1. Colligative Properties
Physical properties that are affected by the concentration of solute.

2. Colligative Properties
Most common examples are freezing point, boiling point, and vapor pressure.

3. Colligative Properties
Freezing point – decreased
Boiling point – increased
Vapor pressure - decreased

4. Colligative Properties
This makes sense based on kinetic theory. It is harder to freeze with a weird shape in the way. It is harder to boil or have a vapor pressure, because these properties are due to movement of molecules and it is harder to get moving with a weird shape in the way.

5. Colligative Properties
For freezing point and boiling point changes, we will use one of two formulas:

6. Colligative Properties
MW = (grams of solute)(k)
(kg of solvent) (T)
MW = molecular weight
T = change in boiling or freezing point
K = a constant that varies depending on the solvent.

7. Colligative Properties
MW = (grams of solute)(k)
(kg of solvent) (T)
For water:
Kf = (freezing)
Kb = (boiling)

8. Colligative Properties
This formula can also be arranged as follows:
Kb = Kf
Tb Tf
Tb = change in boiling temperature
Tf = change in freezing temperature

9. Colligative Properties
The other formula that can be used is
T = m (k) (n)
T = change in freezing or boiling
m = molality of the solution
k = freezing or boiling constant
n = the number of ions the substance dissociates into when dissolved in water