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KVPY Sample Paper KVPY Stream-SX Model Paper-9

  • question_answer
    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 \[\beta =0.4\]
    \[\Rightarrow 40%\]


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