Explain what happens at each electrode when aqueous sodium chloride solution is electrolysed.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Model answer (4 marks)
At the anode chloride ions are attracted and give up electrons:
1. Cl⁻ → Cl₂(g) + 2e⁻
At the cathode hydrogen ions are attracted and gain electrons:
2. 2H⁺ + 2e⁻ → H₂(g)
Sodium ions are not reduced because hydrogen is more easily reduced than sodium.
1. Cl⁻ → Cl₂(g) + 2e⁻
At the cathode hydrogen ions are attracted and gain electrons:
2. 2H⁺ + 2e⁻ → H₂(g)
Sodium ions are not reduced because hydrogen is more easily reduced than sodium.
Examiner tips
- Use the correct half‑reactions and state the products at each electrode.
- Show the direction of ion movement (Cl⁻ to anode, H⁺ to cathode).
- Explain why Na⁺ is not reduced – hydrogen is more reactive.
Mark scheme (4 marks)
- Chloride ions move to the positive electrode (anode)
- Chloride ions lose electrons at the anode, producing chlorine gas
- Sodium/hydrogen ions move to the negative electrode (cathode)
- Hydrogen ions gain electrons at the cathode, producing hydrogen gas, because sodium is more reactive than hydrogen
Related
- All AQA GCSE Chemistry (8462) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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