Question

Acetic acid undergoes dimerisation, when dissolved in benzene

Molecular mass of acetic acid is found 120. Which among the following relation is correct?
D = theroartical vapour density
d = observed vapour density

• A. $\alpha =2\left(\frac{D - d}{d}\right)$
• B. $\alpha =2\left(\frac{D - d}{D}\right)$
• C. $\alpha =2\left(\frac{d - D}{d}\right)$
• D. $\alpha =\frac{2 d}{D - d}$

Answer 1

Answer: (C)

Here $\alpha =1$
Because $CH_{3}COOH$ will have molecualar mass = 120
Due to 100% association n =2 (for dimerisation)
For association of molecule
$\alpha =\frac{d - D}{d \left(1 - \frac{1}{n}\right)}=\frac{d - D}{d \left(1 - \frac{1}{2}\right)}$
$=\frac{2 \left(\right. d - D \left.\right)}{d}$