AQA GCSE Chemistry Chemistry Paper 1 (Foundation), June 2023: Question 8
10 marks · Standard Demand difficulty · Short Answer
Balance a reduction reaction equation, explain reduction in terms of oxygen, calculate relative formula mass, calculate atom economy, and deduce metal reactivity from displacement results.
Practise this questionQuestion
Question text
08 This question is about displacement reactions.
Iron is extracted from iron oxide by a displacement reaction with carbon.
08.1 Balance the equation for the reaction.
[2 marks]
Fe2O3 + 3C → Fe + CO
08.2 Iron oxide is reduced in this reaction.
How does the equation show that iron oxide is reduced?
[1 mark]
08.3 Calculate the relative formula mass (Mr) of Fe2O3
Relative atomic masses (Ar): O = 16 Fe = 56
[2 marks]
24 M =
r
08.4 Copper oxide reacts with hydrogen to produce copper.
The equation for the reaction is:
CuO + H2 → Cu + H2O
Calculate the percentage atom economy for obtaining copper from this reaction.
Use the equation:
Ar of Cu
Percentage atom economy = × 100
*23* Mr of H2 + Mr of CuO
Relative atomic mass (Ar): Cu = 63.5
Relative formula masses (Mr): H2 = 2 CuO = 79.5
[2 marks]
Percentage atom economy = %
A student investigated the reactivity of four different metals, A, B, C and D.
The student:
• added each metal to aqueous solutions of each of the metal sulfates
• observed whether a reaction took place.
08.5 Give one observation that would show a reaction took place.
[1 mark]
08.6 Table 4 shows the results.
Table 4
Metal sulfate solution
Metal A sulfate B sulfate C sulfate D sulfate
A × × ✓ ×
B ✓ × ✓ ×
C × × × ×
D ✓ ✓ ✓ ×
✓ shows that a displacement reaction took place.
× shows that a displacement reaction did not take place.
Write metals A, B, C and D in order of reactivity.
Give a reason for your order of reactivity.
[2 marks]
Most reactive
Least reactive
Reason
Mark scheme
Show the mark scheme
AO /
Question Answers Extra information Mark
Spec. Ref.
08.1 Fe2O3 + 3 C → 2 Fe + 3 CO allow multiples 2 AO2
4.1.1.1
allow 1 mark for 2 Fe
or
allow 1 mark for 3 CO
AO /
Spec. Ref.
08.2 (iron oxide) loses oxygen ignore references to gain of 1 AO2
electrons 4.4.1.1
AO /
Spec. Ref.
08.3 (Mr =) AO2
(2 × 56) + (3 × 16) allow 112 + 48 1 4.3.1.2
= 160 1
AO /
Spec. Ref.
08.4 (percentage atom economy =) AO2
63.5 1 4.3.3.2
× 100
2 + 79.5
= 77.9 (%) allow 77.914110 (%) correctly 1
rounded to at least 2 significant
figures
AO /
Spec. Ref.
08.5 any one from: 1 AO3
• colour change (in solution) 4.1.1.1
• colour change (in metal) 4.4.1.2
• change of temperature
– HEMISTRY – –
allow bubbles
20 AO /
Spec. Ref.
08.6 (most reactive) D 1 AO3
B 4.4.1.2
A
(least reactive) C
(reason) more reactive (metals) allow D has most (displacement) 1
displace less reactive (metals) reactions
and C does not react
allow the more reactive metals
have more (displacement)
reactions
– HEMISTRY – –
Total Question 8 10
Question 9
How to answer it
Displacement Reactions, Metal Extraction & Quantitative Chemistry
This question assesses fundamental GCSE Chemistry skills across Chemical Changes and Quantitative Chemistry:
- Balancing symbol equations and defining reduction in terms of oxygen loss.
- Calculating relative formula mass (Mr) from relative atomic masses (Ar).
- Calculating percentage atom economy using a provided formula.
- Deducing practical observations that indicate a chemical reaction.
- Analysing displacement test data to deduce a reactivity series and justifying the order logically.
