A, B and C (see diagram below).
(a) Identify the three metals A, B and C. Explain your answer. (2 marks) (b) Calculate the amount of electricity, in coulombs, needed to deposit the zinc layer alone.
(3 marks) (c) How many coulombs would be needed to deposit the other two metals? Explain your answer. (2 marks) (Total = 7 marks)
Solution
(a) From the electrochemical series, the oxidants can be placed in decreasing order of oxidising strength, i.e. Cu2+ > Sn2+ > Zn2+. The strongest oxidant will react first and the metal that is highest in the electrochemical series, i.e. the weakest reductant, Cu, is deposited first. Then the next strongest oxidant will react, and Sn will be deposited second. Zinc will be deposited last and will form the outside layer. Hence the metals are A = Cu, B = Sn and C = Zn. (2 marks) (b) n(Zn) deposited = 0.025; n(e) needed = 2 × 0.025 = 0.050 number of coulombs = 0.050 × 96 500 = 4825 C (3 marks) (c) Each of these metal ions has a charge of 2+. Hence in each case 2 mol of electrons will be needed to deposit 1 mol of the metal. The same amount of electricity will be needed to deposit each of the metals. Hence to deposit both Cu and Sn the number of coulombs will be twice that needed to deposit the zinc. 2 × 4825 = 9650 C (2 marks) (Total = 7 marks)
Question 16/ 29 A student sets up a circuit for electroplating copper, silver and gold in three separate cells as shown in the diagram below. The cells are connected in series. A current flows through the circuit for 1.0 hour and 1.30 g of copper is deposited.
(a) At which electrode was the copper deposited? (1 mark) (b) The student measures the masses of the three metals deposited in this experiment, and then calculates the moles of each metal produced. What result would you expect the student to find for the ratio ‘n(Cu) : n(Ag) : n(Au)’? Explain your answer. (2 marks) (c) Calculate the current, in amps, that flowed through the circuit. (3 marks) (d) What were the masses of silver and gold deposited in the other two cells? (4 marks) (Total = 10 marks)
Solution
(a) Cathode or negative electrode (1 mark) (b) The number of moles of metal deposited in an electrolytic cell is inversely proportional to the charge on the ion. If 6 mol of electrons were passed through the three cells, then n(Au) = 6/3 = 2; n(Cu) = 6/2 = 3; n(Ag) = 6/1 = 6. A smaller quantity of electricity would give smaller amounts of the metals but in the same relative proportions. Hence the ratio n(Cu) : n(Ag) : n(Au) will be 3 : 6 : 2 (2 marks) (c) n(Cu) = 1.30 ÷ 63.5 = 0.0205 mol n(e−) = 2 × 0.0205 = 0.0410 mol (1 mark)
No. of coulombs = 0.0410 × 96 500 = 39 565 C (1 mark) Q
Current needed = t
=
39565 3600 = 1.10 A
(1 mark) (d) n(Ag) = 6/3 × n(Cu) = 2 × 0.0205 = 0.0410 mol Mass Ag = 0.0410 × 107.9 = 4.42 g (2 marks) n(Au) =
2×n(Cu) = 2×0.0205 = 0.01367 mol 3 3
Mass Au = 0.01367 × 197 = 2.69 g (2 marks) (Total = 10 marks)
Question 17/ 29 Electrolysis of aqueous solutions containing nickel ions, Ni2+(aq), leads to the formation of nickel metal on the cathode (or negative electrode). However, calcium metal cannot be produced in this way from the electrolysis of aqueous solution containing calcium ions, Ca2+(aq). (a) What would you expect to occur at the cathode when an aqueous solution of calcium chloride is electrolysed? Use an equation to illustrate your answer. (2 marks) (b) How can calcium metal be obtained from calcium chloride by electrolysis? (1 mark) (Total = 3 marks)
Solution
(a) In this cell there are two oxidants that could be reduced at the cathode: Ca2+(aq) or H2O. Water is a better oxidant than Ca2+(aq) and is reduced.
2H2O(l) + 2e− → 2OH−(aq) + H2(g) Hydrogen gas will be produced at the cathode. (2 marks) (b) Calcium metal can only be obtained from the electrolysis of a molten calcium compound, e.g. liquid CaCl2. During electrolysis: Ca2+ + 2e− → Ca occurs at the negative electrode. (1 mark) (Total = 3 marks)
Question 18/ 29 A student connects two cells in series and passes an electric current through both. The first cell contains 2.0 M hydrochloric acid and platinum electrodes. In the second cell, the student uses silver electrodes and silver nitrate solution. The student passes a current of 2.85 A through both cells. A gas is produced at the cathode in the first cell and 2.00 g of silver is deposited on the cathode of the second cell. (a) Draw a labelled diagram to show how the experiment described above would be set up. For each cell, indicate the polarity of the electrodes and label the cathode. (3 marks) (b) Calculate the time for which the current was passed. (2 marks) (c) Identify the gas formed at the cathode in the first cell and give the equation for the reaction that produces this gas. (2 marks) (d) What volume of the gas in part (c) would be formed at SLC? (2 marks) (Total = 9 marks)
Solution
(a)
(3 marks) (b) n(Ag) = 2.00 ÷ 107.9 = 0.0185 n(e−) = n(Ag), since the equation for the reaction is Ag+ + e− → Ag no. of coulombs = 0.0185 × 96 500 = 1789 C time = 1789 ÷ 2.85 = 627.6 s (10 min 28 sec) (2 marks) (c) Hydrogen 2H+(aq) + 2e− → H2(g) (2 marks) (d) n(H2) = 12 × n(e−) = 12 × 0.0185 = 0.00925 (1 mark) V(H2) = n × Vm = 0.00925 × 24.8 = 0.230 L (1 mark) (Total = 9 marks)
Question 19/ 29 A metal ornament of total surface area 48 cm2 is to be completely covered with a nickel coating of 2.50 × 10−3 cm thickness. The nickel is deposited by electrolysis. The ornament is suspended in an aqueous solution containing nickel ions, Ni2+(aq), and is made one of the electrodes of an electrolysis cell. Ni2+(aq) + 2e− → Ni(s) (a) To which electrode (cathode or anode) should the ornament be connected?
