HW4 ENME382 S10 Section0201 solution

HW4 ENME382 S10 Section0201 solution - 4.3 Below, molecular...

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4.3 Below, molecular weight data for a polytetrafluoroethylene material are tabulated. Compute (a) the number-average molecular weight, (b) the weight-average molecular weight, and (c) the degree of polymerization. Molecular Weight Range ( g/mol ) x i w i 10,000–20,000 0.03 0.01 20,000–30,000 0.09 0.04 30,000–40,000 0.15 0.11 40,000–50,000 0.25 0.23 50,000–60,000 0.22 0.24 60,000–70,000 0.14 0.18 70,000–80,000 0.08 0.12 80,000–90,000 0.04 0.07 Solution (a) From the tabulated data, we are asked to compute M n , the number-average molecular weight. Using Equation 4.5a, this is computation is carried out below. Molecular wt Range Mean M i x i x i M i 10,000-20,000 15,000 0.03 450 20,000-30,000 25,000 0.09 2250 30,000-40,000 35,000 0.15 5250 40,000-50,000 45,000 0.25 11,250 50,000-60,000 55,000 0.22 12,100 60,000-70,000 65,000 0.14 9100 70,000-80,000 75,000 0.08 6000 80,000-90,000 85,000 0.04 3400 ____________________________ M n = x i M i = 49,800 g/mol
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(b) From the tabulated data, we are asked to compute M w , the weight-average molecular weight. Thus, using Equation 4.5b, this computation is carried out as follows: Molecular wt. Range
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This note was uploaded on 11/28/2010 for the course ENME 250 taught by Professor Shang during the Spring '10 term at Maryland.

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HW4 ENME382 S10 Section0201 solution - 4.3 Below, molecular...

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