Iron is below carbon in the reactivity series but above copper. Explain why iron can be extracted from iron oxide using carbon, and predict whether copper could also be extracted from copper oxide using iron.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Model answer (4 marks)
Iron is less reactive than carbon but more reactive than copper. In a reduction with carbon the carbon atom donates electrons to the oxygen in iron(III) oxide, forming CO or CO₂ and leaving iron metal:
Fe₂O₃ + 3C → 2Fe + 3CO
Carbon therefore removes the oxygen from the iron oxide, reducing Fe³⁺ to Fe⁰.
Copper cannot be extracted from copper(II) oxide by iron because iron is not more reactive than carbon. For a metal to displace another from its oxide, the displacing metal must be more reactive than the metal in the oxide. Iron is more reactive than copper, but it is less reactive than carbon, so iron cannot reduce CuO to Cu metal.
Thus iron can be extracted from iron oxide using carbon, but copper cannot be extracted from copper oxide using iron as the reducing agent.
Fe₂O₃ + 3C → 2Fe + 3CO
Carbon therefore removes the oxygen from the iron oxide, reducing Fe³⁺ to Fe⁰.
Copper cannot be extracted from copper(II) oxide by iron because iron is not more reactive than carbon. For a metal to displace another from its oxide, the displacing metal must be more reactive than the metal in the oxide. Iron is more reactive than copper, but it is less reactive than carbon, so iron cannot reduce CuO to Cu metal.
Thus iron can be extracted from iron oxide using carbon, but copper cannot be extracted from copper oxide using iron as the reducing agent.
Examiner tips
- State the reactivity relationship (Fe > Cu, C > Fe).
- Show the reduction equation for Fe₂O₃ + C.
- Explain why iron cannot reduce CuO – it is not more reactive than carbon.
- Use the phrase ‘displacement reaction’ to link to the scheme.
Common mistakes
- Confusing the order of reactivity (saying iron is more reactive than carbon).
- Writing the wrong reduction equation (e.g. Fe₂O₃ + C → Fe + CO₂).
- Claiming iron can reduce CuO, ignoring the requirement of a more reactive reducing agent.
Mark scheme (4 marks)
- Metals less reactive than carbon can be extracted from their oxides by reduction with carbon
- Reduction involves the loss of oxygen (from the metal oxide), so carbon removes the oxygen from iron oxide
- Copper could NOT be displaced/extracted from copper oxide by iron because iron is more reactive than copper, not carbon, and the question asks about iron as the reducing agent — iron is less reactive than carbon but MORE reactive than copper, so iron cannot reduce copper oxide (iron cannot displace copper from copper oxide using this method / displacement requires the displacing metal to be more reactive than the metal in the compound, but we are comparing iron to copper oxide here — iron IS more reactive than copper so iron WOULD displace copper from copper oxide)
- This is a displacement reaction — a more reactive element displaces a less reactive element from its compound
Key terms in this question
Related
- All AQA GCSE Chemistry (8462) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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