Transcript 15.4 Colligative Properties

15-4 Colligative Properties
Colligative property:
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A property that depends on the
concentration of solute particles, but is
independent of their nature
The four colligative properties are:
Vapor pressure reduction
2. Boiling point elevation
3. Freezing point depression
4. Osmotic pressure
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Vapor Pressure Reduction (VPR)
Occurs when the pressure of the vapor
over a solvent is reduced when a
nonvolatile solute is dissovled in the
solvent
 Related directly to the conc. of a soln.
 Double conc., double vpr effect
 Raoult’s Law: magnitude of vapor
reduction is proportional to solution
concentration
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Boiling Point Elevation (BPE)
The amount to which the dissolved solute
raises the boiling point of its soln.
 Related directly to the conc. of a soln.
 Double conc., double boiling point
elevation
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BPE – real life examples
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Making candy: use a lot of sugar and a
little flavoring, as water is boiled away,
the conc. of sugar goes up.
Making maple syrup
Need for antifreeze even in the summer
Freezing Point Reduction (FPR)
The amount to which the dissolved solute
lowers the freezing point of its soln.
 Related directly to the conc. of a soln.
 Double conc., double freezing point
depression
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FPR – real life examples
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Salt on winter roads
Antifreeze in your car
Making homemade ice cream
Osmotic Pressure
Semi-permeable: a membrane that allows
some particles to pass, but not others
 Osmosis: the net flow of solvent
molecules from the less concentrated
solution to the more concentrated solution
 Osmotic pressure: the pressure required
to prevent osmosis
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Osmotic Pressure
Isotonic: identical osmotic pressure
results in no osmosis
 Hypotonic: lower osmotic pressure than
another (cells burst)
 Hypertonic: higher osmotic pressure than
another (cells shrivel)
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Osmotic Pressure
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Real life examples:
Feeling bloated when you eat salty foods –
salt solutions in your body are more
concentrated that usual
2. Pickles: cucumbers that have been soaked
in a salt solution – they lose water through
osmosis
3. Country ham: the salt on the ham causes
bacteria on it to shrivel and die
4. Plants: movement of water from soil to
plant roots
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