Mole Concept

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A sample of an oxide of iron contains 7.0 g of iron and 3.0 g of oxygen. If the atomic masses of Fe and O are 56 and 16 respectively, the empirical formula of the oxide is:

RankGuru · Accepted Answer

1. **Convert Masses to Moles**:
   - Moles of Fe = $\frac{7.0}{56} = 0.125$ mol.
   - Moles of O = $\frac{3.0}{16} = 0.1875$ mol.
2. **Find the Simplest Mole Ratio**: Divide each by the smallest value (0.125):
   - Fe: $\frac{0.125}{0.125} = 1$
   - O: $\frac{0.1875}{0.125} = 1.5$
3. **Convert to Whole Numbers**: Multiply both by 2:
   - Fe: $1 	imes 2 = 2$
   - O: $1.5 	imes 2 = 3$
4. **Write the Empirical Formula**: $Fe_2O_3$.
5. **Verification**: In $Fe_2O_3$, the mass ratio is $(2 	imes 56):(3 	imes 16) = 112:48 = 7:3$, which matches the given data exactly.

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