Calculate (a) molality (b) molarity and (c) mole fraction of KI if the density of 20% (mass/mass)aq.

Calculate (a) molality (b) molarity and (c) mole fraction of KI if the density of 20% (mass/mass) aqueous KI is 1.202 g mL-1

Solution -

20% KI (mass/mass) means 20 gms of KI in 100 gms of solution

Therefore, Mass of solvent = 100 - 20 = 80 gms

Therefore, Molality = (w x 1000)/(mm x W) = (20 x 1000)/(166 x 80) = 1.5 moles/kg

Volume of solution = mass/density = 100/1.202 = 83.19

Molarity = (w x 1000)/(mm x V) = (20 x 1000)/(166 x 83.19) = 1.44 moles/L

Mole fraction of KI = Moles of KI/Total moles = (20/166) / ((20/166)+(80/18)) = 0.026