1. Colligative Properties
Colligative properties are properties that depend only on the number of solute particles in solution and not on the nature of the solute particles.
Vapor-Pressure Lowering
Adding a nonvolatile solute reduces the relative amount of solvent, which results in fewer molecules becoming vapor
<100% solvent
100% solvent

3. Boiling-Point Elevation
Adding solute increases the boiling point of the solvent
Ex: adding salt to a pot of water to cook pasta
Explained by vapor pressure lowering

4. Freezing-Point Depression
Adding solute lowers the freezing point of the solvent
Ex: salt or sand on roads to prevent ice

5. Measure of the degree of dissociation of a solute in a solvent
van’t Hoff factor
Measure of the degree of dissociation of a solute in a solvent
(i) =
actual number of particles in soln after dissociation
number of formula units initially dissolved in soln
i should be
nonelectrolytes 1
NaCl 2
CaCl2 3

6. Reality: Ion pairs
The presence of an ion pair reduces the number of particles in solution, causing a reduction in the colligative properties. Electrolytes containing multicharged ions have a greater tendency to form ion pairs than electrolytes that are made up of singly charged ions. a. b.

7. Arrange the following solutions in order of decreasing freezing point: 0.10 m Na3PO4, 0.35 m NaCl, 0.20 m MgCl2, 0.15 m glucose, 0.15 m CH3COOH.