Respuesta :
Number average molecular weight is 110,000 g/mol
Calculation
We have a polymer P made up of two monodisperse fractions.
A with molecular weight of MA = 120000 g/mol and B with MB =100000 g/mol.
The batch contains an equal mole fraction of each component A and B.
Let's suppose a total number (Nt) of mols 2 moles. Equal fraction means XA = 0.5 and XB =0.5
Nt = 2 mol
Na = 2*0.5 = 1 mol
Nb = 2*0.5 = 1 mol.
So, we have 1 mol of A, 1 mol of B and 2 moles in total.
a) The number average molecular weight (NAM) is calculate using the mole numbers of each component. In this case, we will multiple each component molecular weight by the number of moles of each one. After that we will sum them and finally to divide by the total number of moles.
NAM = (Na*MA + Nb*MB)/(Nt)
NAM = (1 mol *120000 g/mol + 1*100000 g/mol ) /(2 mol)
NAM = 110000 g/mol
The number average molecular weight for the polymer P is 110,000 g/mol
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