3.2 Percentage Composition

The relative amounts of each element in a compound are expressed as the percentage composition. For example, the percentage composition by mass in MgO is as follows, To determine the percentage composition of a known compound,

a) Calculate the molar mass of the compound b) Calculate the percentage of each element in one mole of the compound. This is done by dividing the mass of each element in one mole of the compound by the molar mass multiplied by 100.

1. Water ${\mathrm{H}}_2\mathrm{O}$$\mathrm{H}_{2}\mathrm{O}$

Molar mass of $\mathrm{M}\mathrm{g}\mathrm{O}=24+16$$\mathrm{MgO} = 24 + 16$