Colligative Properties

1. Colligative Properties How are solutions different from pure liquids? When you add a solute to a liquid the Freezing point , Boiling point, and Vapor Pressure of the solution change

2. Colligative Properties Water: The freezing point of pure water is 0°C. The normal boiling point of water is 100°C. But if you make a solution using water as the solvent, the freezing point of that solution will not be 0°C nor will the boiling point be 100°C. A SALT WATER SOLUTION: The freezing point will be lower than 0°C, boiling point will be higher than 100°C, & the vapor pressure will decrease.

3. Colligative Properties So… 1. Freezing point depression 2. Boiling point elevation 3. Vapor pressure lowering

5. Vapor Pressure Lowering The pressure over a liquid or solution that results when molecules escape the liquid and enter the gaseous phase. • In order for a molecule in the liquid phase to enter the gaseous phase, the molecule must be at the surface of the liquid and have enough kinetic energy to break the surface.  The addition of a nonvolatile hinders this situation in two ways: • The solute particles occupy space at the surface. • The solute particles introduce a new set of attractive forces with the solvent molecules.

6. The more dissolved solute the greater the changes. • Ex: the more salt you add to salt water the higher the Boiling Point, the lower the vapor pressure and freezing point • Which will have a higher boiling point? 1M solution of CuCl2 vs. 1M solution C6H12O6 1M solution of CuCl2 Because there are more ions in solution that hold onto the water molecules

7. Freezing Point Depression

8. Vapor Pressure Lowering