AQA GCSE Combined Science: Trilogy Chemistry Paper 2 (Foundation), June 2025: Question 2
14 marks · Low Demand difficulty · Short Answer
Analyze an investigation measuring the rate of reaction between calcium carbonate and hydrochloric acid by gas syringe, including reading measurements, tabulating data, calculating mean rate, and collision theory.
Practise this questionQuestion
Question text
02 A student investigated the reaction of calcium carbonate with hydrochloric acid.
Figure 2 shows the apparatus.
Figure 2
This is the method used.
1. Measure 50 cm3 of hydrochloric acid into a conical flask.
2. Add 4.0 g of calcium carbonate to the conical flask.
3. Insert the stopper into the conical flask as quickly as possible.
4. Start a timer.
5. Measure the volume of gas collected every 30 seconds for 3 minutes.
6. Repeat steps 1 to 5 using different concentrations of hydrochloric acid.
02.1 Name a suitable piece of equipment to measure 4.0 g of calcium carbonate.
[1 mark]
02.2 Figure 3 shows the gas syringe during the investigation.
Figure 3
What is the reading on the gas syringe?
[1 mark]
cm3
02.3 What is the independent variable in the investigation?
[1 mark]
Tick ( ) one box.
Concentration of hydrochloric acid
Mass of calcium carbonate
Temperature of the room
02.4 Why did the student insert the stopper into the conical flask as quickly as possible in
step 3?
[1 mark]
02.5 The gas produced during the investigation is carbon dioxide.
The test for carbon dioxide uses limewater.
What is the chemical name for limewater?
[1 mark]
Tick ( ) one box.
Calcium hydroxide solution
Potassium carbonate solution
Sodium chloride solution 9
02.6 The student measured the volume of gas collected every 30 seconds for 3 minutes.
The volume of gas was zero at the start.
For one concentration of hydrochloric acid, the volumes of gas collected were:
43 cm3 66 cm3 78 cm3 83 cm3 84 cm3 85 cm3
Complete Table 3.
You should:
• add headings to each column
• add units
• add all of the results to the table.
[4 marks]
Table 3
02.7 The student used a different concentration of hydrochloric acid.
18 cm3 of gas was collected in the first 30 seconds.
Calculate the mean rate of reaction for the first 30 seconds.
Use the equation:
volume of gas collected in cm3
mean rate of reaction =
time taken in seconds
Choose the unit from the box.
[3 marks]
cm3 cm3/s s s/cm3
Mean rate of reaction = Unit
02.8 Increasing the concentration of hydrochloric acid increases the rate of the reaction.
What are two reasons why?
[2 marks]
Tick ( ) two boxes.
The particles are closer together.
The particles collide more frequently.
The particles have a lower surface area.
The particles have less energy.
The particles move faster.
Mark scheme
Show the mark scheme
Question 2
AO /
Question Answers Extra information Mark
Spec. Ref.
02.1 balance allow (weighing) scales 1 AO1
5.6.1.2
RPA11
AO /
Spec. Ref.
02.2 42 (cm3) 1 AO2
5.6.1.2
RPA11
AO /
Spec. Ref.
02.3 concentration of hydrochloric 1 AO1
acid 5.6.1.2
RPA11
AO /
Spec. Ref.
02.4 allow carbon dioxide for gas AO3
5.6.1.2
to reduce loss of gas do not accept to stop loss of 1 RPA11
gas
AO /
Spec. Ref.
02.5 calcium hydroxide solution 1 AO1
– – – 5.8.2.3
AO /
Spec. Ref.
02.6 time in s(econds) 1 AO2
if neither mark awarded allow 5.6.1.1
1 mark for headings of time 5.6.1.2
volume (of gas collected) in cm3 and volume 1 RPA11
time values in correct order 1
volume values in correct order 1 9
AO /
Spec. Ref.
02.7 18 1 AO2
(mean rate of reaction =) 5.6.1.1
RPA11
= 0.6
cm3/s 1
AO /
Spec. Ref.
02.8 the particles are closer together 1 AO1
5.6.1.2
the particles collide more 1 5.6.1.3
frequently
Total Question 2 14
How to answer it
Investigating Rate of Reaction: Calcium Carbonate & Acid
This question assesses core practical skills and theoretical concepts from AQA GCSE Chemistry / Combined Science (Topic 6: The Rate and Extent of Chemical Change):
- Selecting appropriate laboratory apparatus for measuring mass and gas volume.
- Reading measuring scales accurately on a gas syringe.
- Identifying independent variables in a controlled investigation.
- Understanding experimental errors and methods to minimise loss of gaseous products.
- Chemical identification tests (chemical name of limewater).
- Organising scientific data into a clear results table with complete headings and units.
- Calculating mean rate of reaction and deducing correct units.
- Applying collision theory to explain the effect of concentration on rate.
