Iron and calcium are both metals that react with dilute hydrochloric acid. Describe the differences in how iron and calcium react with dilute hydrochloric acid, and explain why these differences occur.

AQA GCSE Chemistry (8462) — 4.4.2 Reactions of acids · Describe · 4 marks · View as Markdown

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

Model answer (4 marks)

Calcium reacts more quickly and vigorously than iron when it is added to dilute hydrochloric acid. Both metals give off hydrogen gas, so bubbles are seen in each reaction. The difference in rate is because calcium is higher in the reactivity series than iron; it has a greater tendency to lose electrons and form Ca²⁺ ions. Iron, being lower in the series, loses electrons more slowly and so its reaction is less vigorous.

Examiner tips

  • State the rate difference first, then mention hydrogen gas, then explain with reactivity series and ion formation.
  • Use the exact phrase "reacts more quickly" and "hydrogen gas" to match the mark scheme.

Common mistakes

  • Confusing the order of the reactivity series (placing iron above calcium).
  • Failing to mention hydrogen gas or the rate difference, or using vague terms like "fast" without comparison.

Mark scheme (4 marks)

  1. Calcium reacts faster / more vigorously than iron (with dilute hydrochloric acid)
  2. Calcium is higher / more reactive than iron in the reactivity series
  3. Both reactions produce hydrogen gas (bubbles / effervescence seen in both)
  4. Reactivity is related to the tendency of the metal to form positive ions — calcium forms positive ions more readily than iron

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