Question

A solution containing 5 g acetic acid in 100 g $H_{2}O(O_{H_{2}O}^0=23.756mm$ at ${25}^{o}C$) shows a vapour pressure of 23.40 mm, whereas same mass of acetic acid in 100 g $C_6{H}_6(P_{C_6{H}_6}^0=72.5mm$ at ${25}^{o}C$) shows a vapour pressure of 70.0 mm. Assuming non-volatile nature of $C{H}_{3}COOH$, discuss the data given to discuss hydrogen bonding:

• A. acetic acid exists as a monomer
• B. acetic acid exists as a dimer
• C. acetic acid is dissociated
• D. acetic acid exists as an anhydride

Answer 1

Answer: (B)

acetic acid exists as a dimer

Molar mass of $C{H}_{3}COOH$ in $H_{2}O$ and $C_6{H}_6$ are $59.16$ and $109.2$ respectively. Thus, $C{H}_{3}COOH$ is dimerized in $C_6{H}_6$ due to H-bonding.

Hence, option B is correct.