summary of the procedure for making MgSO4 from the MgSO4.xH2O by heating it. Plan to do this for all future labs also. The difference in masses of product and reactant will be the mass of water lost. Divide by 18.0 g/mol to get moles of water. You can calculate the moles of MgSO4 from its mass, the mass of product. Dividing the moles of water by the moles of MgSO4 gives x, an integer.