1. Colligative Properties
Chapter 16.3

2. Learning Objectives Know the definition of colligative properties
Know what the important colligative properties are
Be 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 are
Vapor pressure lowering
Boiling point elevation
Freezing point depression
Osmotic 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.

5. Vapor Pressure Lowering

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 solvent
Presence of a solute interferes with solid formation, requires more kinetic energy be withdrawn for solution to freeze

9. Freezing Point Depression

10. Ionic substances have a greater affect than molecular solutes
How is water affected?
Boiling point of water increases 0.512C per mol of solute particles in 1000 g water
Freezing point of water decreases 1.86C per mol of solute particles in 1000 g water
Ionic substances have a greater affect than molecular solutes

11. Why Ionic Better Than Covalent?

12. Osmotic Pressure

13. Osmotic Pressure