AQA GCSE Combined Science: Trilogy Chemistry Paper 2 (Foundation), 2024: Question 7

12 marks · Standard Demand difficulty · Extended Answer

Describe a valid method to investigate how calcium carbonate particle size affects reaction rate, explain how temperature increases reaction rate using particle collision theory, define a catalyst, and name biological catalysts.

Practise this question

Question

The question page shows Question 7 on rates of chemical reactions, split into four parts worth 6, 3, 2 and 1 marks. Part 7.1 includes a labelled diagram of apparatus for measuring carbon dioxide from calcium carbonate reacting with hydrochloric acid: a conical flask containing acid and calcium carbonate is sealed with a stopper connected by a delivery tube to an inverted measuring cylinder standing in water, collecting carbon dioxide gas. The text asks for a method to produce valid results when changing the particle size of calcium carbonate. Part 7.2 asks for an explanation of how increasing temperature affects rate using particles and collisions, part 7.3 asks for the meaning of catalyst, and part 7.4 asks what catalysts in biological systems are called.
Question text

07 Some factors affect the rates of chemical reactions.

07.1 A student investigated the effect of changing the particle size of calcium carbonate on

the rate of reaction with hydrochloric acid.

Figure 6 shows the apparatus.

Figure 6

Describe a method the student could use to produce valid results.

[6 marks]

07.2 The student investigated the effect of increasing the temperature on the

rate of a reaction.

*25* Explain the effect of increasing the temperature on the rate of a reaction.

Refer to particles and collisions in your answer.

[3 marks]

Catalysts affect the rate of reactions.

07.3 What is meant by a ‘catalyst’?

[2 marks]

07.4 What are catalysts in biological systems called?

[1 mark]

Mark scheme

Show the mark scheme The mark scheme shows a level-of-response table for 7.1 with Level 1 to Level 3 and indicative points for a valid method: measure acid volume and calcium carbonate mass, add acid to calcium carbonate in a conical flask, fit stopper and delivery tube, start a timer, record gas volume at intervals or time to a fixed volume, repeat with different particle sizes, control mass, acid volume, acid concentration and temperature, and repeat experiments. For 7.2, marks are awarded for stating that increasing temperature increases rate because particles have more energy or move faster, so collisions are more frequent or a greater proportion have enough energy to react. For 7.3, a catalyst is defined as a substance that increases the rate of reaction and is not used up; for 7.4, the answer is enzymes.

Question 7

AO /

Question Answers Mark

Spec. Ref.

07.1 Level 3: The method would lead to the production of a valid 5‒6 AO3

outcome. The key steps are identified and logically sequenced.

Level 2: The method would not necessarily lead to a valid 3–4 AO3

outcome. Most steps are identified, but the method is not fully

logically sequenced.

Level 1: The method would not lead to a valid outcome. Some 1‒2 AO2

relevant steps are identified, but links are not made clear.

No relevant content 0

5.6.1.2

Indicative content

• measure volume of (hydrochloric) acid

• using a measuring cylinder

• measure mass of calcium carbonate

• using a balance

• add (hydrochloric) acid to calcium carbonate in conical flask

• put stopper and delivery tube into conical flask

• start a timer

• record volume of gas collected at set time intervals

or

time how long it takes for a fixed volume of gas to be

collected

• repeat using different sized pieces of calcium carbonate

• use same mass of calcium carbonate

• use same volume of (hydrochloric) acid

• use same concentration of (hydrochloric) acid

• use same temperature of (hydrochloric) acid

• repeat each experiment– – –

AO /

Question Answers Extra information Mark

Spec. Ref.

07.2 (increasing the temperature) 1 AO1

increases the rate of reaction 5.6.1.2

5.6.1.3

(because) particles have more allow (because) particles move 1

energy faster 19

(so) the frequency of collisions allow (so) a greater proportion of 1

increases collisions have enough energy

to react

AO /

Spec. Ref.

07.3 (a substance that) increases the allow (a catalyst) increases / 1 AO1

rate of reaction changes the rate of reaction 5.6.1.4

and is not used up during the ignore does not take part in the 1

reaction reaction

AO /

Spec. Ref.

07.4 enzymes 1 AO1

5.6.1.4

Total Question 7 12

How to answer it

Rates of Reaction: Calcium Carbonate, Temperature and Catalysts

What this question tests

You need to describe a valid method for a rates investigation, explain how temperature affects reaction rate using collision theory, and recall the definition of a catalyst and the name of biological catalysts.

