NEET AIPMT SOLVED PAPER SCREENING 2005

  • question_answer
                    At \[{{25}^{\text{o}}}C,\] 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: D

    Solution :

                    Base BOH is dissociate das follows                         \[BOH\,\rightleftharpoons \,{{B}^{+}}+O{{H}^{-}}\]                 So, the dissociation constant of BOH base                 \[{{K}_{b}}=\frac{[{{B}^{+}}]\,\,[O{{H}^{-}}]}{[BOH]}...(i)\]                 At equilibrium \[[{{B}^{+}}]=\frac{{{[O{{H}^{-}}]}^{2}}}{[BOH}\]                         \[\therefore \]            \[{{K}_{b}}=\frac{{{[O{{H}^{-}}]}^{2}}}{[BOH]}\]                 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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