Example 1 - Empirical Formula

Determine the empirical formula of a compound which has a percentage of composition Mg: 20.2%, S: 26.6%, O: 53.2%. [Relative atomic mass: Mg = 24; S = 32; O = 16]

Answer
Element
Mg
S
O
Percentage
20.2%
26.6%
53.2%
Mass in 100g
20.2g
26.6g
53.2g
Number of mole
20.2 24 =0.8417mol
26.6 32 =0.8313mol
53.2 16 =3.325mol
Simple ratio
0.8417 0.8313 =1
0.8313 0.8313 =1
3.325 0.8313 =4

The empirical formula of the compound is MgSO4