Combined with
EQUILIBRIUM
Le Chatelier’s Principle
Explains almost all Solution behaviors
Fourth example of Colligative Properties:
Osmosis – the movement of solvent through a semipermeable membrane from a region of
high solute concentration to low solute concentration.
This is the system at equilibrium
pasta
marshmallow
light
source
This is what creates
the dis-equilibrium
In the beaker
nut
SemiPermeable
Membrane
bag
5% sugar
solution
The system is disturbed away from equilibrium
XH O
2
(outside)
≠X
H2O(inside)
100% H2O(outside) ≠ 95% H2O(inside)
pasta
light
source
marshmallow The system
nut will respond by
shifting equilibrium
H2O(outside)  H2O(inside)
How???
Only water molecules can move thorough membrane
The membrane is invisible to water
When the system responds by
shifting equilibrium:
The diluted sugar solution under
pressure rises up the tube,
like a manometer.
pasta
light
source
The height represents the
marshmallow
nut
Osmotic
Pressure
If diluted to 1% sugar:
0.00278 mol/ 0.095 L = 0.0293 M
Using:
P =cRT
P= 0.0293 M x 0.082057 atm/M K x 298 K
P = 0.716 atm or 544 mm Hg
Carrot
As a
membrane
pipet fits
tightly into hole
core of
carrot
removed
and filled
with
corn syrup
light
source
corn syrup
Water
fills
beaker
pasta
marshmallow
light
source
nut
Combined with
EQUILIBRIUM
Le Chatelier’s Principle
Explains almost all Solution behaviors
Osmosis – the movement of solvent through a semipermeable membrane from a region of high solute
concentration to low solute concentration.
Osmotic Pressure – the pressure created after the
system attains equilibrium, calculated by:
P = c R T
in:
atm
mol/L
kelvin
.0820 L/atm K
Combined with
EQUILIBRIUM
Le Chatelier’s Principle
Explains almost all Solution behaviors
Semi-permeable membrane: now this is a very special
device:
selective
for many
molecular
sizeofselecting
Size exclusion
Living cells:
have
ways
which molecules get inside or stay outside
What is an important example that uses a
Semi-permeable membrane?
What is a Colloid?
Intermediate between
a true solution and a suspension
High molecular weight
Aggregate into large particles, ~micron
Finely divided (“isolated”) dispersions
What
Colloid?
What is
is a
Cool
Whip?
Whipped toppings are essentially an emulsion of oil
(usually around 35%) and sweetened water (around 60%)
with an emulsifier, like phosphatidyl choline (lecithin), to
maintain the suspension. The oil used for whipped
toppings, like Cool Whip™, is hydrogenated vegetable oil,
and after hydrogenation (saturation with hydrogen), all
vegetable oils are the same (saturated), regardless of
where they come from. So hydrogenated olive oil could
easily be used to make whipped toppings.
What is Cool Whip?
Oils (and fats) are fatty acids—
phospholipids—have two parts (as their
name suggests): a phosphate "head", and a
long hydrocarbon "tail" (the fatty part).
O
O
O
“tail”
ester group
O
O
P
O
O
O N
“head”
hydrogenated
"saturated" fat
What is Cool Whip?
An emulsion of oil and water is really just water with
microscopic oil droplets floating in it (this is called a colloidal
suspension). To get the oil to form these droplets, called
micelles, the molecules of fatty acid have to pack together as
closely as possible to minimize the volume of the micelle. To
form a micelle, the heads of the molecules, which are soluble,
form the outside of the drop, while the tails fill the inside.
micelle
No water
wants to
be here!
Lots of micelles
suspended in water
What is Cool Whip?
The defining
characteristic of
unsaturated fats is that
their tails have kinks in
them. These kinks prevent
the molecules from
packing close together, so
they tend to disrupt the
micelles - the more
unsaturated fats, the
fewer and larger the
micelles. Without good
micelles, the emulsion will
separate into its two
phases (oil and water),
and without a good
emulsion, you can't whip
the suspension into a
dessert topping.
kinks
O
O
O
phospate group
O
O
P
O
O
O N
"unsaturated" fat
What is Cool Whip?
The unsaturated
fats have tails have
kinks that prevent
the molecules from
packing close
together, so they
tend to disrupt the
micelles - the more
unsaturated fats,
the fewer and
larger the micelles.
Compare to a
saturated—
hydrogenated— fat
O
O
O
O
ester group
O
O
O
P
O
O
phospate group
O
O-
O
O N+
P
O
hydrogenated
"saturated" fat
OO N+
"unsaturated" fat
Micelles in Medicine
Example 1. self-forming micelles by an eczema drug
http://www2.cnrs.fr/en/1043.htm?debut=72
Designer Micelles – Block Co-Polymer
Note use of weight%
“On the basis of examples already found in literature, one unifying
rule for generating polymersomes predicts that f (the weight
percent of the hydrophilic block) must be equal to 35±10%.
Molecules with f >45% are expected to form spherical micelles,
whereas molecules with f <25% are expected to form inverted
nanostructures.
When the weight percent of the
hydrophilic block f >45 % :
micelles form
When the weight percent of
the hydrophilic block f ~ 35 % :
vesicles (polymersomes)
form
S. Lecommandoux, M. F. Achard, J. F. Langenwalter, H.-A. Klok
Macromolecules 34(26), 9100-9111 (2001)
http://recherche.enscpb.fr/lcpo/
Different realm of colloid investigation:
Dynamics of micelle monomers
http://www.julianhaller.de/Dissertation_e.htm