# A student heats copper carbonate powder in a crucible. The solid turns black and a gas is released. After heating, the student notices that the mass of the crucible contents has decreased. Explain why the total mass of solid in the crucible has decreased, even though the law of conservation of mass applies to this reaction.

> Eduqas GCSE Chemistry — C3 Quantitative chemistry · Explain · 4 marks

## Mark scheme (4 marks)

1. The copper carbonate decomposes / breaks down into copper oxide and carbon dioxide
2. Carbon dioxide is a gas and escapes / is released into the surroundings
3. The mass of solid decreases because the mass of carbon dioxide that escaped is no longer being measured / weighed
4. The law of conservation of mass still holds because the total mass of all products (solid copper oxide + carbon dioxide gas) equals the mass of the original copper carbonate

## Key terms

- [law of conservation of mass](https://www.gradenine.co.uk/glossary/law-of-conservation-of-mass)

## Related

- [Revision notes for Eduqas GCSE Chemistry](https://www.gradenine.co.uk/learn)
- [How to answer "Explain" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
- [Practice this with AI marking (free)](https://www.gradenine.co.uk/start)

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Source: [GradeNine](https://www.gradenine.co.uk/q/a-student-heats-copper-carbonate-powder-3f383a9b) · Published by Druglandscape Ltd.