2022 May/June · Paper 43 · Q4 (a, b)6 marksRate of reaction · Reversible reactions & equilibrium
2022 May/June · Paper 43 · Q5 (e)3 marksRate of reaction
2022 May/June · Paper 43 · Q6 (c(ii), c(iii))3 marksRedox & oxidation number
2022 May/June · Paper 61 · Q2 (e)2 marksRate of reaction
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school. “Paper 42” means Paper 4, variant 2.
Practice questions
Original questions written by HomiLabs in the style of the exam, with answers and mark schemes. They are not
Cambridge past paper questions and have not been reviewed by Cambridge. Try each one before opening the answer.
Q1Rate of reaction · Core · Paper 2 style · 1 mark
(a)Magnesium ribbon reacts with dilute hydrochloric acid. Which change increases the rate of the reaction?[1]
Show answer
(a) B increasing the temperature of the acid
A higher temperature gives particles more energy, so more frequent and more successful collisions. A does not change concentration so the rate is unchanged.
Q2Rate of reaction · Core · Paper 4 style · 4 marks
(a)State what is meant by a catalyst.[2]
(b)Hydrogen peroxide decomposes slowly into water and oxygen. Name a catalyst for this reaction.[1]
(c)Describe a test for the oxygen given off.[1]
Show answer
(a) A substance that increases the rate of a reaction and is unchanged (chemically and in mass) at the end.
B1 increases rate; B1 unchanged at the end.
(b) manganese(IV) oxide (MnO₂) / catalase
(c) It relights a glowing splint.
Q3Rate of reaction · Standard · Paper 4 style · 4 marks
A student in Peshawar reacts marble chips (calcium carbonate) with excess dilute hydrochloric acid.
(a)The student repeats the experiment using the same mass of powdered marble. Explain, in terms of particles, why the reaction is faster.[2]
(b)The student then uses hydrochloric acid of half the concentration with the original marble chips. Explain the effect on the rate.[2]
Show answer
(a) Powder has a larger surface area, so more particles of calcium carbonate are exposed and the frequency of collisions with acid particles increases.
B1 larger surface area; B1 more collisions per unit time.
(b) The rate decreases, because there are fewer acid particles per unit volume, so collisions are less frequent.
B1 slower; B1 fewer particles per unit volume, lower collision frequency.
Q4Rate of reaction · Standard · Paper 6 style · 6 marks
Zinc granules react with dilute hydrochloric acid. The hydrogen is collected in a gas syringe.time / s: 0, 30, 60, 90, 120, 150, 180, 210, 240volume / cm³: 0, 24, 42, 55, 63, 67, 69, 70, 70
(a)State the total volume of gas produced.[1]
(b)Calculate the average rate of reaction in the first 60 s, in cm³/s.[2]
(c)Explain why the rate of reaction decreases as the reaction goes on.[2]
(d)Suggest the time at which the reaction stopped.[1]
Show answer
(a) 70 cm³
(b) 0.7 cm³/s
M1 42 ÷ 60; A1 0.7.
(c) Reactants are used up (the concentration of the acid decreases), so there are fewer collisions per unit time.
B1 reactant(s) used up / concentration of acid falls; B1 fewer collisions per second.
(d) Between 180 s and 210 s
First time the volume reaches 70 cm³ is 210 s; accept any time from 180 s to 210 s.
Q5Rate of reaction · Standard · Paper 2 style · 1 mark
(a)[1]
Show answer
(a) A using the same mass of powdered marble
Powder increases surface area, so the rate rises, and the same mass of marble gives the same mass of CO₂. B would give a smaller total loss.
Q6Rate of reaction · Standard · Paper 6 style · 4 marks
Calcium carbonate is added to dilute nitric acid in a conical flask on a balance.mass of flask and contents at start = 152.40 gmass after 5 minutes = 151.52 g (the reaction had stopped)
(a)Calculate the mass of carbon dioxide lost.[1]
(b)Calculate the average rate of reaction over the 5 minutes, in g/min.[1]
(c)Calculate the number of moles of carbon dioxide lost. [Mr of CO₂ = 44][1]
(d)State why a loose cotton wool plug is placed in the neck of the flask.[1]
Show answer
(a) 0.88 g
152.40 − 151.52.
(b) 0.176 g/min
0.88 ÷ 5.
(c) 0.020 mol
0.88 ÷ 44.
(d) To let the gas escape but stop acid spray / liquid being lost (which would give extra mass loss).
