Electrolysis of brine (aqueous sodium chloride) is one of the most searched IGCSE Chemistry topics because it tests understanding of which ions are discharged and why. You need to state products at anode and cathode, write half equations, and often link to uses (e.g. chlorine for bleach, hydrogen for fuels, sodium hydroxide for soap).

What Happens When You Electrolyse Brine?

• Cathode (negative): Hydrogen is produced (H⁺ reduced; (2H^+ + 2e^- \rightarrow H_2)). Sodium is not discharged (it’s more reactive than hydrogen).
• Anode (positive): Chlorine is produced (Cl⁻ oxidised; (2Cl^- \rightarrow Cl_2 + 2e^-)). Oxygen from water is possible in dilute conditions; for concentrated brine, chlorine is usually the product (syllabus-specific).
• Solution left: Sodium hydroxide (NaOH) builds up.

Learn the half equations and conditions (e.g. concentrated brine) as required by your syllabus.

How to Answer Exam Questions

• State products at each electrode and give a reason (e.g. “hydrogen is less reactive than sodium so H⁺ is discharged”).
• Write balanced half equations; check charge and atom balance.
• Uses – Chlorine (bleach, PVC), hydrogen (fuels, ammonia), sodium hydroxide (soap, paper).

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Exam-Style Questions and Common Mistakes

You may be asked to state the products at each electrode, write half equations, or explain why a particular ion is discharged. For brine, cathode: hydrogen; anode: chlorine; solution left: sodium hydroxide. Common mistakes: Wrong products (e.g. saying sodium at cathode); unbalanced half equations (check charge and atom balance); not giving a reason for which ion is discharged. Learn the half equations and conditions (e.g. concentrated brine) as required by your syllabus.

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