Osmosis & Dialysis
• Conventional solutions
– Gases
• Air is mixture/solution of N2, O2, etc …
– Liquids
• Ionic – Salt in Oceans
• Non-Ionic - Sugar in water
– Solids
• Solder, metal alloys (e.g. Stainless Steel)
• Inorganic oxides, magnetite Fe3O4
– Fe3O4 has impossible valence between 2 & 3 = 2.67
– Fe3O4 is actually FeO “dissolved” in Fe2O3, a “spinel” structure
• Solutions share similar properties
– Homogeneous
– Well mixed, evenly distributed
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CHAPTER 5: Solutions, Colloids, and Membranes
NaCl IN AN AQUEOUS SOLUTION
NaCl in an aqueous solution.
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CHAPTER 5: Solutions, Colloids, and Membranes
MOLECULES IN SOLUTION
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Colligative Properties
• Solute effects the Solvent
– Example of salt on snow covered road
•
•
•
•
Freeze temp. of salty water < than pure water (snow)
Outside temperature the same, so snow melts
Works best when temp close to zero celsius
But salt is tough on cars … promotes corrosion
– Boiling point is increased with solute in solvent
• Sea water boils at higher temperature
– Boiling point decreased with altitude
• Less air pressure, 1 atmosphere < 1bar
• Vapor pressure of water goes to ambient at lower oC
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The equilibrium vapor pressure of a solution with (a) a nonvolatile solute is
always lower than that of (b) the pure solvent by an amount that depends on
the mole fraction of the solvent.
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Special Solutions
• Other kinds of “solutions”
– Colloids
• Small particles, no separation, skim milk
• Particles approaching molecular dimensions, <500 nm
• Kinetic energy keeps in motion, no settling
– “Brownian Motion” observed in microscope
– Suspensions
• Larger particles, may coagulate
– Emulsions
• Mixtures of materials insoluble in each other
• Butter and cream are the same, different organization
• Convert cream to butter with agitation, reverse the emulsion
– Cream is blend of oil particles immersed water solvent
– Butter is blend of water particles immersed in oil matrix
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COMPARING COLLOIDS AND SUSPENSIONS
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EXAMPLES
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9
Osmosis
• Living tissues are porous
– Sweat is example of water through skin
– Pores big enough for water, too small for blood
• Concentration cell
–
–
–
–
Permeable barrier between two different concentrations
∆S favors mixing versus separation (more random)
Tendency to mix generates pressure (& voltage)
Solvent goes through barrier to solution side
• “Osmotic” pressure develops on solution (mixing) side
• Flow will continue until pressure equals mixing tendency
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SEMIPERMEABLE MEMBRANES
• A membrane is a barrier between two environments.
• A semipermeable membrane allows certain
molecules to cross.
• All cells and organelles within cells are surrounded by
semipermeable membranes.
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LeChatelier’s Principle
• If a system at equilibrium experiences a
change in concentration, temperature, or
pressure, the equilibrium will shift to
counteract the imposed change,
establishing a new equilibrium
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13
C
H
A
P
T More solute molecules hit membrane from left, so gradual movement of
E
solute to right. At equilibrium, both sides have equal solute molecules.
R
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i
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OSMOTIC DIFFUSION … a probability issue.
Osmosis
Solvent molecules flow through openings in membrane in
order to equalize concentrations of solutions. Note height of
water column, pressure created by equalizing concentration
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Reverse Osmosis
• A concentration cell, running backwards
– Permeable barrier between two different fluids
– Can apply mechanical pressure (e.g a pump)
• Pump pressure can force water through membrane
• Pressure must exceed osmotic pressure for any flow
• Leaves salt behind, which does not fit through pores
– Preferred method today for making Deionized Water
• Less energy use than heat distillation
• Better screening than ion-exchange resins (particulates pass)
• Sea water to fresh water ? Age-old desire in arid places
– Requires pump energy, rejected water is saltier
• Membranes sensitive to contamination blockage
• High pressures for high flow invite membrane failure
• Polymetrics (Santa Clara) was 1970’s pioneer in field
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Reverse Osmosis
apply enough pressure to overcome osmotic pressure …
flow is reversed and solvent pushed out of solution
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Reverse Osmosis
30 atm*14.7 psi/atm ≈ 450 psi ! (your tires have about 30 psi)
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C
H
A
P
T
E
R
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REVERSE OSMOSIS
When excess
pressure is
applied to impure
water, the
backwards flow is
called reverse
osmosis. This
can be used to
purify water.
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OSMOSIS AND DIALYSIS
• These are two ways by which molecules may cross
semipermeable membranes.
• In osmosis, water may cross the membrane, but
not other substances. Osmosis limited to SOLVENTS
• In dialysis, water or small solutes such as ions or
sugars may cross the membrane, but not large
molecules such as proteins or starch.
• In all cases, molecules move through simple
diffusion to equalize solute concentrations.
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CHAPTER 5: Solutions, Colloids, and Membranes
CELL MEMBRANES
• These surround all cells and maintain different
concentrations of ions and molecules inside and
outside the cells.
• Ions and large molecules require special transport
systems to carry them across the membrane as
needed.
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OSMOSIS IN RED BLOOD CELLS (RBCs)
• If RBCs are immersed in hypotonic or hypertonic
solutions, water will cross the RBC membrane
inappropriately, destroying its function.
Eventually the cells in hypotonic solution will burst in what is called
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hemolysis; the cells in hypertonic solution shrivel during crenation.
Definitions
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OSMOSIS AND DIALYSIS
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CHAPTER 5: Solutions, Colloids, and Membranes
DIALYSIS
• In dialysis, small solutes can cross a special
membrane.
