# Copper reacts with oxygen when heated. The equation for this reaction is: 2Cu + O₂ → 2CuO. The relative atomic mass of copper is 64 and the relative atomic mass of oxygen is 16. Explain why the mass of the solid in the container increases during this reaction.

> AQA GCSE Chemistry (8462) — 4.3.2 Use of amount of substance in relation to masses of pure substances · Explain · 4 marks

> A student heats copper powder in an open crucible. After the reaction, the student notices that the mass of the solid has increased.

## Mark scheme (4 marks)

1. No atoms are lost or made during a chemical reaction (law of conservation of mass)
2. Oxygen (from the air) is a reactant that combines with / is added to the copper
3. The mass of oxygen gained is included in the mass of the product copper oxide (CuO)
4. The mass of the solid product (copper oxide) is greater than the mass of the copper alone because the mass of oxygen has been added

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