Exercise 4 | Colligative Properties of Solutions

Determine the osmotic pressure at 25.0°C of a 0.20 mol.L-1 CaCl2 (aq) solution.

Osmotic pressure (in Pa):
 

Π = i R T

i = van’t Hoff i-factor = number of ions produced per formula unit

M = molarity (in mol.m-3) ⇒ 0.20 mol.L-1 = 0.20 mol.dm-3 = 0.20 x 103 mol.m-3

R = ideal gas constant = 8.314 (in J.K-1.mol-1)

T = temperature (in K) ⇒ 25.0°C = 298 K

 

CaCl2 (aq) → Ca2+ (aq) + 2 Cl- (aq)

⇒ i = 3


Π = i MRT = 3 x 0.20 x 103 x 8.314 x 298 = 1.49 x 106 Pa = 14.9 bar