The atomic weight of iron (Fe) is 55.85, and of oxygen (O) 16.
Your data states that in a sample of 100g, there will be 69.94g of Fe, and 30.06g of O
To determine how many gram atoms those number represent, we divide the mass by the atomic weight
So, Fe = 69.94 / 55.85 = 1.25, and O = 30.06 / 16 = 1.88
The ratio of Fe to O is 1.25 to 1.88
when we divide both numbers by the smallest value, we get 1.25 / 1.25 =1, and 1.88 / 1.25 = 1.5
Since we must have whole numbers, the lowest multiple will be 2, so the empirical formula is 2 to 3
Thus, the formula will be Fe2O3.
