Colligative Properties

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.

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

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.

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?

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 + 1.56°C = 101.56°C

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?

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

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.

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?

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