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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.
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