Colligative properties (PowerPoint)

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					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
     Freezing point depression
           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
       Vapor pressure reduction




   Solute interferes with vaporization of
    water, therefore LOWERS the pressure of
    the vapor pressing down on surface
How does this influence boiling
   point & freezing point?
   Boiling Point: The temperature at which
    the vapor pressure of the liquid phase
    equals atmospheric pressure.
           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.
         Boiling point Elevation




   Since vapor pressure is lowered, boiling
    point is elevated
Application: Adding salt to water
      while cooking pasta
                    Water does not
                     boil faster
                    Water is boiling
                     at a higher
                     temperature so
                     pasta cooks
                     faster
        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        withdrawn from a solution than from the pure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.
Freezing Point Depression
Freezing point depression
                   Since vapor
                    pressure
                    lowered,
                    freezing point
                    is LOWERED
Freezing point depression
         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?
               Therefore…
   Because freezing point of water goes
    down, we can make things like


ICE        CREAM!!!!
          Ice cream directions
                            Partner 2- food
Partner 1 -ice              1. Grab small ziplock bag
1. Grab large ziplock bag   2. Add 1 cup milk
2. Fill ½ way with ice      3. 2 tablespoons sugar
3. Add 1 scoop of salt      4. 1 teaspoon vanilla
                            5. Squeeze air out of bag
                               and shut tight!!!
   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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posted:10/23/2011
language:English
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