Explain what happens at each electrode when molten lead bromide is electrolysed using inert electrodes.

Edexcel GCSE Chemistry (1CH0) — 3.2 Electrolytic processes · Explain · 4 marks · View as Markdown

Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).

Lead bromide is an ionic compound. When solid, it does not conduct electricity. When melted, it can be electrolysed.

Model answer (4 marks)

The cathode is the negative electrode where Pb²⁺ ions are attracted. At the cathode, Pb²⁺ ions gain two electrons (reduction) to form molten lead metal.
The anode is the positive electrode where Br⁻ ions are attracted. At the anode, Br⁻ ions lose two electrons (oxidation) to form bromine gas.

Examiner tips

  • Use the terms ‘cathode’ and ‘anode’ correctly; state the charge of each electrode. Show the half‑reactions with electron transfer. Mention that lead is deposited as metal and bromine is released as a gas.

Common mistakes

  • Confusing the charges of the electrodes (e.g. calling the cathode positive). Forgetting to write the electron transfer in the half‑reaction. Saying ‘bromine is produced’ without specifying it is a gas or that it is an oxidation reaction.

Mark scheme (4 marks)

  1. The cathode is the negative electrode where lead ions (Pb²⁺) are attracted
  2. At the cathode, lead ions gain electrons (reduction) to form lead metal
  3. The anode is the positive electrode where bromide ions (Br⁻) are attracted
  4. At the anode, bromide ions lose electrons (oxidation) to form bromine gas

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