Question

A solution of an inorganic compound was prepared by dissolving 6.8 g in 100 g of water. Calculate the osmotic pressure of this solution 298 K when boiling point of this solution is 100.11°C. Given K_b for water = 0.52 Km^-1 and R = 0.082 L atm K^-1 mol^-1.  

Answer 1

Molecular mass can be calculated from Bpt data as 

M_B = K_b x W_A x 1000 

∆Tb x WA 

WB = 6.8 g WA = 100 g 

T_b = 100.11 K_b = 0.52 K kgmol^-1 

M_B = 0.52 K kgmol^-1 x 6.8 g x 1000 

= 0.11 K x 100 kg 

= 321.45 gmol^-1 

V n = 6.8

V = 100 g = 0.1 

R = 0.082 L atm mol^-1 K^-1  

T = 298 K

∏ = 6.8 mol X 0.082 L atm mol^-1 K^-1 X 298 K 

= 321.95 X 0.1 L = 5.17 atm