Question

1 mol $C{H}_{3}COOH$ is added in 250 g benzene. Acetic acid dimerises in benzene due to hydrogen bond. $K_b$ of benzene is 2 K $kgmo{l}^{-1}$. The boiling point has increased by 6.4 K. % dimerisation of acetic acid is :

• A. $50$
• B. $40$
• C. $30$
• D. $20$

Answer 1

Answer: (B)

$40$

$\Delta T_b=i{K}_b.m$

Given molality $=\frac{1\times 1000}{250}=4m$

$\Delta T_b=i{K}_{b}m$

$6.4=i\times 2\times 4$

$\Rightarrow i=0.8$

For dimerisation,

$i=1-\frac{\beta }{2}\Rightarrow 0.8-1=-\frac{\beta }{2}$

$\beta =0.4$

$\Rightarrow \beta \%=40$%

Option B is correct.