Q77 · CSIR-NET Chemistry, June 2012

Paper: CSIR-NET June 2012 · Subject: Physical Chemistry · Chapter: Polymer Chemistry · Topic: Molecular Weight Averages · Marks: 2 · Difficulty: Medium

A polymer sample has the following composition.
Number of MoleculesMolecular Weight
101000
502000
404000
The polydispersity index (P.D.I) of the polymer is
(a)$85000 / 27$
(b)$85 / 81$
(c)850/729
(d)729/850
Answer
Answer: C ✓ checked by 4AB · confidence high
Explanation
M_n = 270,000/100 = 2700; M_w = (10×10⁶ + 50×4×10⁶ + 40×16×10⁶)/270,000 = 8.5×10⁸/2.7×10⁵ = 3148; PDI = 3148/2700 = 850/729.

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