Question

The osmotic pressure of a solution of a synthetic polyisobutylene in benzene was determined at ${25}^{\circ }C.$ A sample containing 0.20 g of solute per 100 cm${}^3$ of solution developed a rise of 2.4 mm at osmotic equilibrium. The density of the solution was 0.88 $g/c{m}^3.$ What the molecular weight of the polyisobutylene?

• A. $1.2\times {10}^{5}g/mol$
• B. $2.4\times {10}^{5}g/mol$
• C. $4.1\times {10}^{6}g/mol$
• D. $8.1\times {10}^{6}g/mol$

Answer 1

The correct option is B $2.4\times {10}^{5}g/mol$

In terms of osmotic pressure,

Molecular weight of solute is defined as,

$M=\frac{w\times R\times T}{O.P\times V}$

$O.P=0.88\times {10}^3\times 10\times 2.4\times {10}^{-3}=21.12Pa$

$M=\frac{0.20\times 298\times 8.314}{(21.12\times 100\times {10}^{-6})}$

$M=2.4\times {10}^{5}g/mole$

Hence, option B is correct