Suppose you had a sample of MgSO4.7H2O that weighed 61.62g before heating an 30.1 after heating.
loss in weight is 61.62-30.1 = 31.52
30.1 is the mass H2O lost.
30.1 is the mass MgSO4 without the water.
molar mass MgSO4 = 120.37
molar mass H2O = 18
mols = g/molar mass
mols MgSO4 = 30.1/120.27 = 0.25
mols H2O = 31.52/18 = 1.75
So the ratio is 0.25 mol MgSO4 to 1.75 mols H2O. You want whole numbers to fit here. The way you do that is to divide both numbers by the smaller of the two; i.e.
mols MgSO4 = 0.25/0.25 = 1
mols H2O = 1.75/0.25 = 7
So the empirical formula is MgSO4.7H2O
how do you determine the number of waters of hydration per formula unit? the general formula
1 answer
1 answer