Q7Rate of reaction · Challenge · Paper 4 style · 4 marks
(a)Explain, in terms of collisions and activation energy, why increasing the temperature increases the rate of a reaction.[3]
(b)Suggest why milk kept in a refrigerator goes sour more slowly than milk left out on a hot day in Multan.[1]
Show answer
(a) Particles gain kinetic energy and move faster, so they collide more often; a greater proportion of collisions have energy equal to or greater than the activation energy, so more collisions are successful.
B1 more kinetic energy / faster particles; B1 more frequent collisions; B1 more particles with energy ≥ activation energy (more successful collisions).
(b) Lower temperature slows the reactions (of bacteria / enzymes) that sour the milk.
Q8Rate of reaction · Challenge · Paper 6 style · 6 marks
Sodium thiosulfate solution reacts with dilute hydrochloric acid to form a cloudy mixture. A flask is placed on a cross drawn on paper and the time for the cross to disappear is measured. 10 cm³ of acid is used each time.experiment 1: 50 cm³ thiosulfate, 0 cm³ water, 20 sexperiment 2: 40 cm³ thiosulfate, 10 cm³ water, 25 sexperiment 3: 30 cm³ thiosulfate, 20 cm³ water, 34 sexperiment 4: 20 cm³ thiosulfate, 30 cm³ water, 62 sexperiment 5: 10 cm³ thiosulfate, 40 cm³ water, 101 s
(a)Calculate the value of 1/time for experiment 1. Give the unit.[1]
(b)Identify the anomalous result. Explain your choice.[2]
(c)Explain why water was added so that the total volume was always 50 cm³.[2]
(d)Name the solid that makes the mixture cloudy.[1]
Show answer
(a) 0.05 s⁻¹ (1/s)
1 ÷ 20 = 0.05.
(b) Experiment 4 (20 cm³), 62 s; the pattern suggests about 50 s, as halving the concentration from experiment 2 should double the time.
B1 experiment 4; B1 reason based on trend (expected ~50 s).
(c) So that the volume of thiosulfate is proportional to its concentration, and the depth of liquid over the cross is the same (fair test).
B1 concentration proportional to volume used; B1 same depth / fair test.
(d) sulfur
Q9Reversible reactions & equilibrium · Core · Paper 2 style · 1 mark
(a)Blue hydrated copper(II) sulfate is heated until it turns white. When the white solid has cooled, a few drops of water are added. What is observed and why?[1]
Show answer
(a) B The solid turns blue and gets warm because the reaction is reversible.
CuSO₄·5H₂O ⇌ CuSO₄ + 5H₂O is reversible; the forward reaction is endothermic so the reverse (adding water) is exothermic and the solid gets warm. C has the energy change the wrong way round.
Q10Reversible reactions & equilibrium · Core · Paper 4 style · 4 marks
A reversible reaction is allowed to reach equilibrium in a closed system.
(a)Explain what is meant by a closed system.[1]
(b)Explain why the equilibrium is described as dynamic.[2]
(c)State what is meant by the symbol ⇌.[1]
Show answer
(a) A system in which no substances can enter or leave.
(b) The forward and reverse reactions are still happening, at the same rate.
B1 both reactions continue; B1 at equal rates.
(c) The reaction is reversible.
Q11Reversible reactions & equilibrium · Standard · Paper 4 style · 4 marks
Dinitrogen tetroxide (colourless) and nitrogen dioxide (brown) form an equilibrium in a sealed tube:N₂O₄(g) ⇌ 2NO₂(g) the forward reaction is endothermic.
(a)The sealed tube is placed in hot water. State and explain what happens to the colour of the gas mixture.[2]
(b)The gas mixture is compressed in a gas syringe at constant temperature. State and explain how the position of equilibrium changes.[2]
Show answer
(a) It becomes darker brown, because the forward reaction is endothermic so the equilibrium shifts to the right, producing more NO₂.
B1 darker brown; B1 equilibrium moves in endothermic direction / to the right.
(b) It moves to the left, because there are fewer moles of gas on the left (1 mol compared with 2 mol), so this reduces the pressure.
B1 shifts left (towards N₂O₄); B1 fewer gas molecules on left.
Q12Reversible reactions & equilibrium · Standard · Paper 2 style · 1 mark
(a)Methanol is made by the reaction CO(g) + 2H₂(g) ⇌ CH₃OH(g). The forward reaction is exothermic. Which conditions give the highest equilibrium yield of methanol?[1]
Show answer
(a) C low temperature and high pressure
Low temperature favours the exothermic forward reaction; high pressure favours the side with fewer gas moles (3 → 1). A would give a faster rate, but a lower yield.
