1. Colligative Properties of Solutions Section 16.3

2. OBJECTIVES 16.3.1. Identify three colligative properties of solutions. 16.3.2. Explain why the vapor pressure, freezing point and boiling point of a solution different from those properties of the pure solvent

3. Vapor Pressure Lowering The adjective colligative comes from the Latin word colligare, meaning to tie. Colligative property: a property that depends only upon the number of solute particles, and not upon their identity

4. Vapor Pressure Lowering Important colligative Properties of solutions 1. Vapor pressure lowering 2. Boiling point elevation 3. Freezing point depression

5. VAPOR PRESSURE LOWERING Recall that vapor pressure is pressure exerted by a vapor that is in equilibrium with its liquid in a closed system When glucose or salt is dissolved in a solvent, the vapor pressure of the solution is lower than the vapor pressure of the pure solvent.

6. Vapor Pressure Lowering

7. Ionic solutes that dissociate, such as NaCl and CaCl2 have greater effects on the vapor pressure than does a nondissociating solute, such as glucose. Figure The decrease in a solution’s vapor pressure is proportional to the number of particles in the solute mixed in the solution.

8. Freezing Point Depression When substances freeze, the particles of the solid take on an orderly pattern. The presence of a solute in this water disrupts the formation of this pattern. Freezing point depression: the difference in temperature between the freezing point of a solution and the freezing point of the pure solvent

9. Freezing Point Depression The magnitude of freezing-point depression is proportional to the number of solute particles dissolved in the solvent and does not depend upon their identity EX: Putting salt on an icy ground

10. Boiling Point Elevation Boiling Point: temperature at which the vapor pressure of the liquid phase equals the atmospheric pressure. The boiling point of the solution is higher than the boiling point of pure solvent.

11. Boiling Point Elevation Boiling Point Elevation: the difference in temperature between the boiling point of a solution and the boiling point of a pure solvent The magnitude of the boiling point elevation is proportional to the number of solute particles dissolved in the solvent.

12. TO DO Classwork: Pg 23 #24-28 ALL HW: Pg 25 #56-60 ALL