2022 May/June · Paper 41 · Q1 (d(iv))4 marksRate of reaction
2022 May/June · Paper 42 · Q5 (c(ii), c(iii))5 marksRate of reaction
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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 1 style · 1 mark
(a)Magnesium reacts with dilute hydrochloric acid. Which change does NOT increase the rate of this reaction?[1]
Show answer
(a) D using larger pieces of magnesium
Larger pieces have a smaller surface area, so collisions are less frequent and the rate falls. Powder (B) increases surface area and rate.
Q2Rate of reaction · Core · Paper 2 style · 3 marks
Zinc granules react with dilute hydrochloric acid to produce hydrogen gas.
(a)Describe the effect on the rate of reaction of using more concentrated hydrochloric acid.[1]
(b)Explain this effect in terms of particles.[2]
Show answer
(a) The rate increases (the reaction is faster).
B1
(b) There are more acid particles in the same volume, so collisions between particles are more frequent (more collisions per second).
B1 more particles per unit volume; B1 higher collision frequency
Q3Rate of reaction · Core · Paper 3 style · 5 marks
A student follows the rate of reaction of marble chips with dilute hydrochloric acid by measuring the decrease in mass of the flask every 30 seconds.
(a)Name the apparatus used to measure the mass of the flask and its contents.[1]
(b)Explain why a cotton-wool plug is put in the neck of the flask.[1]
(c)State two variables that must be kept the same if the experiment is repeated with smaller marble chips.[2]
(d)Describe one other way of following the rate of this reaction.[1]
Show answer
(a) (top-pan) balance
B1
(b) It lets gas escape but stops acid spray / liquid being lost.
B1
(c) Any two of: mass of marble; volume of acid; concentration of acid; temperature.
1 mark each for any two
(d) Collect the CO₂ in a gas syringe and measure its volume at regular time intervals.
B1
Q4Rate of reaction · Core · Paper 4 style · 4 marks
A student mixes different concentrations of sodium thiosulfate solution with the same volume of dilute hydrochloric acid in a flask standing on a paper marked with a cross. She measures how long it takes for the cross to disappear from view.
(a)Name the independent variable and the dependent variable in this experiment.[2]
(b)State how the time taken is related to the rate of the reaction.[1]
(c)State one way to make the experiment a fair test.[1]
Show answer
(a) independent: concentration of sodium thiosulfate; dependent: time for the cross to disappear
B1 each
(b) The shorter the time, the faster the rate (rate is proportional to 1/time).
B1
(c) Keep the temperature / volume of acid / concentration of acid / total volume / the same cross the same.
B1
Q5Rate of reaction · Standard · Paper 1 style · 1 mark
(a)Which statement explains how a catalyst increases the rate of a reaction?[1]
Show answer
(a) B It provides a pathway with a lower activation energy.
A catalyst provides an alternative pathway of lower activation energy, so a greater proportion of collisions are successful. A describes the effect of heating, not of a catalyst.
Q6Rate of reaction · Standard · Paper 2 style · 4 marks
Sodium thiosulfate solution reacts with dilute hydrochloric acid.
(a)Describe and explain the effect of increasing the temperature on the rate of this reaction. Use ideas about particles and collisions.[4]
Show answer
(a) Rate increases. Particles gain kinetic energy and move faster, so they collide more frequently; a greater proportion of collisions have energy equal to or greater than the activation energy, so there are more successful collisions per second.
B1 rate increases; B1 particles have more kinetic energy / move faster; B1 more frequent collisions; B1 greater proportion of collisions with energy ≥ activation energy
Q7Rate of reaction · Standard · Paper 4 style · 5 marks
Marble chips (calcium carbonate) react with excess dilute hydrochloric acid. The carbon dioxide is collected in a gas syringe.Time / s: 0, 20, 40, 60, 80, 100Volume / cm³: 0, 46, 74, 90, 98, 100
(a)Calculate the average rate of reaction between 0 s and 20 s, in cm³/s.[1]
(b)Calculate the average rate between 40 s and 60 s.[1]
(c)Explain why the rate decreases as the reaction proceeds.[2]
(d)Suggest the total volume of gas that would be collected if the experiment were left to finish.[1]
Show answer
(a) 2.3 cm³/s
46 ÷ 20 = 2.3 B1
(b) 0.8 cm³/s
(90 − 74) ÷ 20 = 0.8 B1
(c) The acid is used up so its concentration decreases; collisions become less frequent.
