Q12.107P - Chemistry: Molecular Nature Of Matter And Change

Question

Why is the average molar mass of a polymer sample different from the molar mass of an individual chain?

Step-by-Step Solution

Answer

When the repeating monomer units are linked to form a large molecule, this large molecule is known as a polymer.

 

Step1: Definition

The molecular weight of a polymer is called the molar mass of the polymer.

 The molar mass of a polymer chain depends on two parameters—the molar mass of the repeat unit ${\text{μ}}_{\text{repeat}}$ and the degree of polymerization n

${\text{μ}}_{\text{polymer}}{\text{=\hspace{0.17em}μ}}_{\text{repeat}}\text{×n}$

Step 2: Concept

The average molar mass of polymer is given by

${\mathbf{\mu }}_n\mathbf{=}\frac{\mathbf{total}\mathbf{mass}\mathbf{of}\mathbf{all}\mathbf{chains}}{\mathbf{number}\mathbf{of}\mathbf{moles}\mathbf{of}\mathbf{chains}}$

Here, ${\mathbf{\mu }}_n$  is the average molar mass of the polymer

 

The polymer is made by repetitive units of monomer molecules. When polymer

forms their length and weight differ. 

No one chain length is there; instead, a wide range of lengths is there. 

Hence, the average molar mass of a polymer is different.