Class Handout - Chapter 12 (Solutions)
Colligative Properties - properties of a solution that only depend on the relative number
of solute and solvent molecules, and not the chemical identity of the solute.
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vapor pressure lowering (P)
boiling point elevation (Tb)
freezing point depression (Tf)
osmotic pressure ()
Vapor Pressure Lowering (P) - the vapor pressure over a solution (P) is less than the
vapor pressure of the pure solvent (Ppure); P=Ppure-P.
Boiling Point (Tb) - the temperature at which the vapor pressure of a liquid equals the
atmospheric pressure
Boiling Point Elevation(Tb) - the addition of a solute to a solvent lowers the vapor
pressure of the solvent. Therefore, the temperature of the solution must be increased
beyond the normal boiling temperature of the solvent by an amount Tb to re-establish
boiling.
Freezing Point Depression (Tf) - the addition of a solute to a solvent lowers the normal
freezing temperature of the solvent.
Semipermeable membrane - a barrier that allows passage of solvent molecules but not
solute molecules.
Osmosis - the natural tendency of solvent to flow through a semipermeable membrane in
order to equalize the solute concentrations on both sides of the membrane.
Osmotic Pressure () - the pressure that must be applied to a solution to stop osmosis.
Ideal Solution - a hypothetical solution in which the intermolecular forces between
solute-solvent molecules are the same as the intermolecular forces between solventsolvent molecules.
Expressions for calculating colligative properties for ideal - nonelectrolytic solutions
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vapor pressure lowering boiling point elevation freezing point depression osmotic pressure -
P=XsolutePpure
Tb=kbm
Tf=kfm
=MRT