Unformatted text preview: 3. boiling point
4. osmotic pressure 1. Changes in vapor pressure: The vapor pressure over a solution is lower than the vapor pressure of a
purexsolvent. The vapor pressure of the solvent, Psolv is proportional'to
Xsolv- \ This is covered by Raoult’s Law Psolv = xsolv osolv Where P°solv is the pure solvent equilibrium vapor pressure Raoult’s is for ideal solutions which have solvent-solute interactions the
same as the solvent-solvent interactions. 2. Freezing Point Depression: ATfszfpmsolute
Kfp = freezing point depression constant in degrees per molal ATfp — Negative in value.
- So that the temperature is decreased. 3. Boiling Point Elevation: Apr=KbpmS(,1ut,e
Kbp = boiling point elevation constant in degrees per molal Apr - Positive in value.
- So that the temperature is increased. Oh, but wait. . ..there is the van’t Hoff factor. . ...if the molality is for an
ionic compound that will dissociate, you need to consider the number of
ions produced and multiply the molality by that number of ions. ATfp=I<fprnsolutei Apr=I<prnsolutei where ‘i’ is the van’t Hoff factor. Most often “i” is experimentally
determined and is slightly less than a whole number. if) ...
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- Fall '08