Colligative Properties of Solutions

The presence of solutes affects the properties of solutions.Some of these properties are not dependant on what dissolved substance but only on how much.Colligative properties are those that depend on the concentration of solute particles but not on their identity.Colligative Properties? What the…

Vapor pressure is the pressure caused by molecules that have escaped from the liquid phase to the gaseous phase.Experiments show that the vapor pressure of a solvent containing a nonvolatile* solute is lower than the vapor pressure of the pure solvent at the same temp.This lowers the freezing point and raises the boiling point.*a substance with little tendency to become a gasVapor Pressure

Phase Diagram

Pure Solvent v. Solution

Freezing Point DepressionThe freezing point of a 1-molal solution of a nonelectrolyte solute in water is found by experiment to be 1.86°C lower than the freezing point of water.When the solution is 2-molal the freezing point is lowered by 3.72°C.In fact, for any concentration of a nonelectrolyte solute in water, the decrease in freezing point can be determined using the value of -1.86°C/m.This value is called the molal freezing-point, Δtf

Freezing-point depression can be calculated by using the following equation.Δtf= KfmKfis the freezing-point depression constant.m is the molality.Each solvent has its own characteristic molal freezing-point constant. See Table 14-2 on page 438.

What is the freezing-point depression of water in a solution of 17.1 g of sucrose, C12H22O11, and 200. g of water? What is the actual freezing point of this solution?Sample Problem 14-3

A water solution containing an unknown quantity of a nonelectrolyte solute is found to have a freezing point of -0.23°C. What is the molal concentration of the solution?Sample Problem 14-4

Page 449 Questions 19-24Assignment