AQA GCSE Chemistry Chemistry Paper 1 (Foundation), June 2024: Question 3
14 marks · Low Demand difficulty · Short Answer
Investigate energy changes in displacement and neutralisation reactions, including calculating percentage by mass, concentration, and interpreting temperature graphs.
Practise this questionQuestion
Question text
03 This question is about energy changes of reactions.
Zinc reacts with copper sulfate solution.
The word equation for the reaction is:
zinc + copper sulfate → zinc sulfate + copper
03.1 What type of reaction is the reaction between zinc and copper sulfate solution?
[1 mark]
Tick ( ) one box.
Combustion
Decomposition
Displacement
03.2 Calculate the percentage (%) by mass of copper in copper sulfate (CuSO4).
Give your answer to 3 significant figures.
Relative atomic mass (Ar): Cu = 63.5
Relative formula mass (Mr): CuSO4 = 159.5
[3 marks]
Percentage by mass (3 significant figures) = %
A student investigated the energy change in the reaction between zinc and
copper sulfate solution.
This is the method used.
1. Measure 25 cm3 of copper sulfate solution into a polystyrene cup.
*12* 2. Weigh 0.20 g of zinc powder.
3. Add the zinc powder to the copper sulfate solution.
4. Measure the highest temperature reached by the mixture.
5. Repeat steps 1 to 4 using different masses of zinc powder.
03.3 Control variables are used to make an investigation a fair test.
Which is a control variable in the investigation?
[1 mark]
Tick ( ) one box.
Highest temperature reached by the mixture
Mass of zinc powder
Volume of copper sulfate solution 14
Figure 6 shows the results.
Figure 6
03.4 What is the minimum mass of zinc powder needed to react with all the
copper sulfate solution?
Use Figure 6.
[1 mark]
15 Minimum mass of zinc powder = g
03.5 What is the maximum temperature change in the reaction between zinc powder and
25 cm3 of copper sulfate solution?
Use Figure 6.
[2 marks]
Maximum temperature change = °C
03.6 25 cm3 of copper sulfate solution contained 6.75 g of copper sulfate.
Calculate the concentration of the solution in g/dm3.
You should:
• calculate the volume of the solution in dm3 (1000 cm3 = 1 dm3)
• use the equation:
3 mass of copper sulfate in grams
concentration of solution in g/dm = 3
volume of solution in dm
[3 marks]
Volume of solution = dm3
16 3
Concentration of solution = g/dm
Another student investigated the energy change of the reaction between
sodium hydrogencarbonate and hydrochloric acid.
This is the method used.
1. Measure 25 cm3 of hydrochloric acid.
2. Weigh 1.0 g of sodium hydrogencarbonate.
3. Add the sample of sodium hydrogencarbonate to the hydrochloric acid.
4. Measure the lowest temperature reached by the mixture.
*15* 5. Repeat steps 1 to 4 using different masses of sodium hydrogencarbonate.
Figure 7 shows the results.
Figure 7
03.7 Draw two straight lines of best fit on Figure 7.
The lines should cross.
[2 marks]
03.8 Which statement describes the energy change in the reaction shown in Figure 7?
[1 mark]
Tick ( ) one box.
Energy is transferred to the surroundings so the reaction is endothermic.
Energy is transferred to the surroundings so the reaction is exothermic.
Energy is taken in from the surroundings so the reaction is endothermic.
Energy is taken in from the surroundings so the reaction is exothermic.
Mark scheme
Show the mark scheme
Question 3
AO /
Question Answers Extra information Mark
Spec. Ref.
03.1 displacement 1 AO1
4.4.1.2
AO /
Spec. Ref.
03.2 (percentage =) AO2
63.5 1 4.3.1.2
× 100
159.5
= 39.81191 (%) 1
= 39.8 % allow an answer correctly 1
rounded to 3 significant figures
from an incorrect calculation
which uses both the values in
the question
AO /
Spec. Ref.
03.3 volume of copper sulfate 1 AO1
solution 4.5.1.1
RPA4
AO /
Spec. Ref.
03.4 0.8(0) g 1 AO3
– – – 4.5.1.1
RPA4
AO /
Spec. Ref.
03.5 (maximum temperature change) 1 AO2
= 47 – 22 (ºC) 4.5.1.1
RPA4
= 25 (ºC) allow correct use of incorrectly 1
determined value(s) from the
graph
AO /
Spec. Ref.
(conversion 25 cm3 =) AO2
03.6 3 1
0.025 dm 4.3.2.5
6.75 allow correct use of an 1
(concentration =) (g/dm3)
0.025 incorrectly determined or
unconverted volume
= 270 (g/dm3) 1
AO /
Spec. Ref.
03.7 max 1 mark if the lines do not AO2
intersect 4.5.1.1
line of best fit using the first five 1 RPA4
points
line of best fit using the last four 1
points
AO /
Spec. Ref.
03.8 energy is taken in from the 1 AO3
surroundings so the reaction is 4.5.1.1
endothermic RPA4
Total Question 3 14
How to answer it
Energy Changes, Quantitative Chemistry & Reactivity
📋 What this question tests
This question assesses fundamental practical skills and quantitative chemistry from AQA GCSE Chemistry Paper 1:
- Reaction types: Identifying displacement reactions from chemical word equations.
- Formula calculations: Calculating percentage by mass using relative atomic mass (Ar) and formula mass (Mr) to specified significant figures.
- Required Practical 4 (Temperature changes): Identifying experimental control variables and interpreting thermometric titration graphs (identifying the limiting reactant and calculating overall temperature change).
- Solution concentration: Converting volume units (cm³ to dm³) and calculating concentration in g/dm³.