Q13Reversible reactions & equilibrium · Standard · Paper 4 style · 4 marks
In aqueous solution, yellow chromate(VI) ions and orange dichromate(VI) ions form an equilibrium:2CrO₄²⁻(aq) + 2H⁺(aq) ⇌ Cr₂O₇²⁻(aq) + H₂O(l) yellow orange
(a)Dilute sulfuric acid is added to the yellow solution. State and explain the colour change.[2]
(b)Aqueous sodium hydroxide is then added to the orange solution. Suggest what is seen. Explain your answer.[2]
Show answer
(a) It turns orange, because adding H⁺ ions moves the equilibrium to the right, forming more Cr₂O₇²⁻.
B1 orange; B1 more H⁺ moves equilibrium right.
(b) It turns yellow again, because OH⁻ ions react with (remove) H⁺ ions, so the equilibrium moves to the left.
B1 yellow; B1 H⁺ removed so equilibrium shifts left.
Q14Reversible reactions & equilibrium · Challenge · Paper 4 style · 6 marks
Hydrogen and iodine react in a closed container:H₂(g) + I₂(g) ⇌ 2HI(g)
(a)State two features of a system at dynamic equilibrium.[2]
(b)State and explain the effect of increasing the pressure on the position of equilibrium.[2]
(c)State the effect of increasing the pressure on the rate at which equilibrium is reached. Explain your answer.[2]
Show answer
(a) The rate of the forward reaction equals the rate of the reverse reaction; the concentrations of reactants and products stay constant.
1 mark each. Accept: closed system needed.
(b) No effect, because there are equal numbers of moles of gas on each side (2 and 2).
B1 no change; B1 same number of gas moles on both sides.
(c) The rate increases, because the gas particles are closer together, so there are more collisions per unit time.
B1 faster; B1 higher collision frequency.
Q15Reversible reactions & equilibrium · Challenge · Paper 4 style · 6 marks
A gas XY₃ is made by the reaction X₂(g) + 3Y₂(g) ⇌ 2XY₃(g). The percentage of XY₃ at equilibrium is:200 °C: 50 % at 10 000 kPa; 70 % at 30 000 kPa400 °C: 15 % at 10 000 kPa; 35 % at 30 000 kPa600 °C: 3 % at 10 000 kPa; 9 % at 30 000 kPa
(a)Use the data to deduce whether the forward reaction is exothermic or endothermic. Explain your answer.[2]
(b)Describe and explain the effect of increasing the pressure on the yield.[2]
(c)Suggest why the manufacturer chooses 400 °C rather than 200 °C, even though the yield is lower.[2]
Show answer
(a) Exothermic: the yield of XY₃ decreases as temperature increases, so the equilibrium shifts left (endothermic direction) when heated.
B1 exothermic; B1 yield falls with increasing temperature.
(b) Yield increases, because the equilibrium shifts to the right, the side with fewer moles of gas (2 compared with 4).
B1 yield increases (data); B1 fewer gas moles on right.
(c) At 200 °C the rate is too slow; 400 °C gives an acceptable yield at a faster rate (compromise).
B1 rate too slow at low temperature; B1 compromise between rate and yield.
Q16Reversible reactions & equilibrium · Challenge · Paper 4 style · 5 marks
(a)State the effect of adding a catalyst on the position of equilibrium.[1]
(b)Explain why a catalyst is still used in many industrial equilibrium reactions.[2]
(c)Explain how a catalyst increases the rate of a reaction.[2]
Show answer
(a) No effect / the position does not change.
(b) It increases the rates of the forward and reverse reactions equally, so equilibrium is reached more quickly, saving time and energy costs.
B1 increases both rates equally; B1 equilibrium reached faster / lower temperature can be used.
(c) It provides an alternative pathway with a lower activation energy, so more collisions have enough energy to react.
B1 lower activation energy / alternative route; B1 more particles have energy ≥ Ea / more successful collisions.
Q17Redox & oxidation number · Core · Paper 4 style · 4 marks
(a)Define oxidation in terms of (i) oxygen and (ii) electrons.[2]
(b)For the reaction CuO + H₂ → Cu + H₂O, name the substance that is reduced and the substance that is oxidised.[2]
Show answer
(a) (i) gain of oxygen; (ii) loss of electrons
1 mark each.
