Cambridge O Level Chemistry · Syllabus 5070 · Stoichiometry
Empirical formula
What is Empirical formula?
The empirical formula of a compound is the simplest whole-number ratio of the different atoms or ions present in that compound, for example CH2 for ethene, whose molecular formula is C2H4.
This definition is part of the Stoichiometry chapter in Cambridge O Level Chemistry.
Common mistakes with Empirical formula
- "The empirical formula of \(\mathrm{CO_2}\) is \(\mathrm{CO}\)." Fix \(1:2\) is already the simplest whole-number ratio, so the empirical formula of carbon dioxide is \(\mathrm{CO_2}\). Simplify only when both numbers share a factor.
Questions students ask about Empirical formula
What is the difference between a molecular formula and an empirical formula?
The molecular formula gives the number and type of atoms in one molecule of a compound, for example \(\mathrm{C_6H_{12}O_6}\) for glucose. The empirical formula gives the simplest whole-number ratio of the different atoms or ions, so for glucose it is \(\mathrm{CH_2O}\). They describe the same substance but answer different questions. Simplify only when the numbers share a common factor: the empirical formula of \(\mathrm{CO_2}\) is still \(\mathrm{CO_2}\), because 1 : 2 is already the simplest ratio.