# A student tests two solutions, X and Y, using Universal Indicator. Solution X gives a red colour and solution Y gives a purple colour. The student then adds an excess of sodium hydroxide solution to solution X and re-tests the resulting mixture with Universal Indicator, which now gives a green colour. Explain what these observations tell us about solutions X and Y, and explain what has happened chemically when sodium hydroxide was added to solution X.

> WJEC GCSE Chemistry (Wales) — 2.2 Acids, bases and salts · Explain · 4 marks

## Mark scheme (4 marks)

1. Solution X is acidic / is an acid
2. Solution Y is alkaline / is a base / has a pH above 7
3. The sodium hydroxide neutralised the acid in solution X
4. The green colour shows the resulting mixture is neutral / has a pH of 7, so a salt and water were formed

## Key terms

- [Universal Indicator](https://www.gradenine.co.uk/glossary/universal-indicator)

## 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)

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Source: [GradeNine](https://www.gradenine.co.uk/q/a-student-tests-two-solutions-x-4a3e924a) · Published by Druglandscape Ltd.