# 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
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
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withdrawn from a solution than from the pure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
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