Describe what happens when calcium carbonate reacts with dilute hydrochloric acid. Include the name of the salt produced and the observations a student would make during the reaction.

WJEC GCSE Chemistry (Wales) — 1.6 Limestone · 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 carbonate reacts with dilute hydrochloric acid to give calcium chloride, water and carbon dioxide:

CaCO₃(s) + 2 HCl(aq) → CaCl₂(aq) + H₂O(l) + CO₂(g)

The solid calcium carbonate dissolves and the solution becomes clear. Carbon dioxide is released as bubbles, giving a vigorous effervescence. The calcium chloride remains in solution as a clear, colourless salt.

Examiner tips

  • Write the balanced equation to show the salt and gas formed.
  • Mention the solid disappearing and the bubbling effervescence.
  • Use the correct UK spelling (colourless, colour).
  • Include the reaction conditions (dilute HCl).

Common mistakes

  • Forgetting to state the gas produced (CO₂).
  • Using the wrong salt name (e.g. calcium hydroxide).
  • Not describing the disappearance of the solid or the bubbling.

Mark scheme (4 marks)

  1. Calcium carbonate reacts with dilute hydrochloric acid
  2. Calcium chloride is the salt produced
  3. Carbon dioxide gas is produced / effervescence / bubbling is observed
  4. The solid calcium carbonate disappears / dissolves / the solid gets smaller

Key terms in this question

calcium carbonate

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