# A student reacts zinc with dilute hydrochloric acid in an open conical flask placed on a balance. The student notices that the reading on the balance decreases as the reaction proceeds. Explain why the mass appears to decrease, even though mass is conserved during the reaction.

> 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. Hydrogen gas is produced as a product of the reaction
2. The gas escapes / is released into the atmosphere (from the open flask)
3. The mass of the escaping gas is not measured / not included in the balance reading
4. The law of conservation of mass is still obeyed because no atoms are lost or made during the reaction

## Key terms

- [balance](https://www.gradenine.co.uk/glossary/balance)

## 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)
- [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-reacts-zinc-with-dilute-d0df18a8) · Published by Druglandscape Ltd.