Determine the empirical formula of an oxide of iron which has 69.9% iron and 30.1 % dioxygen by mass.

• Empirical formula of a compound may be defined as the formula which gives the simplest whole number ratio of the atoms of various elements present in one molecule of the compound.

Step 1: Given that, the iron oxide has 69.9% iron and 30.1% dioxygen by mass.

Thus, 100 g of iron oxide contains 69.9 g iron and 30.1 g dioxygen.

The number of moles of iron present in 100 g of iron oxide are $\frac{69.9}{55.8}=1.25$

The number of moles of dioxygen present in 100 g of iron oxide are $\frac{30.1}{32}=0.94$

Step 2:

The ratio of the number of oxygen atoms to the number of iron atoms present in one formula unit of iron oxide is $\frac{2\times 0.94}{1.25}=1.5:1=3:2$

Hence, the formula of the iron oxide is ${Fe}_2{O}_3$