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JEE Main & Advanced JEE Main Solved Paper-2017

  • question_answer
    The freezing point of benzene decreases by \[0.45{{\,}^{o}}C\]when 0.2 g of acetic acid is added to 20 g of benzene. If acetic acid associates to form a dimer in benzene, percentage association of acetic acid in benzene will be :- (\[{{K}_{f}}\]for benzene \[=5.12\,K\,kg\,mo{{l}^{-1}}\])     JEE Main Solved Paper-2017

    A)  64.6%                  

    B)  80.4%

    C)  74.6%                  

    D)  94.6%

    Correct Answer: D

    Solution :

     In benzene                 \[2C{{H}_{3}}COOH\rightleftharpoons {{(C{{H}_{3}}COOH)}_{2}}\]                 \[i=1+\left( \frac{1}{2}-1 \right)\alpha \] \[i=1-\frac{\alpha }{2}\]Here \[\alpha \]is degree of association \[\Delta {{T}_{f}}=i{{K}_{f}}m\]\[0.45=\left( 1-\frac{\alpha }{2} \right)(5.12)\frac{\left( \frac{0.2}{60} \right)}{\frac{20}{1000}}\] \[1-\frac{\alpha }{2}=0.527\] \[\alpha =0.945\] % degree of association =94.5%


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