Grade 11 · Chemistry
Percentage composition
Why it matters
Finding the mass percent of each element in a compound.
Core20m readingPrerequisite: Moles, mass, volume and particles
What is percent composition?
Short answer
Percent composition gives the percentage by mass of each element in a compound. You find it by dividing the total mass of each element in one mole of the compound by the compound’s molar mass and multiplying by 100. For example, water is about 11% hydrogen and 89% oxygen by mass. It is the first step toward finding an empirical formula.
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Frequently asked questions
- How do you calculate percent composition?
- Divide the mass of each element in one mole of the compound by the molar mass, then multiply by 100.
- Why is percent composition useful?
- It lets you compare compounds by mass and is the starting point for determining an empirical formula from experimental data.