1. Colligative Properties
Learning Target:
What are the four colligative properties of solutions?
Determine the boiling point elevation and freezing point depression of a solution.

2. Main Idea
Colligative properties depend on the number of solute particles in a solution.

3. Colligative Property
Colligative properties are physical properties of solutions that are affected by the number of particles but not by the identity of dissolved solute particles.
Ionic compounds are electrolytes because they dissociate in water to form a solution that conducts electricity.
Some molecular compounds are also electrolytes.

4. 4 colligative properties:
Vapor Pressure Reduction
Boiling Point Elevation
Freezing point depression
Osmotic Pressure

5. Vapor Pressure Reduction
Molecules of nonvolite solute take up space, thus preventing some solvent molecules to vaporize.
Condensation continues at the same rate, but vaporization slows down.
Since condensation > vaporization, vapor pressure is reduced.

6. Boiling Point Elevation (ΔTb)
Adding a nonvolite 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.

7. Boiling Point Elevation

8. Boiling Point Elevation (ΔTb)
ΔTb = Kbm
Kb = boiling point elevation constant
m= molality

9. Freezing Point Depression (ΔTf)
The ability of a solute to lower freezing point of the solution.
Directly proportional to the molality of the solute.
ΔTf = Kfm
Kf = freezing point depression constant
m= molality

10. B.P. & F.P. – colligative property
Simulation

11. Osmotic Pressure
Osmosis: The movement of water molecules from high water concentration to low water concentration.
Osmotic pressure is the amount of additional pressure caused by water molecules that moved into the concentrated solution.

13. Osmotic Pressure & types of solutions
Isotonic concentration: solute concentration is the same on both sides of the membrane.
Hypertonic: higher solute concentration than the solution
Hypotonic: lower solute concentration than the solution

14. Examples
1. How much will the boiling point of water be elevated if 100. g of sucrose (C12H22O11) is added to 500.g of water? Kb for water is 0.52 °C/m.
ΔTb = kbx m

15. Example 2
What is the freezing point depression when 153g of bromine is added to g of benzene?