Oxidation & Reduction in Terms of Electrons (Oxford AQA IGCSE Chemistry)
Revision Note
Written by: Philippa Platt
Reviewed by: Stewart Hird
Oxidation & Reduction in Terms of Electrons
As well as understanding oxidation and reduction in terms of oxygen, you need to understand these reactions in terms of electrons
When a substance loses electrons it is oxidised
When a substance gains electrons it is reduced
If this occurs in the same reaction, the reaction is a redox reaction
For example, when iron reacts with a compound of copper such as copper sulfate, a displacement reaction occurs
iron + copper sulfate → iron(II) sulfate + copper
Fe + CuSO4 → FeSO4 + Cu
We can write this as an ionic equation
Fe + Cu2+ + SO42– → Fe2+ + SO42– + Cu
We can then remove the spectator ions to see the overall change
Fe + Cu2+→ Fe2+ + Cu
The iron has lost electrons to become a positive ion, so has been oxidised
The positive copper ion has gained electrons to become an atom, so have been reduced
The redox reaction between Fe and Cu2+
Worked Example
Which change in the following equation is oxidation?
V3+ + Fe3+ → V4+ + Fe2+
Answer:
Step 1
Identify the changes for each species:
V3+ to V4+
V3+ has lost 1 electron
Fe3+ to Fe2+
Fe3+ has gained 1 electron
Step 2
Identify each change as either oxidation and reduction
V3+ to V4+ is oxidation
Fe3+ to Fe2+ is reduction
Therefore V3+ has been oxidised
Examiner Tips and Tricks
You can use OILRIG to remember which way round oxidation and reduction is:
Oxidation is the Loss of electrons
Reduction is the Gain of electrons
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