(1 mark) (b) What volume of nickel is needed to plate the ornament? (volume (mL) ≈ surface area (cm2) × thickness (cm)) (1 mark) (c) What mass of nickel will be used? (Density of nickel = 8.90 g mL−1) (1 mark) (d) Calculate the time needed to deposit the nickel coating if a steady current of 0.750 A is passed through the cell. (4 marks) (Total = 7 marks)
Solution
(a) Cathode (negative electrode) (1 mark) (b) Volume of Ni needed = 48 × 2.50 × 10−3 = 0.12 cm3 (1 mark) (c) Mass of Ni = 0.12 × 8.90 = 1.07 g (1 mark) 1.07 (d) n(Ni) = 58.71 = 0.0182 mol
(1 mark) No. of faradays = n(Ni) × 2 = 0.0182 × 2 = 0.0364 F (1 mark) (since 1 mol of Ni is deposited by 2 mol of electrons) No. of coulombs = 0.0364 × 96 500 = 3513 C (1 mark) 3513 Time = 0.750 = 4681 sec = 4.7 × 103 sec or 78 min
(1 mark) (Total = 7 marks)
Question 20/ 29 A student is asked to determine a value for the Faraday constant by electrolysis of a copper sulfate solution using copper electrodes. Copper is deposited at the cathode, which is washed and dried at the end of the experiment. 0.175 g of copper was deposited by a current of 0.863 A in 10.00 minutes. (a) Calculate a value for the Faraday constant from these results in C mol−1. (3 marks) (b) The data table gives the value of the Faraday constant as 96 500 C mol−1. Suggest a reason why the value determined from the student's results differs from the value in the data table. (1 mark) (c) The student repeats the experiment using a different solution of copper sulfate and this time obtains a value for the Faraday constant of 98 900 C mol−1. The student then discovers that the copper sulfate solution used contained small amounts of nickel sulfate and zinc sulfate. What effect would these impurities have (if any) on the result? (1 marks) (Total = 5 marks)
Solution
(a) The Faraday constant is the amount of charge that contains 1 mole of electrons. n(Cu) = 0.175 ÷ 63.54 = 2.754 × 10−3; Q = 0.863 × 10.00 × 60 = 517.8 C Since it takes 2 mol of electrons to deposit 1 mol of Cu, then n(e−) used = 2 × 2.754 × 10−3 = 5.508 × 10−3 mol 517.8 Hence 1 mol of electrons requires 5.508×10 −3 = 94 009 = 94 000 C
(3 marks) (b) The value is lower than that given in the data table. Either Q is too small, i.e. the time or the current has been underestimated, or n(e−) is too large. This could occur if the mass of Cu was too large. Cu may have contained water or some other impurity. (1 mark) (c) Both Ni2+ and Zn2+ are weaker oxidants than Cu2+. Provided the [Cu2+] remains high compared with [Ni2+] or
[Zn2+] only Cu should be deposited at the cathode. These impurities should not affect the result. (1 mark) (Total = 5 marks)
Question 21/ 29 When current is drawn from a lead-acid accumulator, the electrode reactions are Pb(s) + SO42−(aq) → PbSO4(s) + 2e− PbO2(s) + 3H+(aq) + HSO4−(aq) + 2e− → PbSO4(s) + 2H2O(l) (a) As the accumulator discharges, describe what happens to the (i) sulfuric acid concentration (ii) number of ions in solution (iii) pH (1 + 1 + 1 = 3 marks) (b) In the overall cell reaction, what are the changes in oxidation number? (2 marks) (c) Give the equation of the reaction that occurs at the positive electrode during discharge. (1 mark) (d) Give the equation of the reaction that occurs at the negative electrode when the accumulator is being recharged. (1 mark) (Total = 7 marks)
Solution
(a) (i) The discharging process consumes HSO4−(aq), SO42−(aq) and H+(aq). Hence the [H2SO4] decreases.
(ii) The number of ions decreases. HSO4−(aq), SO42−(aq) and H+(aq) are all removed and replaced with H2O which is not extensively ionised. (iii) [H+] decreases and so pH increases. (3 marks) (b) Pb is oxidised to PbSO4 and the oxidation number of Pb has changed from 0 to +2. PbO2 is reduced to PbSO4 and the oxidation number of Pb has changed from +4 to +2. (2 marks) (c) PbO2(s) + 3H+(aq) + HSO4−(aq) + 2e− → PbSO4(s) + 2H2O(l) This process consumes electrons and thus makes the electrode positive. (1 mark) (d) During recharging, electrons are supplied to one electrode and removed from the other one. The electrode where electrons are supplied will be negative and the reaction that occurs will consume electrons, i.e. PbSO4(s) + 2e− → Pb + SO42−(aq) (1 mark) (Total = 7 marks)
Question 22/ 29 [Adapted VCAA 2013 SB Q7] An electrolytic process known as electrorefining is the final stage in producing highly purified copper. In a smallscale trial, a lump of impure copper is used as one electrode and a small plate of pure copper is used as the other electrode. The electrolyte is a mixture of aqueous sulfuric acid and copper sulfate. (a) Indicate in the box labelled ‘polarity’ on the diagram below, the polarity of the impure copper electrode. (1 mark)
In a trial experiment, the electrodes were weighed before and after electrolysis. The results are provided in the following table. Mass of lump of impure copper
Mass of pure copper
before electrolysis
10.30 kg
1.55 kg
after electrolysis
0.855 kg
9.80 kg
