Chemistry
Basic

Percent Composition

Mass percentage of an element in a compound.

Formula

%=mass of elementmolar mass×100\% = \frac{\text{mass of element}}{\text{molar mass}} \times 100

Variables

massElement mass
molar massCompound mass

Example

In water (18 g/mol), oxygen is 16/18 × 100% ≈ 89% by mass.

Did You Know?

Percent composition reveals what fraction of a compound's mass each element contributes.

compositionstoichiometry