B1 concentration of acid (reactant) decreases; B1 fewer collisions per second
(d) about 100 cm³ (reaction almost complete)
B1 accept 100–102 cm³
Q8Rate of reaction · Standard · Paper 2 style · 4 marks
(a)Explain why fine coal dust in the air of a coal mine in Balochistan can explode when a spark occurs, but a lump of coal burns slowly.[3]
(b)Suggest one other industry where fine powders could cause an explosion.[1]
Show answer
(a) Dust has a much larger surface area (per unit mass); more coal particles are exposed to oxygen, so collisions are much more frequent; the reaction is so fast that heat and gas are released almost instantly (explosion).
B1 larger surface area; B1 more frequent collisions with oxygen; B1 very fast reaction / rapid release of energy
Q9Rate of reaction · Standard · Paper 4 style · 5 marks
Hydrogen peroxide solution decomposes slowly into water and oxygen. When a little solid manganese(IV) oxide is added, oxygen is given off rapidly.2H₂O₂ → 2H₂O + O₂
(a)Describe how the student could show that the manganese(IV) oxide is unchanged in mass at the end.[3]
(b)The student repeats the experiment with the same mass of manganese(IV) oxide as a fine powder instead of granules. State and explain the effect on the rate.[2]
Show answer
(a) Weigh the manganese(IV) oxide before; after the reaction filter the mixture to collect the solid; wash and dry it, then weigh again; the mass is the same.
B1 weigh before; B1 filter, wash and dry; B1 reweigh, same mass
(b) The rate increases because the powder has a larger surface area, so more collisions happen at the catalyst surface per second.
B1 faster; B1 larger surface area / more frequent collisions
Q10Rate of reaction · Challenge · Paper 2 style · 6 marks
0.50 g of calcium carbonate lumps is added to 50 cm³ of 1.0 mol/dm³ hydrochloric acid.CaCO₃ + 2HCl → CaCl₂ + H₂O + CO₂ [Mr: CaCO₃, 100; molar volume 24 dm³ at r.t.p.]
(a)Show that the acid is in excess and calculate the volume of carbon dioxide produced at r.t.p.[3]
(b)For each change, state how the initial rate and the final volume of gas compare with the original experiment.(i) 0.50 g of powdered calcium carbonate is used.(ii) 50 cm³ of 0.50 mol/dm³ hydrochloric acid is used.(iii) 1.00 g of calcium carbonate lumps is used.[3]
(b) (i) faster, same volume (120 cm³); (ii) slower, same volume (120 cm³, acid still in excess); (iii) faster or similar rate, double volume (240 cm³)
B1 each; in (ii) 0.025 mol HCl still exceeds the 0.010 mol needed; in (iii) acid still in excess (0.020 needed), so 0.010 mol CO₂ = 240 cm³ (allow 'faster' as larger total surface area)
Q11Rate of reaction · Challenge · Paper 2 style · 6 marks
(a)Explain why increasing the pressure increases the rate of a reaction between two gases.[2]
(b)Explain why food kept in a refrigerator goes bad more slowly than food left in a hot kitchen in Hyderabad in summer.[2]
(c)A student says 'a catalyst increases the energy of the colliding particles'. Explain why this is wrong.[2]
Show answer
(a) The same number of gas particles occupy a smaller volume (higher concentration), so collisions are more frequent.
B1 particles closer together / more per unit volume; B1 more frequent collisions
(b) At low temperature the reacting particles (in the decay reactions) have less kinetic energy; fewer collisions per second have energy ≥ activation energy, so the rate of decay is lower.
B1 less kinetic energy / move slower; B1 fewer successful collisions (fewer with energy ≥ Ea)
(c) A catalyst does not change the particles' energy; it provides an alternative route with a lower activation energy, so more of the existing collisions are successful.
B1 particle energy unchanged; B1 lower activation energy pathway
Q12Rate of reaction · Challenge · Paper 2 style · 5 marks
0.12 g of magnesium ribbon reacts completely with excess dilute sulfuric acid in 40 s.Mg + H₂SO₄ → MgSO₄ + H₂ [Ar: Mg, 24; molar volume 24 dm³ at r.t.p.]
(a)Calculate the volume of hydrogen produced at r.t.p.[2]
(b)Calculate the mean rate of reaction in cm³ of hydrogen per second.[1]
(c)Calculate the mean rate in moles of magnesium used per second.[1]
(d)Explain why the rate in the first 10 seconds is greater than the mean rate.[1]
(d) The acid concentration is highest at the start, so collisions are most frequent then.
