Anode – IGCSE Chemistry Definition
IGCSE Chemistry definition of anode: the positive electrode where oxidation occurs during electrolysis. Covers OILRIG, anion discharge, and exam applications.
Published by IGCSEChemistry.com.my
Chemistry teaching team: K. S. Tan (15+ years teaching IGCSE Chemistry) and Ms Yash (10+ years teaching IGCSE Chemistry) and Ms Kartini (15+ years teaching IGCSE Chemistry).
Mapped to Cambridge IGCSE Chemistry 0620 (2026–2028). Last updated 2026-08-19.
The anode is the positive electrode in electrolysis. It is where oxidation occurs — anions migrate to it and lose electrons. Understanding what happens at each electrode is essential for Paper 2 and Paper 4 questions on electrolysis, and the mnemonic OILRIG (Oxidation Is Loss, Reduction Is Gain) connects the anode to oxidation.
The 0620 definition
The anode is the positive electrode. During electrolysis, negatively charged ions (anions) are attracted to the anode and are discharged by losing electrons. This is oxidation.
Memory aids
- Anode = Anions go here
- OILRIG: Oxidation Is Loss (of electrons) — happens at the anode
- AN OX: ANode = OXidation
What happens at the anode
Anions are attracted to the positive anode. When they reach it, they lose electrons (are oxidised) and are discharged as atoms or molecules.
| Electrolyte | Ion at anode | Half-equation | Product |
|---|---|---|---|
| Molten lead(II) bromide | Br⁻ | 2Br⁻ → Br₂ + 2e⁻ | Bromine |
| Brine (NaCl solution) | Cl⁻ | 2Cl⁻ → Cl₂ + 2e⁻ | Chlorine gas |
| Dilute sulfuric acid | OH⁻ (from water) | 4OH⁻ → 2H₂O + O₂ + 4e⁻ | Oxygen gas |
| Copper sulfate (carbon electrodes) | OH⁻ (from water) | 4OH⁻ → 2H₂O + O₂ + 4e⁻ | Oxygen gas |
Selective discharge at the anode (Supplement)
When more than one anion is present (e.g. in aqueous solutions), the ion that is preferentially discharged depends on concentration:
- Halide ions (Cl⁻, Br⁻, I⁻) are discharged if concentrated
- OH⁻ ions (from water) are discharged if the halide is dilute
- Sulfate and nitrate ions are never discharged — they stay in solution
Worked exam question
During the electrolysis of concentrated sodium chloride solution, gas is produced at the anode. (a) Name the gas. (1) (b) Write the half-equation for the reaction at the anode. (2) (c) Is this oxidation or reduction? Explain. (2)
Mark scheme
(a) Chlorine [1]
(b) 2Cl⁻ → Cl₂ + 2e⁻ [1 for equation, 1 for balance]
(c) Oxidation [1]; because the chloride ions lose electrons / electron loss is oxidation [1]
Common exam mistakes
- Confusing anode and cathode. The anode is positive, the cathode is negative. Anions (negative) go to the anode; cations (positive) go to the cathode.
- Writing the half-equation with the wrong number of electrons. Balance the charge: 2Cl⁻ (total charge -2) needs 2e⁻ on the right to balance.
- Saying “reduction” happens at the anode. Oxidation (loss of electrons) always occurs at the anode.
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