Electrolysis of Aqueous Solutions

This lesson covers the electrolysis of aqueous solutions for Edexcel GCSE Chemistry (1CH0). Aqueous electrolysis is more complex than molten electrolysis because water introduces additional competing ions. You need to know the rules for predicting products at each electrode and be able to write half equations.

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Why Is Aqueous Electrolysis Different?

When an ionic compound is dissolved in water, there are more than two types of ion present. In addition to the ions from the dissolved compound, water itself produces a small number of ions:

H₂O(l) ⇌ H⁺(aq) + OH⁻(aq)

This means:

• At the cathode, there is competition between the metal cation (from the compound) and H⁺ (from water).
• At the anode, there is competition between the non-metal anion (from the compound) and OH⁻ (from water).

The product formed depends on which ion is preferentially discharged at each electrode.

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Rules for Predicting Products

At the Cathode (Negative Electrode)

The cathode attracts cations. The competing ions are the metal ion and H⁺ from water.