Benzoic acid () is dissolved in benzene. The experimentally determined molar mass based on colligati — Solutions and Colligative Properties Chemistry Question
Question
Benzoic acid ($C_6H_5COOH$) is dissolved in benzene. The experimentally determined molar mass based on colligative property measurements approaches $244\text{ g mol}^{-1}$. Based on this specific observation, what is the predominantly existing state of the benzoic acid molecules in this solution, and what is its approximate degree of association?
Answer: C
💡 Solution & Explanation
The normal theoretical molar mass of benzoic acid is $122\text{ g mol}^{-1}$. The van't Hoff factor is $i = \frac{M_{normal}}{M_{obs}} = \frac{122}{244} = 0.5$. The association formula is $i = 1 + \alpha(\frac{1}{n} - 1)$. If we assume complete dimerization ($n=2, \alpha=1$), then $i = 1 + 1(\frac{1}{2} - 1) = 0.5$. Thus, it exists predominantly as a dimer with nearly $100\%$ association.
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