Electrolysis of Molten Ionic Compounds — AQA GCSE Chemistry

Electrolysis uses electricity to break down ionic compounds into their elements.

What is electrolysis?

Electrolysis is the breaking down of an ionic compound (the electrolyte) using electricity. It only works when the ions are free to move — when the compound is molten or dissolved.

The electrodes are usually inert (e.g. graphite or platinum):

• Cathode — the negative electrode.
• Anode — the positive electrode.

What happens at the electrodes

• Positive ions (cations) move to the cathode, where they gain electrons (this is reduction).
• Negative ions (anions) move to the anode, where they lose electrons (this is oxidation).

Molten ionic compounds

For a molten ionic compound, the metal is produced at the cathode and the non-metal at the anode.

Example: molten lead bromide (PbBr₂)

• At the cathode: lead metal forms (Pb²⁺ + 2e⁻ → Pb).
• At the anode: bromine forms (2Br⁻ → Br₂ + 2e⁻).

Exam tips

• Electrolysis needs ions to be free to move (molten or dissolved).
• Cathode = negative = reduction (gain electrons); anode = positive = oxidation (lose electrons).
• For molten compounds: metal at cathode, non-metal at anode.
• Use PANIC: Positive Anode, Negative Is Cathode.