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Colligative Properties

Colligative Properties. Depend on the concentration of solute particles, but not on chemical identity. In the case of a solute that does not ionize, “concentration of solute particles” has the same meaning as “solute concentration”. Some Colligative Properties. Vapor pressure lowering

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Colligative Properties

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  1. Colligative Properties • Depend on the concentration of solute particles, but not on chemical identity. • In the case of a solute that does not ionize, “concentration of solute particles” has the same meaning as “solute concentration”.

  2. Some Colligative Properties • Vapor pressure lowering • Boiling point elevation • Freezing point depression • Osmotic pressure

  3. Why Vapor Pressure Lowering? • Results when a non-volatile solute is dissolved in a volatile solvent. • Only some of the surface molecules have the ability to vaporize, compared to all of the surface molecules in the case of a pure solvent. • As a result, the vapor pressure of the solution is less than that of a pure solvent.

  4. Molecular-Level Explanation for Vapor Pressure Lowering (image 1 of 3)

  5. Molecular-Level Explanation for Vapor Pressure Lowering (image 2 of 3)

  6. Molecular-Level Explanation for Vapor Pressure Lowering (image 3 of 3)

  7. An Interesting Illustration of the Difference in Vapor Pressure Between Solvent and Solution

  8. Raoult’s Law • P = X . Po • Obeyed exactly, only for ideal solutions • For non-ideal solutions, Raoult’s law is more closely followed for dilute solutions

  9. Raoult’s Law Applied to Both Solvent and Solute (when both are volatile) • P = X . Po • P = X . Po • P = P + P = X . Po+ X . Po= (1-X) .Po+ X . Po

  10. Vapor Pressure Lowering Changes the Boiling and Freezing Points

  11. Equations for Boiling Point Elevation and Freezing Point Depression • DTb = Tb – Tob and DTb= Kb. cm • DTf = Tf – Tof and DTf = -Kf. cm

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