Iron can be extracted from iron oxide by heating it with carbon. In this reaction, iron oxide is reduced and carbon is oxidised. Explain what is meant by the terms 'oxidised' and 'reduced' in terms of oxygen, and explain why this reaction is described as a redox reaction.

Eduqas A-Level Chemistry — 1.8 Redox · Explain · 5 marks · View as Markdown

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

Iron oxide reacts with carbon at high temperatures. The equation for the reaction is: 2Fe₂O₃ + 3C → 4Fe + 3CO₂

Model answer (5 marks)

Oxidised means that a substance has gained oxygen. In the reaction, carbon reacts with oxygen from the iron oxide to form CO₂, so carbon gains oxygen and is oxidised.

Reduced means that a substance has lost oxygen. The iron oxide loses oxygen atoms to form elemental iron, so iron oxide is reduced.

This is a redox reaction because it involves both oxidation (carbon gaining oxygen) and reduction (iron oxide losing oxygen) occurring at the same time.

Examiner tips

  • Use the definition of oxidised/reduced in terms of oxygen gain/loss. Explain the role of carbon and iron oxide explicitly. Show that both processes happen simultaneously to justify ‘redox’.

Common mistakes

  • Confusing ‘oxidised’ with ‘oxidation state increase’ rather than oxygen gain. Forgetting to mention that iron oxide loses oxygen. Saying ‘carbon is oxidised’ without stating it gains oxygen to form CO₂.

Mark scheme (5 marks)

  1. Oxidised means oxygen has been gained
  2. Carbon gains oxygen (to form carbon dioxide), so carbon is oxidised
  3. Reduced means oxygen has been lost
  4. Iron oxide loses oxygen (to form iron), so iron oxide is reduced
  5. A redox reaction is one in which both oxidation and reduction occur simultaneously

Key terms in this question

oxidised · reduced · redox reaction

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