Part 02.1: Measuring Mass
Equipment selection (1 mark)
✅ Correct Answer
Balance (or weighing scales / digital balance)
🧠 Exam Technique
Read the unit carefully: 4.0 g is a mass, which requires a balance. A measuring cylinder or pipette measures volume ( cm³ ), not mass.
Part 02.2: Reading a Gas Syringe
Scale reading (1 mark)
✅ Correct Answer
42 cm³
💡 Key Knowledge
Look at the scale between 40 and 50:
- There are 10 small divisions for 10 cm³, meaning 1 small division = 1 cm³.
- The edge of the plunger rests exactly 2 marks past 40 cm³, giving 40 + 2 = 42 cm³ .
Part 02.3: Identifying Variables
Independent variable (1 mark)
✅ Correct Answer
Tick: Concentration of hydrochloric acid
🧠 Variable Types Revision
- Independent variable: What the scientist deliberately changes (Concentration of acid).
- Dependent variable: What is measured as an outcome (Volume of gas collected).
- Control variables: Kept constant for a fair test (Mass of calcium carbonate, Temperature).
Part 02.4: Experimental Method & Accuracy
Minimising experimental error (1 mark)
✅ Correct Answer
To reduce the loss of gas (or to reduce the loss of carbon dioxide).
❌ Common Error & Examiner Warning
Do NOT write "to stop loss of gas" or "to prevent gas escaping completely".
Why? The reaction starts the instant the reactants meet. It is impossible to prevent 100% of the gas from escaping in the split second before inserting the bung; you can only reduce or minimise the escape.
Part 02.5: Chemical Test for Carbon Dioxide
Recall of chemical names (1 mark)
✅ Correct Answer
Tick: Calcium hydroxide solution
💡 Key Knowledge
Limewater is an aqueous solution of calcium hydroxide: Ca(OH)₂(aq) .
When carbon dioxide gas is bubbled through limewater, it forms insoluble white calcium carbonate, turning the solution cloudy/milky:
Ca(OH)₂(aq) + CO₂(g) → CaCO₃(s) + H₂O(l)
Part 02.6: Tabulating Scientific Data
Drawing and completing Table 3 (4 marks)
The student measured gas volume every 30 seconds for 3 minutes (180 seconds). The completed table must include column headings with units and all data points in order.
✅ Completed Table 3
| Time in s (or Time in seconds) | Volume of gas in cm³ (or Volume collected in cm³) |
|---|---|
| 0 | 0 |
| 30 | 43 |
| 60 | 66 |
| 90 | 78 |
| 120 | 83 |
| 150 | 84 |
| 180 | 85 |
🧠 Mark Scheme Breakdown (4 Marks)
- Mark 1: Column 1 heading with unit: Time in s or Time (seconds) .
- Mark 2: Column 2 heading with unit: Volume in cm³ or Volume of gas collected (cm³) .
- Mark 3: Time values correct and ordered: 0, 30, 60, 90, 120, 150, 180 .
- Mark 4: Volume values entered in correct sequential order matching times.
Part 02.7: Calculating Mean Rate of Reaction
Calculation and unit selection (3 marks)
📐 Step-by-Step Calculation
Step 1: Identify values from the question
- Volume of gas collected = 18 cm³
- Time taken = 30 s
Step 2: Substitute into the given formula
Mean rate = Volume / Time = 18 / 30
Mark 1: Correct substitution ( 18 / 30 )
Step 3: Calculate the numerical value
18 ÷ 30 = 0.6
Mark 2: Correct value = 0.6
Step 4: Select unit from the box
Units are: volume ( cm³ ) divided by time ( s ) = cm³/s
Mark 3: Unit = cm³/s
❌ Common Errors
- Inverting the fraction: Calculating 30 / 18 = 1.67 instead of volume / time . Always follow the formula provided.
- Wrong unit: Choosing s/cm³ or cm³ . Look at the formula: cm³ is on top, s is on the bottom, giving cm³/s .
Part 02.8: Collision Theory & Concentration
Explaining why rate increases (2 marks)
✅ Correct Answers (Tick two boxes)
- ☑ The particles are closer together. [1 mark]
- ☑ The particles collide more frequently. [1 mark]
💡 Collision Theory Masterclass
- Higher concentration means there are more reactant particles per unit volume (they are packed closer together).
- Because they are closer together, collisions happen more often (greater frequency of collisions).
❌ Major Trap: Concentration vs Temperature
- "The particles move faster" and "The particles have more energy" are caused by increasing temperature, NOT increasing concentration!
- At a higher concentration, particles have the same average kinetic energy and move at the same speed, but there are simply more of them in the same space.
Topics
Chemistry · C6: The Rate and Extent of Chemical Change · C8: Chemical Analysis
Question and mark scheme from the AQA GCSE Combined Science: Trilogy examination, Chemistry Paper 2 (Foundation), June 2025. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.