4.1 Oxidation and reduction
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What is oxidation, in terms of oxygen?
Choose one answer.
Correct Not quite: the answer is Gain of oxygen
Mark scheme
A
Model answer
A: oxidation is the gain of oxygen.
Copper oxide reacts with hydrogen: CuO + H2 → Cu + H2O
Identify the substance that is reduced and the substance that is oxidised. Explain your answers.
Mark scheme
- copper oxide is reduced because it loses oxygen (1)
- hydrogen is oxidised because it gains oxygen (1)
Model answer
Copper oxide loses oxygen, so it is reduced; hydrogen gains oxygen to become water, so it is oxidised.
Iron is extracted from iron oxide in a blast furnace: Fe2O3 + 3CO → 2Fe + 3CO2
Which substance is reduced?
Mark scheme
- iron oxide / Fe2O3 (1)
Model answer
Iron oxide is reduced because it loses oxygen.
Explain why the reaction 2CuO + C → 2Cu + CO2 is described as a redox reaction.
Mark scheme
- copper oxide loses oxygen / is reduced (1)
- carbon gains oxygen / is oxidised, and both happen at the same time (1)
Model answer
Copper oxide is reduced (it loses oxygen) and carbon is oxidised (it gains oxygen) in the same reaction, so it is a redox reaction.
When copper is heated in air, its mass increases and it turns black.
Name the product and explain the increase in mass.
Mark scheme
- copper oxide (1)
- copper gains / combines with oxygen from the air (1)
Model answer
Copper is oxidised to copper oxide; the oxygen atoms from the air add to the mass.
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