A quantity of 2.0 g of benzoic acid dissolved in 26.0 g of benzene shows a depression in freezing po — Solutions and Colligative Properties Chemistry Question

💡 Solution & Explanation

The theoretical molar mass of benzoic acid ($C_6H_5COOH$) is 122 g/mol. The observed molar mass $M_{obs} = (1000 \times K_f \times w) / (\Delta T_f \times W) = (1000 \times 4.88 \times 2.0) / (1.60 \times 26.0) = 9760 / 41.6 \approx 234.6 \text{ g/mol}$. The van't Hoff factor $i = M_{theo} / M_{obs} = 122 / 234.6 = 0.52$. For dimerization, $i = 1 - \alpha/2 \implies 0.52 = 1 - \alpha/2 \implies \alpha/2 = 0.48 \implies \alpha = 0.96$. The percentage association is 96%. Therefore, correct answer is 0096.