(b) On the basis of these results • calculate a percentage purity of the lump of impure copper • indicate one factor that may affect the accuracy of these results. (4 marks) (c) Conditions in the electrolytic cell shown in the diagram above are carefully controlled to ensure a high degree of copper purity and electrical efficiency. Use the mass of pure copper deposited that is given in the table in part (a) to determine the time, in days, taken for this electrolysis reaction to be completed. Assume the current was a constant 24 A. (5 marks) Lumps of impure copper typically contain impurities such as silver, gold, cobalt, nickel and zinc. Cobalt, nickel and zinc are oxidised from the copper lump and exist as ions in the electrolyte. Silver and gold are not oxidised and form part of an insoluble sludge at the base of the cell. (d) Why is it important that silver and gold are not present as cations in the electrolyte? (1 mark) (Total = 11 marks)
Solution
(a) The electrode is positive, i.e. ‘+’. (1 mark) (b) Mass lost from impure electrode = 10.30 – 0.855 = 9.445 g Mass gained by pure Cu electrode = 9.80 – 1.55 = 8.25 g % purity of impure Cu electrode = 8.25×100 9.445 = 87.34 = 87.3% The accuracy of the result would be affected if • either of the electrodes were not carefully dried before weighing, i.e. the electrodes should be dried to constant mass. • some of the copper produced at the pure Cu electrode fails to adhere to the pure electrode and falls to the bottom of the container. (4 marks) (c) n(Cu) = 8250 ÷ 63.5 = 129.9 mol Equation for the reduction of copper ions is Cu2+(aq) + 2e− → Cu(s) Hence n(e−) = 2 × 129.9 = 259.8 mol Charge needed to deposit Cu = 259.8 × 96 500 = 2.507 × 107 C Time taken = 2.507 × 107 ÷ 24 = 1.0445 × 107 seconds 7 Time taken (in days) = 1.0445×10 60×60×24 = 12.09 = 12 days
(5 marks) (d) The silver (Ag+) and gold (Au+) cations are stronger oxidants than Cu2+. During electrolysis if any of these cations were present in the electrolyte, they will be reduced instead of the copper ions. Silver and gold would be deposited on the pure copper electrode thus lowering the purity of the copper. (1 mark) (Total = 11 marks)
Question 23/ 29 [Adapted VCAA 2011 E2 SB Q8] A chemical engineer designs a pilot plant to determine the conditions that will give the best results for copper plating different objects. A range of experiments indicates that an electroplating cell with an aqueous electrolyte containing copper(I) cyanide, CuCN, potassium cyanide, KCN, and potassium hydroxide, KOH, will produce a uniform copper
coating. (a) Write a balanced half-equation for the cathode reaction in this electrolytic cell. (1 mark) The quality of the copper coating depends on maintaining a low, constant concentration of copper(I) ions in the electrolyte. This is achieved by making use of the following reaction, which takes place in the electrolyte bath. In this reaction, copper(I) ions, Cu+, react with the cyanide ions, CN−, according to the equation Cu+(aq) + 4CN−(aq) ⇌ Cu(CN)43− K = 1 × 1028 (b) Refer to this information to explain how the presence of excess potassium cyanide in the electrolyte maintains a low concentration of Cu+(aq) ions in solution. (1 mark) The cyanide ion, CN−, is the conjugate base of the acid hydrogen cyanide, HCN. CN−(aq) + H2O(l) ⇌ HCN(aq) + OH−(aq); K = 10−4.8 Hydrogen cyanide is highly toxic and can bubble out of solution. (c) Explain how the presence of potassium hydroxide in the electrolyte is essential to the safe operation of this cell. (1 mark) Any gas produced at the cathode is found to damage the quality of the copper plate. This is avoided by maintaining a low current. (d) Write a balanced equation for the gas most likely to be produced at the cathode if the current is too high. (1 mark) (e) In one trial, a medal is copper plated in the cell. The experimental data is given below. Mass of medal before copper plating = 25.2 g Mass of medal after copper plating = 36.4 g Current = 0.900 A Calculate the time, in minutes, taken to copper plate the medal. (4 marks) (Total = 8 marks)
Solution
(a) Reduction of copper(I) ions will occur at the cathode.
Cu+(aq) + e− → Cu(s) (1 mark) (b) Addition of KCN will increase [CN−] in the electrolyte. This will push the position of equilibrium to the right and so keep [Cu+] low. (1 mark) (c) Addition of KOH increases [OH−] in the electrolyte. This will push the position of the equilibrium to the left. [HCN] is reduced and there is less chance of HCN bubbling out of solution. (1 mark) (d) 2H2O(l) + 2e− → H2(g) + 2OH−(aq) (1 mark) [Note 2H+(aq) + 2e− → H2(g) is incorrect since the electrolyte is basic and not acidic.] (e) Mass of Cu deposited = 36.4 – 25.2 = 11.2 g n(Cu) = 11.2 ÷ 63.6 = 0.176 mol n(e−) = n(Cu) = 0.176 mol (since reaction is Cu+(aq) + e− → Cu(s)) Q = n(e−) × F = 0.176 × 96 500 = 16 994 C Q
time = I
=
16994 0.900 = 18 882 s or 314.7 min
time = 315 min (4 marks) (Total = 8 marks)
Question 24/ 29 [VCAA 2017 SB Q8] Fluorine, F2, gas is the most reactive of all non-metals. Anhydrous liquid hydrogen fluoride, HF, can be electrolysed to produce F2 and hydrogen, H2, gases. Potassium fluoride, KF, is added to the liquid HF to increase electrical conductivity. The equation for the reaction is 2HF(l) → F2(g) + H2(g)
F2 is used to make a range of chemicals, including sulfur hexafluoride, SF6, an excellent electrical insulator, and xenon difluoride, XeF2, a strong fluorinating agent. The diagram below shows an electrolytic cell used to prepare F2 gas.
