AQA GCSE Chemistry Chemistry Paper 1 (Higher), 2023: Question 9

12 marks · High Demand difficulty · Short Answer

This question covers redox reactions, displacement reactions, reactivity series, ionic charges, and atom economy calculations.

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Question

A multi-part chemistry exam question (09) involving displacement reactions. It includes a chemical equation for iron extraction, questions on redox, a table (Table 6) showing reaction results for metals A, B, C, and D, and a final calculation task regarding atom economy for a metal X.
Question text

09 This question is about displacement reactions.

Iron is extracted from iron oxide by a displacement reaction with carbon.

The equation for the reaction is:

Fe2O3 + 3 C → 2 Fe + 3 CO

09.1 Which substance in the equation is reduced?

Give one reason for your answer.

Answer in terms of oxygen.

[2 marks]

Substance reduced

Reason

09.2 Which expression shows how to calculate the mass of carbon needed to produce

1 mole of iron from iron oxide?

Relative atomic mass (Ar): C = 12

[1 mark]

Tick ( ) one box.

× 12 g

× 12 g

1 × 12 g

3 × 12 g 28

A student investigated displacement reactions of four different metals represented by

A, B, C and D.

A, B, C and D are not the actual chemical symbols for the metals.

The student:

• added each metal to aqueous solutions of the metal nitrates

• observed whether a reaction took place.

Table 6 shows information about three of the reaction mixtures.

Table 6

Reaction Metal Metal nitrate solution Equation

1 A BNO3 A + 2 BNO3 → 2 B + A(NO3)2

2 C A(NO3)2 2 C + 3 A(NO3)2 → 3 A + 2 C(NO3)3

3 C D(NO3)2 no reaction

09.3 The ionic equation for Reaction 1 is:

A + 2 B+ → 2 B + A2+

Why is this a redox reaction?

[1 mark]

Tick ( ) one box.

A gains electrons and B+ loses electrons.

A loses electrons and B+ gains electrons.

Both A and B+ gain electrons.

Both A and B+ lose electrons.

09.4 Which of the four metals has the greatest tendency to form positive ions?

Use Table 6.

[1 mark]

Tick ( ) one box.

A B C D

09.5 –

The nitrate ion has the formula NO3

Which of the four metals could be aluminium?

Explain your answer.

Use Table 6.

[3 marks]

Metal

Explanation

09.6 Metal X is extracted from an oxide of metal X by reaction with hydrogen.

The equation for the reaction is:

XO3 + 3 H2 → X + 3 H2O

The percentage atom economy for obtaining metal X by this method is 77.3%.

Calculate the relative atomic mass (Ar) of metal X.

Relative atomic masses (Ar): H = 1 O = 16

[4 marks]

Relative atomic mass (Ar) =

Mark scheme

Show the mark scheme The mark scheme for question 9, detailing the correct answers and marking points for each sub-question (09.1 to 09.6), including the step-by-step calculation for the atom economy problem.

AO /

Question Answers Extra information Mark

Spec. Ref.

09.1 (substance reduced) Fe2O3 allow iron oxide 1 AO2

4.4.1.1

(reason)

(Fe2O3) loses oxygen MP2 is dependent upon MP1 1

being awarded

ignore Fe3+ gains electrons

AO /

Spec. Ref.

09.2 3 1 AO2

× 12g 4.3.1.1

4.3.2.1

4.3.2.2

AO /

Spec. Ref.

+ AO2

09.3 A loses electrons and B gains 1

electrons 4.4.1.4

AO /

Spec. Ref.

09.4 D 1 AO3

4.4.1.2

AO /

Spec. Ref.

09.5 (metal) C 1 AO3

4.4.1.2

(explanation) aluminium forms allow aluminium forms Al3+ 1 4.4.3.3

ions with a charge 3+ (ions)

(so) 3 nitrate ions are needed allow (so) 3 nitrate ions are 1

for 1 aluminium ion needed to balance the 3+–HEMISTRY – –

charge on 1 aluminium (ion)

AO / 27

Spec. Ref.

