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

Given:

Percentage of Iron in the oxide = 69.9%

Percentage of oxygen in the oxide = 30.1%

To determine the empirical formula of iron oxide, we need to find the simplest whole number ratio.

Therefore, the empirical formula for iron oxide is Fe₂O₃.