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Colligative properties

Colligative properties. Colligative properties. Colligative property- a property of a solution that depends on concentration of solute (the number of solute particles dissolved) but NOT on type of solute 3 colligative properties: Vapor pressure reduction Boiling point elevation

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Colligative properties

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  1. Colligative properties

  2. Colligative properties • Colligative property- a property of a solution that depends on concentration of solute (the number of solute particles dissolved) but NOT on type of solute • 3 colligative properties: • Vapor pressure reduction • Boiling point elevation • Freezing point depression

  3. Vapor pressure • The pressure DIRECTLY above the surface of a liquid exerted by the molecules that have evaporated • LOW vapor pressure = not much evaporation occurring • HIGH vapor pressure = lots of evaporation

  4. Vapor pressure reduction • Solute interferes with vaporization of water, therefore LOWERS the pressure of the vapor pressing down on surface

  5. How does this influence boiling point & freezing point? • Boiling Point: The temperature at which the vapor pressure of the liquid phase equals atmospheric pressure.

  6. Boiling-Point Elevation • Boiling point elevation: The difference in temperature between the boiling point of a SOLUTION and the boiling point of the pure solvent (water). • Because of the decrease in vapor pressure, additional kinetic energy must be added to raise the vapor pressure of the liquid phase of the solution to atmospheric pressure to initiate boiling.

  7. Boiling point Elevation • Since vapor pressure is lowered, boiling point is elevated

  8. Application: Adding salt to water while cooking pasta • Water does not boil faster • Water is boiling at a higher temperature so pasta cooks faster

  9. Freezing-Point Depression • Freezing-Point Depression: The difference in temperature between the freezing point of a solution and the freezing point of the pure solvent (water). • The presence of a solute in water disrupts the formation of the orderly pattern of ice. Therefore more kinetic energy must be withdrawn from a solution than from the pure solvent to cause the solution to solidify.

  10. Freezing Point Depression

  11. Freezing point depression • Since vapor pressure lowered, freezing point is LOWERED

  12. Freezing point depression

  13. Freezing-Point Depression • The magnitude of the freezing-point depression is proportional to the number of solute particles dissolved in the solvent and does not depend upon their identity. • Which would be a better salt for putting on icy roads, NaCl or CaCl2?

  14. Therefore… • Because freezing point of water goes down, we can make things like • ICE CREAM!!!!

  15. Ice cream directions Partner 1 -ice Partner 2- food Grab small ziplock bag Add 1 cup milk 2 tablespoons sugar 1 teaspoon vanilla Squeeze air out of bag and shut tight!!! • Grab large ziplock bag • Fill ½ way with ice • Add 1 scoop of salt Smaller bag goes in larger bag– agitate & toss (about 10 minutes) Once milk has hardened, 1 person eats out of bag, 1 person eats out of bowl Do not throw away spoons or ice

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