JCECE Medical JCECE Medical Solved Paper-2012

  • question_answer
    At\[25{{\,}^{o}}C,\] the dissociation constant of a base, BOH, is \[1.0\times {{10}^{-12}}.\]The concentration of hydroxyl ions in 0.01 M aqueous solution of the base would be

    A) \[2.0\times {{10}^{-6}}mol\,{{L}^{-1}}\]

    B)  \[1.0\times {{10}^{-5}}mol\,{{L}^{-1}}\]

    C)  \[1.0\times {{10}^{-6}}mol\,{{L}^{-1}}\]

    D)  \[1.0\times {{10}^{-7}}mol\,{{L}^{-1}}\]

    Correct Answer: B

    Solution :

     Base BOH is dissociated as follows \[BOH{{B}^{+}}+O{{H}^{-}}\] So, the dissociation constant of base BOH \[{{K}_{b}}=\frac{[{{B}^{+}}][O{{H}^{-}}]}{[BOH]}\] ?(i) At equilibrium, \[[{{B}^{+}}]=[O{{H}^{-}}]\] \[\therefore \] \[{{K}_{b}}=\frac{{{[O{{H}^{-}}]}^{2}}}{[BOH]}\] Given that \[{{k}_{b}}=1.0\times {{10}^{-12}}\] and \[[BOH]=0.01\,M\] Thus, \[1.0\times {{10}^{-12}}=\frac{{{[O{{H}^{-}}]}^{2}}}{0.01}\] \[{{[O{{H}^{-}}]}^{2}}=1\times {{10}^{-14}}\] \[[O{{H}^{-}}]=1.0\times {{10}^{-7}}mol\,{{L}^{-1}}\]


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