colligative properties_00

Published on March 24, 2009

Author: amitmgupta31

Source: authorstream.com

COLLIGATIVE PROPERTIES OF SOLUTIONS : COLLIGATIVE PROPERTIES OF SOLUTIONS Colligative Properties : 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 Vapor Pressure of Ideal Solution : Vapor Pressure of Ideal Solution Raoult’s Law PA = PAo.xA PB = PBo.xB Solvent pressure lowering (PAo-PA)/PAo = xB A + B Solvent B Solvent A PAo PBo PA + PB ?Tf and ?Tb : ?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} Osmotic Pressure : Osmotic Pressure van’t Hoff equation: Molecular Weight Determination : Molecular Weight Determination Osmotic Pressure: Cryoscopy and Ebulioscopy: Non-Ideal Solutions : Non-Ideal Solutions ?Emix ? 0, ?Hmix ? 0 na nb na + nb Non-Ideal Solution Vapor Pressure : Non-Ideal Solution Vapor Pressure Henry’s Law: PA = PAo. ?A xA PB = PBo. ?A xB PBo PAo 1.0 0 Mole fraction of B (xB) 0.5 PBo PAo 1.0 0 Mole fraction of B (xB) 0.5 “Repellent” components “Attracting” components positive deviation negative deviation Activity and Activity Coefficient : Activity and Activity Coefficient “Activity”: ai = ?ici Activity coefficient: ?i To account for non-ideality of solutions “activity” is used instead of concentration in all equations

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