JCECE Engineering JCECE Engineering Solved Paper-2011

  • question_answer
    Which of the following acids has the smallest dissociation constant?

    A) \[C{{H}_{3}}CHFCOOH\]               

    B) \[FC{{H}_{2}}C{{H}_{2}}COOH\]

    C) \[BrC{{H}_{2}}C{{H}_{2}}COOH\]              

    D) \[C{{H}_{3}}CBrCOOH\]

    Correct Answer: C

    Solution :

    Lower the acidic character, smaller is the value of dissociation constant.                 Acidity\[\propto \] dissociation constant. \[-I\](inductive effect) of \[F\] is more than\[Br\], so \[C{{H}_{3}}CHFCOOH\] is a stronger acid as compared to\[C{{H}_{3}}CHBrCOOH\]. As the distance between electron withdrawing group and \[-COOH\] group increases, acidity decreases. Thus, the order of acidity and thus, of dissociation constant is \[\underset{(smallest\,\,{{K}_{a}})}{\mathop{BrC{{H}_{2}}C{{H}_{2}}COOH}}\,>FC{{H}_{2}}C{{H}_{2}}COOH\] \[<C{{H}_{3}}CHBrCOOH<C{{H}_{3}}CHFCOOH\]


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