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Osmosis

Osmosis. There are many times in nature when a solvent will pass spontaneously through a semipermeable membrane , which is a membrane permeable to solvent, but not solute . The osmotic pressure , П , is the pressure that must be applied to stop the influx of solvent. Osmosis.

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Osmosis

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  1. Osmosis There are many times in nature when a solvent will pass spontaneously through a semipermeable membrane, which is a membrane permeable to solvent, but not solute. The osmotic pressure, П, is the pressure that must be applied to stop the influx of solvent.

  2. Osmosis • Examples: • Transport of fluids through living cell • membranes , • (b) Basis of osmometry, determination of • molecular mass by measurement of osmotic • pressure.

  3. pV = nRT n = g/M c = g/V p = cRT Osmometry: Real Science h Semipermeable membrane: stops polymers, passes solvent.

  4. Osmosis Eventually the pressure difference between the arms stops osmosis.

  5. Van’t Hoff Eq.

  6. An Example

  7. A solution of polystyrene in benzene contains 10 g/L. The equilibrium height of the column of solution (density 0.88 g cm-3) in the osmometer corrected for capillary rise is 11.6 cm at 25oC. What is the molar mass of polystyrene, assuming the solution is ideal. The osmotic pressure of an aqueous solution at 300 K is 120 kPa. Calculate the freezing point of the solution.

  8. The Virial form of the Van’t Hoff Equation Osmotic pressure is easily measured, and is quite large. Osmometry can be applied for the determination of molecular weights of large molecules (proteins, synthetic polymers), which dissolve to produce less than ideal solutions. The Van’t Hoff equation can be rewritten in the virialform: where B is the empirically determined osmotic virial coefficient Π= [B] RT {1 + B [B] + ...}

  9. Consider poly (vinyl chloride) PVC, in cyclohexanone at 298 K Pressures are expressed in terms of heights of solution, ρ=0.980 g cm-3 in balance with the osmotic pressure c (g L-1) 1.00 2.00 4.00 7.00 9.00 h (cm) 0.28 0.71 2.01 5.10 8.00 Use Π = [B] RT {1 + B [B] + …} with [B] = c/M, where c is the mass concentration and M is the molar mass. The osmotic pressure is related to the hydrostatic pressure by Π = ρgh, where g = 9.81 m s-2. Then:

  10. Plot h/ c vs. c to find M, expecting a straight line with intercept RT/ ρgM at c = 0. Data set: c(g L-1) 1.00 2.00 4.00 7.00 9.00 h/c(cm g-1 L) 0.28 0.36 0.53 0.729 0.889

  11. The data give an intercept of 0.21.

  12. The data give an intercept of 0.21 cm g-1 L, which is equal to RT/ ρgM Thus: where we have used 1 kg m2 s-2=1J

  13. Viscometery

  14. In a Viscometery Experiment, We Use, Solutions and Count the Time

  15. Capillary viscometers: • (A) Ubbelohde, and • (B) Cannon-Fenske.

  16. t rel = = o to IUPAC terminology of solution viscosities  : solution viscosity o: solvent viscosity                                          t : flow time of solution                                         t o: flow time of solvent • IUPAC suggested the terminology of solution viscosities as following. •   Relative viscosity :

  17. IUPAC terminology of solution viscosities Specific Viscosity Reduced Viscosity Inherent Viscosity Intrinsic Viscosity

  18. B. Mark-Houwink-Sakurada Equation Mw> Mv > Mn ? Derive The MHS equation (use Phys. Chem references

  19. Representative Viscosity-Molecular Weight Constants Solvent Cyclohexane Cyclihexane Benzene Decalin Benzyl alcohol Cyclohexanone Toluene Toluene DMFg DMF 1-Chlorobutane 1-Chlorobutane M-Cresol M-Cresol Temperature, oC 35 d 50 25 135 155.4d 20 30 30 25 25 30 30 25 25 Molecular Weight Range  10-4 8-42e 4-137e 3-61f 3-100e 4-35e 7-13f 5-50f 5-16f 5-27e 3-100f 5-55e 4.18-81e 0.04-1.2f 1.4-5f Polymer Polystyrene (atactic)c Polyethylene (low pressure) Poly(vinyl chloride) Polybutadiene 98% cis-1,4, 2% 1,2 97% trans-1,4, 3% 1,2 Polyacrylonitrile Poly(methyl methacrylate-co-styrene) 30-70 mol% 71-29 mol% Poly(ethylene terephthalate) Nylon 66 a 0.50 0.599 0.74 0.67 0.50 1.0 0.725 0.753 0.81 0.75 0.67 0.63 0.95 0.61 K 103 80 26.9 9.52 67.7 156 13.7 30.5 29.4 16.6 39.2 17.6 24.9 0.77 240 cAtactic defined d temperature. eWeight average. fNumber average. gN,N-dimethylformamide.

  20. Representative Plot

  21. Viscosity and Units ? Prepare a report with the definitions for: 1) Dynamic Viscosity; 2) Shear Viscosity; 3) Bulk Viscosity and 4) Extensional Viscosity.

  22. Viscosity and Terms Viscosity; is Thickness: “Thin” like water, “Thick” like honey

  23. GPC

  24. Moo! Woof! A riddle After a hurricane, many trees fall over and bend into a river. Also, a cow and a dog fall into a flooded river. Which one reaches the ocean first, cow or dog?

  25. GPC • Solvent flow carries molecules from left to right; big ones come • out first while small ones get caught in the pores. • It is thought that particlevolume controls the order of elution. • But what about shape?

  26. The following plot of relative amount of the large solute (blue) and of the smaller solute (red) goes with the animation. • Larger solutes elute EARLIER, smaller solutes LATER, from a size exclusion column.

  27. Molecular Weight Distribution Gel Permeation Chromatography (GPC) a. GPC or SEC (size exclusion chromatography) b. GPC method is modified column chromatography. c. Packing material: Poly(styrene-co-divinylbezene), glass or silica bead swollen and porous surface. d. Detector : RI, UV, IR detector, light scattering detector e. Pumping and fraction collector system for elution. f. By using standard (monodisperse polystyrene), we can obtain Mn , Mw .

  28. Schematic representation of a gel permeation chromatograph.

  29. c c log10M DRI degas c log10M Simple SEC log10M Ve pump injector

  30. Detector response Baseline Elution volume (Vr) (counts) Typical gel permeation chromatogram. Dotted lines represent volume “counts.”

  31. 106 Molecular weight (M) 105 104 103 Retention volume (Vr) (counts) Typical semilogarithmic calibration plot of molecular weight versus retention volume.

  32. 109 108 107 106 105 Universal calibration for gel permeation chromatography. THF, tetrahydrofuran. Log([η]M)            Polystyrene (linear) Polystyrene (comb) Polystyrene (star) Heterograft copolyner Poly (methyl methacrylate) Poly (vinyl chloride) Styrene-methyl methacrylate graft copolymer Poly (phenyl siloxane) (ladder) Polybutadiene           18 20 22 24 26 28 30 Elution volume ,5 ml counts, THF solvent

  33. 1 K1 K2 logM2 = ( )log( ) + ( 1 + a1 )logM1 1 + a2 1 + a2 Universal calibration method [η]1M1 = [η]2M2

  34. Universal Calibration Equations []AMA = []SMS= f (Ve) Universal Calibration A = analyte; S = standard [h] = KMa Mark-Houwink Relation Combine to get these two equations, useful only if universal calibration works!

  35. Using Universal Calibration Curve

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