# Calcium hydroxide solution is used to test for carbon dioxide gas. Explain what is observed when carbon dioxide is bubbled through calcium hydroxide solution, and describe what happens if excess carbon dioxide continues to be passed through the same solution.

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

## Mark scheme (4 marks)

1. The calcium hydroxide solution turns milky/cloudy/white precipitate forms
2. Because calcium carbonate is produced/formed
3. When excess carbon dioxide is added, the solution clears/goes clear again
4. Because calcium carbonate reacts with water and excess carbon dioxide to form calcium hydrogencarbonate, which is soluble

## Key terms

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

## 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-hydroxide-solution-is-used-to-081866a0) · Published by Druglandscape Ltd.