AQA · GCSE · Combined Science
Course version: 8464 · Version from Sept 2018
Metal oxides: Students should be able to explain reduction and oxidation in terms of loss or gain of oxygen.
Oxidation is the gain of oxygen and reduction is the loss of oxygen.
- 4 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
Oxidation is the gain of oxygen and reduction is the loss of oxygen. In metal oxide reactions, these processes occur simultaneously. For example, in the reaction 2CuO + C → 2Cu + CO₂, copper(II) oxide loses oxygen and is reduced to copper, while carbon gains oxygen and is oxidised to carbon dioxide. A substance removing oxygen is a reducing agent; one supplying it is an oxidising agent. Explaining these reactions requires naming the specific reactant gaining or losing oxygen and stating the consequence. Always refer to the full name of the reactant, such as copper(II) oxide, rather than just the metal, to ensure accurate identification of the species involved.
What earns the marks
- Oxidation is defined as the gain of oxygen by a substance during a chemical reaction.
- Reduction is defined as the loss of oxygen from a substance during a chemical reaction.
- In the reaction 2CuO + C → 2Cu + CO₂, copper(II) oxide is reduced because it loses oxygen.
- In the same reaction, carbon is oxidised because it gains oxygen to form carbon dioxide.
- A reducing agent removes oxygen from another substance, while an oxidising agent gives oxygen to another substance.
Common mistakes and how to put them right
Writing 'copper is reduced' instead of 'copper(II) oxide is reduced'.
Put it right: Name the full reactant losing oxygen.
Confusing the products with the reactants when identifying what has been oxidised or reduced.
Put it right by selecting the substance from the left-hand side of the equation.
Stating that oxygen itself is oxidised or reduced.
Put it right by identifying the element or compound that is gaining or losing the oxygen atoms.
Exam tips
- Underline 'gain' and 'loss' in the question to ensure you correctly identify both the substance gaining and the substance losing oxygen.
- When asked to explain which species is reduced, explicitly state 'it loses oxygen' rather than just identifying the substance.
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
Oxidation is the gain of oxygen and reduction is the loss of oxygen. In metal oxide reactions, these processes occur simultaneously. For example, in the reaction 2CuO + C → 2Cu + CO₂, copper(II) oxide loses oxygen and is reduced to copper, while carbon gains oxygen and is oxidised to carbon dioxide. A substance removing oxygen is a reducing agent; one supplying it is an oxidising agent. Explaining these reactions requires naming the specific reactant gaining or losing oxygen and stating the consequence. Always refer to the full name of the reactant, such as copper(II) oxide, rather than just the metal, to ensure accurate identification of the species involved. A strong answer earns marks for these points. Oxidation is defined as the gain of oxygen by a substance during a chemical reaction. Reduction is defined as the loss of oxygen from a substance during a chemical reaction. In the reaction 2CuO + C → 2Cu + CO₂, copper(II) oxide is reduced because it loses oxygen. In the same reaction, carbon is oxidised because it gains oxygen to form carbon dioxide. A common slip: Confusing the products with the reactants when identifying what has been oxidised or reduced. Instead, selecting the substance from the left-hand side of the equation. Exam tip: Underline 'gain' and 'loss' in the question to ensure you correctly identify both the substance gaining and the substance losing oxygen.
See it
Key words
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Oxidation
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Reduction
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Reducing agent
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Oxidising agent
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See every definition
- Oxidation
- The gain of oxygen by a substance during a chemical reaction.
- Reduction
- The loss of oxygen from a substance during a chemical reaction.
- Reducing agent
- A substance that removes oxygen from another substance.
- Oxidising agent
- A substance that gives oxygen to another substance.
Label the diagram
Some boxes have lost their names. Pick the right name for each number.
1Box 1
2Box 2
3Box 3
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