Question

A solution is prepared by dissolving 61.5 mL of methanol in 115.0 mL of water at 25 ∘C . The final volume of the solution is 173.4 mL . The densities of methanol and water at this temperature are 0.782 g/mL and 1.00 g/mL , respectively. For this solution, calculate each of the following. [Molarity, molality, mass percent]

Answer 1

mass of methanol = volume * density

                            = 61.5*0.782 = 48.093 gm

mass of water     = 115*1 = 115gm

molarity = weight of solute*1000/gram molar mass*volume of solution in ml

              = 48.093*1000/32*173.4

              = 48093/5548.8 = 8.66M

molality = weight of solute*1000/gram molar mass*Weight of solvent in gm

            = 48.093*1000/32*115

            = 48093/3680 = 13.068m

mass % =