Date post: | 19-Dec-2015 |
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contemplated with
Combined with
Explains almost all Solution behaviors
We saw three examples of Colligative Properties:colligative – depends only on the number of particles
Tfp = Kfp msolute
Tbp = Kbp msolute
Psolv = Xsolvent Posolvent
Tfp = Kfp msolute
Tbp = Kbp msolute
Psolv = Xsolvent Posolvent
See why we need to deal with new types of concentration: mole fraction, molality.These relationships depend on numbers of particles
Ideal behavior, no association of ions ---------------------------------------------------- 2.00
Ideal behavior, no association of ions ---------------------------------------------------- 3.00
Let’s watch this association ….
Combined with
Explains almost all Solution behaviors
Fourth example of Colligative Properties:
Osmosis – the movement of solvent through a semi- permeable membrane from a region of high solute concentration to low solute concentration.
pasta marshmallow nut
light source
Semi-PermeableMembrane bag
5% sugarsolution
This is the system at equilibriumThis is what createsthe dis-equilibriumIn the beaker
pasta marshmallow nut
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The system is disturbed away from equilibrium
X H2O(outside) ≠ X H2O(inside)
100% H2O(outside) ≠ 95% H2O(inside)
The system will respond by shifting equilibrium
H2O(outside) H2O(inside)
How???
Only water molecules can move thorough membrane
The membrane is invisible to water
pasta marshmallow nut
light source
When the system responds by shifting equilibrium:
If diluted to 1% sugar:
0.00278 mol/ 0.095 L = 0.0293 MUsing:
= c R T
= 0.0293 M x 0.082057 atm/M K x 298 K
= 0.716 atm or 544 mm Hg
The sugar solution under pressurerises up the tube, like a manometer.
The height represents the Osmotic Pressure
light source
Waterfills beaker
corn syruppipet fits tightly into
hole
core of carrot
removed and filled
withcorn syrup
CarrotAs amembrane
pasta marshmallow nut
light source
= c R T
in: atm mol/L kelvin .0820 L/atm K
Combined with
Explains almost all Solution behaviors
Osmosis – the movement of solvent through a semi-permeable membrane from a region of high solute concentration to low solute concentration.
Osmotic Pressure – the pressure created after the system attains equilibrium, calculated by:
Combined with
Explains almost all Solution behaviors
Semi-permeable membrane: now this is a very specialdevice: selective for molecular size Size exclusion
What is an important example that uses a Semi-permeable membrane?
Living cells: have many ways of selecting which molecules get inside or stay outside
Previously in Chem 104:
• Equilibrium &•LeChatelier’s Principle
• 4 (or 3?) Colligative Properties:
Psolv = Xsolvent Posolvent
Tbp = Kbp msolute
Tfp = Kfp msolute
= c R T
TODAY
• Example Calcs
•Equilibrium and Osmosis
• Examlette Monday
• For the Future:Enthalpies Do Not Predict Dissolution—they can be exo- and endothermic