Oxidation and Reduction

This lesson covers oxidation and reduction (redox reactions) as required by the Edexcel GCSE Combined Science specification (1SC0). You need to understand the definitions of oxidation and reduction in terms of oxygen transfer and electron transfer, identify which species is oxidised and which is reduced in a reaction, and recognise oxidising and reducing agents.

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Oxidation and Reduction — Oxygen Transfer

The simplest definitions of oxidation and reduction involve oxygen:

Term	Definition (Oxygen Transfer)
Oxidation	The gain of oxygen
Reduction	The loss of oxygen

Remembering the Definitions

A useful mnemonic for the oxygen-transfer definitions is:

Oxidation Is Gain (of oxygen), Reduction Is Loss (of oxygen)

But be careful — when we move to electron transfer, the mnemonic changes.

Example 1: Burning Magnesium

2Mg + O₂ → 2MgO

• Magnesium gains oxygen → magnesium is oxidised.
• Oxygen is the oxidising agent (it provides the oxygen / causes the oxidation).

Example 2: Reduction of Copper Oxide with Carbon

2CuO + C → 2Cu + CO₂