A student investigates the reaction between zinc metal and dilute sulfuric acid. Explain what type of reaction is taking place, identifying which substance is oxidised and which is reduced, and describe what the student would observe during the reaction.

OCR A-Level Chemistry A (H432) — 2.3 Acid-base and redox reactions · Explain · 5 marks · View as Markdown

Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).

Zinc is a metal that reacts with dilute sulfuric acid to produce zinc sulfate solution and hydrogen gas. The reaction can be represented by the equation: Zn + H₂SO₄ → ZnSO₄ + H₂

Model answer (5 marks)

This is a redox reaction. Zinc is oxidised, losing two electrons to form Zn²⁺ ions. The hydrogen ions are reduced, gaining the electrons to form H₂ gas. The student will see bubbles of hydrogen gas and the zinc metal will dissolve, becoming smaller as the reaction proceeds.

Examiner tips

  • Use the word "redox" first, then state which species is oxidised and which is reduced.
  • Mention the loss/gain of electrons and the formation of Zn²⁺ and H₂.
  • Describe the observable changes – gas bubbles and dissolution of zinc.

Common mistakes

  • Calling the reaction a simple substitution instead of redox.
  • Forgetting to identify the electron transfer (oxidation/reduction).
  • Not describing the physical changes such as bubbling or zinc dissolving.

Mark scheme (5 marks)

  1. This is a redox reaction
  2. Zinc is oxidised because it loses electrons (forming Zn²⁺ ions)
  3. Hydrogen ions are reduced because they gain electrons (forming H₂)
  4. Bubbles of gas are observed (hydrogen gas is produced)
  5. The zinc solid disappears / dissolves (gets smaller) as the reaction proceeds

Key terms in this question

oxidised · reduced · ion

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