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CMC Medical CMC-Medical VELLORE Solved Paper-2011

  • question_answer
    The dissociation constant of acetic acid \[{{K}_{a}}\]is\[1.74\times {{10}^{-5}}\] at 298 K. The pH of a solution of 0.1 M acetic acid is

    A)  2.88                                      

    B)  3.6

    C)  4.0                                        

    D)  1.0

    E)  2.0

    Correct Answer: A

    Solution :

                                    \[C=0.1\,M\] \[{{K}_{a}}=1.74\times {{10}^{-5}}\] According to Ostwald dilution formula, \[[{{H}^{+}}]=\sqrt{{{K}_{a}}\times C}\] \[=\sqrt{1.74\times {{10}^{-5}}\times 0.1}\] \[=\sqrt{0.017\times {{10}^{-4}}}\] \[pH=-{{\log }_{10}}[{{H}^{+}}]\] \[=-{{\log }_{10}}[\sqrt{0.017\times {{10}^{-4}}}]\] \[pH=2.88\]


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