AMU Medical AMU Solved Paper-2004

  • question_answer
    Some chemists at ISRO wished to prepare a saturated solution of a silver compound and they wanted it to have the highest concentration of silver ion possible. Which of the following compounds, would they use? \[{{K}_{sp}}(AgCl)=1.8\times {{10}^{-10}}\]                                 \[{{K}_{sp}}(AgBr)=5.0\times {{10}^{-13}}\]                                 \[{{K}_{sp}}(A{{g}_{2}}Cr{{O}_{4}})=2.4\times {{10}^{-12}}\]

    A)  AgCl                                     

    B)  AgBr

    C)  \[A{{g}_{2}}Cr{{O}_{4}}\]                            

    D)  Any of these

    Correct Answer: C

    Solution :

                     For binary salts (like AgCl, AgBr)                 \[AgClA{{g}^{+}}+C{{\underset{S}{\mathop{l}}\,}^{-}}\]                 \[{{K}_{sp}}=[A{{g}^{+}}+C{{\underset{S}{\mathop{l}}\,}^{-}}\]                                 \[=(s)\,\,(s)\]                 \[{{K}_{sp}}={{s}^{2}}\]                 \[s=\sqrt{{{K}_{sp}}}\] \[\therefore \] Solubility of \[AgCl=\sqrt{1.8\times {{10}^{-10}}}\]                                 \[=1.35\times {{10}^{-5}}mol/L\] Solubility of AgBr \[=\sqrt{5.0\times {{10}^{-13}}}\]                                 \[=7.1\times {{10}^{-7}}mol/L\] For ternary salt-like \[A{{g}_{2}}Cr{{O}_{4}}\]                                 \[{{K}_{sp}}4{{s}^{3}}\]                                 \[s={{\left[ \frac{{{K}_{sp}}}{4} \right]}^{1/3}}\] \[\therefore \] Solubility of \[A{{g}_{2}}Cr{{O}_{4}}=\sqrt[3]{\frac{{{K}_{sp}}}{4}}\]                                 \[=\sqrt[3]{\frac{2.4\times {{10}^{-12}}}{4}}\]                                 \[=\sqrt[3]{600\times {{10}^{-15}}}\]                                 \[=8.44\times {{10}^{-5}}mol/L\] The solubility of \[A{{g}_{2}}Cr{{O}_{4}}\] is maximum so, it will give maximum \[A{{g}^{+}}\] ions in solution. Hence, it will be used.


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