Manipal Medical Manipal Medical Solved Paper-2007

  • question_answer
    The solubility product of a sparingly soluble salt\[A{{X}_{2}}\]is\[3.2\times {{10}^{-11}}\]. Its solubility (in mol/L) is

    A)  \[5.6\times {{10}^{-6}}\]     

    B)  \[3.1\times {{10}^{-4}}\]

    C)  \[2\times {{10}^{-4}}\]    

    D)  \[4\times {{10}^{-4}}\]

    Correct Answer: C

    Solution :

     \[A{{X}_{2}}\]is ionised as follows \[\underset{S\,mol\,{{L}^{-1}}}{\mathop{A{{X}_{2}}}}\,\underset{S}{\mathop{{{A}^{2+}}}}\,+\underset{2S}{\mathop{2{{X}^{-}}}}\,\] Solubility product of\[A{{X}_{2}}\] \[({{K}_{sp}})=[{{A}^{2+}}]{{[{{X}^{-}}]}^{2}}=S\times {{(2S)}^{2}}=4{{S}^{3}}\] \[\because \] \[{{K}_{sp}}\]of\[A{{X}_{2}}=3.2\times {{10}^{-11}}\] \[\therefore \] \[3.2\times {{10}^{-11}}=4{{S}^{3}}\] \[{{S}^{3}}=0.8\times {{10}^{-11}}=8\times {{10}^{-12}}\] Solubility\[=2\times {{10}^{-4}}mol/L\]


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