# Calcium carbonate, calcium oxide and calcium hydroxide are all useful materials obtained from limestone. Explain why calcium hydroxide solution is used to test for carbon dioxide gas.

> WJEC GCSE Chemistry (Wales) — 1.6 Limestone · Explain · 4 marks

> Calcium hydroxide dissolves slightly in water to form limewater. When carbon dioxide is bubbled through limewater, a change is observed.

## Mark scheme (4 marks)

1. Calcium hydroxide reacts with carbon dioxide
2. Calcium carbonate is produced / formed
3. Calcium carbonate is insoluble (in water)
4. This causes the limewater to turn milky / cloudy

## Key terms

- [calcium hydroxide](https://www.gradenine.co.uk/glossary/calcium-hydroxide)
- [carbon dioxide](https://www.gradenine.co.uk/glossary/carbon-dioxide)
- [calcium carbonate](https://www.gradenine.co.uk/glossary/calcium-carbonate)

## Related

- [Revision notes for WJEC GCSE Chemistry (Wales)](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/calcium-carbonate-calcium-oxide-and-calcium-8aeb1fa0) · Published by Druglandscape Ltd.