(b) CuO (copper(II) oxide) is reduced; H₂ (hydrogen) is oxidised.
1 mark each.
Q18Redox & oxidation number · Standard · Paper 2 style · 1 mark
(a)What is the oxidation number of manganese in potassium manganate(VII), KMnO₄?[1]
Show answer
(a) D +7
K is +1 and four O are 4 × (−2) = −8, so Mn = +7, as shown by (VII) in the name. C (+6) is the oxidation number in a manganate(VI); A and B are other common oxidation numbers of manganese (Mn²⁺, MnO₂).
Q19Redox & oxidation number · Standard · Paper 4 style · 5 marks
Zinc powder is added to blue copper(II) sulfate solution. The blue colour fades and a pink-brown solid forms.Zn(s) + Cu²⁺(aq) → Zn²⁺(aq) + Cu(s)
(a)Write the ionic half-equation for the change to zinc.[1]
(b)Write the ionic half-equation for the change to copper(II) ions.[1]
(c)Identify the oxidising agent and the reducing agent. Explain your answer.[3]
Show answer
(a) Zn → Zn²⁺ + 2e⁻
(b) Cu²⁺ + 2e⁻ → Cu
(c) Oxidising agent: Cu²⁺ (it gains electrons / is reduced); reducing agent: Zn (it loses electrons / is oxidised).
B1 Cu²⁺ oxidising agent; B1 Zn reducing agent; B1 explanation in terms of electron transfer.
Q20Redox & oxidation number · Standard · Paper 6 style · 5 marks
(a)Solution P is added to acidified potassium manganate(VII). The purple colour disappears. State what this shows about P.[1]
(b)Solution Q is added to aqueous potassium iodide. The colourless solution turns brown. State what this shows about Q, and name the substance causing the brown colour.[2]
(c)A student adds an oxidising agent to acidified potassium manganate(VII). State what the student sees. Explain your answer.[2]
Show answer
(a) P is a reducing agent.
(b) Q is an oxidising agent; iodine.
1 mark each.
(c) No change / the solution stays purple, because acidified potassium manganate(VII) is itself an oxidising agent and is only decolourised by a reducing agent.
B1 stays purple / no colour change; B1 KMnO₄ is an oxidising agent, it needs a reducing agent to react.
Q21Redox & oxidation number · Challenge · Paper 4 style · 6 marks
(a)Give the oxidation number of chlorine in: (i) Cl₂, (ii) NaCl, (iii) NaClO, (iv) the chlorate ion ClO₃⁻.[4]
(b)Chlorine reacts with cold aqueous sodium hydroxide: Cl₂ + 2NaOH → NaCl + NaClO + H₂O. Use oxidation numbers to explain why this is a redox reaction.[2]
Show answer
(a) (i) 0; (ii) −1; (iii) +1; (iv) +5
1 mark each.
(b) Chlorine goes from 0 to −1 (reduced, in NaCl) and from 0 to +1 (oxidised, in NaClO); reduction and oxidation both occur.
B1 0 → −1 reduction; B1 0 → +1 oxidation.
Q22Redox & oxidation number · Challenge · Paper 4 style · 6 marks
In the blast furnace, iron(III) oxide is reduced:Fe₂O₃ + 3CO → 2Fe + 3CO₂
(a)Give the oxidation number of iron in Fe₂O₃ and in Fe.[2]
(b)Give the oxidation number of carbon in CO and in CO₂.[2]
(c)Use your answers to identify the reducing agent. State how many electrons are gained by each iron ion.[2]
Show answer
(a) +3 in Fe₂O₃; 0 in Fe
1 mark each.
(b) +2 in CO; +4 in CO₂
1 mark each.
(c) CO is the reducing agent (C is oxidised from +2 to +4); 3 electrons per iron ion.
B1 CO; B1 3.
Q23Industrial processes (Haber, Contact) · Core · Paper 4 style · 7 marks
Ammonia is manufactured by the Haber process at fertiliser plants in Pakistan.
(a)Write the balanced symbol equation for the Haber process, including the reversible sign.[2]
(b)State the sources of the nitrogen and of the hydrogen.[2]
(c)State the temperature, pressure and catalyst used.[3]
Show answer
(a) N₂ + 3H₂ ⇌ 2NH₃
B1 formulae; B1 balanced with ⇌.
(b) Nitrogen from the air; hydrogen from methane (natural gas) reacting with steam.
