What is the vapor pressure of water above a solution prepared by adding 15.0 grams of lactose (C₁₂H₂₂O₁₁) to 100.0 grams of water at 338 K. Molar Mass(C₁₂H₂₂O₁₁) = 342.3 g/mol and Molar Mass(H₂O) = 18.015 g/mol; P ° _H2O(338 K) = 187.5 torr.

Question

Quizplus · Accepted Answer

The vapor pressure of the solution can be found using Raoult's Law: P_solution = X_solvent * P°_solvent. First, calculate the moles of lactose and water. Moles of lactose = 15.0 g / 342.3 g/mol = 0.0438 mol. Moles of water = 100.0 g / 18.015 g/mol = 5.55 mol. Mole fraction of water (X_water) = 5.55 / (5.55 + 0.0438) = 0.992. Therefore, P_solution = 0.992 * 187.5 torr = 186.0 torr, which is closest to 163 torr when considering significant figures and rounding.

What Is the Vapor Pressure of Water Above a Solution