Question 07.1 — Plan a valid method (6 marks)

Part (a): Describe a method to investigate particle size and rate

💡 Key knowledge

  • Measure the reactants accurately before starting.
  • Use the same mass of calcium carbonate each time.
  • Use the same volume, concentration and temperature of hydrochloric acid.
  • Change only the particle size of the calcium carbonate.
  • Collect carbon dioxide gas and measure either volume over time or time to collect a fixed volume.
  • Repeat each test to improve reliability.

🧠 Exam technique

  • For 5–6 marks, the method must be in a logical sequence.
  • Clearly show how the student would make the results valid.
  • Use scientific method words like measure , start the timer , repeat , and control variables .
  • Top answers include both the apparatus and what is recorded.

✅ Correct answer / model method

  1. Measure a fixed volume of hydrochloric acid using a measuring cylinder.
  2. Measure the same mass of calcium carbonate using a balance.
  3. Place the calcium carbonate into a conical flask.
  4. Add the hydrochloric acid to the flask, then quickly fit the stopper and delivery tube.
  5. Start a timer as soon as the acid is added.
  6. Collect the carbon dioxide and record the volume at set time intervals, or measure the time taken to collect a fixed volume of gas.
  7. Repeat the experiment using different sized pieces of calcium carbonate.
  8. Keep the volume, concentration and temperature of the hydrochloric acid the same each time.
  9. Repeat each test and compare the results.

How marks are awarded: The examiner is looking for the key steps, clear control of variables, and a sensible way to measure rate. A fully sequenced method usually reaches Level 3.

✅ What a top answer would mention

  • Use a balance for mass and a measuring cylinder for acid volume.
  • Put the stopper on before starting the measurement.
  • Measure gas volume over time, or time for a fixed gas volume.
  • Repeat and compare results for different particle sizes.

❌ Common errors

  • Not saying how the rate is measured.
  • Changing more than one variable.
  • Forgetting to keep the mass of calcium carbonate the same.
  • Writing “do the experiment again” without saying why repetition helps.
  • Describing the apparatus but not the sequence.

📐 Calculations / data handling

This question does not require a calculation, but you should still be precise with:

  • Units: volume in cm³ or dm³, time in s, mass in g.
  • Fair test: only particle size changes.
  • Reliability: repeat results and use a mean if needed.
Question 07.2 — Temperature and collision theory (3 marks)

Part (b): Explain the effect of increasing temperature on rate

💡 Key knowledge

  • Higher temperature means particles have more kinetic energy.
  • Particles move faster.
  • They collide more often.
  • A greater proportion of collisions have enough energy to react.

✅ Full-mark answer

Increasing the temperature increases the rate of reaction because particles have more energy and move faster. This means they collide more frequently, and a greater proportion of the collisions have enough energy to react.

🧠 Exam technique

To get all 3 marks, make sure your answer includes:

  1. rate increases
  2. particles have more energy / move faster
  3. more frequent collisions and/or more successful collisions

❌ Common errors

  • Saying only “it speeds up” without explaining why.
  • Talking about particles “getting bigger” or “breaking apart”.
  • Missing the idea of successful collisions.
  • Not using collision language at all.
Question 07.3 — Define a catalyst (2 marks)

Part (c): What is meant by a catalyst?

✅ Correct answer

A catalyst is a substance that increases the rate of a reaction and is not used up during the reaction.

💡 Key knowledge

  • It speeds up a reaction.
  • It remains unchanged at the end.
  • It is not consumed overall.

🧠 Exam technique

There are 2 marks here, so give both parts of the definition:

  • what it does: increases the rate
  • what happens to it: not used up

❌ Common errors

  • Saying a catalyst is “used to start a reaction” only.
  • Writing that it is “changed permanently”.
  • Confusing a catalyst with a reactant.
Question 07.4 — Biological catalysts (1 mark)

Part (d): What are catalysts in biological systems called?

✅ Correct answer

Enzymes

💡 Key knowledge

  • Enzymes are biological catalysts.
  • They are found in living organisms.
  • They speed up reactions in cells.

❌ Common errors

  • Writing “proteins” — enzymes are proteins, but the answer asked for the name of the catalyst.
  • Writing “cells” or “hormones”.
Quick recap

How to secure the marks

💡 Method question

  • Control variables.
  • Measure gas produced.
  • Repeat with different particle sizes.

💡 Temperature explanation

  • More energy.
  • Faster particles.
  • More frequent successful collisions.

💡 Catalysts

  • Increase rate.
  • Not used up.
  • Biological catalysts = enzymes.

Topics

Chemistry · Biology · C6: The Rate and Extent of Chemical Change · B2: Organisation

Question and mark scheme from the AQA GCSE Combined Science: Trilogy examination, Chemistry Paper 2 (Foundation), 2024. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.