2 Learning Objectives Know the definition of colligative properties Know what the important colligative properties areBe able to think through logically the lowering or raising of these properties due to colligative processes
3 Colligative Properties: Definition Colligative properties depend only on the number of solute particles present (concentration), not on the identity of the solute particles.Among colligative properties areVapor pressure loweringBoiling point elevationFreezing point depressionOsmotic pressure (book does not cover)
4 Vapor Pressure Lowering As solute molecules are added to a solution, the solvent become less volatile ( = decreased vapor pressure).Solute-solvent interactions contribute to this effect. Shells of water of solvation reduce the availability of solvent molecules for vaporization.
6 Boiling Point Elevation Adding a solute, reduces vapor pressure, more energy is needed to make the solutions boil, raising the boiling point.Boiling point elevation = BP of the solution - BP of the solvent.Directly proportional to the number of solute molecules.
8 What is freezing point depression? Freezing point depression is the temperature difference between the freezing point of a solution and the pure solventPresence of a solute interferes with solid formation, requires more kinetic energy be withdrawn for solution to freeze
10 Ionic substances have a greater affect than molecular solutes How is water affected?Boiling point of water increases 0.512C per mol of solute particles in 1000 g waterFreezing point of water decreases 1.86C per mol of solute particles in 1000 g waterIonic substances have a greater affect than molecular solutes