1. Colligative Properties

2. What are colligative properties?
“Colligative” means properties that depend only on the number of molecules in a solution.
Colligative properties depend on the concentration of the solution only.

3. What are some colligative properties?
Some colligative properties are:
Boiling point elevation
Freezing point depression
Osmosis

4. Boiling Point Elevation
Every liquid has a molal boiling point elevation constant.
This number describes how much the boiling point of the liquid will increase for each mole of any chemical added.

5. Sample Boiling Point Elevation Problem 1
Water has a molal boiling point elevation constant of 0.52°C and boils at 100°C. What would the boiling point of a 3 m solution be?

6. Sample Boiling Point Elevation Problem 1
Step One: Multiply the molal boiling point elevation constant by the number of moles.
0.52°C x 3 = 1.56°C
Step Two: Add the answer from step one to the boiling point of the liquid.
100°C °C = °C

7. Sample Boiling Point Elevation Two
Benzene boils at 80.1°C with a molal boiling point elevation constant of 2.53°C. What would the boiling point of a 5m solution be?

8. Sample Problem Two Step One: Step Two: 2.53°C x 5 = 12.65°C
80.1°C °C = 92.75°C

9. Freezing Point Depression
Every liquid has a molal freezing point depression constant.
This number describes how much one mole of any chemical will lower the freezing point of that solution.

10. Freezing Point Depression Problem One:
Water freezes at 0°C with a molal freezing point depression of 1.86°C. What is the freezing point of a 2 m solution?

11. Freezing Point Depression Problem One:
Step One: Multiply the molal freezing point depression constant by the concentration in m
1.86°C x 2 m = 3.72°C
Step Two: Subtract the answer from step one from the freezing point.
0°C – 3.72°C = -3.72°C