Liquid HF, like water, is an excellent solvent for ionic compounds. In the same way that water molecules in an aqueous solution form the ions K+(aq) and F−(aq), when KF is dissolved in HF, the K+ and F− ions form ions that are written as K+(HF) and F−(HF). (a) Label the polarities of each electrode in the circles provided on the diagram above. (1 mark) (b) Write the equation for the half-reaction occurring at the anode. (1 mark) (c) Suggest why the diaphragm, shown in the diagram above, is important for the safe operation of the electrolytic cell. (1 mark) (d) Explain why the carbon electrode cannot be replaced with an iron electrode. (3 marks) (e) Calculate the volume of F2 gas, measured at standard laboratory conditions (SLC), that would be produced when a current of 1.50 A is passed through the cell for 2.00 hours. (3 marks) (Total = 9 marks)
Solution
(a)
(1 mark) (b) 2F−(HF)→ F2(g) + 2e− (1 mark) (Note F−(aq) is incorrect as there is no water in this electrolysis cell!) (c) The diaphragm keeps the two gases produced by the electrolysis apart. H2 and F2 are very reactive, and if they make contact they would react to reform HF. (1 mark) (d) Iron (Fe) is a much stronger reductant that fluoride ion (F−). If the carbon electrode is replaced with an iron electrode the iron would be preferentially oxidised. Fe(s) → Fe2+(HF) + 2e− Production of F2 at the anode would cease. (3 marks) (e) Q = It = 2.00 × 60 × 60 × 1.50 = 10 800 C n(e−) = Q/F = 10 800 ÷ 96 500 = 0.1119 mol From part (b), n(F2) = n(e−) ÷ 2 = 0.1119 ÷ 2 = 0.0560 mol Volume F2 = 0.0560 24.8 = 1.388, i.e. 1.39 L (3 marks) (Total = 9 marks)
Question 25/ 29 [VCAA 2014 SB Q9] Magnesium is one of the most abundant elements on Earth. It is used extensively in the production of magnesiumaluminium alloys. It is produced by the electrolysis of molten magnesium chloride. A schematic diagram of the electrolytic cell is shown below. The design of this cell takes into account the following properties of both magnesium metal and magnesium chloride:
Molten magnesium reacts vigorously with oxygen. At the temperature of molten magnesium chloride, magnesium is a liquid. Molten magnesium has a lower density than molten magnesium chloride and forms a separate layer on the surface. (a) Write a balanced half-equation for the reaction occurring at each of the cathode and the anode. (2 marks)
(b) Explain why an inert gas is constantly blown through the cathode compartment. (1 mark) (c) The melting point of a compound can often be lowered by the addition of small amounts of other compounds. In an industrial process, this will save energy. In this cell, NaCl and CaCl2 are used to lower the melting point of MgCl2. Why can NaCl and CaCl2 be used to lower the melting point of MgCl2 but ZnCl2 cannot be used? (2 marks) (d) What difference would it make to the half-cell reactions if the graphite anode were replaced with an iron anode? Write the half-equation for any different half-cell reaction. Justify your answer. (3 marks) (Total = 8 marks)
Solution
(a) Cathode reaction: Mg2+(l) + 2e− → Mg(l) (1 mark) Anode reaction: 2Cl−(l) → Cl2(g) + 2e− (1 mark)
(b) The inert gas prevents air from entering the cell. If air entered the cell, the oxygen would react with the molten magnesium. (1 mark) (c) Adding NaCl and CaCl2 to MgCl2 will release Na and Ca2+ ions into the molten electrolyte. The presence of Na+ and Ca2+ will have no effect on the cathode reaction since Na+ and Ca2+ ions are weaker oxidants than Mg2+ and Mg2+ will be reduced in preference. However, Zn2+ is a stronger oxidant than Mg2+, and if ZnCl were used Zn would be formed at the cathode instead of Mg. (2 marks) (d) Iron is a stronger reductant than Cl− and would be oxidised in preference at the anode. Fe(s) → Fe2+(l) + 2e− Eventually Fe2+ ions would migrate to the cathode. Since Fe2+ ions are stronger oxidants than Mg2+ ions they would be reduced preferentially, and Fe would form at the cathode instead of Mg. Fe2+(l) + 2e− → Fe(s) (3 marks) (Total = 8 marks)
Question 26/ 29 [VCAA 2020 SB Q2] The electrolysis of carbon dioxide gas, CO2, in water is one way of making ethanol, C2H5OH. The diagram below shows a CO2-H2O electrolysis cell. The electrolyte used in the electrolysis cell is sodium bicarbonate solution, NaHCO3(aq).
The following half-cell reactions occur in the CO2–H2O electrolysis cell. O2(g) + 2H2O(l) + 4e− ⇌ 4OH−(aq) E° = +0.40 V 2CO2(g) + 9H2O(l) + 12e− ⇌ C2H5OH(l) + 12OH−(aq) E° = −0.33 V (a) Identify the Cu-Zn electrode as either the anode or the cathode in the box provided in the diagram above. (1 mark) (b) Determine the applied voltage required for the electrolysis cell to operate. (1 mark) (c) Write the balanced equation for the overall electrolysis reaction. (1 mark) (d) Identify the oxidising agent in the electrolysis reaction. Give your reasoning using oxidation numbers. (2 marks) (e) A current of 2.70 A is passed through the CO2–H2O electrolysis cell. The cell has an efficiency of 58%. Calculate the time taken, in minutes, for this cell to consume 6.05 × 10−3 mol of CO2(g). (3 marks) (Total = 8 marks)
Solution
(a) Cathode (1 mark) (b) Greater than 0.73 V (1 mark) (c) 2CO2 + 3H2O → C2H5OH + 3O2 (states not required for mark) (1 mark) (d) One mark for identifying the oxidising agent and one mark for using oxidation numbers to correctly explain: the oxidation number of carbon decreases from +4 in CO2 to −2 in C2H5OH meaning that it has gained electrons making CO2 the oxidising agent (1 mark) (e) One mark for calculating the moles of electrons from moles of CO2: n(e−) = 6 × n(CO2) = 6 × 6.05 × 10−3 = 0.0363 mol One mark for calculating the correct time based on the moles of CO2: Q = n(e−) × F = 0.0363 × 96500 = 3.5 × 103 C Q
t= I
=
3.5×103 3 2.70 = 1.3 × 10 s
One mark for accurate use of efficiency and correct units for final answer: 3 3 t = 1.3×10 0.58 = 2.24 × 10 s 3 t = 2.24×10 = 37 minutes 60
(3 marks) (Total = 8 marks)
Question 27/ 29 [Adapted VCAA 2015 SB Q10] A car manufacturer is planning to sell hybrid cars powered by a type of hydrogen fuel cell connected to a nickel metal hydride, NiMH, battery. A representation of the hydrogen fuel cell is given below.
The overall cell reaction is 2H2(g) + O2(g) → 2H2O(g) (a) (i) On the diagram above, indicate the polarity of the anode and the cathode in circles A and B, and identify the product of the reaction in box C. (2 marks) (ii) Write an equation for the reaction that occurs at the cathode when the switch is closed. (1 mark) (iii) Identify one advantage and one disadvantage of using this fuel cell instead of a petrol engine to power the car. (2 marks) (b) The storage battery to be used in the hybrid cars is comprised of a series of nickel metal hydride, NiMH, cells. MH represents a metal hydride alloy that is used as one electrode. The other electrode contains nickel oxide hydroxide, NiOOH. The electrolyte is aqueous KOH. The simplified equation for the reaction at the anode while recharging is Ni(OH)2(s) + OH−(aq) → NiOOH(s) + H2O(l) + e− The simplified equation for the reaction at the cathode while recharging is M(s) + H2O(l) + e− → MH(s) + OH−(aq) (i) What is the overall equation for the discharging reaction? (1 mark)
(ii) In the boxes on the diagram above, indicate which is the MH electrode and which is the NiOOH electrode. (1 mark) (iii) In the box provided in the cell diagram, use an arrow, → or ←, to indicate the direction of the electron flow as the cell is discharging. (1 mark) (iv) The battery discharged for 60 minutes, producing a current of 1.15 A. What mass, in grams, of NiOOH would be used during this period? (3 marks) (Total = 11 marks)
Solution
(a) (i) anode – and cathode +; product is water (2 marks) (ii) O2(g) + 4H+(aq) + 2e− → 2H2O(l) (1 mark) (iii) Advantage: - higher efficiency than a petrol engine. - no CO2, NOx, CO, unburnt hydrocarbons produced. - H2 is a renewable fuel. Disadvantage: - more expensive than petrol engines. - H2 leaks could lead to an explosion. - difficulties in obtaining and storing H2.
