KVPY Sample Paper KVPY Stream-SX Model Paper-17

\[1\,mol\,C{{H}_{3}}COOH\] is added in \[250\text{ }g\] 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 \[6.4K.\text{ }%\] dimerisation of acetic acid is :

A) 50

B) 40

C) 30

D) 20

Correct Answer: B

Solution :

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

Given molality \[\text{=}\frac{1\times 1000}{250}=4m,\] \[6.4=i\times 2\times 4\] or \[i=0.8\]

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

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

or \[\beta =0.4\]\[\Rightarrow \]40%