Molten lead(II) bromide is electrolysed using inert electrodes. Describe what happens at each electrode, naming the products formed.

Pearson Edexcel International GCSE Chemistry (4CH1) — 1.9 Electrolysis · Describe · 4 marks · View as Markdown

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

Lead(II) bromide is an ionic compound. When melted, it undergoes electrolysis and decomposes into its elements.

Model answer (4 marks)

Anode (positive): Bromide ions are attracted and lose two electrons to form bromine gas: 2 Br⁻ → Br₂ + 2 e⁻.
Cathode (negative): Lead ions are attracted and gain two electrons to form lead metal: Pb²⁺ + 2 e⁻ → Pb.

Examiner tips

Use the correct electrode names (anode/cathode) and state the direction of ion movement. Include the half‑reactions with electron transfer. Mention the products (Br₂ gas and Pb metal).
Show the oxidation at the anode and reduction at the cathode – this demonstrates understanding of electron flow.

Common mistakes

Confusing the electrodes (calling the anode negative). Forgetting to include the electron transfer in the half‑reaction. Not naming the products (e.g. writing ‘bromine’ as ‘Br⁻’).

Mark scheme (4 marks)

Bromide ions (anions) move towards the anode (positive electrode)
Bromine is produced at the anode as bromide ions lose electrons (oxidation)
Lead ions (cations) move towards the cathode (negative electrode)
Lead is produced at the cathode as lead ions gain electrons (reduction)

Key terms in this question

inert electrode