BCECE Medical BCECE Medical Solved Papers-2003

  • question_answer
    An acid has pH = 5 and its concentration is 1M. What is the value of \[{{K}_{a}}\] for the acid?

    A)  \[{{10}^{-7}}\]          

    B)  \[{{10}^{-5}}\]

    C)  \[{{10}^{-10}}\]        

    D)  \[{{10}^{-8}}\]

    Correct Answer: C

    Solution :

    Key Idea :                 \[pH=-\log \,\,\sqrt{{{K}_{a}}\times C}\] Given    \[pH=5,\,\,C=1\,M\]                 \[pH-\log \,\sqrt{{{K}_{a}}\times 1}\] or            \[5=-\log \,\,\sqrt{{{K}_{a}}}\] or            \[5=-\frac{1}{2}\log \,\,{{K}_{a}}\] or            \[\log \,\,{{K}_{a}}=10\] \[\therefore \] \[{{K}_{a}}={{10}^{-10}}\]


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