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

Sure, here are the steps to determine the empirical formula:

1. Assume that you have 100g of the substance. This means you have 69.9g of iron (Fe) and 30.1g of oxygen (O).

2. Convert the mass of each element to moles. The atomic mass of Fe is about 55.85g/mol and the atomic mass of O is about 16.00g/mol. So, you have (69.9g ÷ 55.85g/mol) = 1.25 mol of Fe and (30.1g ÷ 16.00g/mol) = 1.88 mol of O.

3. Write the ratio of the moles. This is Fe1.25O1.88.

4. To find the empirical formula, we need to divide by the smallest number of moles, which is 1.25. So, the ratio becomes Fe1O1.5.

5. Since we can't have half of an oxygen atom in the formula, we multiply through by 2 to get the empirical formula Fe2O3.

So, the empirical formula of the oxide of iron in the problem is Fe2O3.