Lecture 3 (1/10/2013)
• Colligative Properties of Solutions
o Colligative Properties:
Solution properties that depend on concentration of solute
particles, not the identity of particles.
• Solute Concentration: Molality
o Changes in boiling point/freezing point of solutions depends on molality:
moles of solute
o kg of solvent
o Preferred concentration unit for properties involving temperature changes
because it is independent of temperature.
o For typical solutions: molality > molarity.
• BoilingPoint Elevation and FreezingPoint Depression
o Boiling Point Elevation (ΔT ): b
ΔT b= K ∙b
K b= boiling point elevation constant of solvent; m = molality.
o Freezing Point Depression (ΔT): f
ΔT f K∙mf
K f freezingpoint depression constant; m = molality.
• The van’t Hoff Factor