1. COLLIGATIVE PROPERTIES OF SOLUTIONS

2. Colligative Properties Colligative properties depend on the number of particles rather than their nature Lowering of the vapor pressure (Raoult’s law) Elevation of the boiling point (“ebulioscopy”) Depression of the freezing point (“cryoscopy”) Osmotic pressure

3. Vapor Pressure of Ideal Solution Raoult’s Law P A = P A o. x A P B = P B o. x B Solvent pressure lowering (P A o -P A )/P A o = x B A + BSolvent BSolvent A PAoPAo PBoPBo P A + P B PBoPBo PAoPAo P A = P A o. x A P B = P B o. x B Total pressure (P A + P B ) 1.00 Mole fraction of B (x B ) 0.5

4.  T f and  T b Freezing point depression: K f - “cryoscopic constant” or “molar depression constant” { o C/M} Boiling point elevation: K b - “ebulioscopic constant” or “molar elevation constant” { o C/M}

5. Osmotic Pressure  p =  Semipermeable membrane van’t Hoff equation:

6. Molecular Weight Determination Osmotic Pressure: Cryoscopy and Ebulioscopy:

7. Non-Ideal Solutions  E mix  0,  H mix  0 nana nbnb n a + n b

8. Non-Ideal Solution Vapor Pressure Henry’s Law: P A = P A o.  A x A P B = P B o.  A x B PBoPBo PAoPAo 1.00 Mole fraction of B (x B ) 0.5 PBoPBo PAoPAo 1.00 Mole fraction of B (x B ) 0.5 “Repellent” components “Attracting” components positive deviationnegative deviation

9. Activity and Activity Coefficient “Activity”: a i =  i c i Activity coefficient:  i To account for non-ideality of solutions “activity” is used instead of concentration in all equations