B1
Q13Reversible reactions & equilibrium · Core · Paper 1 style · 1 mark
(a)Which statement is correct for a reversible reaction at equilibrium in a closed system?[1]
Show answer
(a) C The rates of the forward and reverse reactions are equal.
At dynamic equilibrium both reactions continue at equal rates, so concentrations stay constant. B is a common error: concentrations are constant, not necessarily equal.
Q14Reversible reactions & equilibrium · Core · Paper 2 style · 4 marks
CoCl₂·6H₂O ⇌ CoCl₂ + 6H₂O
(a)State the meaning of the symbol ⇌.[1]
(b)Describe what is seen when pink hydrated cobalt(II) chloride is heated, and what is seen when water is then added to the product.[2]
(c)State what is meant by a closed system.[1]
Show answer
(a) The reaction is reversible.
B1
(b) It turns blue on heating; adding water turns it pink again.
B1 pink → blue; B1 blue → pink
(c) No substances can enter or leave (reactants and products cannot escape).
B1
Q15Reversible reactions & equilibrium · Standard · Paper 2 style · 4 marks
A sealed glass tube contains an equilibrium mixture of colourless dinitrogen tetroxide and brown nitrogen dioxide.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.[2]
(b)State and explain the effect on the position of equilibrium of increasing the pressure.[2]
Show answer
(a) It becomes darker brown; the forward reaction is endothermic, so increasing temperature moves the position of equilibrium to the right (more NO₂).
B1 darker; B1 equilibrium shifts in endothermic direction / to the right
(b) Moves to the left; there are fewer moles of gas on the left (1) than on the right (2).
B1 left; B1 fewer gas molecules on left
Q16Reversible reactions & equilibrium · Standard · Paper 2 style · 5 marks
H₂(g) + I₂(g) ⇌ 2HI(g)
(a)State and explain the effect of increasing the pressure on the position of equilibrium.[2]
(b)State the effect of adding a catalyst on the position of equilibrium and on the time taken to reach equilibrium.[2]
(c)The forward reaction is exothermic. State the effect of lowering the temperature on the amount of hydrogen iodide at equilibrium.[1]
Show answer
(a) No change; there are equal numbers of moles of gas on each side (2 and 2).
B1 no effect; B1 equal moles of gas
(b) Position unchanged; equilibrium is reached more quickly.
B1 each
(c) It increases.
B1 (equilibrium shifts to the exothermic direction)
Q17Reversible reactions & equilibrium · Standard · Paper 2 style · 4 marks
Ethanol is made industrially from ethene and steam at about 300 °C and 6000 kPa with a phosphoric acid catalyst.C₂H₄(g) + H₂O(g) ⇌ C₂H₅OH(g)
(a)State the effect on the yield of ethanol of increasing the pressure. Explain.[2]
(b)The forward reaction is exothermic. State the effect on the yield of increasing the temperature.[1]
(c)Unreacted ethene is separated and passed back through the reactor. Suggest why.[1]
Show answer
(a) Yield increases; there are fewer moles of gas on the right (1) than on the left (2).
B1; B1
(b) Yield decreases.
B1
(c) To increase the overall conversion / avoid waste of reactant and save cost.
B1
Q18Reversible reactions & equilibrium · Challenge · Paper 2 style · 6 marks
Methanol, used as a fuel, is made from carbon monoxide and hydrogen.CO(g) + 2H₂(g) ⇌ CH₃OH(g)
(a)Explain why a high pressure is used.[2]
(b)The forward reaction is exothermic. Explain why a moderate temperature of about 250 °C is used rather than a much lower temperature.[3]
(c)Suggest one disadvantage of using a very high pressure.[1]
Show answer
(a) There are fewer moles of gas on the right (1) than the left (3), so high pressure moves the equilibrium to the right, increasing the yield; it also increases the rate.
B1 fewer gas moles on right / shifts right; B1 higher yield (allow faster rate)
(b) A low temperature would give a higher yield because the equilibrium shifts in the exothermic direction, but the rate would be too slow; 250 °C is a compromise giving an acceptable yield at a reasonable rate (a catalyst is also used).
B1 lower T gives higher yield; B1 but rate too slow; B1 compromise between yield and rate
(c) Expensive equipment / energy costs / safety risk.
