Electrolysis is a process that uses electricity to split up a compound. It’s commonly used to extract reactive metals and to understand redox reactions.

What is electrolysis?

• Electrolysis means splitting up a substance using electricity
• It breaks down ionic compounds into their elements
• The substance being broken down is called the electrolyte

💡 The electrolyte must be molten or dissolved in water so the ions are free to move

Key components

What happens during electrolysis?

• Positive ions (cations) move to the cathode and gain electrons → reduction
• Negative ions (anions) move to the anode and lose electrons → oxidation

💡 Use OIL RIG to remember:Oxidation Is Loss, Reduction Is Gain (of electrons)

Example: Electrolysis of molten lead bromide (PbBr₂)

• At cathode: Pb²⁺ + 2e⁻ → Pb (reduction)
• At anode: 2Br⁻ → Br₂ + 2e⁻ (oxidation)
• Products: lead at the cathode, bromine gas at the anode

Why is electrolysis used for metal extraction?

• Some metals (e.g. aluminium) are too reactive to be extracted by carbon
• These are extracted by electrolysis of their molten oxides
• Electrolysis is expensive because it uses a lot of electricity

Half equations

Half equations show what happens at each electrode:

Example: Aluminium extraction

• At cathode: Al³⁺ + 3e⁻ → Al
• At anode: 2O²⁻ → O₂ + 4e⁻