Mole Fraction

Question

A solution of Sodium Chloride in water has a vapor pressure of 26.8 torr at 30C. What is the mole fraction of NaCl in this solution? (Vapor Pressure of pure water is 31.824 torr at 30C)

Answer 1

Dalton's Law

 

Vapor pressure = mole fraction x original vapor pressure

mole fraction = vapor pressure/original vapor pressure = 26.8 torr/31.824 torr = 0.842 

This is the mole fraction of water.

mole fraction NaCl = 1.000 - 0.842 = 0.158