What was the mass of FeSO4⋅7H2O in the 3.025 g sample?

Question

A powder contains FeSO4⋅7H2O (molar mass=278.01 g/mol), among other components. A 3.025 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 0.311 g Fe2O3.

What was the mass of FeSO4⋅7H2O in the 3.025 g sample?

mass of FeSO4⋅7H2O:

Answer 1

0.311 g / 159.69 g/mol = 0.0019475 mol of Fe2CO3

0.0019475 mol of Fe2CO3 x (1 mol Fe / 2 mol Fe2CO3) = 0.00097376 mol of Fe

So, there was 0.00097376 mol of FeSO4 in the sample.

0.00097376 mol of FeSO4-7H2O x 169.923 g/mol = 0.165 g of FeSO4-7H2O