A powder contains FeSO4·7H2O (molar mass = 278.01 g/mol) among other components. A 2.750-g sample of the powder was dissolved in HNO3 and heated to convert all iron to Fe3 . The addition of NH3 precipitated Fe2O3·xH2O which was subsequently ignited to produce 0.455 g of Fe2O3. What was the mass of FeSO4·7H2O in the 2.750-g sample?
Supposing the original mixture contained no other source of Fe:
(0.455 g Fe2O3) / (159.6882 g Fe2O3/mol) x (2 mol Fe / 1 mol Fe2O3) x (1 mol FeSO4·7H2O / 1 mol Fe) x
(278.01 g FeSO4·7H2O/mol) = 1.58 g FeSO4·7H2O