# A student burns copper in air inside an open crucible. After the reaction, the student notices that the mass of the crucible and its contents has increased. Explain why the mass increases, and explain why the total mass of all substances involved has not changed.

> AQA GCSE Chemistry (8462) — 4.3.1 Chemical measurements, conservation of mass and the quantitative interpretation of chemical equations · Explain · 4 marks

## Mark scheme (4 marks)

1. Copper reacts with oxygen (from the air)
2. Oxygen is a reactant / has mass that is added to the copper, so the product (copper oxide) is heavier than the copper alone
3. No atoms are created or destroyed during the reaction (law of conservation of mass)
4. The total mass of reactants (copper + oxygen) equals the total mass of products (copper oxide), so overall mass is conserved

## Related

- [Revision notes for AQA GCSE Chemistry (8462)](https://www.gradenine.co.uk/learn)
- [How to answer "Explain" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
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