Question

The formula for calculating $\overline{M_n}$ of a polymer is:

• A. $\frac{\sum NiMi}{\sum Ni}$
• B. $\frac{\sum NiMi}{\sum Mi}$
• C. $\frac{\sum NiM{i}^2}{\sum Mi}$
• D. $\frac{\sum NiM{i}^2}{\sum NiMi}$

Answer 1

The correct option is A $\frac{\sum NiMi}{\sum Ni}$

$\overline{M_n}$ is the number average molecular mass of a polymer which is calculated as the ratio of total mass of all the molecules of a sample polymer divided by the total number of molecules.
Hence, $\overline{M_n}=\frac{\sum NiMi}{\sum Ni}$.