1.3 Determine the empirical formula of an oxide of iron, which has 69.9% iron and 30.1% dioxygen by mass.
Given there is an oxide of iron which has iron and dioxygen by mass:
Relative moles of iron in iron oxide:
Relative moles of oxygen in iron oxide:
The simplest molar ratio of iron to oxygen:
Therefore, the empirical formula of the iron oxide is .