Question

How to calculate the Number Average Molecular Weight for Polycarbonate

Answer #1

The number average molecular weight is the total weight of the sample divided by the number of molecules in the sample.

In mathematical form, the total mass is N_{i}M_{i},
where N_{i} is the number of molecules of weight
M_{i}.

For example is you have the following data

Number of Molecules, N_{i} |
Mass of Each Molecule, M_{i} |
Total Mass of Each Type of Molecule,
N_{i}M_{i} |
---|---|---|

1 | 20000 | 20000 |

3 | 24000 | 72000 |

5 | 27000 | 135000 |

8 | 30000 | 240000 |

5 | 33000 | 165000 |

3 | 35000 | 105000 |

2 | 40000 |
80000 |

Then N_{i}M_{i},
= 817000, The total number of molecules is summation of the first
column which is 27

So number average molecular weight will be 817000/27 = 30259 is the number avergae molecular weight.

Molecular weight data for some polymer are tabulated.
Determine:
a) The number-average molecular weight
b) The weight-average molecular weight
c) What is the number-average degree of polymerization for this
polymer?
d) What is the weight-average degree of polymerization for this
polymer?
Molecular Weight
Range (g/mol)
xi
wi
8,000-16,000
0.05
0.02
16,000-24,000
0.20
0.10
24,000-32,000
0.20
0.25
32,000-40,000
0.25
0.25
40,000-48,000
0.23
0.20
48,000-56,000
0.07
0.18

The tensile strength of a poly(methyl methacrylate) (PMMA)
polymer with a number-average molecular weight of 30,00 g/mol is
found to be 50 MPa, while the tensile strength of a second sample
having a number average molecular weight of 50,000 g/mol is 150
MPa.
a) Estimate the tensile strength at a number average molecular
weight of 40,000 g/mol.
b) Estimate the tensile strength at a number average molecular
weight of 1,000 g/mol.
c) Estimate the tensile strength at a number average...

The following table lists molecular weight data for a
polypropylene material. Compute (a) the number-average molecular
weight, (b) the weight-average molecular weight, and (c) the degree
of polymerization. please show equations and calculations used.
thank you
Molecular Weight Range (g/mol) xi wi
8,000–16,000 0.05 0.02
16,000–24,000 0.16 0.10
24,000–32,000 0.24 0.20
32,000–40,000 0.28 0.30
40,000–48,000 0.20 0.27 48,000–56,000 0.07 0.11

The number-average molecular weight of a poly(styrene-butadiene)
alternating copolymer is 1346000 g/mol; determine the average
number of (a) styrene and
(b)butadiene repeat units per molecule.

The glass transition temperature of a linear polymer with number
average molecular weight MN =2300 was measured at 120°C. This
increased to 155°C for the same linear polymer with MN =9000. A
branched version of this polymer with MN =7200 was found to have a
Tg=105°C. Calculate the average number of branches per molecule in
this branched polymer.

Poly(vinyl acetate) of number-average molecular weight of
100,000 is hydrolyzed to poly(vinyl alcohol). Oxidation of the
latter with periodic acid to cleave 1,2-diol linkages yield a
poly(vinyl alcohol) with Xn = 200. Calculate the
percentage of head-to-tail and head-to-head linkages in the
poly(vinyl acetate).

How do you calculate the molecular weight of an unknown salt
given the concentration and known mass?
Unknown starting mass: 0.0484g
Unknown concentration: 0.00552 mM

The genome of E. coli has a molecular weight of 2.5 x 109 Da (Da
stands for Dalton).
1. Knowing that the average molecular weight of a nucleotide is 300
Da, the distance between two adjacent nucleotides is 0.34 nm, and
the number of base pairs per turn of helix is 10, you are asked to
calculate.
- The number of base pairs in the E. coli genome
- The length of the E. coli genome
- The number of...

Using the total structure weight (= molecular weight) given in
the PDB entry, calculate the molarity of a 0.3 mg/mL solution of a
lactate dehydrogenase solution. You must state your chosen PDB
entry ID

If 100 g of air consists of 77% by weight of nitrogen (N2,
molecular weight = 28), and 23% by weight of oxygen (O2, molecular
weight = 32), calculate (a) the mean molecular weight of air, (b)
mole fraction of oxygen, (c) concentration of oxygen in mol/m3 and
kg/m3, if the total pressure is 1.5 atm and the temperature is
25°C.

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