SCIENCE & ENGINEERING MATERIALS plz i need hepe how o solve this question Molecu
ID: 915802 • Letter: S
Question
SCIENCE & ENGINEERING MATERIALS
plz i need hepe how o solve this question
Molecular weight data for polypropylene are tabulated in Table 2. Calculate: i) The number-average molecular weight ii) The weight-average molecular weight iii) The number-average degree of polymerization iv) The weight-average degree of polymerization (Repeat unit for polypropylene = CH2CH(CH3) and relative molecular mass for carbon and hydrogen is 12 and 1, respectively) Table 2: Molecular weight distribution for polypropylene
Molecular weight data for polypropylene are tabulated in Table 2. Calculate i) The number-average molecular weight ii) The weight-average molecular weight iii) The number-average degree of polymerization iv) The weight-average degree of polymerization (Repeat unit for polypropylene-CH2CH(CH3) and relative molecular mass for carbon and hydrogen is 12 and 1, respectively) Table 2: Molecular weight distribution for polypropylene Molecular weight distributiorn 8000-16000 16000-24000 24000-32000 32000-40000 40000-48000 48000-56000 Xi 0.05 0.16 0.24 0.28 0.20 0.07 0.02 0.10 0.20 0.30 0.27 0.11Explanation / Answer
The number average molecular weight is the total weight of the sample divided by the number of molecules in the sample.
The formula to calculate number average molecular weight is Mn = XiMi
The formula to calculate weight average molecular weight is Wn= XiWi
Where Mi is the mean value of molecular weight distribution
Molecular weight distribution (Mi)
Mean Mi
Xi
Wi
XiMi
WiMi
8000-16000
12000
0.05
0.02
600
240
16000-24000
20000
0.16
0.10
3200
2000
24000-32000
28000
0.24
0.20
6720
5600
32000-40000
36000
0.28
0.30
10080
10800
40000-48000
44000
0.20
0.27
8800
11880
48000-56000
52000
0.07
0.11
3640
5720
Notice that the number average and the weight average molecular are not the same.
The repeated unit MW for polypropylene = 3*12 + 6*1 = 42 g/mol
Therefore NDOP = 33040/42 = 786
Therefore WDOP = 36240/42 = 862
Molecular weight distribution (Mi)
Mean Mi
Xi
Wi
XiMi
WiMi
8000-16000
12000
0.05
0.02
600
240
16000-24000
20000
0.16
0.10
3200
2000
24000-32000
28000
0.24
0.20
6720
5600
32000-40000
36000
0.28
0.30
10080
10800
40000-48000
44000
0.20
0.27
8800
11880
48000-56000
52000
0.07
0.11
3640
5720
Related Questions
Navigate
Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.