# A student is investigating how the mass of iron wool changes when it is heated in a sealed container. Before heating, the student records the mass of the sealed container and its contents. After heating, the student notices the iron wool has turned black and records the mass again. Explain why the mass of the sealed container and its contents remains the same before and after heating, and describe how this investigation demonstrates the law of conservation of mass.

> OCR GCSE Chemistry A: Gateway Science (J248) — C7 Practical activity skills · Explain · 4 marks

> Iron wool reacts with oxygen when heated. The reaction can be represented as: iron + oxygen → iron oxide.

## Mark scheme (4 marks)

1. No atoms are created or destroyed during a chemical reaction
2. The oxygen used in the reaction comes from inside the sealed container, so no matter enters or leaves the system
3. The total mass of reactants equals the total mass of products
4. This shows the law of conservation of mass: mass is neither created nor destroyed in a chemical reaction

## Key terms

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

## Related

- [Revision notes for OCR GCSE Chemistry A: Gateway Science (J248)](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)

---
Source: [GradeNine](https://www.gradenine.co.uk/q/a-student-is-investigating-how-the-57e1ea0b) · Published by Druglandscape Ltd.