B1
Q19Reversible reactions & equilibrium · Challenge · Paper 2 style · 5 marks
A gaseous reaction X₂(g) + 3Y₂(g) ⇌ 2XY₃(g) is studied. The table shows the percentage of XY₃ at equilibrium.At 200 atm: 300 °C 59%; 400 °C 34%; 500 °C 18%At 400 °C: 100 atm 22%; 200 atm 34%; 300 atm 42%
(a)Use the data to deduce whether the forward reaction is exothermic or endothermic. Explain.[2]
(b)Describe and explain the effect of pressure on the yield.[2]
(c)Predict the yield at 300 °C and 400 atm, choosing from: less than 40%, between 40% and 59%, more than 59%.[1]
Show answer
(a) Exothermic: at constant pressure the yield decreases as the temperature increases, so equilibrium shifts left (the endothermic direction) on heating.
B1 exothermic; B1 yield falls as temperature rises
(b) Yield increases with pressure because there are fewer moles of gas on the right (2) than on the left (4).
B1 increases; B1 fewer gas moles on right
(c) more than 59%
B1 (yield at 300 °C is 59% at 200 atm and increases with pressure)
Q20Redox, oxidation number, oxidising & reducing agents · Core · Paper 1 style · 1 mark
(a)What is the oxidation number of sulfur in the sulfate ion, SO₄²⁻?[1]
Show answer
(a) D +6
x + 4(−2) = −2, so x = +6. C (+4) is sulfur in SO₂ or SO₃²⁻.
Q21Redox, oxidation number, oxidising & reducing agents · Core · Paper 2 style · 5 marks
(a)Define oxidation in terms of electrons.[1]
(b)Define reduction in terms of oxygen.[1]
(c)Magnesium reacts with copper(II) sulfate solution: Mg + CuSO₄ → MgSO₄ + Cu. Identify the substance oxidised and the substance reduced. Explain using electrons.[3]
Show answer
(a) Loss of electrons.
B1
(b) Loss of oxygen.
B1
(c) Magnesium is oxidised because it loses electrons (Mg → Mg²⁺ + 2e⁻); copper(II) ions are reduced because they gain electrons (Cu²⁺ + 2e⁻ → Cu).
B1 Mg oxidised; B1 Cu²⁺ reduced; B1 electron transfer explanation
Q22Redox, oxidation number, oxidising & reducing agents · Standard · Paper 1 style · 1 mark
(a)Hot copper(II) oxide reacts with hydrogen: CuO + H₂ → Cu + H₂O. Which substance is the reducing agent?[1]
Show answer
(a) B H₂
Hydrogen removes oxygen from copper(II) oxide and is itself oxidised, so it is the reducing agent. CuO (A) is the oxidising agent.
Q23Redox, oxidation number, oxidising & reducing agents · Standard · Paper 2 style · 5 marks
Chlorine gas is bubbled into colourless aqueous potassium iodide.Cl₂ + 2KI → 2KCl + I₂
(a)State the colour change seen.[1]
(b)Give the oxidation numbers of iodine before and after the reaction.[2]
(c)Identify the oxidising agent. Explain your answer.[2]
Show answer
(a) colourless to brown (orange-brown)
B1
(b) −1 in KI; 0 in I₂
B1 each
(c) Chlorine; it gains electrons / its oxidation number decreases from 0 to −1, so it oxidises iodide ions.
B1 chlorine; B1 reason
Q24Redox, oxidation number, oxidising & reducing agents · Standard · Paper 2 style · 5 marks
(a)Describe the colour change when a reducing agent is added to acidified aqueous potassium manganate(VII).[1]
(b)Describe the colour change when an oxidising agent is added to aqueous potassium iodide.[1]
(c)Iron(II) sulfate solution decolourises acidified potassium manganate(VII). State what happens to the iron(II) ions, giving the change in oxidation number.[2]
(d)Give the change in oxidation number of manganese when MnO₄⁻ forms Mn²⁺.[1]
Show answer
(a) purple to colourless
B1
(b) colourless to brown
B1
(c) They are oxidised to iron(III) ions; oxidation number changes from +2 to +3.