- Graph skills & Energetics: Constructing two intersecting lines of best fit to determine endpoints, and linking temperature drops to endothermic energy profiles.
Identifying the Reaction Type
zinc + copper sulfate → zinc sulfate + copper
✅ Correct Answer
Tick: Displacement
💡 Key Knowledge
A displacement reaction occurs when a more reactive element displaces (kicks out) a less reactive element from its compound. Zinc is more reactive than copper, so it displaces copper from copper sulfate.
Percentage by Mass of an Element in a Compound
Calculate percentage (%) by mass of Cu in CuSO₄ to 3 significant figures
📐 Step-by-Step Calculation
- Write down the formula:
Percentage mass = (Total Ar of element / Mr of compound) × 100 - Substitute the values:
(63.5 / 159.5) × 100 = 39.81191... % [1 mark] - Round to 3 significant figures:
The first 3 significant figures are 3, 9, and 8. The next digit is 1 (round down).
= 39.8 % [1 mark]
🧠 Exam Technique: Significant Figures
Whenever a question explicitly states "Give your answer to X significant figures", a standalone mark is almost always reserved solely for rounding correctly. Even if your arithmetic is incorrect, you can still gain the final mark via error carried forward (ECF) if you round your incorrect value to 3 s.f.
❌ Common Errors
- Leaving the answer as 39.81% (4 sig figs) or 40% (2 sig figs).
- Inverting the fraction ( 159.5 / 63.5 ), leading to a percentage over 100%.
Variables in Practical Investigations
Which is a control variable in the investigation?
✅ Correct Answer
Tick: Volume of copper sulfate solution
💡 Variable Types Recap
- Independent variable: The factor you change (Mass of zinc powder).
- Dependent variable: The factor you measure (Highest temperature reached).
- Control variable: The factor kept constant for a fair test (Volume of copper sulfate solution, 25 cm³).
Interpreting Reaction Endpoints from a Graph
Minimum mass of zinc powder needed to react with all the copper sulfate solution (Figure 6)
✅ Correct Answer
0.8 g (or 0.80 g)
🧠 Exam Technique: Spotting the Plateau
Look at where the temperature stops increasing and the graph levels off completely flat (plateaus). The reaction finishes when all copper sulfate is used up (limiting reactant). Adding more zinc beyond this point causes no extra temperature increase because there is no copper sulfate left to react.
Calculating Maximum Temperature Change
What is the maximum temperature change in the reaction? (Figure 6)
📐 Step-by-Step Calculation
- Read initial temperature (mass = 0.00 g):
At 0.00 g of zinc, initial temperature = 22 °C . - Read maximum temperature reached (plateau):
The horizontal plateau is at 47 °C . - Calculate the temperature change (ΔT):
ΔT = Final – Initial = 47 – 22 = 25 °C
❌ Common Errors
Many students write 47 °C as their final answer, confusing the maximum temperature reached with the temperature change. Always check if the question asks for "temperature" or "temperature change".
Calculating Concentration in g/dm³
25 cm³ contains 6.75 g of copper sulfate. Calculate concentration in g/dm³.
📐 Step-by-Step Calculation
- Convert volume from cm³ to dm³:
There are 1000 cm³ in 1 dm³.
Volume = 25 / 1000 = 0.025 dm³ [1 mark] - Substitute into the concentration formula:
Concentration = Mass (g) / Volume (dm³)
Concentration = 6.75 / 0.025 [1 mark] - Calculate final value:
= 270 g/dm³ [1 mark]
🧠 Exam Technique: Follow the Scaffolding
The exam paper provided two bullet points showing the exact steps required:
- "calculate the volume of the solution in dm³"
- "use the equation: concentration = mass / volume"
Always complete each bullet in order!
❌ Common Errors
Forgetting to convert cm³ to dm³ and calculating 6.75 / 25 = 0.27 g/dm³ . If you do this, you lose the conversion mark, though you can still get 2 marks via ECF if set out clearly.
Drawing Two Lines of Best Fit (Thermometric Titration)
Draw two straight lines of best fit on Figure 7. The lines should cross.
✅ Required Examiner Drawing
- Line 1 (Downward slope): Use a ruler to draw a straight line of best fit through the first five points ( 0.0 g, 1.0 g, 2.0 g, 3.0 g, 4.0 g ). It slopes down from (0.0 g, 22.2 °C) down to around (4.0 g, 16.9 °C). [1 mark]
- Line 2 (Horizontal line): Use a ruler to draw a horizontal straight line through the last four points ( 4.0 g, 5.0 g, 6.0 g, 7.0 g ) at exactly 16.9 °C . [1 mark]
- The two straight lines must clearly intersect (cross).
❌ Common Errors
- Drawing a single smooth curve instead of two straight lines (the question explicitly asks for "two straight lines").
- Drawing freehand lines without a ruler.
- Stopping the lines before they touch/cross (maximum 1 mark allowed if lines do not intersect).
Energy Changes: Endothermic Reactions
Which statement describes the energy change shown in Figure 7?
✅ Correct Answer
Tick: Energy is taken in from the surroundings so the reaction is endothermic.
💡 Exothermic vs. Endothermic Recall
- Endothermic: Takes in thermal energy from the surroundings → temperature of surroundings decreases (cools down).
- Exothermic: Releases thermal energy to the surroundings → temperature of surroundings increases (heats up).
Figure 7 shows the temperature falling from 22.2 °C to 16.9 °C, so energy is taken in (endothermic).
Topics
Chemistry · Required Practicals · C3: Quantitative Chemistry · C4: Chemical Changes · C5: Energy Changes · Required Practicals
Question and mark scheme from the AQA GCSE Chemistry examination, Chemistry Paper 1 (Foundation), June 2024. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.