Electrolysis — Principles

This lesson covers the principles of electrolysis as required by the AQA GCSE Combined Science Trilogy specification (8464). You need to understand what electrolysis is, the conditions required, the role of electrodes, and what happens at each electrode — including half equations for higher tier.

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What Is Electrolysis?

Electrolysis is the process of using an electric current to decompose (break down) an ionic compound that is either molten or dissolved in water (aqueous).

Key Conditions

• The ionic compound must be molten or in aqueous solution so that the ions are free to move.
• In a solid ionic compound, the ions are held in a fixed lattice and cannot move — so solid ionic compounds do not conduct electricity and cannot be electrolysed.

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The Electrolysis Setup

graph TD
    PS["Power Supply<br/>(DC)"] --> |"—"| Cat["CATHODE<br/>(negative electrode)"]
    PS --> |"+"| An["ANODE<br/>(positive electrode)"]
    Cat --> Elec["Electrolyte<br/>(molten or aqueous<br/>ionic compound)"]
    An --> Elec

    subgraph At the Cathode
        CatR["Positive ions (CATIONS)<br/>move here<br/>↓<br/>GAIN electrons<br/>= REDUCTION"]
    end

    subgraph At the Anode
        AnR["Negative ions (ANIONS)<br/>move here<br/>↓<br/>LOSE electrons<br/>= OXIDATION"]
    end

    style PS fill:#f9a825,color:#000
    style Cat fill:#1565c0,color:#fff
    style An fill:#d32f2f,color:#fff
    style Elec fill:#7b1fa2,color:#fff

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