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JEE Main & Advanced Sample Paper JEE Main Sample Paper-18

  • question_answer
    A certain buffer contains equal concentration of\[{{X}^{-}}\]and\[HX\]and\[{{K}_{b}}\]for\[{{X}^{-}}\]is\[{{10}^{-10}}\]. The pH of buffer solution is

    A)  4                                            

    B)  7

    C)  10                         

    D)  14

    Correct Answer: A

    Solution :

     \[{{K}_{a}}\times {{K}_{b}}={{K}_{w}}\] \[\Rightarrow \] \[{{K}_{a}}=\frac{{{K}_{w}}}{{{K}_{b}}}=\frac{1\times {{10}^{-14}}}{1\times {{10}^{-10}}}={{10}^{-4}}\] Now, \[pH=p\,{{K}_{a}}+\log \,\frac{[{{X}^{-}}]}{[HX]}\] \[\Rightarrow \] \[pH=p{{K}_{a}}+\log 1=-\,\log \,{{10}^{-4}}+0\] \[=\,4\,\log 10\,=4.\]


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