Sometimes solutions are prepared by weighing solutes that contain some weakly bonded solvent. Copper sulfate pentahydrate, CuSO₄•5H₂O, is a good example. The 'trick' when using these solutes is to remember that the mass measured includes some solvent. Therefore, when weighing, the mass of the hydrate is used -- and not just the formula mass of the anhydrous (dry, not solvated) solute.

Example:

Find the mass in grams of CuSO₄•5H₂O required to make 1500 mL of 0.20 M solution.

Mass CuSO₄•5H₂O = 1500 mL x 1 L/1000 mL x 0.20 mol/L x 249.686 g/mol = 74.9058 g CuSO₄•5H₂O. To the correct number of significant figures, 75 g.