This higher tier covers Higher Tier: Half Equations within Oxidation & Reduction for GCSE Chemistry. Revise Oxidation & Reduction in Chemical Changes for GCSE Chemistry with 20 exam-style questions and 20 flashcards. This topic appears regularly enough that it should still be part of a steady revision cycle. It is section 5 of 14 in this topic. This section is most useful once the core foundation idea is secure, because it adds the detail that pushes answers higher.
🎓 Higher Tier: Half Equations
Half equations show what happens to each species separately. They must balance for atoms AND charge.
Example: Magnesium + Copper Sulfate
Oxidation: Mg → Mg²⁺ + 2e⁻ (Mg loses electrons)
Reduction: Cu²⁺ + 2e⁻ → Cu (Cu²⁺ gains electrons)
Example: Zinc + Hydrochloric Acid
Oxidation: Zn → Zn²⁺ + 2e⁻ (Zn loses electrons)
Reduction: 2H⁺ + 2e⁻ → H₂ (H⁺ gains electrons)
Balancing tips:
- Electrons lost in oxidation = Electrons gained in reduction
- Total charge must be same on both sides
- e⁻ appears on RIGHT for oxidation (electrons leave)
- e⁻ appears on LEFT for reduction (electrons arrive)
Practice questions for Oxidation & Reduction
What does OIL stand for in the mnemonic OIL RIG?
In the reaction Mg + CuSO₄ → MgSO₄ + Cu, identify which species is oxidised and which is reduced. (2 marks)