Electrolysis of Molten Compounds

This lesson covers the electrolysis of molten ionic compounds for Edexcel GCSE Chemistry (1CH0). You need to be able to predict the products, write half equations, describe observations, and explain the extraction of aluminium.

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Why Molten?

An ionic compound must be molten (or dissolved) for electrolysis to work. In the solid state, the ions are locked in a rigid lattice and cannot move. When the compound is melted, the lattice breaks down and the ions become free to move towards the electrodes.

In a molten ionic compound, the only ions present are those from the compound itself. There are no water molecules or competing ions. This makes predicting the products straightforward:

• The metal is always produced at the cathode.
• The non-metal is always produced at the anode.

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Electrolysis of Molten Lead Bromide

Lead bromide (PbBr₂) is a common example used in Edexcel exams.

Setup

• Lead bromide is heated until it melts (melting point: 373 °C).
• Two graphite (carbon) electrodes are dipped into the molten lead bromide.
• A d.c. power supply is connected.

What Happens

When the electricity is switched on: