📋 Structured Questions
These questions test key concepts from Topic 6. Attempt each question on paper, then click "Show Mark Scheme" to check your answer.
Question 1: Surface Area & Collision Theory
2 marksStudents investigated the rate of decomposition of hydrogen peroxide: 2H₂O₂(aq) → 2H₂O(l) + O₂(g). The catalyst is manganese dioxide. Student A investigated using fine powder vs coarse lumps.
(a) The rate of reaction is different when manganese dioxide is used as a fine powder rather than coarse lumps. Explain why. Answer in terms of collision theory. [2]
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- The surface area of the fine powder is greater [1]
- (So) there are more frequent collisions / more collisions per unit time [1]
Question 2: How Catalysts Work
2 marksManganese dioxide catalyses the decomposition of hydrogen peroxide solution. Oxygen and water are produced.
(a) Explain how a manganese dioxide catalyst increases the rate of decomposition of hydrogen peroxide. [2]
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- (A catalyst) provides a different pathway / mechanism / route for the reaction [1]
- (Which has a) lower activation energy [1]
Question 3: Le Chatelier's Principle (Temperature)
2 marksMethanol is produced from CO + 2H₂ ⇌ CH₃OH at 250 °C and 100 atm. The forward reaction is exothermic.
(a) Explain what happens to the yield of methanol if a temperature higher than 250 °C is used. [2]
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- Smaller yield / less methanol is produced [1]
- (Because) a higher temperature favours the endothermic reaction / reverse direction / equilibrium shifts left [1]
Question 4: Measuring Rates & Concentration
2 marksA student investigated the effect of changing the concentration of sodium thiosulfate solution on the rate of the reaction. A graph shows the percentage of light reaching a sensor decreasing over 120 seconds.
(a) Explain why the rate of reaction changes between 0 and 60 seconds. Answer in terms of concentration. [2]
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- The rate decreases [1]
- (Because) the concentration of reactants decreases (as they are used up) [1]
Question 5: Effect of Temperature on Rate
3 marksA student investigated the rate of the reaction between zinc and sulfuric acid: Zn(s) + H₂SO₄(aq) → ZnSO₄(aq) + H₂(g).
(a) Explain how increasing the temperature would affect the rate of reaction. [3]
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- (Increasing the temperature) increases the rate of reaction [1]
- (Because) particles have more energy / move faster [1]
- (So) the frequency of collisions increases OR a greater proportion of collisions have enough energy to react [1]
Question 6: Concentration & Collision Theory
4 marksA student investigated the reaction between marble chips (calcium carbonate) and dilute hydrochloric acid. The student plotted a graph of the volume of gas produced against time using 0.5 mol/dm³ hydrochloric acid. The marble chips are in excess.
(a) Explain how the shape of the graph would change if 1.0 mol/dm³ hydrochloric acid was used instead. Use collision theory in your answer. [4]
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- The line/curve would be steeper initially [1]
- The line would level off sooner / become horizontal at an earlier time [1]
- (Because at a higher concentration) there are more reactant particles per unit volume [1]
- (Which results in) a higher frequency of collisions / more collisions per second [1]
Question 7: Factors Affecting Rate of Reaction ⭐ Extended Response
6 marksA student investigates the effect of changing the concentration of hydrochloric acid on the rate of its reaction with magnesium ribbon.
(a) Describe and explain, using collision theory, how increasing the concentration of the hydrochloric acid affects the rate of this reaction. [6]
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Level 3 (5–6 marks): Detailed, logically sequenced explanation linking concentration to particles per unit volume, leading to increased collision frequency and reaction rate.
Level 2 (3–4 marks): Partial explanation mentioning more particles and more collisions leading to a faster rate, but may lack precise terminology (e.g. missing "per unit volume" or "frequency").
Level 1 (1–2 marks): Simple statements, e.g. stating higher concentration means faster reaction, or more collisions without explaining why.
Indicative content:
- Increasing concentration means more reactant particles per unit volume
- Particles are closer together, so the frequency of collisions increases (more collisions per second)
- Higher frequency of successful collisions (those with energy ≥ activation energy)
- Therefore the rate of reaction increases
Question 8: Required Practical — Rate of Reaction (Disappearing Cross) 🔬
4 marksA student investigates how temperature affects the rate of reaction between sodium thiosulfate solution and hydrochloric acid. They place a conical flask over a black cross drawn on paper.
(a) Describe how the student should carry out this experiment and explain how they measure the rate of reaction. [4]
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- Heat the sodium thiosulfate to a specific temperature; add a fixed volume of HCl and start a timer [1]
- A yellow sulfur precipitate forms, making the solution go cloudy [1]
- Time how long it takes for the cross to disappear from view (looking down from above) [1]
- Repeat at different temperatures; a shorter time = faster rate of reaction [1]
Question 9: Required Practical — Rate of Reaction (Gas Collection) ⭐🔬 Extended Response
6 marksA student investigates the effect of concentration on the rate of reaction between magnesium ribbon and hydrochloric acid by collecting the hydrogen gas produced.
(a) Describe the full method the student should use, including how they would ensure the experiment is valid and how they would process their results. [6]
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Level 3 (5–6 marks): Full, logically sequenced method describing the gas collection technique, control variables for validity, and how to process results (graph of volume vs time).
Level 2 (3–4 marks): Describes the method with some correct control variables or result processing, but may lack one element.
Level 1 (1–2 marks): Basic steps given (e.g. "add magnesium to acid and collect gas") but lacks control variables and result processing.
Indicative content:
- Measure a fixed volume of HCl at a known concentration into a conical flask
- Connect the flask to a gas syringe (or use an inverted measuring cylinder over water)
- Add a fixed length of magnesium ribbon; start the timer immediately
- Record the volume of gas collected every 10 seconds
- Control variables: same mass/length of Mg ribbon, same volume of acid, same temperature
- Repeat with different concentrations of HCl; plot a graph of volume of gas (y-axis) against time (x-axis) — steeper gradient = faster rate