Grade 11 · Chemistry
Empirical and molecular formulae
Why it matters
Finding the simplest ratio and then the true molecular formula.
Core20m readingPrerequisite: Percentage composition
What is the difference between empirical and molecular formula?
Short answer
An empirical formula gives the simplest whole-number ratio of atoms in a compound; a molecular formula gives the actual number of each atom in one molecule. The molecular formula is always a whole-number multiple of the empirical formula — for example, hydrogen peroxide is empirical HO but molecular H₂O₂ (twice the empirical unit).
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Frequently asked questions
- How do you find the molecular formula from the empirical formula?
- Divide the compound’s molar mass by the empirical formula mass to get a whole number, then multiply the empirical formula by it.