Question

a 0.4 solution of KCN freezes at -0.75C. find i and the osmotic pressure at 5C. repeat the calculations for a 0.4 M solution of H2SO4, which freeze at -1.75C.

Answer 1

1)

freezing point of KCN = - 0.75 oC

delta Tf = i x Kf x m

0 - (- 0.75) = i x 1.86 x 0.4

i = 1.008

i - value = 1.01

osmatic pressure = i x M x S x T

                            = 1.01 x 0.4 x 0.0821 x 278

osmatic pressure = 9.22 atm

2)

delta Tf = i x Kf x m

1.75 = i x 1.86 x 0.4

i = 2.35

i- value = 2.35

Osmatic pressure = 2.35 x 0.4 x 0.0821 x 278

                           = 21.5 atm