1. Colligative Properties of Solutions
Honors Chemistry

2. How do you get from this…

3. …to this?

4. Add an ionic compound!

5. Colligative Properties
Properties that depend only on the number of solute particles and not on their identity.

6. Some Colligative Properties are:
Boiling point elevation
Freezing Point depression

7. Ionic vs Molecular Solutes
Ionic solutes produce two or more ion particles in solution.
They affect the colligative properties proportionately more than molecular solutes (that do not ionize).
The effect is proportional to the number of particles of the solute in the solution.

8. How many particles do each of the following give upon solvation?
NaCl
CaCl2
Glucose

9. Freezing Point Depression

10. Example
Salt is added to melt ice by reducing the freezing point of water.

11. Boiling Point Elevation

12. Example
Addition of ethylene glycol C2H6O2 (antifreeze) to car radiators.

13. Freezing Point Depression and Boiling Point Elevation
∆Tb =mikb (for water kb=0.51 oC/m)
Freezing Point Depression
∆Tf=mikf (for water kf=1.86 oC/m)
Note: m is the molality of the particles and i is the # of particles in solution

14. Which is more effective for lowering the freezing point of water?
NaCl or CaCl2

15. Example 1:
Find the new freezing point of 3m NaCl in water.

16. Example 2:
Find the new boiling point of 3m NaCl in water.