Calculate the molality of a solution of copper(ii) sulfate, cuso4, where 11.25 g of the crystals have been dissolved in 325 g of water.

            Molality  =  0.216 mol.Kg⁻¹

Solution:
              Molality is the amount of solute dissolved per Kg of solvent. It is expressed as,

                          Molality  =  Moles / Kg of Solvent    (1)

Data Given;
                   Mass  =  11.25 g

                   Mass of Solvent  =  325 g  =  0.325 Kg

First calculate Moles for given mass as,

                    Moles  =  Mass / M.mass

                    Moles  =  11.25 g / 159.6 g.mol⁻¹

                    Moles  =  0.0704 mol

Now, putting value of Moles and Volume in eq. 1,

                         Molality  =  0.0704 mol ÷ 0.325 Kg

                         Molality  =  0.216 mol.Kg⁻¹

They are all solids.