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Colligative Properties of Nonelectrolyte Solutions

Vapor-Pressure Lowering. Boiling-Point Elevation. D T b = K b m. 0. P 1 = X 1 P 1. Freezing-Point Depression. D T f = K f m. p = MRT. Osmotic Pressure ( p ). Colligative Properties of Nonelectrolyte Solutions.

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Colligative Properties of Nonelectrolyte Solutions

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  1. Vapor-Pressure Lowering Boiling-Point Elevation DTb = Kbm 0 P1 = X1 P 1 Freezing-Point Depression DTf = Kfm p = MRT Osmotic Pressure (p) Colligative Properties of Nonelectrolyte Solutions Colligative properties are properties that depend only on the number of solute particles in solution and not on the nature of the solute particles.

  2. Lowering Vapor Pressure 0 Vapor-Pressure Lowering (Raoult’s Law) P1 = X1 P 1 Vapor pressure – pressure exerted by the vapor over the solution Nonvolatile – no vapor pressure

  3. Glycerin (C3H8O3) is a nonvolatile nonelectrolyte with a density of 1.26 g/mL at 25˚C. Calculate the vapor pressure at 25˚C of a solution made by adding 50.0mL of glycerin to 500.0mL of water. The vapor pressure of pure water at 25˚C is 23.8 torr. 0 Vapor-Pressure Lowering P1 = X1 P 1 P1 = new vapor pressure of solution X1 = mole fraction of solvent P1 = vapor pressure of pure solvent 0 0 Pwater/glycerinsolution= XwaterP purewater 50.0 mL glycerin x 1.26 g x mol = 0.680 mol glycerin mL 92.11g 500.0 mL H2O x 1g x mol = 27.75 mol H2O mL 18.02g Pwater/glycerinsoln = 0.9800 (23.8 torr) Psolution = 23.3 torr XH2O = 27.75 moL H2O = 0.9800 27.75 mol + 0.680 mol

  4. 0 0 0 0 PA = XA P A PB = XB P B PT = XA P A +XB P B Ideal Solution When both the solute and solvent are volatile (have measureable vapor pressures) … PT = PA + PB

  5. Force A-A Force A-A Force B-B Force B-B Force A-B Force A-B < > & & PT is greater than predicted by Raoults’s law PT is less than predicted by Raoults’s law

  6. Osmotic Pressure (p) Osmosis is the selective passage of solvent molecules through a porous membrane from a dilute solution to a more concentrated one. A semipermeable membrane allows the passage of solvent molecules but blocks the passage of solute molecules. Osmotic pressure (p) is the pressure required to stop osmosis. more concentrated dilute

  7. Osmotic Pressure (p) time solution solvent High P Low P p = iMRT M is the molarity of the solution R is the gas constant T is the temperature (in K)

  8. A cell in an: isotonic solution hypotonic solution hypertonic solution

  9. Chemistry In Action: Reverse Osmosis

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