colligative properties part 3.ppt
DESCRIPTION
Colligative Properties of matterTRANSCRIPT
Colligative Properties
Colligative properties
Properties that depend on the TOTAL number of dissolved particles
Colligative properties
Properties that depend on the TOTAL number of dissolved particles Vapor pressure lowering Boiling point elevation Freezing point depression Osmotic pressure
Vapor pressure lowering
Adding solute leads to more intermolecular attractions
It becomes harder for solvent molecules to escape into the gas phase
Vapor pressure lowering
More solute lower vapor pressure than pure solvent
Raoult’s Law
oAAA PXP
Effects of non-volatile solutes
Boiling Point Elevation
bbp kmT
Freezing Point Depression
ffp kmT
Electrolytes vs. non-electrolytes
Colligative properties depend on total number of dissolved particles
Electrolytes vs. non-electrolytes
Colligative properties depend on total number of dissolved particles Non-electrolytes don’t dissociate Electrolytes DO dissociate into ions in solution
Van’t Hoff factor, i
For non-electrolyte, i = 1 For electolytes, i = # of ions in formula
(theoretical maximum)
Predict the van’t Hoff factor:
Glucose, C6H12O6
NaCl AlCl3 Methanol, CH3OH
Ion pairing
One mole of NaCl does not yield two moles of ions
Some ions will reassociate for a short time
The actual van’t Hoff factor will be slightly lower than predicted
van’t hoff factors
More ion pairing occurs at higher concentrations
van’t hoff factors
More ion pairing occurs at higher concentrations
Incorporating the van’t Hoff factor
Boiling point elevation:
bbp kimT
Incorporating the van’t Hoff factor
Boiling point elevation:
Freezing point depression:
bbp kimT
ffp kimT
Problem 33.5 g of potassium chloride are dissolved in 459 g of water.
Calculate the boiling point and freezing point of the resulting solution.
Problem 17.8 g of an unknown solute are dissolved in 276 g of water. If the
new freezing point is -1.67oC, calculate the molar mass of the unknown substance.