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AQA · GCSE · Chemistry · Higher

Calculating carbon dioxide gas volume

Q07.6 5 marks

Fe₂O₃ reacts with carbon to produce carbon dioxide.

The equation for the reaction is:

2 Fe2O3(s)+3 C(s)→4 Fe(s)+3 CO2(g)2\,\mathrm{Fe_2O_3(s)} + 3\,\mathrm{C(s)} \rightarrow 4\,\mathrm{Fe(s)} + 3\,\mathrm{CO_2(g)}

Relative formula mass (Mᵣ): Fe₂O₃ = 160. The volume of 1 mole of any gas at room temperature and pressure is 24 dm³.

Calculate the volume of carbon dioxide gas at room temperature and pressure that is produced from 40.0 kg of Fe₂O₃ using excess carbon.

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Marking points

  1. 1 Converts 40.0 kg to 40 000 g.
  2. 2 Calculates 250 mol Fe₂O₃.
  3. 3 Uses the equation ratio to obtain 375 mol CO₂.
  4. 4 Uses 24 dm³ per mole for CO₂.
  5. 5 Final volume is 9000 dm³.

Full-mark answer

40.0 kg = 40 000 g. Moles Fe₂O₃ = 40 000 ÷ 160 = 250 mol. From 2 Fe₂O₃ : 3 CO₂, moles CO₂ = 250 × 3/2 = 375 mol. Volume = 375 × 24 = 9000 dm³.

Why this answer loses marks

I treated the given mass as moles and multiplied by gas volume.

Convert units, use formula mass, apply the equation ratio, and only then use molar gas volume.

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