Colligative Properties

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solution and the pure solvent • Presence of a solute interferes with solid formation, requires more kinetic energy be withdrawn for solution to freeze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