09.6 (percentage atom economy =) AO2

4.3.3.2

ArX 1

× 100 = 77.3

ArX + 54

100 ArX = 77.3 (ArX + 54) allow ArX = 0.773 (ArX + 54) 1

allow correct use of an

incorrectly determined value of

the Mr of the non-useful reactant

atoms

22.7 ArX = 4174.2 allow 0.227 ArX = 41.742 1

ArX = 184 allow 183.8854626 correctly 1

rounded to at least three

significant figures

alternative approach 1:

(3Mr H2O = (3 × 16) + (6 × 1) =)

and (percentage = 100 – 77.3 =)

22.7% (1)

(total Mr of reactants =) allow correct use of an

100 incorrectly determined value for

× 54 (1) 3Mr H2O and/or percentage of

22.7

unwanted products

= 238 (1)

( = 238 – 54) allow correct use of an

ArX

incorrectly determined value of

or

total Mr of reactants and/or

77.3

(ArX = 238 × ) value for 3Mr H2O

= 184 (1) allow 183.8854626 correctly

rounded to at least three

significant figures

– HEMISTRY – –

alternative approach 2:

(3Mr H2O = (3 × 16) + (6 × 1) =)

and (percentage = 100 – 77.3 =)

22.7% (1)

( × 54 =) 2.3788546 (1) allow correct use of an

22.7 incorrectly determined value for

3Mr H2O and/or percentage of

unwanted products

2.3788546 × 77.3 (1) allow correct use of an

incorrectly determined value for

1% of the total Mr of reactants

= 184 (1) allow 183.8854626 correctly

rounded to at least three

significant figures

– HEMISTRY – –

Total Question 9 12

Question 10

How to answer it

Displacement, Redox, and Atom Economy

What this question tests

This question assesses your understanding of Redox reactions (in terms of both oxygen and electrons), the Reactivity Series of metals, and complex Atom Economy calculations involving algebraic rearrangement.

Part 9.1

Reduction in terms of Oxygen

Correct Answer

  • Substance reduced: Fe₂O₃ (or iron oxide)
  • Reason: It loses oxygen

Key Knowledge

In terms of oxygen:

  • Oxidation is the gain of oxygen.
  • Reduction is the loss of oxygen.

Common Error

Do not just say "Iron" is reduced. The reactant is Iron Oxide (Fe₂O₃). It is the compound that loses the oxygen atoms.

Part 9.2

Reacting Masses & Ratios

Step-by-Step Calculation

  1. Look at the ratio: The equation shows 3 C reacts to produce 2 Fe.
  2. Scale to 1 mole: If 2 moles of Fe need 3 moles of C, then 1 mole of Fe needs 1.5 moles of C (which is 3/2).
  3. Convert to mass: Mass = Moles × Ar. So, Mass = 1.5 × 12g.

Correct Box: 3/2 × 12 g

Part 9.3

Redox and Electrons

Correct Answer

A loses electrons and B⁺ gains electrons.

Key Knowledge

Use the mnemonic OIL RIG:

  • Oxidation Is Loss (of electrons)
  • Reduction Is Gain (of electrons)

A becomes A²⁺ (lost negative charge), B⁺ becomes B (gained negative charge).

Part 9.4

The Reactivity Series

Exam Technique: Logic Chain

  • Reaction 1: A displaces B. (A is more reactive than B).
  • Reaction 2: C displaces A. (C is more reactive than A).
  • Reaction 3: C does not displace D. (D is more reactive than C).
  • Order: D > C > A > B

Correct Answer: D

Part 9.5

Identifying Aluminium

Correct Answer

Metal: C

Explanation: Aluminium forms ions with a 3+ charge (Al³⁺). Therefore, 3 nitrate ions (NO₃⁻) are needed to balance the charge of one aluminium ion.

How to spot the answer

Look at the formula in Table 6: C(NO₃)₃ . The subscript '3' tells you there are three nitrate ions. Since each nitrate is 1-, the metal C must be 3+.

Part 9.6

Calculating Relative Atomic Mass (Ar)

The Calculation Steps

  1. Formula: Atom Economy = (Mass of Desired Product / Total Mass of Reactants) × 100
  2. Identify masses:
    Desired Product = X
    Reactants = XO₃ + 3H₂
    Mass of 3H₂ = 3 × (2 × 1) = 6
    Mass of XO₃ = X + (3 × 16) = X + 48
  3. Set up the equation:
    77.3 = [ X / (X + 48 + 6) ] × 100
    0.773 = X / (X + 54)
  4. Rearrange and solve:
    0.773(X + 54) = X
    0.773X + 41.742 = X
    41.742 = 0.227X
    X = 183.88...

Final Answer: 184 (rounded to 3 significant figures)

Common Calculation Traps

  • The "3": Forgetting that there are 3 moles of H₂ in the reactants.
  • Total Mass: Forgetting that the "Total Mass of Reactants" must include the mass of X itself.
  • Rounding: Always round your final answer to a sensible number of significant figures (usually 3).

Topics

Chemistry · C3: Quantitative Chemistry · C4: Chemical Changes

Question and mark scheme from the AQA GCSE Chemistry examination, Chemistry Paper 1 (Higher), 2023. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.