A polydisperse polymer sample has ten molecules of molar mass 20,000 g mol⁻¹ and fifteen molecules of molar mass 10,000 g mol⁻¹. The number-average molar mass (g mol⁻¹) (Mn) of the sample is

Q68 · CSIR-NET Chemistry, June 2017

Paper: CSIR-NET June 2017 · Subject: Physical Chemistry · Chapter: Polymer Chemistry · Topic: Polymer Chemistry – General · Marks: 2 · Difficulty: Medium

A polydisperse polymer sample has ten molecules of molar mass $20,000 \mathrm{g} \mathrm{mol}^{-1}$ and fifteen molecules of molar mass $10,000 \mathrm{g} \mathrm{mol}^{-1}$. The number-average molar mass $\left(\mathrm{g} \mathrm{mol}^{-1}\right)\left(\overline{\mathrm{M}}_{\mathrm{n}}\right)$ of the sample is

(a)13,000

(b)14,000

(c)15,000

(d)16,000

Answer

Answer: B ✓ checked by 4AB · confidence high

Explanation

M_n = (10×20,000 + 15×10,000)/25 = 350,000/25 = 14,000 g mol⁻¹.

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