(2 marks) (b) (i) MH(s) + NiOOH(s) → M(s) + Ni(OH)2(s) (1 mark) (ii) Upper box: NiOOH; lower box: MH (1 mark) (iii) Arrow should point to the left ←. (1 mark) (iv) Charge Q = It = 1.15 × 60 × 60 = 4140 C n(e−) = 4140 ÷ 96 500 = 0.0429 mol n(NiOOH) = n(e−) = 0.0429 mol Mass NiOOH = 0.0429 × 91.7 = 3.9 g (3 marks) (Total = 11 marks)
Question 28/ 29 [VCAA 2019 SB Q7] The zinc-cerium battery is a commercial rechargeable battery that comprises a series of cells. During recharging, the cells use energy from wind farms or solar cell panels. During discharging, energy is supplied to electric grids to power local factories and homes. The electrolytes are stored in separate storage tanks and are pumped into and out of each cell when in use. A membrane separates the two electrodes that are immersed in 1 M methanesulfonic acid, CH3SO3H. A diagram representing a zinc-cerium cell is shown below.
The following half-cell reactions occur in the zinc-cerium cell. Zn(CH3SO3)2(aq) + 2H+(aq) + 2e− ⇌ Zn(s) + 2CH3SO3H(aq) E° = −0.76 V Ce(CH3SO3)4(aq) + H+(aq) + e− ⇌ Ce(CH3SO3)3(aq) + CH3SO3H(aq) E° = 1.64 V (a) Write the equation for the overall discharge reaction. (1 mark) (b) Identify the oxidising agent during discharging and justify your answer using oxidation numbers. (2 marks) (c) Determine the theoretical voltage produced by a single cell as it discharges. (1 mark) (d) Write the ionic equation for the reaction occurring at the positive electrode during recharging. (1 mark) (e) Other than transporting ions between the electrodes, describe one function of the membrane in the zinc-cerium cell. (1 mark) (f) Specify one factor that would limit the life of the zinc-cerium cell. (1 mark) (g) Experts have regarded the zinc-cerium cell as a hybrid of a fuel cell and a secondary cell. Why would this be the case? (1 mark) (Total = 8 marks)
Solution
(a) 2Ce(CH3SO3)4(aq) + Zn(s) → 2Ce(CH3SO3)3(aq) + Zn(CH3SO3)2(aq) (1 mark) (b) Ce4+(aq) or Ce(CH3SO3)4 is the oxidising agent. CH3SO3 has a −1 charge so cerium changes from Ce4+ to Ce3+ and thus its oxidation number changes from +4 to +3. This shows that cerium has gained electrons and acted as the oxidising agent. (2 marks) (c) E°(cell) = E°(oxidising agent) – E°(reducing agent) = 1.64 −(−0.76) = 2.40 V (1 mark) (d) Ce3+(aq) → Ce4+(aq) + e− (1 mark) (e) To prevent cerium and zinc ions from moving between the two half-cells (1 mark) (f) One of the following responses: • The prevalence of side reactions that render the active material unusable in the desired reactions for the cell to function • Exposure to increased temperature for prolonged periods. (1 mark) (g) The cell is like a secondary cell as it is rechargeable and is like a fuel cell as the reactants are continuously supplied from outside of the cell. (1 mark) (Total = 8 marks)
Question 29/ 29 [VCAA 2021 SB Q2] Research scientists are developing a rechargeable magnesium-sodium, Mg-Na, hybrid cell for use in portable devices. The Mg-Na hybrid cell uses magnesium metal and sodium ion electrodes and a hybrid organic/salt electrolyte, X.
A simplified diagram of the rechargeable Mg-Na hybrid cell is shown below.
(a) The equation for the overall reaction during recharge is 2NaX + Mg2+ →Mg + 2Na2+ + 2X (i) Identify the polarity of the Mg electrode when the cell is discharging by placing a positive (+) or a negative (-) sign in the box provided in the diagram above. (1 mark) (ii) Write the half-cell equation of the reaction that occurs at the Mg electrode when the cell is discharging. (1 mark) (b) A pacemaker is a small electronic device that is implanted in the body to regulate a person's heart rate. If the MgNa hybrid cell were to be used to power pacemakers, what would be two potential safety hazards of having this cell in the body? (2 marks) (c) One source of Mg is magnesium chloride, MgCl2, which can be obtained from seawater. Explain how Mg can be produced from MgCl2 in an electrolytic cell. (3 marks) (Total = 7 marks)
Solution
(a) (i) The electrode is negative (–). Mg is changing from Mg2+ to Mg during recharge, which is reduction. Reduction occurs at the cathode which is negative during electrolytic (recharging) processes. (1 mark)
(ii) Mg → Mg2+ + 2e− (1 mark) (b) Any two from: • the content of device/electrolyte is toxic/harmful/corrosive to the body if it leaks • the battery may overheat • Mg is relatively reactive so may react in the body • leakage would cause an imbalance in natural Mg2+/Na+ ion levels in the body (2 marks) (c) One mark: MgCl2 must be heated to a molten state within a container/vessel. One mark: Two electrodes should be placed into the molten MgCl2 and connected to a power supply. An electric current should be applied with just over 3.73 V using inert electrodes. One mark: A barrier should be placed between the electrodes to ensure that the products at each do not come into direct contact and then the liquid magnesium produced can be collected from the surface of the molten MgCl2. (3 marks) (Total = 7 marks)
Question 2/ 5 The highest yield of ammonia would be obtained using A. high temperatures and high pressures. B. low temperatures and high pressures. C. high temperatures and low pressures. D. low temperatures and low pressures.
Solution
B. The L to R reaction is exothermic and so is favoured by low temperatures. The number of moles of products is less than the number of moles of reactants. High pressures will move the position of equilibrium to the right.
