# Aluminium sulfate has the formula Al₂(SO₄)₃. State the number of atoms of each element present in one formula unit of aluminium sulfate, and use this information to explain what the formula tells us about the empirical formula of aluminium sulfate.

> Pearson Edexcel International GCSE Chemistry (4CH1) — 1.5 Chemical formulae, equations and calculations · State · 4 marks

> Aluminium sulfate, Al₂(SO₄)₃, is used in water treatment and in the paper industry.

## Mark scheme (4 marks)

1. 2 aluminium atoms identified
2. 3 sulfur atoms identified
3. 12 oxygen atoms identified
4. Al₂(SO₄)₃ is already the empirical formula because the ratio 2:3:12 cannot be simplified to smaller whole numbers / the numbers 2, 3 and 12 share no common factor greater than 1 that reduces all three simultaneously

## Key terms

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

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Source: [GradeNine](https://www.gradenine.co.uk/q/aluminium-sulfate-has-the-formula-al-so-b27c99eb) · Published by Druglandscape Ltd.