A student adds copper carbonate powder to dilute sulfuric acid. The mixture fizzes and the copper carbonate gradually disappears. Explain what type of chemical change has taken place and give two pieces of evidence from the description that support this.

WJEC GCSE Chemistry (Wales) — 2.2 Acids, bases and salts · Explain · 4 marks · View as Markdown

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

Copper carbonate is a green powder that is insoluble in water. When added to dilute sulfuric acid, the mixture fizzes and the green powder gradually disappears, leaving a blue solution.

Model answer (4 marks)

The reaction is a chemical change.

A chemical change produces new substances with a different chemical composition to the reactants.

Evidence 1: fizzing shows a gas (CO₂) is released.

Evidence 2: the green solid disappears and a blue solution appears, indicating a new substance has formed.

Examiner tips

  • Use the word ‘chemical change’ first; then explain composition change; list each evidence separately; keep sentences short and factual.

Common mistakes

  • Writing ‘physical change’ instead of ‘chemical change’; omitting the colour change evidence; not stating that the products differ chemically from the reactants.

Mark scheme (4 marks)

  1. Identifies the change as a chemical change
  2. States that a chemical change produces products with a different chemical composition to the reactants
  3. First piece of evidence: a gas is produced (fizzing / bubbling)
  4. Second piece of evidence: a new substance with a different colour/appearance is formed (blue solution / green solid disappears)

Key terms in this question

chemical change

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