A given polymer sample contains 30% molecules with a molecular mass of 20,000, 40% with a mass of 30 — Polymers Chemistry Question

💡 Solution & Explanation

$M_w = \frac{\sum N_i M_i^2}{\sum N_i M_i}$. The numerator is $30(20k)^2 + 40(30k)^2 + 30(60k)^2 = 1.56 \times 10^{11}$. The denominator is $30(20k) + 40(30k) + 30(60k) = 3.6 \times 10^6$. $1.56 \times 10^{11} / 3.6 \times 10^6 \approx 43,333.33$.