# A water company routinely monitors its treated drinking water for traces of dissolved substances. Scientists use instrumental methods of analysis rather than traditional chemical tests to check the water quality. Explain why instrumental methods are preferred for this purpose, and describe one instrumental technique that could be used to identify the substances present in the water sample.

> Eduqas A-Level Chemistry — 2.8 Instrumental analysis · Explain · 5 marks

> Water companies are required by law to ensure drinking water is safe and free from harmful dissolved substances. Even tiny amounts of certain substances can make water unsafe to drink.

## Mark scheme (5 marks)

1. Instrumental methods are more sensitive than traditional chemical tests
2. Instrumental methods are faster/quicker than traditional chemical tests
3. Instrumental methods can analyse very small samples
4. Named instrumental technique — gas chromatography (GC) or mass spectrometry (MS) or gas chromatography–mass spectrometry (GC–MS)
5. Correct description of how the named technique works or what information it gives — e.g. gas chromatography separates the substances in the mixture / the time taken to travel through the column (retention time) identifies each substance; OR mass spectrometry identifies substances by their mass (relative molecular mass / mass-to-charge ratio)

## Key terms

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

## Related

- [Revision notes for Eduqas A-Level Chemistry](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-water-company-routinely-monitors-its-a9d459a6) · Published by Druglandscape Ltd.