520. For solutions of one of the fractions of polyisobutylene in benzene, the osmotic pressure was measured depending on the concentration at two temperatures (table below). Determine the molar mass of the fraction from these data. (Note that temperature affects the second virial coefficient, so the two series of results should be considered separately and the resulting molar masses, if they differ not significantly, should be averaged).

s, g/L 1.94 3.06 5.05 7.42 9.90 14.95 23.82
π, mm Hg st., 20 °C 0.179 0.283 0.456 0.627 0.797 1.088 1.472
π, mm Hg st., 40 °С 0.209 0.341 0.569 0.900 1.308 2.210 4.305

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