posted by San .
when 1.40 g of hydrated magnesium salfate is heated to constant mass, 0.68 g of the anhydrous salt remains. find the formula for the hydrated magnesium sulfate.
MgSO4*xH2O ==> MgSO4 + xH2O
grams water = 1.40 - 0.68 = ??
mols H2O = ??/molar mass H2O.
mols MgSO4 = 0.68/molar mass MgSO4.
Then find ratio of mol H2O per 1 mol MgSO4. That will be x. Post your work if you get stuck.