Polymers are compounds with a repeating structural unit. Consider a sample of po
ID: 566674 • Letter: P
Question
Polymers are compounds with a repeating structural unit. Consider a sample of polystyrene having a molecular weight of 2.50 x 10* g/mol; the formula of polystyrene is (CH2CHX)n, where X is CsHs (here, C&Hs; is a ring of six carbon atoms with one hydrogen atom bonded to five of the six carbon atoms) and n is an integer a. What is the value for n for this polymer sample? b. At 25°C, is this polystyrene sample most likely to be a solid, liquid, gas, or cannot be determined? Justify your choice. What mass in grams of polystyrene is needed to give 10.0 mL of a solution of polystyrene in benzene, CGHs (ring of six carbon atoms, with one hydrogen atom bonded to each carbon atom), having an osmotic pressure of 2.00 mmHg at 25°C? Polystyrene is soluble at room temperature in acetone, (H3C)2CO. Does this surprise you? Be complete in explaining why you are or are not surprised. The freezing point depression constant and the boiling point elevation constant for benzene are 5.12 C m 1, and 2.53 C.mt, respectively. The freezing point and boiling point of benzene are 5.33°C and 80.10°C, respectively, what mass of polystyrene must be dissolved in 10.0 g of benzene (density-0874 g/mL) to lower the freezing point of benzene by 1.00°C. If you did not know the molecular weight of polystyrene and wished to determine its value, would you measure freezing point depression or osmotic pressure? Justify your choice. c. d. e. f.Explanation / Answer
a. Molecular weight of a single polystyrene unit = 104 g/mol
Given molecular weight = 25000 g/mol
Therefore, value of n = 25000/104 = 240 (approx).
b. At 25 degree celcius, polystyrene would be solid because it is a thermoplastic.
c. We know, osmotic pressure = MRT (M: Molarity)
Also, 2mm Hg = 0.00263158 atm
Therefore, 0.00263158 = M*0.08*298
Molarity = 0.00011 M
Also, Molarity = moles/ volume (in litres)
Therefore, moles = 0.00011*(0.01) = 0.0000011 moles
Mass = molecular weight*moles = 25000*0.0000011 = 0.0275g
d. Hildebrand Solubility Parameter determines whether a ploymer is soluble in any solvent or not. In order to be able to dissolve a polymer, the liquid must have an HSP value close to that of the polymer. The values for polystyrene and acetone are 9.13 and 9.77, respectively. Therefore, it is soluabe in acetone.
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