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Unformatted text preview: ChemE 178 HW7 Due Oct31 1.) The following osmotic pressure data was obtained for polystyrene in toluene at 25 C. Concentration (g/cm 3 x 10 3 ) (cm toluene) 2.56 0.325 3.8 0.545 5.38 0.893 7.8 1.578 8.86 1.856 The density of toluene is 0.8618g/cm 3 and g=981 cm/s 2 . a) Calculate the number average molecular weight. Osmotic pressure can be related to molecular weight and the second virial coefficient by: c A M RTc n 2 1 + = To find M n , plot /RTc vs c. The yintercept of the plot is 1/M n . In order to make the plot, put all of the data into a consistent set of units. I used MKS (meter, kilogram, second units), but CGS (centimeter, gram, second units) is also good. Pressure expressed in terms of centimeters of Toluene is a rather ungainly unit. It is better to convert it to Pascals immediately . So convert concentration to kg/m 3 and convert osmotic pressure to Pa: C (g/cm 3 x 103 ) (cm toluene) (Pa) C (kg/m 3 ) 2.56 0.325 27.47634 2.56 3.8 0.545 46.07571 3.8 5.38 0.893 75.49652 5.38 7.8 1.578 133.4082 7.8 8.86 1.856 156.911 8.86 Now calculate gh...
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This note was uploaded on 12/09/2011 for the course CHEM ENG 178 taught by Professor Segalman during the Fall '08 term at University of California, Berkeley.
 Fall '08
 SEGALMAN

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