COLLIGATIVE
PROPERTIES
COLLIGATIVE PROPERTIES
• Physical properties of solutions
affected by the number of particles
• Vapor Pressure Lowering
• Boiling Point Elevation
• Freezing Point Depression
• Osmotic Pressure
• Molecule that produce many
ions in solution
• Example: NaCl
NON ELECTROLYTES
• Molecules that dissolve but do
not produce ions in solution
• Example: Sugar
VAPOR PRESSURE LOWERING
• More Particles=Lower Vapor Pressure
• Adding a nonvolatile solute (one that
has a lower tendency to become a
gas) lowers the vapor pressure
• Electrolytes have more effect because
they break down into more particles
VAPOR PRESSURE LOWERING
BOILING POINT ELEVATION
• When the vapor pressure is equal to the
atmospheric pressure, boiling occurs
• Lower vapor pressure = higher boiling point
• More particles=higher boiling point
BOILING POINT ELEVATION
• ∆Tb=Kbm
• m= molality
• Molality must be multiplied by the number of
particles in solution (ex: NaCl = 2 particles)
• Table 15-4 shows common Kb values
FREEZING POINT DEPRESSION
• Solute particles interfere with the
attractive forces that allow a solvent
to become a solid.
• More particles=lower freezing point
• ∆Tf=Kfm
FREEZING POINT DEPRESSION
DISCUSS WITH A PARTNER…
• This frog is frozen but is still alive because the water
in it did not turn into ice crystals, which would have
ruptured the cells in its body. Why didn’t ice crystals
form?
ANSWER…
• Glucose and glycerin in its blood and cells prevent
water from freezing. Glucose and glycerin dilutes
the water, so that reduces the number of water
molecules available to make ice crystals. Also, their
presence created disorder in the water. So water
has to overcome that disorder in order to arrange
itself neatly into ice crystals.
QUESTION #33
What are the boiling and freezing point
if a 0.625m aqueous solution of any
nonvolatile, nonelectrolyte solute?
OSMOTIC PRESSURE
• The diffusion of solvent particles through a
semipermeable membrane from an area of high
concentration to lower concentration
• Pressure depends on the amount of molecules
• Alien Egg Video
ASSIGNMENT
•pg 475 #33-36