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MyGCSEScience · AQA Chemistry
Electrolysis — watch on MyGCSEScience
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Key facts
Key definitions — fill in the table
| Term | Definition |
|---|---|
| Electrolysis | |
| Electrolyte | |
| Cathode (–) | |
| Anode (+) | |
| OILRIG | |
| OA CA |
Products of electrolysis — fill in the table
| Scenario | Products |
|---|---|
| Molten ionic compounds | |
| Aqueous solutions (general) | |
| At cathode | |
| At anode | |
| Dilute aqueous NaCl | |
| Concentrated aqueous NaCl (brine) |
Half equations — how to write them
- At cathode (reduction): Cu²⁺ + 2e⁻ → Cu or 2H⁺ + 2e⁻ → H₂
- At anode (oxidation): 2Cl⁻ → Cl₂ + 2e⁻ or 4OH⁻ → 2H₂O + O₂ + 4e⁻
- Check: charges must balance on both sides.
- Electrolysis of brine half equations: Cathode: 2H⁺ + 2e⁻ → H₂. Anode: 2Cl⁻ → Cl₂ + 2e⁻
- Uses of electrolysis products of brine: H₂ → fuel/margarine production. Cl₂ → disinfectants/PVC. NaOH → soap/paper.
Exam questions — 4 questions · 12 marks
Copper sulfate solution is electrolysed using copper electrodes. What is produced at the cathode?
What are the three useful products of the electrolysis of concentrated sodium chloride solution (brine)?
Write the half equations for the reactions at the cathode and anode during the electrolysis of concentrated brine. State what is produced at each electrode. (4 marks)
Hint: OILRIG: cathode = reduction = gain electrons. Anode = oxidation = lose electrons. H⁺ ions at cathode, Cl⁻ ions at anode (high concentration).
+40 XP
Dilute sodium chloride solution is electrolysed. Explain why the products at each electrode are different from those obtained from concentrated sodium chloride solution. (4 marks)
Hint: The key difference is concentration of Cl⁻ ions vs OH⁻ ions at the anode. In dilute solution, OH⁻ dominates → O₂. In concentrated, Cl⁻ dominates → Cl₂.
+40 XP
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