Question

A polymer has following molar mass distribution:

Number of molecules Molar mass ($g/mol$)

$50$ $5000$

$75$ $6000$

Calculate the number average molar mass (${\stackrel{-}{M}}_n$) of the polymer.

Answer 1

Given,

$n_1=50$

$n_2=75$

$M_1=5000g/mol$

$M_2=6000g/mol$

The number average molar mass ${\stackrel{-}{M}}_n$ is given as:

${\stackrel{-}{M}}_n=\frac{\sum n_i{M}_i}{\sum n_i}$

By putting the values in the formula we get,

${\stackrel{-}{M}}_n=\frac{n_1{M}_1+n_2{M}_2}{n_1+n_2}=\frac{50\times 5000+75\times 6000}{50+75}=5600g/mol$