Exercise 5 | Colligative Properties of Solutions

What is the vapor pressure in Pa of an aqueous solution that has a solute mole fraction of 0.250?


Data: Vapor pressure of water = 25.756 mmHg at 25°C

1.00 mmHg = 133.3 Pa

Raoult’s Law:
 

Pwater = xwater P0water

Pwater = vapor pressure of the aqueous solution

xwater = mole fraction of water in the solution

P0water = vapor pressure of the pure water

 

xwater + xsolute = 1 ⇒ xwater = 1 - 0.250 = 0.750

Pwater = 0.750 x 25.756 = 19.3 mmHg


Pwater = 19.3 mmHg x 133.3 Pa1.00 mmHg = 2.57 x 103 Pa