Q113 · CSIR-NET Chemistry, December 2015

Paper: CSIR-NET December 2015 · Subject: Physical Chemistry · Chapter: Polymer Chemistry · Topic: Molecular Weight Averages · Marks: 2 · Difficulty: Medium

The correct expression for the product $\left(\left(\overline{\mathrm{M}}_{\mathrm{n}}\right) \cdot\left(\left(\overline{\mathrm{M}}_{\mathrm{w}}\right)\right)\right)\left[\left(\left(\overline{\mathrm{M}}_{\mathrm{n}}\right.\right.\right.$ and $\left(\left(\overline{\mathrm{M}}_{\mathrm{w}}\right.\right.$ are the number average and weight average molar masses, respectively, of a polymer] is
(a)$\mathrm{N}^{-1} \sum_{\mathrm{i}} \mathrm{N}_{\mathrm{i}} \mathrm{M}_{\mathrm{i}}$
(b)$\mathrm{N}^{-1} \sum_{\mathrm{i}} \mathrm{N}_{\mathrm{i}} \mathrm{M}_{\mathrm{i}}^{2}$
(c)$\mathrm{N} / \sum_{\mathrm{i}} \mathrm{N}_{\mathrm{i}} \mathrm{M}_{\mathrm{i}}$
(d)$\mathrm{N} / \Sigma_{\mathrm{i}} \mathrm{N}_{\mathrm{i}} \mathrm{M}_{\mathrm{i}}^{2}$
Answer
Answer: B ✓ checked by 4AB · confidence high
Explanation
M_n M_w = (ΣN_iM_i/N)(ΣN_iM_i²/ΣN_iM_i) = N⁻¹ ΣN_iM_i².

Study loop for Polymer Chemistry

1. Practise the PYQsPrevious-year questions, with answers

· Browse this chapter in the app