Does the water of hydration get counted in the molar mass of a hydrated salt?
Yes, in fact a common laboratory exercise is to observe the change in mass before and after heating a sample of a hydrated salt and relate this change to the number of moles of “water of hydration”. For example, hydrated copper(II) sulfate has the formula, CuSO4 x5(H2O) meaning the hydrated salt has five water molecules per copper sulfate unit in the crystal structure and the molar mass would be 249.61 g/mol. Anhydrous CuSO4 has a molar mass of 159.61 g/mol which is the molar mass of the hydrated minus 5x the molar mass of H2O.
