KVPY Sample Paper KVPY Stream-SX Model Paper-15

  • question_answer
    The solubility of \[Pb{{(OH)}_{2}}\]in water is \[6.7\times {{10}^{-\,6}}M.\] Calculate the solubility of \[Pb\,{{(OH)}_{2}}\] in a buffer solution of \[pH=8.\]

    A) \[1.2\times {{10}^{-\,3}}M\]

    B) \[1.8\times {{10}^{-\,5}}M\]

    C) \[3.6\times {{10}^{-\,3}}M\]     

    D) \[4.1\times {{10}^{-\,4}}M\]

    Correct Answer: A

    Solution :

    In water,
    \[Pb{{(OH)}_{2}}P{{\underset{S}{\mathop{b}}\,}^{2}}+2{{\underset{2S}{\mathop{OH}}\,}^{-}}\]
    \[{{K}_{sp}}=4.{{S}^{3}}=4{{(6.7\times {{10}^{-\,6}})}^{3}}\]
    \[=1.2\times {{10}^{-\,15}}\]
    In buffer of \[pH=8\]
    \[pOH=6,\]                    \[[O{{H}^{-}}]={{10}^{-\,6}}\]
    \[{{K}_{sp}}=S\,{{[O{{H}^{-}}]}^{2}}\]
    \[S=\frac{1.2\times {{10}^{-\,15}}}{{{10}^{^{-\,12}}}}=1.2\times {{10}^{\,-3}}M\]


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