1

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

2NaCl in an aqueous solution.

CHAPTER 5: Solutions, Colloids, and Membranes

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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10

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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• 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.

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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CHAPTER 5: Solutions, olloids, and Membranes

OSMOTIC DIFFUSION … a probability issue. More solute molecules hit membrane from left, so gradual movement of solute to right. At equilibrium, both sides have equal solute molecules.

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OsmosisSolvent 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 Osmosisapply enough pressure to overcome osmotic pressure …

flow is reversed and solvent pushed out of solution

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Reverse Osmosis30 atm*14.7 psi/atm ≈ 450 psi ! (your tires have about 30 psi)

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When excess pressure is applied to impure water, the backwards flow is called reverse osmosis. This can be used to purify water.

CHAPTER 5: Solutions, Colloids, andMembrnes

REVERSE OSMOSIS

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• 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.

OSMOSIS AND DIALYSIS

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• 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.

CHAPTER 5: Solutions, Colloids, and Membranes

CELL MEMBRANES

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• 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 hemolysis; the cells in hypertonic solution shrivel during crenation.

OSMOSIS IN RED BLOOD CELLS (RBCs)

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Definitions

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OSMOSIS AND DIALYSIS

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• 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.

CHAPTER 5: Solutions, Colloids, and Membranes

DIALYSIS

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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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In dialysis, small molecules and ions can flow from a solution of higher concentration to a lower concentration

solution.

DIALYSIS

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Tubing PumpEccentric wheel squeezes tubing, pushing liquid forwardnothing 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 sugarsBoth are C6H12O6, but have different structures

Glucose has 6 member ring, while Fructose has 5

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Sucrose is Sucrose + FructoseJoined via oxygen bond between molecules,

a simple natural table-sugar polymer we use every day

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Starch polymersimilar bonding structure as sucrose, but n≈600

note that simplified diagram does not show all hydrogen

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Starch polymersimilar 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 blueorange 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

18

VIIIA 8A

1 1 H

1.008

2

IIA 2A

13

IIIA 3A

14

IVA 4A

15

VA 5A

16

VIA 6A

17

VIIA 7A

2 He 4.003

2 3

Li 6.941

4 Be 9.012

5 B

10.81

6 C

12.01

7 N

14.01

8 O

16.00

9 F

19.00

10 Ne 20.18

8 9 10

3 11

Na 22.99

12 Mg 24.31

3

IIIB 3B

4

IVB 4B

5

VB 5B

6

VIB 6B

7

VIIB 7B

------- VIII -------

------- 8 -------

11

IB 1B

12

IIB 2B

13 Al 26.98

14 Si

28.09

15 P

30.97

16 S

32.07

17 Cl

35.45

18 Ar 39.95

4 19 K

39.10

20 Ca 40.08

21 Sc 44.96

22 Ti

47.88

23 V

50.94

24 Cr 52.00

25 Mn 54.94

26 Fe 55.85

27 Co 58.47

28 Ni 58.69

29 Cu 63.55

30 Zn 65.39

31 Ga 69.72

32 Ge 72.59

33 As 74.92

34 Se 78.96

35 Br 79.90

36 Kr 83.80

5 37

Rb 85.47

38 Sr

87.62

39 Y

88.91

40 Zr

91.22

41 Nb 92.91

42 Mo 95.94

43 Tc (98)

44 Ru 101.1

45 Rh 102.9

46 Pd 106.4

47 Ag 107.9

48 Cd 112.4

49 In

114.8

50 Sn 118.7

51 Sb 121.8

52 Te 127.6

53 I

126.9

54 Xe 131.3

6 55

Cs 132.9

56 Ba 137.3

57 La* 138.9

72 Hf 178.5

73 Ta 180.9

74 W

183.9

75 Re 186.2

76 Os 190.2

77 Ir

190.2

78 Pt

195.1

79 Au 197.0

80 Hg 200.5

81 Tl

204.4

82 Pb 207.2

83 Bi

209.0

84 Po (210)

85 At (210)

86 Rn (222)

7 87 Fr

(223)

88 Ra (226)

89 Ac~ (227)

104 Rf (257)

105 Db (260)

106 Sg (263)

107 Bh (262)

108 Hs (265)

109 Mt (266)

110 ---

()

111 ---

()

112 ---

()

114 ---

()

116 ---

()

118 ---

()

Lanthanide Series*

58 Ce 140.1

59 Pr

140.9

60 Nd 144.2

61 Pm (147)

62 Sm 150.4

63 Eu 152.0

64 Gd 157.3

65 Tb 158.9

66 Dy 162.5

67 Ho 164.9

68 Er

167.3

69 Tm 168.9

70 Yb 173.0

71 Lu 175.0

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Variation on experiment

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http://www.chemistry.wustl.edu/~edudev/LabTutorials/Dialysis/Kidneys.html