# A pharmaceutical company is checking the purity of a newly synthesised compound. The compound contains only nitrogen and oxygen. A sample of the compound is found to contain 1.4 g of nitrogen and 3.2 g of oxygen. Use this information to determine the empirical formula of the compound. Show your reasoning clearly.

> OCR A-Level Chemistry A (H432) — 2.2 Amount of substance · Explain · 5 marks

> Nitrogen has a relative atomic mass of 14. Oxygen has a relative atomic mass of 16.

## Mark scheme (5 marks)

1. Divide mass of nitrogen by its relative atomic mass: 1.4 ÷ 14 = 0.1 (moles of nitrogen)
2. Divide mass of oxygen by its relative atomic mass: 3.2 ÷ 16 = 0.2 (moles of oxygen)
3. Divide both values by the smallest (0.1) to find the simplest ratio: N = 0.1 ÷ 0.1 = 1, O = 0.2 ÷ 0.1 = 2
4. States the empirical formula as NO₂
5. Correctly describes the empirical formula as the simplest whole number ratio of atoms of each element in the compound

## Key terms

- [empirical formula](https://www.gradenine.co.uk/glossary/empirical-formula)

## Related

- [Revision notes for OCR A-Level Chemistry A (H432)](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-pharmaceutical-company-is-checking-the-90d7a3ff) · Published by Druglandscape Ltd.