B1 oxidised to Fe³⁺; B1 +2 → +3
(d) +7 to +2
B1
Q25Redox, oxidation number, oxidising & reducing agents · Challenge · Paper 2 style · 6 marks
Aqueous iron(III) chloride is added to aqueous potassium iodide.2Fe³⁺(aq) + 2I⁻(aq) → 2Fe²⁺(aq) + I₂(aq)
(a)Write the two half-equations for this reaction.[2]
(b)Identify the oxidising agent and the reducing agent.[2]
(c)State how many moles of electrons are transferred when 1 mole of iodine is formed.[1]
(d)Suggest an observation that shows the reaction has occurred.[1]
Show answer
(a) Fe³⁺ + e⁻ → Fe²⁺; 2I⁻ → I₂ + 2e⁻
B1 each
(b) oxidising agent: Fe³⁺; reducing agent: I⁻
B1 each
(c) 2
B1
(d) The solution turns from yellow/orange to brown (iodine formed) — accept darker brown.
B1
Q26Redox, oxidation number, oxidising & reducing agents · Challenge · Paper 2 style · 6 marks
Railway lines in Pakistan are welded using the thermite reaction.Fe₂O₃ + 2Al → Al₂O₃ + 2Fe [Ar: O, 16; Al, 27; Fe, 56]
(a)Give the oxidation number of iron in Fe₂O₃ and in Fe.[1]
(b)Identify the reducing agent and explain your answer in terms of oxidation number.[2]
(c)Calculate the mass of aluminium needed to react with 1.6 kg of iron(III) oxide, and the mass of iron formed.[3]
Show answer
(a) +3 and 0
B1 both
(b) Aluminium; its oxidation number increases from 0 to +3 (it is oxidised).
B1; B1
(c) 540 g aluminium; 1120 g iron
moles Fe₂O₃ = 1600 ÷ 160 = 10 M1; Al = 20 mol × 27 = 540 g A1; Fe = 20 mol × 56 = 1120 g A1
Q27Industrial processes (Haber, Contact) & sulfur compounds · Standard · Paper 1 style · 1 mark
(a)Which catalyst is used in the Haber process?[1]
Show answer
(a) A iron
Iron is the catalyst for N₂ + 3H₂ ⇌ 2NH₃. Vanadium(V) oxide (D) is the Contact process catalyst.
Q28Industrial processes (Haber, Contact) & sulfur compounds · Standard · Paper 2 style · 7 marks
A fertiliser factory near Daharki makes ammonia by the Haber process.
(a)Write the equation for the reaction in the Haber process, including the reversible sign.[2]
(b)State the sources of the nitrogen and the hydrogen.[2]
(c)State the typical temperature and pressure used.[2]
(d)Suggest what is done with the unreacted nitrogen and hydrogen.[1]
Show answer
(a) N₂ + 3H₂ ⇌ 2NH₃
B1 formulae and balance; B1 ⇌
(b) nitrogen: air; hydrogen: methane (natural gas) reacted with steam
B1 each
(c) about 450 °C and 20 000 kPa (200 atm)
B1 each
(d) They are recycled back into the reactor.
B1
Q29Industrial processes (Haber, Contact) & sulfur compounds · Challenge · Paper 2 style · 8 marks
Sulfuric acid is made by the Contact process. The sulfur trioxide is first dissolved in concentrated sulfuric acid to make oleum, which is then diluted with water. [Ar: H, 1; O, 16; S, 32]
(a)State two sources of the sulfur dioxide used.[2]
(b)Write the equation for the conversion of sulfur dioxide to sulfur trioxide and state the catalyst, temperature and pressure used.[3]
(c)Explain why a pressure much higher than 200 kPa is not used.[1]
(d)Calculate the mass of sulfuric acid, in tonnes, made from 16 tonnes of sulfur if the overall yield is 96%.[2]
Show answer
(a) burning sulfur; roasting sulfide ores
B1 each
(b) 2SO₂ + O₂ ⇌ 2SO₃; vanadium(V) oxide; about 450 °C and 200 kPa (2 atm)
B1 equation; B1 V₂O₅; B1 both conditions
(c) The yield is already high at low pressure, so higher pressure would add cost for little gain.
B1
(d) 47.0 tonnes
1 mol S → 1 mol H₂SO₄: 16 × 98/32 = 49 t M1; × 0.96 = 47.0 t A1
Q30Physical & chemical change · Core · Paper 2 style · 4 marks
(a)Classify each change as physical or chemical: (i) ice melting in a glass of water; (ii) LPG burning in a stove; (iii) an iron gate rusting; (iv) sugar dissolving in tea.[2]
(b)State two features that show a change is chemical.[2]
Show answer
(a) (i) physical; (ii) chemical; (iii) chemical; (iv) physical
B2 all four correct; B1 for three
(b) A new substance is formed; it is usually not easily reversed; there is often an energy change (heat/light), colour change or gas given off.
1 mark each for any two
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