This exam focus covers Worked Model Answer 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 13 of 14 in this topic. Treat this as a marking guide for what examiners are looking for, not just a fact list.
📝 Worked Model Answer
Question: "Explain why the reaction between zinc and hydrochloric acid is a redox reaction." (4 marks)
Zinc loses electrons during this reaction, so it is oxidised — oxidation is loss of electrons (OIL). [1] The half equation for zinc is: Zn → Zn²⁺ + 2e⁻. [1] The hydrogen ions from the hydrochloric acid gain electrons, so they are reduced — reduction is gain of electrons (RIG). [1] The half equation for the hydrogen ions is: 2H⁺ + 2e⁻ → H₂. [1]
Examiner note: A "redox reaction" means both oxidation AND reduction occur simultaneously. The examiner awards a mark for each of the four elements: zinc is oxidised, the oxidation half equation, hydrogen ions are reduced, the reduction half equation. Simply writing the full equation Zn + 2HCl → ZnCl₂ + H₂ earns no marks here — the question specifically asks you to explain the electron transfer using the OIL RIG framework.
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)