Oxidation, Reduction and Redox

This lesson covers oxidation, reduction and redox reactions as required by the Edexcel GCSE Chemistry specification (1CH0), Topic 4. You need to understand the definitions of oxidation and reduction in terms of oxygen transfer and electron transfer, identify what is oxidised and reduced in reactions, and write half equations (Higher tier).

---

Definitions of Oxidation and Reduction

There are two ways to define oxidation and reduction at GCSE level.

Definition 1: In Terms of Oxygen

Term	Definition	Example
Oxidation	Gain of oxygen	Magnesium + oxygen → magnesium oxide (Mg gains O)
Reduction	Loss of oxygen	Copper oxide + carbon → copper + carbon dioxide (CuO loses O)

Definition 2: In Terms of Electrons (Higher)

Term	Definition	Memory Aid
Oxidation	Loss of electrons	Oxidation Is Loss (OIL)
Reduction	Gain of electrons	Reduction Is Gain (RIG)

graph LR
    subgraph "OIL RIG"
    A["<b>O</b>xidation<br/><b>I</b>s<br/><b>L</b>oss<br/>(of electrons)"] --- B["<b>R</b>eduction<br/><b>I</b>s<br/><b>G</b>ain<br/>(of electrons)"]
    end

    style A fill:#e74c3c,color:#fff
    style B fill:#3498db,color:#fff