Iron is produced in a blast furnace by the reduction of iron(III) oxide with carbon monoxide. The equation for this reaction is: Fe₂O₃ + 3CO → 2Fe + 3CO₂. A student states that 160 g of iron(III) oxide would produce 112 g of iron. Show whether the student is correct by using mole calculations. (Relative atomic masses: Fe = 56, O = 16, C = 12.) (5 marks)

Edexcel A-Level Chemistry (9CH0) — 5.1 Calculations using moles · Justify · 5 marks · View as Markdown

Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).

Iron is produced industrially in a blast furnace. The theoretical yield of iron can be calculated from the balanced equation for the reaction.

Model answer (5 marks)

Molar mass of Fe₂O₃ = 2(56)+3(16)=160 g mol⁻¹

Moles of Fe₂O₃ = 160 g ÷ 160 g mol⁻¹ = 1 mol

From the balanced equation 1 mol Fe₂O₃ gives 2 mol Fe

Moles of Fe = 1 mol × 2 = 2 mol

Mass of Fe = 2 mol × 56 g mol⁻¹ = 112 g

Therefore the student’s calculation is correct.

Examiner tips

  • Show the molar mass calculation first, then the moles of Fe₂O₃, use the 1:2 ratio, calculate moles of Fe, convert to mass, and state the conclusion. Keep the steps clear and labelled.

Mark scheme (5 marks)

  1. Correct molar mass of Fe₂O₃ calculated as 160 g/mol
  2. Correct calculation of moles of Fe₂O₃ as 1 mol
  3. Correct use of molar ratio to determine moles of Fe produced
  4. Correct molar mass of Fe used as 56 g/mol
  5. Correct mass of Fe calculated as 112 g AND conclusion that the student is correct

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