A chemist heats 100.0 g of FeSO4 x 7H2O in a crucible to drive off the water. If all the water is driven off, what is the mass of the remaining salt?

FeSO₄*7H₂O (s) = FeSO₄ (s) + 7H₂O (g)

M (FeSO₄*7H₂O) = 278.0 g/mol

M (FeSO₄) = 151.9 g/mol

m (FeSO₄*7H₂O) / M (FeSO₄*7H₂O) = m (FeSO₄) / M (FeSO₄)

m (FeSO₄) = M (FeSO₄) m (FeSO₄*7H₂O) / M (FeSO₄*7H₂O)

m (FeSO₄) = 151.9*100.0/278.0=54.6 g

m (FeSO₄) = 54.6 g