NEET NEET SOLVED PAPER 2015 (C)

  • question_answer
    The \[{{K}_{sp}}\] of \[A{{g}_{2}}Cr{{O}_{4}},\,AgCl,\,AgBr\] and \[AgI\] are respectively, \[1.1\times {{10}^{-12}},1.8\times {{10}^{-10}}\] \[5.0\times {{10}^{-13}},8.3\times {{10}^{-17}}\]. Which one of the following salts will precipitate last if \[AgN{{O}_{3}}\]solution is added to the solution containing equal moles of \[NaCl,NaBr,NaI\] and \[N{{a}_{2}}CrC{{O}_{4}}\]?                                                                       

    A)  \[Agl\]                

    B)  \[AgCl\]              

    C)  \[AgBr\]             

    D)  \[A{{g}_{2}}Cr{{O}_{4}}\]

    Correct Answer: D

    Solution :

    \[A{{g}_{2}}Cr{{O}_{4}}2A{{g}^{+}}+CrO_{4}^{2-}\] Solubility product \[{{K}_{sp}}={{(2s)}^{2}}\times s=4{{s}^{3}}\] \[{{K}_{sp}}=(1.1\times {{10}^{-12}})\] \[S=\sqrt[3]{\frac{{{K}_{sp}}}{4}}\,=0.65\times {{10}^{-4}}\] \[AgClA{{g}^{+}}+C{{l}^{-}}\] \[{{K}_{sp}}=S\times S\]               \[({{K}_{sp}}=1.8\times {{10}^{-10}})\] \[S=\sqrt{{{K}_{sp}}}\,=1.34\times {{10}^{-5}}\] \[AgBr\,A{{g}^{+}}+B{{r}^{-}}\] \[{{K}_{sp}}=S\times S\]                               \[({{K}_{sp}}=5\times {{10}^{-13}})\] \[S=\sqrt{{{K}_{sp}}}=0.71\times {{10}^{-6}}\] \[AgIA{{g}^{+}}+{{I}^{-}}\] \[{{K}_{sp}}=S\times S\]          \[({{K}_{sp}}=8.3\times {{10}^{-17}})\] \[S=\sqrt{{{K}_{sp}}}=0.9\times {{10}^{-8}}\] \[\because \] Solubility of \[A{{g}_{2}}Cr{{O}_{4}}\] is highest. So, it will precipitate last.


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