Chapter 14: Solutions

Colligative Properties

Properties of a solution that depend on the number of solute particles, not their identity.

Vapor Pressure Depression

The lowering of a solvent’s vapor pressure due to the presence of solute particles.

Boiling Point Elevation

The increase in the boiling point of a solvent when a solute is added.

Freezing Point Depression

The decrease in the freezing point of a solvent when a solute is added.

Osmotic Pressure

The pressure required to stop osmosis across a semipermeable membrane.

Colligative Property Equations

Boiling Point Elevation

ΔT_b = i ⋅ K_b ⋅ b_solute

Freezing Point Depression

ΔT_f = i ⋅ K_f ⋅ b_solute

Osmotic Pressure

Π = i ⋅ M ⋅ R ⋅ T

Example Applications

• Boiling Point Elevation: Adding salt to boiling water raises its boiling temperature.
• Freezing Point Depression: Spreading salt on roads lowers the freezing point of water, preventing ice formation.
• Osmotic Pressure: Red blood cells swell or shrink depending on the salt concentration of their surrounding solution.

Questions for Students

1. What are colligative properties, and why do they depend on the number of solute particles?
2. Explain vapor pressure depression and how it affects the boiling point.
3. Calculate the freezing point depression for a 3.00 m NaCl solution (K_f = -1.86°C ⋅ kg/mol).
4. Why does adding salt to water make it boil at a higher temperature?
5. How does osmosis relate to the movement of water in and out of cells?