# A bakery uses sodium hydrogencarbonate (NaHCO₃) as a raising agent in bread. A chemist analyses the composition of sodium hydrogencarbonate and states that its empirical formula is NaHCO₃. Explain what is meant by the term 'empirical formula' and describe how a chemist would determine the empirical formula of a compound from data showing the mass of each element present in a sample.

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

> Sodium hydrogencarbonate contains sodium, hydrogen, carbon and oxygen. A 16.8 g sample of sodium hydrogencarbonate contains 6.9 g of sodium, 0.2 g of hydrogen, 2.4 g of carbon and 7.2 g of oxygen.

## Mark scheme (5 marks)

1. The empirical formula is the simplest whole number ratio of atoms of each element in a compound
2. Divide the mass of each element by its relative atomic mass to find the number of moles of each element
3. Divide all mole values by the smallest mole value obtained
4. The resulting whole number ratio gives the empirical formula
5. If the ratio values are not whole numbers, multiply all values by an appropriate integer to obtain whole numbers

## 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-bakery-uses-sodium-hydrogencarbonate-nahco-d09ddb5a) · Published by Druglandscape Ltd.