The vapor pressure of pure water at 25 °C is 23.8 torr. Determine the vapor pressure (torr)of water at 25 °C above a solution prepared by dissolving 25 g of urea (a nonvolatile, non-electrolyte, MW = 60.0 g/mol)in 75 g of water.
A)2.9
B)0.42
C)22
D)27
E)0.91

Question

Quizplus · Accepted Answer

The vapor pressure of the solution is calculated using Raoult's Law. First, calculate the mole fraction of water in the solution. Moles of urea = 25 g / 60 g/mol = 0.417 mol. Moles of water = 75 g / 18 g/mol = 4.167 mol. Mole fraction of water = 4.167 / (4.167 + 0.417) = 0.909. Vapor pressure of solution = 0.909 * 23.8 torr = 21.6 torr, which is closest to 22 torr.

The Vapor Pressure of Pure Water at 25 °C Is