at 25 C, 34.5 g K2SO4 is dissolved in 750 mL water. the volume of the solution is 749 mL. what is the molarity and molality?

Answer 1

Molality = moles solute per kg of solvent

Molarity = moles solute per liter of solution

Finding molality:

moles solute = 34.5 g K2SO4 x 1 mol K2SO4 / 174 g = 0.198 mols K2SO4

kg of solvent = 750 mls H2O x 0.995 g / ml = 746.3 g (using density of H2O = 0.995 g/ml @ 25ºC) = 0.764 kg

molality = 0.198 mols / 0.764 kg = 0.259 m

Finding molarity

moles solute = 0.198 mols (see above calculation)

liters of solution = 749 mls x 1 L / 1000 mls = 0.749 L

molarity = 0.198 mols / 0.749 L = 0.264 M