Gold is found naturally as the pure metal in the Earth's crust, whilst copper is found mainly as copper oxide ore. Explain why gold is found as the pure metal and describe how copper can be obtained from copper oxide, identifying the type of reaction that occurs.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Model answer (4 marks)
Gold is found as the pure metal because it is very unreactive – it sits low in the reactivity series and therefore does not readily react with other elements or form compounds.
Copper can be obtained from copper oxide by heating the ore with carbon:
C + CuO → Cu + CO₂
In this process the carbon removes the oxygen from the copper oxide – the copper oxide loses oxygen and copper is produced.
This is a redox reaction: the carbon is oxidised (it gains oxygen) while the copper oxide is reduced (it loses oxygen).
Copper can be obtained from copper oxide by heating the ore with carbon:
C + CuO → Cu + CO₂
In this process the carbon removes the oxygen from the copper oxide – the copper oxide loses oxygen and copper is produced.
This is a redox reaction: the carbon is oxidised (it gains oxygen) while the copper oxide is reduced (it loses oxygen).
Examiner tips
- Use the exact phrase ‘low in the reactivity series’ for gold’s stability.
- Show the balanced equation for the reduction of CuO with carbon.
- Explain both oxidation and reduction steps to justify the redox classification.
- Keep the answer concise – 4 points can be earned with 4 short sentences.
Common mistakes
- Writing that gold is found as a compound instead of a pure metal.
- Omitting the balanced chemical equation for the copper extraction.
- Failing to recognise the reaction as redox by not mentioning oxidation of carbon.
Mark scheme (4 marks)
- Gold is found as the pure metal because it is very unreactive / low in the reactivity series and so does not readily react with other elements / does not form compounds
- Copper can be extracted by heating copper oxide with carbon (reduction with carbon)
- Carbon removes the oxygen from copper oxide / copper oxide loses oxygen to form copper
- This is a redox reaction because both oxidation and reduction occur / carbon is oxidised (gains oxygen) and copper oxide is reduced (loses oxygen)
Related
- All Edexcel GCSE Chemistry (1CH0) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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