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JIPMER Jipmer Medical Solved Paper-2001

  • question_answer
    The dissociation constant of HCN is \[5\times {{10}^{-8}}\]. The pH of the solution prepared by mixing 1.5 moles of HCN and 0.15 moles of KCN in water and making up die total volume to \[0.5\,d{{m}^{3}}\]is:

    A)  7.3020 

    B)                         5.3020 

    C)         6.3010           

    D)         6.6990

    Correct Answer: C

    Solution :

    The solution of HCN and KCN is an acidic Buffer solution. Hence, from Hendarsons equation: \[pH=-\log \,{{K}_{a}}+\log \frac{[Salt]}{[Acid]}\] \[=-\log \,(5\times {{10}^{-8}})+\log \frac{0.15\text{/}0.5}{1.5\text{/}0.5}\] \[=-\log 5-\log {{10}^{-8}}+\log \frac{1}{10}\] \[=-\,0.6990+8+(-1)\] \[=6.3010\]


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