Question

At 25 ∘C, the osmotic pressure of a solution of the salt XY is 60.8 torr . What is the solubility product of XY at 25 ∘C?

Answer 1

T = 25 + 273 = 298K

osmotic pressure P = 60.8 torr = 60.8 /760 = 0.08 atm

S = 0.0821 L-atm / mol K

for XY vanthoff factor i = 2

P = i M S T

0.08 = 2 x M x 0.0821 x 298

M = 1.64 x 10^-3 molar

solubility = 1.64 x 10^-3 M

XY -------------------> X+ + Y-

                                S        S

Ksp = [X+][Y-]

Ksp = S^2

Ksp = (1.64 x10^-3)^2

Ksp = 2.67 x 10^-6

solubility product = 2.67 x 10^-6