Punjab Medical Punjab - MET Solved Paper-2011

  • question_answer
    The\[{{K}_{sp}}\]of\[Mg{{(OH)}_{2}}\]is\[1\times {{10}^{-12}}\]. \[0.01M\]\[Mg{{(OH)}_{2}}\]will precipitate at the limited\[pH\]of

    A)  3                                            

    B)  9

    C)  5                                            

    D)  8

    Correct Answer: B

    Solution :

    \[Mg{{(OH)}_{2}}M{{g}^{2+}}+2O{{H}^{-}}\] The solubility product,                 \[{{K}_{sp}}\]of\[Mg{{(OH)}_{2}}={{[Mg]}^{2+}}{{[O{{H}^{-}}]}^{2}}\]                 \[1\times {{10}^{-12}}=[0.01]{{[O{{H}^{-}}]}^{2}}\]                 \[{{[O{{H}^{-}}]}^{2}}=\frac{1\times {{10}^{-12}}}{0.01}=1\times {{10}^{-10}}\]                 \[[O{{H}^{-}}]={{10}^{-5}}\] \[\because \]     \[[{{H}^{+}}][O{{H}^{-}}]={{10}^{-14}}\]                 \[[{{H}^{+}}][{{10}^{-5}}]={{10}^{-14}}\]                 \[[{{H}^{+}}]=\frac{{{10}^{-14}}}{{{10}^{-5}}}={{10}^{-9}}\]                 \[pH=-\log [{{H}^{+}}]\]                 \[=-\log {{10}^{-9}}=9\]


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