AQA A-Level Chemistry AS Paper 1, June 2025: Question 1

6 marks · Easy difficulty · State/Explain/Numerical

Calculate the atom economy of TiCl4 formation, suggest an economic advantage of high atom economy, write the equation for reduction of TiCl4 using magnesium, and explain why magnesium is expensive.

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Question

Question 01 contains four sub-questions about the extraction of titanium. The intro gives the equation: TiO2(s) + 2C(s) + 2Cl2(g) -> TiCl4(l) + 2CO(g). Part 01.1 asks to calculate the percentage atom economy to form TiCl4 in this first stage (2 marks). Part 01.2 asks to suggest one economic advantage of using a process with a high percentage atom economy (1 mark). Part 01.3 asks for the equation between TiCl4 and magnesium, and the role of magnesium (2 marks). Part 01.4 asks why magnesium is expensive (1 mark).
Question text

01 This question is about the extraction of titanium.

The first stage in the extraction of titanium is the formation of

titanium(IV) chloride, TiCl4

TiO2(s) + 2C(s) + 2Cl2(g) ⟶ TiCl4(l) + 2CO(g)

01.1 Calculate the percentage atom economy to form TiCl4 in this first stage of the

extraction.

[2 marks]

Percentage atom economy

01.2 Suggest one economic advantage of using a process with a

high percentage atom economy.

[1 mark]

The second stage of the extraction is the reaction between TiCl4 and magnesium.

01.3 Give the equation for the reaction between TiCl4 and magnesium.

State the role of magnesium in this reaction.

[2 marks]

Equation

Role of magnesium

01.4 Titanium is an expensive metal because its extraction process uses magnesium.

Suggest why magnesium is expensive.

*02* [1 mark]

Mark scheme

Show the mark scheme Mark scheme for Question 01: 01.1 awards 1 mark for (Mr of product / total Mr of reactants) x 100 = (189.9 / 245.9) x 100, and 1 mark for 77.2%. 01.2 gives 1 mark for maximising mass of reactants into useful products or minimising waste/byproducts. 01.3 gives 1 mark for equation TiCl4 + 2Mg -> 2MgCl2 + Ti, and 1 mark for reducing agent or electron donor. 01.4 awards 1 mark for high energy consumption to extract magnesium or extraction uses electrolysis.

Question Marking guidance Additional Comments/Guidelines Mark

M1: (Mr of product ÷ total Mr of reactants) × 100

(189.9 ÷ 245.9) × 100

01.1

(2 x AO1)

M2: 77.2% Allow ECF from incorrect Mr values in M1

Do not allow M2 if greater than or equal to 100%

Idea of maximising the mass of reactants/atoms that ends up in the Ignore references to yield and energy

useful products

01.2

OR (1 x AO3)

Do not allow it costs less–ASCHEMISTRYunless qualified.–7404/1 –

Idea of minimising waste / biproduct (to be disposed of)

TiCl4 + 2Mg → 2MgCl2 + Ti allow multiples

01.3 ignore state symbols

(2 x AO1)

Reducing agent / electron donor

The process to extract magnesium uses a lot of energy

OR 1

01.4 11

(1 x AO3)

The extraction uses electrolysis

How to answer it

Extraction of Titanium & Atom Economy

📌 What This Question Tests

This question assesses core physical and inorganic chemistry concepts across AQA Year 1:

  • Quantitative Chemistry: Calculating percentage atom economy using stoichiometric equations and molar masses ( Mr ).
  • Green Chemistry: Explaining the economic and industrial significance of a high atom economy.
  • Extraction of Titanium (Group 2 Chemistry): Writing the reduction equation of TiCl₄ with magnesium and identifying redox roles.
  • Industrial Economics: Explaining the high cost associated with reactive metal extraction (electrolysis and energy costs).
Question 01.1 • 2 Marks

Percentage Atom Economy Calculation

Calculate the percentage atom economy to form TiCl₄ in the first stage of extraction

Reaction: TiO₂(s) + 2 C(s) + 2 Cl₂(g) → TiCl₄(l) + 2 CO(g)

