Question

In a polymer sample, 30% of molecules have a molecular mass of 20,000, 40% have 30,000 and the rest 60,000. What is the weight average molecular mass of the polymer ?

• A. 40300
• B. 30600
• C. 43333
• D. 50400

Answer 1

Answer: (C)

43333

Answer 2

$\bar{M}_w = \frac{30(20000)^2 + 40 (30000)^2 + 30(60000)^2}{30 \times 2000) + (40 + 30000)+(30 \times 60000)} = 43.333$