Question

The formula for calculating $\overline{M_w}$ 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 D $\frac{\sum NiM{i}^2}{\sum NiMi}$

$\overline{M_W}$ is the mass average molecular mass of a polymer, which is calculated as the ratio of total mass of groups of molecules having different molecular masses multiplied with their respective molecular mass to the the total mass of all the molecules.
Therefore, $\overline{M_W}=$ $\frac{\sum NiM{i}^2}{\sum NiMi}$.