Manipal Medical Manipal Medical Solved Paper-2009

  • question_answer
    Both\[HCOOH\]and\[C{{H}_{3}}COOH\]solutions have equal pH. If\[\frac{{{K}_{1}}}{{{K}_{2}}}\](ratio of acid ionization constants) of these acids is 4, their molar concentration ratio will be

    A)  2                 

    B)  0.5

    C)  4                 

    D)  0.25

    Correct Answer: D

    Solution :

     As pH of HCOOH sol. = pH of\[C{{H}_{3}}COOH\]sol.\[[{{H}^{+}}]\]in HCOOH sol.\[=[{{H}^{+}}]\]in\[C{{H}_{3}}COOH\]sol. \[{{K}_{1}}=\frac{[HCO{{O}^{-}}][{{H}^{+}}]}{[HCOOH]}=\frac{{{[{{H}^{+}}]}^{2}}}{[HCOOH]}\] \[{{K}_{2}}=\frac{[C{{H}_{3}}CO{{O}^{-}}][{{H}^{+}}]}{[C{{H}_{ & 3}}COOH]}=\frac{{{[{{H}^{+}}]}^{2}}}{[C{{H}_{3}}COOH]}\] \[\Rightarrow \]\[{{K}_{1}}[HCOOH]={{K}_{2}}[C{{H}_{3}}COOH]\] \[\therefore \]\[\frac{[HCOOH]}{[C{{H}_{3}}COOH]}=\frac{{{K}_{2}}}{{{K}_{1}}}=\frac{1}{4}=0.25\]


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