Explain what happens at each electrode when molten sodium chloride 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).

Sodium chloride can be electrolysed in its molten state. Inert electrodes are used so that the electrodes do not react during the process.

Model answer (4 marks)

Sodium ions (Na⁺) migrate to the cathode, where they gain electrons (reduction) to form sodium metal:
Na⁺ + e⁻ → Na(s)

Chloride ions (Cl⁻) migrate to the anode, where they lose electrons (oxidation) to form chlorine gas:
2Cl⁻ → Cl₂(g) + 2e⁻

Examiner tips

  • Use the word ‘migrate’ or ‘move’ to show ion movement. Show the half‑reactions with electrons. Mention that the electrodes are inert so they do not take part in the reaction. Keep the answer concise – 4 marks only.
  • common_mistakes
  • :
  • Writing the wrong direction of ion movement. Forgetting to include the electron transfer. Using the wrong product (e.g. NaCl instead of Na or Cl₂).

Mark scheme (4 marks)

  1. Sodium ions (Na⁺) move towards the cathode (negative electrode)
  2. At the cathode, sodium ions gain electrons (reduction) to form sodium metal
  3. Chloride ions (Cl⁻) move towards the anode (positive electrode)
  4. At the anode, chloride ions lose electrons (oxidation) to form chlorine gas

Related

More Electrolytic processes questions

▶ Try answering this question with AI marking (free) →