Colligative properties

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Colligative properties
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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

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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

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Vapor pressure reduction

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

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How does this influence boiling point freezing
point?

• Boiling Point The temperature at which the vapor
  pressure of the liquid phase equals atmospheric
  pressure.

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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.

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Boiling point Elevation

• Since vapor pressure is lowered, boiling point is
  elevated

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Application Adding salt to water while cooking
pasta

• Water does not boil faster
• Water is boiling at a higher temperature so pasta
  cooks faster

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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  Therefore more kinetic energy must be withdrawn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.

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Freezing Point Depression
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Freezing point depression

• Since vapor pressure lowered, freezing point is
  LOWERED

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Freezing point depression
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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?

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Therefore

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

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Ice cream directions

• Partner 2- food

• Partner 1 -ice

1. Grab small ziplock bag
2. Add 1 cup milk
3. 2 tablespoons sugar
4. 1 teaspoon vanilla
5. 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