A rubber sample has three groups of chains: 250 chains of molar mass $26000 g mo l^{- 1}$ , 450 chains of $58000 g mo l^{- 1}$ and 300 chains of $97000 g mo l^{- 1}$ . Using $\overline{M}_{n} = \sum N_{i} M_{i} / \sum N_{i}$ , calculate the number-average molar mass to the nearest integer.

Numerical answer type, answer in g/mol, tolerance 0.5.

Answer: 61700 g/mol

\sum N_{i} M_{i} = 250 (26000) + 450 (58000) + 300 (97000) = 6.5 \times 1 0^{6} + 2.61 \times 1 0^{7} + 2.91 \times 1 0^{7} = 6.17 \times 1 0^{7}

\sum N_{i} = 1000

. So

\overline{M}_{n} = 61700 g mo l^{- 1}