A hematite sample contains 34.97 g of iron and 15.03 g of oxygen. What is its empirical formula, given Fe = 55.85 and O = 16.00 g/mol?

1. Convert iron to moles: 34.97 g / 55.85 g/mol = 0.6261 mol Fe. 2. Convert oxygen to moles: 15.03 g / 16.00 g/mol = 0.9394 mol O. 3. Divide both by the smaller amount, 0.6261 mol. 4. Iron gives 0.6261 / 0.6261 = 1.000 and oxygen gives 0.9394 / 0.6261 = 1.500. 5. The tentative formula is FeO1.5, which still carries a decimal subscript. 6. Multiplying both subscripts by 2 clears it and gives Fe2O3. 7. Rounding 1.500 down to 1 would give FeO, and rounding up would give FeO2, which are the two traps. _Source: OpenStax Chemistry (CC BY 4.0), Ch 3 "Composition of Substances and Solutions", section 3.2 Determining Empirical and Molecular Formulas_