Benzoic acid dimerises in benzene to the extent $α = 0.60$ in benzene ( $2 A <=> A X_{2}$ ; use $i = 1 - α /2$ ). A solution has stoichiometric concentration $0.020 mol L^{- 1}$ of benzoic acid at $300 K$ . With $R = 0.0821 L atm mo l^{- 1} K^{- 1}$ and $1 atm = 760 mmHg$ , find its osmotic pressure in mmHg (nearest integer).

Numerical answer type, answer in mmHg, tolerance 1.

Answer: 262 mmHg

With

α = 0.60

i = 1 - 0.30 = 0.70

π = i CRT = 0.70 \times 0.020 \times 0.0821 \times 300 = 0.3448

atm. In mmHg:

0.3448 \times 760 = 262.1

, about 262 mmHg.