colligative properties part 3.ppt
DESCRIPTION
Colligative Properties of matterTRANSCRIPT
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Colligative Properties
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Colligative properties
Properties that depend on the TOTAL number of dissolved particles
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Colligative properties
Properties that depend on the TOTAL number of dissolved particles Vapor pressure lowering Boiling point elevation Freezing point depression Osmotic pressure
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Vapor pressure lowering
Adding solute leads to more intermolecular attractions
It becomes harder for solvent molecules to escape into the gas phase
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Vapor pressure lowering
More solute lower vapor pressure than pure solvent
Raoult’s Law
oAAA PXP
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Effects of non-volatile solutes
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Boiling Point Elevation
bbp kmT
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Freezing Point Depression
ffp kmT
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Electrolytes vs. non-electrolytes
Colligative properties depend on total number of dissolved particles
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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
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Van’t Hoff factor, i
For non-electrolyte, i = 1 For electolytes, i = # of ions in formula
(theoretical maximum)
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Predict the van’t Hoff factor:
Glucose, C6H12O6
NaCl AlCl3 Methanol, CH3OH
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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
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van’t hoff factors
More ion pairing occurs at higher concentrations
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van’t hoff factors
More ion pairing occurs at higher concentrations
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Incorporating the van’t Hoff factor
Boiling point elevation:
bbp kimT
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Incorporating the van’t Hoff factor
Boiling point elevation:
Freezing point depression:
bbp kimT
ffp kimT
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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.
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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.