Question 3/ 5 In the industrial process a catalyst is used. The catalyst A. increases the rates of the forward and back reactions but does not change the equilibrium constant. B. increases the rates of the forward and back reactions and increases the equilibrium constant. C. increases the rate of the forward reaction only but does not change the equilibrium constant. D. increases the rate of the forward reaction only and increases the equilibrium constant.
Solution
A. Catalysts lower the activation energy of a reaction. This does not change K but does make the forward and back reactions more rapid.
Question 4/ 5 In a certain equilibrium mixture [N2] = 0.100 M, [H2] = 0.200 M and [NH3] = 0.800 M. The value of the equilibrium constant is A. 1.00 × 10 B. 40.0 C. 800 D. 2.67
Solution
C. K
=
[NH3 ]2 [N2 ][H2 ]3
=
0.800×0.800 0.100×(0.200)3 =800M−2
Question 5/ 5 An alloy of iridium and rhodium is used to catalyse the following reaction. 4NH3(g) + 5O2(g) ⇌ 4NO(g) + 6H2O(g); ΔH = −900 kJ mol−1 The purpose of the catalyst is to A. increase the equilibrium constant, K, of the reaction. B. increase the activation energy of the reaction. C. decrease the equilibrium constant, K, of the reaction. D. decrease the activation energy of the reaction.
Solution
D. Catalysts lower the activation energy of a reaction.
Question 6/ 5 Butane can be ‘cracked’ into two smaller molecules. C4H10(g) ⇌ C2H6(g) + C2H4(g); ΔH = +93 kJ mol−1 Which of the following sets of conditions would lead to the greatest amount of cracking? A. 280°C and 2 atmospheres pressure B. 280°C and 10 atmospheres pressure C. 350°C and 2 atmospheres pressure D. 350°C and 10 atmospheres pressure
Solution
C. Since the L to R process is endothermic, more products will be produced at the higher temperature. There are more moles of products than reactants; hence a low pressure is required.
Question 7/ 5 When limestone, CaCO3, reacts with hydrochloric acid, the following reaction occurs. CaCO3(s) + 2HCl(aq) → CaCl2(aq) + CO2(g) + H2O(l) Which of the following would not increase the rate of the reaction? A. Increasing the volume of the container B. Using finely powdered limestone C. Changing the temperature from 15°C to 25°C D. Using 2.0 M acid instead of 1.0 M acid
Solution
A. This one will not increase the number of collisions between particles.
Question 8/ 5 In the conversion of carbon monoxide to carbon dioxide, the following reaction is used. CO(g) + H2O(g) ⇌ CO2(g) + H2(g); ΔH = −40 kJ mol−1 Which of the following would not increase the percentage conversion of CO into CO2?
A. Decreasing the temperature B. Decreasing the pressure C. Adding more steam D. Removing CO2
Solution
B. Changing the pressure will have no impact on the position of equilibrium because the number of moles of reactants is the same as that of products.
Question 9/ 5 [VCAA 2020 SA Q6] Which one of the following pairs of statements is correct for both electrolysis cells and galvanic cells? Electrolysis cell Both electrodes are always inert.
Galvanic cell Both electrodes are always made of metal.
Electrical energy is converted to chemical energy.
The voltage of the cell is independent of the electrolyte concentration.
Chemical energy is converted to electrical energy.
The products are dependent on the half-cell components.
The products are dependent on the half-cell components.
Chemical energy is converted to electrical energy.
Solution
D. A is incorrect as both statements are false. B is incorrect as the concentration of the electrolyte can alter the voltage of a galvanic cell. C has an incorrect energy conversion for the electrolysis cell. D is correct as the products are always dependent on the half-cell components and the energy conversion for galvanic cells is correct.
Question 10/ 5 [Adapted VCAA 2012 E2 SA Q11] The following reaction is used in some industries to produce hydrogen. CO(g) + H2O(g) ⇌ CO2(g) + H2(g); ΔH = −41 kJ mol−1 In trials, the reaction is carried out with and without a catalyst in the sealed container. All other conditions are unchanged. The change in hydrogen concentration with time between an uncatalysed and a catalysed reaction is represented by a graph. Which graph below is correct?
A.
B.
C.
D.
Solution
C. The catalysed reaction will be faster, i.e. the equilibrium concentration of H2 will be produced in a shorter time.
Question 12/ 5 Which of the following will increase the yield of ethene, C2H4? A. Adding more hydrogen at constant pressure B. Increasing the overall pressure C. Lowering the temperature D. Removing hydrogen
Solution
D. All other responses will cause the equilibrium to move to the left.
Question 13/ 5
When the volume of the container is reduced A. there will be no change in the position of equilibrium. B. the equilibrium constant will decrease. C. more ethene, C2H4, and hydrogen will be produced. D. more ethane, C2H6, will be formed.
Solution
D. Reducing the volume will not change K but will favour the side with the least number of moles.
Question 14/ 5 When galvanic and electrolytic cells are compared A. the cathode is positive in galvanic cells but negative in electrolytic cells. B. the anode is positive in galvanic cells but negative in electrolytic cells. C. the cathode is negative in galvanic cells but positive in electrolytic cells. D. the anode is negative in both galvanic and electrolytic cells.
Solution
A. In galvanic cells, electrons are consumed at the cathode (reduction). Hence the cathode is positive. In electrolytic cells, electrons are removed from the anode, making it positive in this case.
Question 16/ 5
Which one of the following is correct? Steel rod is connected to battery at
Reaction occurring at the steel rod is
positive terminal
an oxidation
positive terminal
a reduction
negative terminal
an oxidation
negative terminal
a reduction
Solution
D. To produce copper Cu2+ ions must be reduced, i.e. Cu2+(aq) + 2e− → Cu(s). This reaction will occur at the negative electrode.
