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 21 g of urea (a nonvolatile, non-electrolyte, MW = 60.0g/mol)in 75 g of water.
A)2.9
B)0.35
C)22
D)27
E)0.92

Question

Quizplus · Accepted Answer

The vapor pressure of the solution can be found using Raoult's Law: P_solution = X_solvent * P_pure solvent. First, calculate the moles of urea (21 g / 60 g/mol = 0.35 mol) and water (75 g / 18 g/mol = 4.17 mol). The mole fraction of water is 4.17 / (4.17 + 0.35) = 0.923. Thus, the vapor pressure of the solution is 0.923 * 23.8 torr = 22 torr.

The Vapor Pressure of Pure Water at 25°C Is 23