AQA · GCSE · Chemistry
Course version: 8462 · Version from Sept 2018
Students should be able to explain reduction and oxidation in terms of…
Full specification wording
Metal oxides: Students should be able to explain reduction and oxidation in terms of loss or gain of oxygen.
This statement asks you to use oxygen transfer as the defining idea for reduction and oxidation in reactions involving metal oxides.
Checked against the AQA 8462 specification (opens in a new tab) on .
- Point 2 of 2
- 3 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
This statement asks you to use oxygen transfer as the defining idea for reduction and oxidation in reactions involving metal oxides. Oxidation is the gain of oxygen by a substance; reduction is the loss of oxygen. In a reaction between a metal and a metal oxide, the metal that gains oxygen is oxidised while the metal oxide that loses oxygen is reduced. For example, in 2Mg + CO₂ → 2MgO + C, magnesium gains oxygen and is oxidised, while carbon dioxide loses oxygen and is reduced. The two processes happen together, so such a reaction is a redox reaction. You should be able to inspect a symbol equation, identify which reactant gains oxygen and which loses oxygen, and name the substance oxidised and the substance reduced. This oxygen-based definition is the one required at GCSE; electron transfer is not needed here.
What earns the marks
- Oxidation is defined as the gain of oxygen by a substance.
- Reduction is defined as the loss of oxygen from a substance.
- In a given equation, the substance that gains oxygen is identified as oxidised.
- In the same equation, the substance that loses oxygen is identified as reduced.
- A reaction in which one substance is oxidised and another is reduced is described as a redox reaction.
- The explanation is applied correctly to a named example such as 2Mg + CO₂ → 2MgO + C.
Common mistakes and how to put them right
Reversing the definitions by saying oxidation is loss of oxygen.
Put it right by linking oxidation to gain of oxygen and reduction to loss of oxygen.
Naming only one of the two changes in a redox reaction.
Put it right by stating both the substance oxidised and the substance reduced.
Assuming the metal always gains oxygen without checking the equation.
Put it right by tracing oxygen atoms from reactants to products before deciding.
Exam tips
- Underline the oxygen atoms in the reactants and products before deciding which substance gains or loses oxygen.
- Write both conclusions explicitly, for example 'magnesium is oxidised and carbon dioxide is reduced', rather than giving only one.
- If asked to explain, include the words gain and loss of oxygen in your answer so the definition is visible to the examiner.
Try the lesson
The start of the Metal oxides: Students should be able to explain reduction and oxidation in terms of loss or gain of oxygen. lesson, made from checked teaching notes for this specification point.
Have a go first
In the reaction CuO + H₂ → Cu + H₂O, copper oxide loses oxygen. What name is given to this change?
Listen
This statement asks you to use oxygen transfer as the defining idea for reduction and oxidation in reactions involving metal oxides. Oxidation is the gain of oxygen by a substance; reduction is the loss of oxygen. In a reaction between a metal and a metal oxide, the metal that gains oxygen is oxidised while the metal oxide that loses oxygen is reduced. For example, in 2Mg + CO₂ → 2MgO + C, magnesium gains oxygen and is oxidised, while carbon dioxide loses oxygen and is reduced. The two processes happen together, so such a reaction is a redox reaction. You should be able to inspect a symbol equation, identify which reactant gains oxygen and which loses oxygen, and name the substance oxidised and the substance reduced. This oxygen-based definition is the one required at GCSE; electron transfer is not needed here. A strong answer earns marks for these points. Oxidation is defined as the gain of oxygen by a substance. Reduction is defined as the loss of oxygen from a substance. In a given equation, the substance that gains oxygen is identified as oxidised. In the same equation, the substance that loses oxygen is identified as reduced. A common slip: Reversing the definitions by saying oxidation is loss of oxygen. Instead, linking oxidation to gain of oxygen and reduction to loss of oxygen. Exam tip: Underline the oxygen atoms in the reactants and products before deciding which substance gains or loses oxygen.
See it
Key words
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Oxidation
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Reduction
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Redox reaction
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See every definition
- Oxidation
- The gain of oxygen by a substance, as when magnesium gains oxygen in a reaction with a metal oxide.
- Reduction
- The loss of oxygen from a substance, as when carbon dioxide loses oxygen in a reaction with a metal.
- Redox reaction
- A reaction in which one substance is oxidised and another is reduced, the two processes happening together.
Label the diagram
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1Box 1
2Box 2
3Box 3
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