# When copper carbonate is heated, it decomposes to form copper oxide and carbon dioxide gas. A student heats 6.2 g of copper carbonate and collects the carbon dioxide produced. After the reaction, the student finds that some solid remains in the tube. Explain why the mass of solid remaining is less than 6.2 g, and describe what the student would observe happening to the solid during heating.

> Eduqas A-Level Chemistry — 3.5 Aromatic chemistry (A-Level only) · Explain · 5 marks

> Copper carbonate (CuCO₃) decomposes on heating: CuCO₃(s) → CuO(s) + CO₂(g)

## Mark scheme (5 marks)

1. Carbon dioxide gas is released/escapes into the surroundings during the reaction
2. The law of conservation of mass states that no atoms are lost or made, so the missing mass is accounted for by the carbon dioxide gas produced
3. The solid changes colour from green (copper carbonate) to black (copper oxide)
4. The solid appears to shrink in size / the amount of solid decreases
5. The carbon dioxide produced is a gas at room temperature and pressure, so it is not included in the mass of the solid product

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