# A scientist uses mass spectrometry and infrared spectroscopy to analyse an unknown organic compound. Explain how these two techniques provide different types of information about the compound, and state what specific information each technique gives the scientist.

> WJEC A-Level Chemistry (Wales) — 3.7 Spectroscopy and chromatography · Explain · 5 marks

> Mass spectrometry can be used to find the relative formula mass of a compound. Infrared spectroscopy can be used to identify the functional groups present in a compound.

## Mark scheme (5 marks)

1. Mass spectrometry gives the relative formula mass (Mr) of the compound
2. The molecular ion peak (M+) in the mass spectrum corresponds to the relative formula mass of the whole molecule
3. Infrared spectroscopy identifies the functional groups present in the compound
4. Different functional groups absorb infrared radiation at different (characteristic) frequencies/wavelengths
5. Together the two techniques allow the scientist to determine both the size of the molecule (Mr) and its functional groups, helping to identify the compound fully

## Key terms

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

## Related

- [Revision notes for WJEC A-Level 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/a-scientist-uses-mass-spectrometry-and-e3901f30) · Published by Druglandscape Ltd.