RAJASTHAN ­ PET Rajasthan PET Solved Paper-2005

  • question_answer
    The solubility product of PbS is\[3.4\times {{10}^{-28}}\]. If the concentration of\[P{{b}^{2+}}\]is\[1\times {{10}^{-2}}\]mol then the concentration of\[{{S}^{2-}}\]at which\[PbS\]will precipitated

    A)  \[3.4\times {{10}^{-26}}\]

    B)  \[3.4\times {{10}^{-30}}\]

    C)  \[1\times {{10}^{-2}}\]

    D)  \[3.4\times {{10}^{-22}}\]

    Correct Answer: A

    Solution :

     \[PbSP{{b}^{2+}}+{{S}^{2-}}\] For precipitation, the ionic product of PbS should be greater than solubility product. Hence the concentration of\[{{S}^{2-}}\]ions will be minimum. Concentration of \[{{S}^{2-}}>\frac{Solubility\text{ }product}{concentration\text{ }of\text{ }P{{b}^{2+}}}\] \[>\frac{3.4\times {{10}^{-28}}}{1\times {{10}^{-2}}}\] \[>3.4\times {{10}^{-26}}mol\]


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