Question 17/ 5 The mass of copper deposited on the steel rod is 0.247 g. If the current used in the experiment was 1.50 A, then the time, in seconds, needed for the experiment is closest to A. 250 B. 500 C. 750 D. 1000
Solution
B. n(Cu) = 0.247 ÷ 63.55 = 3.887 × 10−3 mol n(e−) = 2 × 3.887 × 10−3 = 7.773 × 10−3 mol No. of coulomb = 7.773 × 10−3 × 96 500 = 750 C
Time = 750 ÷ 1.5 = 500 s
Question 18/ 5 A student passed 750 C of electricity through an aqueous solution of an ionic salt, MCln 0.81 g of metal, M, is deposited at the cathode. The metal and the value of n are most likely to be Metal, M
n
lead
2
chromium
2
palladium
2
silver
1
Solution
A. n(Pb) = 0.81 ÷ 207.2 = 3.909 × 10−3 mol No. of coulomb = 3.909 × 10−3 × 2 × 96 500 = 754 C
Question 19/ 5 An important reaction in the production of nitric acid is the conversion of nitric oxide into nitrogen dioxide. 2NO(g) + O2(g) ⇌ 2NO2(g); ΔH = −114 kJ mol−1 For each of the actions (a) and (b), indicate what effect it would have on (i) the equilibrium constant, K, and (ii) the yield of nitrogen dioxide. Action (a) Changing the temperature from 400°C to 450°C (b) Adding more oxygen at constant temperature and pressure
(i) Effect on K
(ii) Effect on yield of NO2
(Total = 4 marks)
Solution
(a) Changing the temperature will (i) reduce K. (ii) reduce the yield of NO2. (2 marks) (b) Adding more oxygen will (i) have no effect on K. (ii) increase the yield of NO2. (2 marks) (Total = 4 marks)
Question 20/ 5 Hydrogen iodide will decompose when heated according to the following reaction: 2HI(g) ⇌ H2(g) + I2(g) 0.100 mol of hydrogen iodide was placed in a 1.00 L flask and heated to 350 K. When equilibrium had been established, 0.033 mol of HI remained. (a) How many moles of HI have been reacted at equilibrium? (1 mark) (b) How many moles of H2 have been formed at equilibrium? (2 marks) (c) Calculate the numerical value for the equilibrium constant for this reaction at 350 K. (2 marks) (Total = 5 marks)
Solution
(a) n(HI) reacted = 0.100 – 0.033 = 0.067 mol (1 mark) (b) Ratio n(H2) : n(HI) = 1 : 2, hence n(H2) = 0.067 ÷ 2 = 0.0335 mol (2 marks) (c) n(I2) = n(H2) since the ratio is 1 : 1
K=
[H2 ][I2 ] [HI]2
=
0.0335×0.0335 0.033×0.033 = 1.03 = 1.0 (2 sig. figures)
(2 marks) (Total = 5 marks)
Question 21/ 5 When steam and carbon monoxide are heated, the following reaction occurs CO(g) + H2O(g) ⇌ CO2(g) + H2(g); ΔH = −40 kJ mol−1 For each of the actions mentioned in the table below, state how it would affect the (a) yield of hydrogen. (2 marks) (b) equilibrium constant, K, for the reaction. (2 marks) (c) rate of reaction. (2 marks) Action Increasing the pressure Increasing the temperature (Total = 6 marks)
(a) Yield of hydrogen
(b) K
(c) Rate of reaction
Solution
(a) Increasing the pressure will not change the yield of H2 since the number of moles of reactants is the same as that of the products. (1 mark) Increasing the temperature will decrease the yield of H2. K is reduced and so fewer products are formed. (1 mark) (b) Increasing the pressure will not change K. Equilibrium constants are independent of pressure. (1 mark) Increasing the temperature will decrease K since the L to R process is exothermic. (1 mark) (c) Increasing the pressure will increase the rate of reaction. The molecules will be pushed closer together and there will be more collisions per second. (1 mark) Increasing the temperature will increase the rate of reaction. The molecules will move faster and there will be more collisions per second. (1 mark) (Total = 6 marks)
Question 22/ 5 When methane is heated with steam at 650°C, the following reaction occurs CH4(g) + H2O(g) ⇌ CO(g) + 3H2(g); ΔH = +220 kJ mol−1 In one equilibrium mixture, the following concentrations were measured. [CH4] = 0.15 M, [H2O] = 3.25 M, [CO] = 1.05 M, [H2] = 1.05 M (a) Write an expression for the equilibrium constant for this reaction. (1 mark) (b) Calculate a value for the equilibrium constant at 650°C. (3 marks)
(c) How would you expect the value of the equilibrium constant at 400°C to differ from the value at 650°C? Give a reason for your answer. (2 marks) (Total = 6 marks)
Solution
(a) K
=
[CO][H2 ]3 [CH4 ][H2 O]
(1 mark) (b) K
=
1.05×(1.05)3 2 0.15×3.25 = 2.49 M
(3 marks) (c) The equilibrium constant at 400°C will be smaller than that at 650°C. (1 mark) The L to R reaction is endothermic. For endothermic reactions, equilibrium constants are smaller at lower temperatures. (1 mark) (Total = 6 marks)
Question 23/ 5 A student sets up the electrolysis cell shown below. Two graphite rods are placed in an aqueous solution that contains 0.40 mol of AgNO3 and 0.40 mol of Cu(NO3)2.
(a) If a current of 9.65 A is passed through the cell for 8000 seconds, describe what will happen at the negative electrode. (3 marks) (b) For how much longer must the electrolysis be continued to completely deposit all of the two metals? (2 marks) (Total = 5 marks) Total marks for test = 41 marks
Solution
(a) The species that could undergo reduction at the negative electrode in this cell are Ag+, Cu2+ and H2O. The order of reactivity of these oxidants is Ag+ > Cu2+ > H2O. Hence Ag+ will be reduced first. No. of coulombs = 9.65 × 8000 = 77 200 No. of faradays = 77 200 ÷ 96 500 = 0.800 Since 0.80 mol of electrons are used, then all of the Ag+ (0.40 mol) will be reduced. The remaining 0.40 mol of electrons will reduce 0.20 mol of Cu2+. (3 marks) (b) To deposit the remaining Cu (0.20 mol), a further 0.40 mol of electrons will be required. Thus, the electrolysis will need to be continued for another 4000 s. (2 marks) (Total = 5 marks)
Chapter 3: Unit 3 revision paper Question 1/ 20 [VCAA 2011 E2 SA Q7]
Consider the following combustion reactions for graphite and diamond. C(graphite) + O2(g) → CO2(g); ΔH = −393 kJ mol−1 C(diamond) + O2(g) → CO2(g); ΔH = −395 kJ mol−1 The following diagram summarises this information.