Balancing the Chemical Equation
Reaction: Fe₂O₃ + 3 C → ___ Fe + ___ CO
✅ Correct Answer
Fe₂O₃ + 3 C → 2 Fe + 3 CO
• 1 mark for either 2 Fe or 3 CO
• 2 marks for both correct balancing numbers ( 2 and 3 )
(Allow correct multiples, e.g. 2 Fe₂O₃ + 6 C → 4 Fe + 6 CO)
🧠 Exam Technique
Count the atoms on each side:
- Oxygen: 3 on the left in Fe₂O₃ → needs 3 CO on the right.
- Carbon: 3 on the left in 3 C → matches the 3 carbons in 3 CO.
- Iron: 2 on the left in Fe₂O₃ → needs 2 Fe on the right.
Explaining Reduction from the Equation
How does the equation show that iron oxide is reduced?
✅ Correct Answer
Iron oxide loses oxygen (to form iron).
• 1 mark for stating that (iron oxide) loses oxygen.
• Ignore references to gain of electrons.
❌ Common Errors
- Giving electron transfer explanations: While reduction is the gain of electrons (OIL RIG), the question specifically asks: "How does the equation show...". The equation explicitly shows oxygen being removed, not electron transfers.
- Writing "carbon gains oxygen" — this explains why carbon is oxidised, not why iron oxide is reduced!
Calculating Relative Formula Mass (Mr)
Calculate the Mr of Fe₂O₃ (Ar: O = 16, Fe = 56)
📐 Step-by-Step Calculation
- Identify the number of each atom in the formula:
2 × Fe and 3 × O - Multiply each by its relative atomic mass (Ar):
(2 × 56) + (3 × 16) = 112 + 48 - Add them together:
Mr = 160
✅ Marking Points
Answer: 160
• 1 mark: Correct answer of 160
Note: An answer of 160 with no working scores both marks.
Calculating Percentage Atom Economy
Reaction: CuO + H₂ → Cu + H₂O
📐 Step-by-Step Calculation
Formula given:
Atom economy = [Ar of Cu / (Mr of H₂ + Mr of CuO)] × 100
- Substitute values:
Desired product: Ar of Cu = 63.5
Total reactants: Mr of H₂ + Mr of CuO = 2 + 79.5 = 81.5 - Set up the calculation:
(63.5 / 81.5) × 100 - Calculate and round:
= 77.9141...% → 77.9%
✅ Mark Breakdown
Answer: 77.9%
• 1 mark: Final calculated value correctly rounded to at least 2 significant figures (e.g. 78% or 77.9% )
Observing a Displacement Reaction
Give one observation that would show a reaction took place.
✅ Any One Acceptable Observation
- Colour change of the solution (e.g. blue copper sulfate fading).
- Colour change of the metal / solid coating forming (e.g. brown metal depositing on the surface).
- Temperature change (displacement is exothermic, so the mixture warms up).
- Also allowed: Bubbles / effervescence (if acid or side reaction occurs).
❌ Common Errors
- Writing vague non-observations like "a displacement reaction happens" or "it changes" — you must state what you see or measure!
- Stating "a precipitate forms" without describing an actual colour change or solid appearing on the metal surface.
Deducing the Reactivity Series from Experimental Data
Table 4 Analysis: Displacement Results
💡 Data Breakdown
A more reactive metal displaces a less reactive metal from its compound.
- Metal D: Reacts with A, B, and C sulfates (3 reactions) → displaces all three metals → Most reactive
- Metal B: Reacts with A and C sulfates (2 reactions)
- Metal A: Reacts only with C sulfate (1 reaction)
- Metal C: Displaces none of the metals (0 reactions) → Least reactive
✅ Correct Order & Reason
Order of reactivity:
Most reactive: D
B
A
Least reactive: C
Reason (1 mark):
- A more reactive metal displaces a less reactive metal; D reacts with the most solutions / has the most reactions and C has no reactions.
• 1 mark for correct order: D, B, A, C
• 1 mark for linking reactions to reactivity (e.g. "more reactive metals have more reactions" or "D displaces 3 metals whereas C displaces none").
Topics
Chemistry · C3: Quantitative Chemistry · C4: Chemical Changes
Question and mark scheme from the AQA GCSE Chemistry examination, Chemistry Paper 1 (Foundation), June 2023. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.