What is the empirical formula of a compound that is composed of 72.4% Fe and 27.6% O by mass?

• A. Fe2O3
• B. FeO2
• C. Fe3O4
• D. FeO

Answer: (A)

Verified step by step guidance

1. Step 1: Assume you have 100 grams of the compound, so the mass of Fe is 72.4 grams and the mass of O is 27.6 grams.
2. Step 2: Convert the masses to moles by dividing each by their respective molar masses: for Fe, use 55.85 g/mol, and for O, use 16.00 g/mol. Calculate moles of Fe as \(\frac{72.4}{55.85}\) and moles of O as \(\frac{27.6}{16.00}\).
3. Step 3: Determine the simplest mole ratio by dividing both mole values by the smaller number of moles obtained in Step 2.
4. Step 4: If the mole ratios are not whole numbers, multiply both ratios by the smallest integer that converts them into whole numbers.
5. Step 5: Write the empirical formula using the whole number mole ratios as subscripts for Fe and O.