From the data provided it can be determined that the enthalpy change, ΔH, for the conversion of graphite to diamond C(graphite) → C(diamond) is A. −2 kJ mol−1 B. +2 kJ mol−1 C. −788 kJ mol−1 D. +788 kJ mol−1
Solution
B. When graphite and O2 react to form CO2, the energy released is 393 kJ, whereas conversion of CO2 to diamond and O2 would absorb 395 kJ. The energy change for the overall conversion of graphite to diamond is thus −393 + 395 kJ.
Question 2/ 20 VCAA 2011 E2 SA Q8]
What mass of butane (M = 58.0 g mol−1) must undergo complete combustion to raise the temperature of 100.0 g of water by 1.00°C? Assume that there is no heat loss. A. 8.44 g B. 6.88 g C. 0.399 g D. 8.44 × 10−3 g
Solution
D. Energy required to heat the water = 4.18 × 0.1 × 1.00 kJ Amount of butane needed = 0.418 ÷ 2874 = 1.454 × 10−3 mol Mass of butane = 1.454 × 10−3 × 58.0 = 8.436 × 10−3 g
Question 3/ 20 [Adapted VCAA 2012 E2 SA Q2] Which one of the following fuels is the most sustainable? A. biodiesel B. petrol C. coal D. natural gas
Solution
A. Biodiesel can be obtained from renewable sources, such as vegetable oils or animal fats. Reserves of the other three fuels will eventually be exhausted.
Question 4/ 20 Consider the enthalpy changes for the decomposition of two oxides of nitrogen. 2NO2(g) → N2(g) + 2O2(g) ΔH = −66 kJ mol−1 (reaction 1) 2NO(g) → N2(g) + O2(g) ΔH = −180 kJ mol−1 (reaction 2) From this information, the enthalpy change for the reaction represented by the equation NO(g) + ½O2(g) → NO2(g) is A. −57 kJ mol−1 B. −114 kJ mol−1 C. −123 kJ mol−1 D. −246 kJ mol−1
Solution
A. The desired equation can be obtained if reaction 1 is halved and added to half the reverse of reaction 2. Hence ΔH is (−180 ÷ 2) + (+66 ÷ 2) = −57 kJ mol−1
Question 5/ 20 [Adapted VCAA 2012 E2 SA Q12] Consider the following energy profile diagram for a reaction represented by the equation X + Y → Z.
Which one of the following provides the correct values of the activation energy and enthalpy change for the reaction X + Y → Z? Activation energy (kJ mol−1)
Enthalpy change (kJ mol−1)
+75
+100
+100
+175
+175
+100
+200
−125
Solution
C. The activation energy = 200 – 25 = +175 kJ mol−1 and ΔH = 125 – 25 = +100 kJ mol−1.
Question 6/ 20 One methanol oxygen fuel cell uses 2.00 × 10−7 mol of methanol per second. The current (in mA) produced by this cell is A. 3.22 B. 19.3 C. 77.2
D. 116
Solution
D. n(e−) = 6 × 2.00 × 10−7 = 1.2 × 10−6 mol Q = 1.2 × 10−6 × 96 500 = 0.116 C Since this amount of charge is produced each second, the current is 0.116 A or 116 mA.
Question 7/ 20 [VCAA 2011 E2 SA Q10] Two galvanic cells were constructed under standard conditions in an experiment to determine the relative positions in the electrochemical series of the standard electrode potential, E°, for the following reactions. Both cells generate a potential difference.
Ag(NH3)2+(aq) + e− ⇌ Ag(s) + 2NH3(aq) E°1 Ag+(aq) + e− ⇌ Ag(s) E°2 Ag(CN)2−(aq) + e− ⇌ Ag(s) + 2CN−(aq) E°3 The values of the electrode potentials in order from highest to lowest would be A. E°1, E°2, E°3 B. E°1, E°3, E°2 C. E°2, E°1, E°3
D. E°3, E°2, E°1
Solution
C. Since the Ag(CN)2−/CN− half-cell is the negative electrode, E°3 will be lower (more negative) than E°1. Similarly, E°1 will be lower than E°2. Thus the order will be E°2 > E°1 > E°3.
Question 9/ 20 [Adapted VCAA 2012 E2 SA Q16] Which one of the following is correct as the cell discharges? Electrons would flow from the
In the salt bridge
zinc electrode to the silver electrode.
anions migrate to the Ag+/Ag half-cell.
silver electrode to the zinc electrode.
cations migrate to the Zn2+/Zn half-cell.
silver electrode to the zinc electrode.
cations migrate to the Ag+/Ag half-cell.
zinc electrode to the silver electrode.
anions migrate to the Zn2+/Zn half-cell.
Solution
D. Zinc is a more reactive metal than silver and will be oxidised. [Zn2+] will increase and anions will migrate into the half-cell to maintain electroneutrality.
Question 10/ 20 [VCAA 2012 E2 SA Q17]
In this cell A. Ag+(aq) is reduced and the Zn(s) is oxidised. B. Ag(s) is oxidised and the Zn2+(aq) is reduced. C. Ag(s) is reduced and the Zn2+(aq) is oxidised. D. Ag+(aq) is oxidised and the Zn(s) is reduced.
Solution
A. Ag+ is a more reactive oxidant than Zn2+ and zinc is a more reactive metal than silver.
Question 11/ 20 [VCAA 2012 E2 SA Q18] The cathode in this cell and the maximum voltage produced by this cell, under standard conditions, are respectively A. Ag and 0.16 V B. Ag and 1.56 V C. Zn and 0.16 V D. Zn and 1.56 V
Solution
B. E°(cell) = E°(oxidant) – E°(reductant) = 0.80 – (−0.76) E°(cell) = 1.56 V. Reduction will occur at the cathode, i.e. Ag+(aq) + e− → Ag(s).
Question 12/ 20 [VCAA 2017 SA Q18] Ammonia, NH3, can be produced by the reaction of hydrogen, H2, and nitrogen, N2. When this reaction takes place in a sealed container of fixed volume, an equilibrium system is established. The equation for the reaction is shown below. N2(g) + 3H2(g) ⇌ 2NH3(g); ΔH = −92 kJ mol−1 If the pressure and volume remain constant when the temperature is increased, the forward reaction rate will A. increase and the [NH3] will increase. B. increase and the [NH3] will decrease. C. decrease and the [NH3] will decrease. D. decrease and the [NH3] will remain the same.
Solution
B. Increasing the temperature increases the rate of the reaction but decreases the amount of NH3 since ΔH is