AQA · GCSE · Chemistry
Course version: 8462 · Version from Sept 2018
Student should be able to: write ionic equations for displacement…
Full specification wording
Oxidation and reduction in terms of electrons (HT only): Student should be able to: write ionic equations for displacement reactions identify in a given reaction, symbol equation or half equation which species are oxidised and which are reduced.
A displacement reaction occurs when a more reactive metal takes the place of a less reactive metal in a compound.
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
A displacement reaction occurs when a more reactive metal takes the place of a less reactive metal in a compound. To write the ionic equation, show only the ions that change: the solid metal atom loses electrons to form aqueous ions, while the aqueous ion of the less reactive metal gains electrons and forms a solid atom. For example, zinc added to copper(II) sulfate solution gives Zn(s) + Cu²⁺(aq) → Zn²⁺(aq) + Cu(s). The zinc is oxidised because it loses electrons; the copper ion is reduced because it gains electrons. Spectator ions, such as sulfate, are omitted. In a half equation, electrons appear on the right for oxidation and on the left for reduction. Identifying which species is oxidised or reduced means tracking electron loss or gain, not simply naming the more reactive metal.
What earns the marks
- Write the full symbol equation first, then cancel spectator ions to leave the ionic equation.
- Show the solid metal atom losing electrons to form a positive ion in the ionic equation.
- Show the metal ion in solution gaining electrons to form a solid metal atom.
- State that oxidation is loss of electrons and reduction is gain of electrons.
- Identify the species oxidised as the one that loses electrons and the species reduced as the one that gains electrons.
- Check that charge and mass balance on both sides of the ionic equation.
Common mistakes and how to put them right
Including spectator ions such as sulfate in the ionic equation.
Put it right: Cancel ions that appear unchanged on both sides.
Saying the more reactive metal is reduced because it 'wins'.
Put it right: Track electrons: the more reactive metal loses electrons and is oxidised.
Writing electrons on the wrong side of a half equation.
Put it right: Electrons on the right for oxidation and on the left for reduction.
Exam tips
- Underline the ions that change before writing the final ionic equation.
- For each half equation, count the charge on each side to confirm electrons are placed correctly.
- Use the phrase 'loss of electrons is oxidation, gain of electrons is reduction' to justify your identification.
Try the lesson
The start of the Oxidation and reduction in terms of electrons (HT only): Student should be able to: write ionic equations for displacement reactions identify in a given reaction, symbol equation or half equation which species are oxidised and which are reduced. lesson, made from checked teaching notes for this specification point.
Have a go first
Zinc metal is added to copper(II) sulfate solution and a displacement reaction occurs. Which ionic equation correctly represents this displacement?
Listen
A displacement reaction occurs when a more reactive metal takes the place of a less reactive metal in a compound. To write the ionic equation, show only the ions that change: the solid metal atom loses electrons to form aqueous ions, while the aqueous ion of the less reactive metal gains electrons and forms a solid atom. For example, zinc added to copper(II) sulfate solution gives Zn(s) + Cu²⁺(aq) → Zn²⁺(aq) + Cu(s). The zinc is oxidised because it loses electrons; the copper ion is reduced because it gains electrons. Spectator ions, such as sulfate, are omitted. In a half equation, electrons appear on the right for oxidation and on the left for reduction. Identifying which species is oxidised or reduced means tracking electron loss or gain, not simply naming the more reactive metal. A strong answer earns marks for these points. Write the full symbol equation first, then cancel spectator ions to leave the ionic equation. Show the solid metal atom losing electrons to form a positive ion in the ionic equation. Show the metal ion in solution gaining electrons to form a solid metal atom. State that oxidation is loss of electrons and reduction is gain of electrons. A common slip: Including spectator ions such as sulfate in the ionic equation. Instead, cancel ions that appear unchanged on both sides. Exam tip: Underline the ions that change before writing the final ionic equation.
See it
Key words
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Displacement reactions
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Ionic equations
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Oxidation and reduction
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See every definition
- Displacement reactions
- A reaction in which a more reactive metal takes the place of a less reactive metal in a compound.
- Ionic equations
- Equations that show only the ions that change, with spectator ions such as sulfate omitted.
- Oxidation and reduction
- Oxidation is loss of electrons and reduction is gain of electrons.
Label the diagram
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1Box 1
2Box 2
3Box 3
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