# Describe what is meant by the term empirical formula and explain how the empirical formula of a compound may differ from its molecular formula. Use the compound ethane, C₂H₆, as an example in your answer.

> Cambridge International IGCSE Chemistry (0620) — 3.1 Formulae · Describe · 4 marks

## Mark scheme (4 marks)

1. Empirical formula is the simplest whole-number ratio of atoms of each element in a compound
2. The molecular formula shows the actual number of atoms of each element in one molecule
3. The empirical formula of ethane is CH₃
4. The molecular formula (C₂H₆) is a whole-number multiple of the empirical formula (CH₃), so they are different / the molecular formula is twice the empirical formula

## Key terms

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

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