📐 Step-by-Step Calculation

  1. Identify desired product Mr :
    TiCl₄ = 47.9 + (4 × 35.5) = 189.9
  2. Calculate total Mr of all reactants:
    TiO₂ = 47.9 + (2 × 16.0) = 79.9
    2 C = 2 × 12.0 = 24.0
    2 Cl₂ = 2 × (2 × 35.5) = 142.0
    Total Reactant Mass = 79.9 + 24.0 + 142.0 = 245.9
    (Alternatively, total products: 189.9 + 2(28.0) = 245.9)
  3. Apply formula:
    % Atom Economy = (189.9 ÷ 245.9) × 100 = 77.2%

✅ Mark Scheme Breakdown

  • [1 mark] (M1): Correct working showing (189.9 ÷ 245.9) × 100 (or equivalent fraction).
  • [1 mark] (M2): Final answer of 77.2% (3 sig figs).

❌ Common Pitfalls

  • Forgetting balancing numbers: Omitting the coefficients (e.g., using 1 mole of Cl₂ instead of 2 moles) gives an incorrect total mass.
  • Confusing atom economy with percentage yield: Atom economy depends entirely on the balanced equation, not experimental yield.
  • Values ≥ 100%: An atom economy can never exceed 100%. If your answer is over 100%, you inverted the fraction!
Examiner Note: Allow Error Carried Forward (ECF) for M2 if an arithmetic error is made in the Mr values, provided the final value is strictly below 100%.
Question 01.2 • 1 Mark

Economic Advantage of High Atom Economy

Suggest one economic advantage of using a process with a high percentage atom economy

✅ Acceptable Answers (Any One)

  • Maximises the proportion/mass of reactants that ends up as the desired/useful product.
  • Minimises the production of unwanted waste products (which saves on disposal/treatment costs).

🧠 Exam Technique

  • Qualify financial terms: Never just state "it is cheaper" or "costs less". Always explain why (e.g., "reduces costs of separating and disposing of toxic waste").
  • Keep it relevant to atom economy: Do not mention yield, rate of reaction, or catalysts here. Atom economy is strictly about waste minimization and atom utilization.

❌ What Lost Marks

Examiners specifically directed: "Ignore references to yield and energy. Do not allow 'it costs less' unless qualified."

Question 01.3 • 2 Marks

Reduction of TiCl₄ Using Magnesium

Give the equation and state the role of magnesium

✅ Correct Answer

Equation:

TiCl₄ + 2 Mg → 2 MgCl₂ + Ti

Role of Magnesium:

Reducing agent (or electron donor)

💡 Key Knowledge

  • Titanium cannot be extracted using carbon reduction because it forms brittle titanium carbide (TiC).
  • Instead, magnesium is used in an expensive batch process under an inert argon atmosphere.
  • Redox transfer: Mg starts at oxidation state 0 and increases to +2 in MgCl₂ (it loses electrons, so it is oxidized and acts as the reducing agent). Titanium goes from +4 to 0 (reduced).
Mark Breakdown: 1 mark for balanced equation (multiples allowed, state symbols not required). 1 mark for stating "reducing agent" or "electron donor".
Question 01.4 • 1 Mark

Cost of Magnesium

Suggest why magnesium is expensive

✅ Acceptable Answers (Either)

  • The extraction of magnesium uses a lot of energy / electricity.
  • Magnesium is extracted by electrolysis (which has high electrical energy requirements).

🧠 Connecting the Specification

Magnesium is a reactive metal positioned high in the electrochemical series. It cannot be reduced by carbon, so molten electrolysis of magnesium chloride ( MgCl₂ ) is required. Large amounts of electrical power make electrolysis inherently expensive.

❌ Common Errors

  • Stating magnesium is "rare" or "hard to find" (it is abundant in seawater and minerals).
  • Vague statements like "it requires high heat" without linking to high energy demand or electrolysis.

Topics

Physical Chemistry · Inorganic Chemistry · 3.1.2 Amount of Substance · 3.1.7 Oxidation, Reduction and Redox Equations · 3.2.2 Group 2, The Alkaline Earth Metals

Question and mark scheme from the AQA A-Level Chemistry examination, AS Paper 1, June 2025. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.