• They always cross from high to low concentration.
• Dialysis is used to separate solute molecules from
colloidal particles.
• Kidneys carry out dialysis by
• removing urea and creatinine
and
•retaining water and electrolytes
•Artificial dialysis can be used if kidneys are diseased.
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Creatinine is muscular waste
product, removed by kidneys
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Muscles release Creatinine, healthy kidneys release it
in urine, diseased kidneys require filtration removal.
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CHAPTER 5: Solutions, Colloids, and Membranes
BLOOD HAS PROPERTIES OF ALL THREE
TYPES OF MIXTURES
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Dialysis Methodology
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Small molecules move through pores
to equalize solute concentration
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DIALYSIS
In dialysis, small
molecules and
ions can flow
from a solution
of higher
concentration to
a lower
concentration
solution.
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Tubing Pump
Eccentric wheel squeezes tubing, pushing liquid forward
nothing touches fluid except the tubing, no contamination
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Dialysis treatment center
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Ethylene gas to Polyethylene Plastic
most common plastic, “Poly” n ≥ 1000 ethylene units
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Glucose & Fructose in sugars
Both are C6H12O6, but have different structures
Glucose has 6 member ring, while Fructose has 5
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Sucrose is Sucrose + Fructose
Joined via oxygen bond between molecules,
a simple natural table-sugar polymer we use every day
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Starch polymer
similar bonding structure as sucrose, but n≈600
note that simplified diagram does not show all hydrogen
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Starch polymer
similar bonding structure as sucrose, but n≈600
note that simplified diagram does not show all hydrogen
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Starch polymer can also be branched,
n can be>1000
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Today’s Experiment
• We will observe osmosis
– Solvent goes through the membrane
– Inside pure water moves to salty outside
– Inside salty water absorbs water from outside
• We will observe dialysis
– Smaller molecules (sugar) go through bag
– Large molecules (starch) cannot pass
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Our experiment
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Experiment basics
• Weigh bag before and after osmosis
– Did water bags get heavier or lighter?
• If heavier, water moving into salty bag
• If lighter, water moving out of pure water bag
• Weigh bags before and after dialysis
– Did honey filled bags get heavier?
• Which one gained the most?
– Did sugar pass through the bag?
• Benedict test will detect sugar passage
– Did starch pass through the bag?
• Iodine test will detect starch
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Which was it? (maybe both)
• Chem. test to see of solute moved out
– BOTH osmosis and dialysis can occur
– Test for osmosis is weight gain
– Test for dialysis is passage of sugar
• Test for sugar using reagent
– Turns blueorange if sugar present
– Run 4 test tubes
• One blank, a water only control, expect no change
• One with sugar, test the test …make sure it works
• Water from outside 2 dialysis bags
– If it turns color, sugar = dialysis (unless you’re sloppy)
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Questions
• Google, text, or handbook for structures
– Fructose, Glucose, Vitamin C, Starch
– Computer available at desk, or your own
• Pore size based on formula weight
– Little molecules pass, big ones don’t
• Benedict test for sugars
– Change blue to yellow if sugar present
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Los Alamos National Laboratory's Periodic Table
Group**
Period
1
IA
1A
2
3
1.008
3
4
H
Li
Be
6.941
9.012
11
12
Na Mg
22.99
4
5
8
9
10
3
4
5
6
7
11 12
------- VIII IIIB IVB VB VIB VIIB
IB IIB
-----3B
4B 5B 6B
7B
1B 2B
------- 8 ------
20
21
Ca
Sc
39.10
40.08
37
38
Rb
Sr
85.47
87.62
Cs
87
Fr
(223)
56
88
6
7
8
9
B
C
N
O
F
22
23
24
25
26
27
28
29
30
13
14
Al Si
32
Y
40
41
42
44
45
46
47
48
49
50
72
73
74
(98)
75
17
18
Cl
Ar
33
34
35
51
52
53
I
101.1 102.9 106.4 107.9 112.4 114.8 118.7 121.8 127.6 126.9
76
77
78
79
80
81
82
83
84
85
Pt Au Hg Tl Pb Bi Po At
138.9 178.5 180.9 183.9 186.2 190.2 190.2 195.1 197.0 200.5 204.4 207.2 209.0 (210) (210)
107
108
109
86
Rn
(222)
116
118
---
()
()
()
59
60
61
62
63
64
111
Xe
131.3
---
(257) (260) (263) (262) (265) (266)
110
54
114
58
106
83.80
---
Lanthanide
Series*
105
36
Kr
112
(227)
104
39.95
Ra Ac~ Rf Db Sg Bh Hs Mt --- --- --(226)
89
Ne
20.18
S
Zr Nb Mo Tc Ru Rh Pd Ag Cd In Sn Sb Te
88.91 91.22 92.91 95.94
57
43
10
16
44.96 47.88 50.94 52.00 54.94 55.85 58.47 58.69 63.55 65.39 69.72 72.59 74.92 78.96 79.90
39
4.003
15
26.98 28.09 30.97 32.07 35.45
31
2
He
P
Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br
Ba La* Hf Ta W Re Os Ir
137.3
5
10.81 12.01 14.01 16.00 19.00
19
132.9
7
24.31
13
14
15 16
17
IIIA IVA VA VIA VIIA
3A 4A 5A 6A 7A
K
55
6
8A
2
IIA
2A
1
1
18
VIIIA
()
()
()
65
66
67
68
69
70
71
Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu
140.1 140.9 144.2 (147) 150.4 152.0 157.3 158.9 162.5 164.9 167.3 168.9 173.0 175.0
48
Variation on experiment
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http://www.chemistry.wustl.edu/~edudev/LabTutorials/Dialysis/Kidneys.html
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