The vapor pressure of an aqueous solution is found to be 24.9 mm Hg at 25 $\circ$ C. What is the mole fraction of solute in this solution? The vapor pressure of water is 25.756 mm Hg at 25 $\circ$ C.
A)0.967
B)0.0332
C)1.03
D)0.0344
E)0.976

Question

Quizplus · Accepted Answer

The mole fraction of the solute in the solution can be calculated using Raoult's law, which states that the vapor pressure of a solution is equal to the mole fraction of the solvent times the vapor pressure of the pure solvent. First, calculate the mole fraction of the solvent (water) by dividing the vapor pressure of the solution by the vapor pressure of pure water: $ \frac{24.9 \, \text{mm Hg}}{25.756 \, \text{mm Hg}} = 0.9668 $. The mole fraction of the solute is then $1 - 0.9668 = 0.0332$, since the total mole fraction in a solution must equal 1.

The Vapor Pressure of an Aqueous Solution Is Found to Be