Question

At ${25}^{0}C$ a solution containing 0.2 g of polyisobutene in 100 mL of benzene developed a rise of 2.4mm at osmotic equilibrium. Calculate the molecular weight of polyisobutene if the density of solution is 0.88 g/mL.

Answer 1

Osmotic pressure of polyisobutene in benzene $=hpg$

$=(2.4\times {10}^{-3})\times 0.88\times 9.8$

$=20.6976\times {10}^{-3}Pa$

Now, as osmotic pressure $=conc\times R\times T$

$=\frac{m}{M.W}\times \frac{1000}{V}\times PT$

$\Rightarrow M.W=\frac{0.2\times 1000\times 8.31u\times 298}{20.6976\times {10}^{-3}\times 100}$

$=2.39\times {10}^{3}g$ ${mol}^{-}$