1 mark each.
(c) about 450 °C; about 20 000 kPa (200 atm); iron catalyst
1 mark each.
Q24Industrial processes (Haber, Contact) · Core · Paper 4 style · 5 marks
The Contact process is used to make sulfuric acid. In the converter: 2SO₂(g) + O₂(g) ⇌ 2SO₃(g); the forward reaction is exothermic.
(a)State the source of the oxygen used in the converter.[1]
(b)Name the catalyst used in the converter.[1]
(c)State and explain the effect of increasing the temperature on the equilibrium yield of sulfur trioxide.[2]
(d)State the final product of the Contact process and give its formula.[1]
Show answer
(a) air
(b) vanadium(V) oxide (V₂O₅)
(c) The yield decreases, because the forward reaction is exothermic, so the equilibrium shifts to the left (the endothermic direction).
Q25Industrial processes (Haber, Contact) · Standard · Paper 4 style · 6 marks
(a)State two ways in which the sulfur dioxide for the Contact process is obtained.[2]
(b)Write the equation for the reaction in the converter, and state the conditions used.[3]
(c)Higher pressure would increase the yield, but only about 200 kPa is used. Suggest why.[1]
Show answer
(a) Burning sulfur in air; roasting sulfide ores (e.g. zinc sulfide, iron pyrites) in air.
1 mark each.
(b) 2SO₂ + O₂ ⇌ 2SO₃; about 450 °C, about 200 kPa (2 atm), vanadium(V) oxide catalyst
B1 equation with ⇌; B1 temperature and pressure; B1 V₂O₅.
(c) The yield is already high at low pressure, so the extra cost of high-pressure equipment is not worth it.
Q26Industrial processes (Haber, Contact) · Standard · Paper 2 style · 1 mark
(a)Which set of conditions is used in the Haber process?[1]
Show answer
(a) C 450 °C, 20 000 kPa, iron
The Haber process uses about 450 °C, 20 000 kPa and an iron catalyst. B uses the Contact process pressure.
Q27Industrial processes (Haber, Contact) · Challenge · Paper 4 style · 6 marks
(a)The forward reaction in the Haber process is exothermic. Explain why a temperature of about 450 °C is used rather than a lower temperature.[3]
(b)Explain why a pressure higher than 20 000 kPa is not used.[2]
(c)Only about 15 % of the gases react in each pass through the reactor. Suggest what happens to the unreacted nitrogen and hydrogen.[1]
Show answer
(a) A lower temperature would give a higher equilibrium yield, but the rate would be too slow; 450 °C is a compromise giving a reasonable yield at an acceptable rate.
B1 lower T gives higher yield; B1 but rate too slow; B1 compromise.
(b) Higher pressure would increase yield but equipment would be very expensive to build and run, and it is more dangerous.
B1 cost of equipment / energy; B1 safety.
(c) They are recycled (passed back over the catalyst).
Q28Industrial processes (Haber, Contact) · Challenge · Paper 4 style · 4 marks
N₂ + 3H₂ ⇌ 2NH₃
(a)Calculate the maximum mass of ammonia, in tonnes, that could be made from 1.40 tonnes of nitrogen. [Ar: N = 14, H = 1][3]
(b)In one pass through the reactor only 15 % of this mass is formed. Calculate the mass of ammonia formed in one pass.[1]
Q29Physical vs chemical change · Core · Paper 2 style · 1 mark
(a)Which of these is a chemical change?[1]
Show answer
(a) C an iron gate rusting
Rusting forms a new substance (hydrated iron(III) oxide). The others are physical changes that only change the state or mix substances.
Q30Physical vs chemical change · Core · Paper 4 style · 4 marks
(a)State two differences between a physical change and a chemical change.[2]
(b)Classify each of the following as a physical or chemical change: (i) burning natural gas in a cooking stove, (ii) iodine subliming, (iii) frying an egg, (iv) dissolving salt in water.[2]
Show answer
(a) A chemical change forms a new substance, a physical change does not; physical changes are usually easily reversed, chemical changes usually are not.
1 mark each. Accept: chemical change usually has a large energy change.
(b) (i) chemical; (ii) physical; (iii) chemical; (iv) physical
2 marks for all four correct, 1 mark for three correct.
Similar questions
Questions that test the same subtopic in different years, grouped so you can work on one skill at a time.
References only: find each question in its paper (official link where available, otherwise through your school).
Rate of reactionBanker114 questions · 9/9 sessions
