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2. Colligative
Properties

3. Learning Objectives
 Know the definition of colligative properties
 Know what the important colligative properties
are
 Be able to think through logically the lowering
or raising of these properties due to colligative
processes

4. CsNHS Senior High School
Caestebanan National High School

5. CsNHS Senior High School
Caestebanan National High School
Colligative Properties: Definition
• Colligative Property: A property that depends
only upon the number of solute particles
(concentration), and NOT upon their identity.
• Three Important Colligative Properties of
Solutions.
–Vapor-pressure lowering
–Boiling-point elevation
–Freezing-point depression

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Caestebanan National High School
Vapor-Pressure Lowering
• As solute molecules are added to a
solution, the solvent become less
volatile (= decreased vapor pressure)

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Caestebanan National High School
Effect of Pressure on Boiling Point
Boiling Point of Water at Various Locations
Location
Feet
above
sea level
Patm
(kPa)
Boiling
Point
(C)
Top of Mt. Everest, Tibet 29,028 32 70
Top of Mt. Denali, Alaska 20,320 45.3 79
Top of Mt. Whitney, California 14,494 57.3 85
Leadville, Colorado 10,150 68 89
Top of Mt. Washington, N.H. 6,293 78.6 93
Boulder, Colorado 5,430 81.3 94
Madison, Wisconsin 900 97.3 99
New York City, New York 10 101.3 100
Death Valley, California -282 102.6 100.3

8. Why do we spread SALT
on the roads in the
winter?

9. CsNHS Senior High School
Caestebanan National High School
Freezing-Point Depression (tf )
•Freezing-Point Depression: The difference in temperature
between the freezing point of a solution and the freezing
point of the pure solvent (water).

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Caestebanan National High School
Freezing-Point Depression

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Caestebanan National High School
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.

12. CsNHS Senior High School
Caestebanan National High School
Boiling-Point Elevation (tb)
•Boiling Point: The temperature at
which the vapor pressure of the liquid
phase equals atmospheric pressure.
•Boiling point Elevation = BP of the
solution – BP of the solvent

13. CsNHS Senior High School
Caestebanan National High School
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.

14. CsNHS Senior High School
Caestebanan National High School
Boiling-Point Elevation
•The magnitude of the boiling-
point elevation is
proportional to the number
of solute particles dissolved
in the solvent.

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Caestebanan National High School
Boiling-Point Elevation

16. CsNHS Senior High School
Caestebanan National High School
Applications
 salting icy roads
 making ice cream
 Antifreeze
 cars (-64°C to 136°C)
 fish & insects