Question

The formula for a hydrate of magnesium sulfate is MgSO4•xH2O. If 1 mol of anhydrous magnesium sulfate is 48.82% of the mass of 1 mol of the hydrate, what is the value of x?

Answer 1

M(MgSO₄) = 120.366 g/mol;

M(H₂O) = 18.015 g/mol;

Proportion:

120.366 g (mass of 1 mole of MgSO₄) — 48.82 %

Total mass of 1 mole of MgSO₄•xH₂O — 100 %

M(MgSO₄•xH₂O) = 246.55 g/mol;

M(MgSO₄) + M(xH₂O) = M(MgSO₄•xH₂O);

M(xH₂O) = M(MgSO₄•xH₂O) - M(MgSO₄) = 246.55 g/mol - 120.366 g/mol = 126.184 g/mol;

x = M(xH₂O)/M(H₂O) = (126.184 g/mol) / (18.015 g/mol) = 7;

Answer: 7