During the electrolysis of molten lead(II) bromide, describe what happens at each electrode and identify the product formed at each electrode.

Cambridge International IGCSE Chemistry (0620) — 4.1 Electrolysis · Describe · 4 marks · View as Markdown

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

Model answer (4 marks)

At the cathode (negative electrode) Pb²⁺ ions from the molten salt are attracted and are reduced:
Pb²⁺ + 2e⁻ → Pb (metal, liquid)

At the anode (positive electrode) Br⁻ ions are attracted and are oxidised:
2Br⁻ → Br₂ (gas, liquid or vapour)

Examiner tips

  • Use the correct electrode names (cathode/anode) and the direction of electron flow. Show the half‑reactions with electrons to demonstrate reduction/oxidation. State the products explicitly (lead metal, bromine gas/liquid).

Common mistakes

  • Confusing cathode with anode or vice versa. Omitting the electron transfer in the half‑reaction. Failing to specify the state of the bromine product.

Mark scheme (4 marks)

  1. At the cathode (negative electrode), lead ions / Pb²⁺ ions are attracted and gain electrons / are reduced, forming lead metal
  2. Lead (metal / liquid) is the product at the cathode
  3. At the anode (positive electrode), bromide ions / Br⁻ ions are attracted and lose electrons / are oxidised, forming bromine
  4. Bromine (gas / liquid / vapour) is the product at the anode

Key terms in this question

electrolysis · molten

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