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

NON ELECTROLYTES

•Molecule that produce many ions in solution• Example: NaCl

•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 #33What 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