KVPY Sample Paper KVPY Stream-SX Model Paper-9

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 2K \[kg\,mo{{l}^{-\,1}}\]. The boiling point has increased by 6.4 K. % dimerisation of acetic acid is -

A) 50

B) 40

C) 30

D) 20

Correct Answer: B

Solution :

\[\Delta {{T}_{b}}i\,\,{{K}_{b}}.m\]

Given molality \[=\frac{1\times 1000}{250}=4m,\]

\[6.4=i\times 2\times 4\,\,or\,\,i=0.8\]

For dimerization

\[i=1-\frac{\beta }{2}\]

\[\Rightarrow 0.8-1=\frac{-\,\beta }{2}\]

Or \[\beta =0.4\]

\[\Rightarrow 40%\]