# A forensic scientist has found an unknown white powder at a crime scene. She uses two instrumental methods to identify the substance: mass spectrometry and infrared spectroscopy. Describe what information each technique provides and explain why instrumental methods are preferred over traditional chemical tests for forensic analysis.

> WJEC A-Level Chemistry (Wales) — 2.8 Instrumental analysis · Describe and Explain · 5 marks

## Mark scheme (5 marks)

1. Mass spectrometry gives the relative molecular mass (or molecular mass) of the substance
2. Infrared spectroscopy identifies the functional groups or bonds present in the substance
3. Instrumental methods are more sensitive / can detect very small amounts (trace amounts) of a substance
4. Instrumental methods are more accurate / give more reliable results than traditional chemical tests
5. Instrumental methods are faster / give results more quickly than traditional chemical tests

## Key terms

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

## Related

- [Revision notes for WJEC A-Level Chemistry (Wales)](https://www.gradenine.co.uk/learn)
- [How to answer "Describe and 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-forensic-scientist-has-found-an-ed076eb2) · Published by Druglandscape Ltd.