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COLLIGATIVE PROPERTIES OF SOLUTIONS

COLLIGATIVE PROPERTIES OF SOLUTIONS. 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”)

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COLLIGATIVE PROPERTIES OF SOLUTIONS

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  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. Total pressure (PA + PB) PAo PBo PA = PAo.xA PB = PBo.xB 0 0.5 1.0 Mole fraction of B (xB) Vapor Pressure of Ideal Solution PAo PBo PA + PB Solvent A Solvent B A + B Raoult’s Law PA = PAo.xA PB = PBo.xB Solvent pressure lowering (PAo-PA)/PAo= xB

  4. Tf and Tb • Freezing point depression: • Kf - “cryoscopic constant” or “molar depression constant” {oC/M} • Boiling point elevation: • Kb - “ebulioscopic constant” or “molar elevation constant” {oC/M}

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

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

  7. Non-Ideal Solutions Emix 0, Hmix 0 na + nb na nb

  8. Non-Ideal Solution Vapor Pressure Henry’s Law: PA = PAo. AxA PB = PBo. AxB “Attracting” components “Repellent” components positive deviation negative deviation PAo PAo PBo PBo 0 0.5 1.0 0 0.5 1.0 Mole fraction of B (xB) Mole fraction of B (xB)

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

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