III. Colligative Properties
(p. 436 - 446)
Ch. 13 & 14 - Solutions
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A. Definition
• Colligative Property
– property that depends on the concentration of
solute particles, not their identity
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B. Types
• Freezing Point Depression (tf)
– f.p. of a solution is lower than f.p. of the pure
solvent
• Boiling Point Elevation (tb)
– b.p. of a solution is higher than b.p. of the
pure solvent
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B. Types
Freezing Point Depression
View Flash animation.
C. Johannesson
B. Types
Boiling Point Elevation
Solute particles weaken
IMF in the solvent.
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B. Types
• Applications
– salting icy roads
– making ice cream
– antifreeze
• cars (-64°C to 136°C)
• fish & insects
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B. Types
• Vapor Pressure: pressure of the vapor resulting
from evaporation of a liquid above a sample of
the liquid in a closed container.
– Depends on
• Type of sample: greater intermolecular force results in lower
vapor pressure
• Temperature: higher temp, greater vapor pressure
• Dissolved particles
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B. Types
• Vapor Pressure Reduction
– When a solute is added to a solvent, the
vapor pressure of the solvent is lower than the
pure solvent.
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B. Types
Vapor pressure of sucrose solution
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B. Types
Pure Water
1.0M NaCl Solution
-more water molecules above
surface
-fewer water molecules
above surface
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• Osmosis: water flow through a semipermeable membrane that blocks the
transport of salts or other solutes through
it
– from the volume of low solute concentration,
to the volume of high solute concentration
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B. Types
Osmotic Pressure
-the pressure required to stop osmosis
-The osmotic pressure does not depend on the
solute type, or its molecular size, but only on
its molar concentration
If there is only water in the device, the level will be the same at both
arms. When solute molecules are added to one arm, water will start to
flow into it, so that its level will go up at this arm, and down at the
other arm.
C. Johannesson