WB JEE Medical WB JEE Medical Solved Paper-2014

  • question_answer
    The quantity of electricity needed to separately electrolyze 1 M solution of \[ZnS{{O}_{4}},AlC{{l}_{3}}\]and \[AgN{{O}_{3}}\]completely is in the ratio of

    A)  2 : 3 : 1              

    B)  2 : 1 : 1

    C)  2 : 1 : 3              

    D)  2 : 2 : 1

    Correct Answer: A

    Solution :

     From the Faradays Und law, we know that \[W\propto Zit,\,\,\] \[\,W\propto \frac{E}{96500}\]it or it \[\propto \frac{1}{E}\]or electricity \[\propto \frac{1}{E}\] Thus, the amount of electricity required for \[\text{ZnS}{{\text{O}}_{\text{4}}}\text{,}\,\text{AlC}{{\text{l}}_{\text{3}}}\]and\[\text{AgN}{{\text{O}}_{\text{3}}}\] is in the ratio of 2:3:1. (Here, 2, 3 and 1 are the valencies of metal atom in the given compounds).  Alternatively In \[\text{ZnS}{{\text{O}}_{4}},\] \[\underset{\text{1mol}}{\mathop{Z{{n}^{2+}}}}\,+\underset{\begin{smallmatrix}  \text{2}\,\text{mol} \\  \text{or}\,\text{Faraday} \end{smallmatrix}}{\mathop{2{{e}^{-}}}}\,\xrightarrow{{}}Zn\] In \[AlC{{l}_{3}},\] \[\underset{\text{1}\,\text{mol}}{\mathop{A{{l}^{3+}}}}\,+\underset{3F}{\mathop{3{{e}^{-}}}}\,\xrightarrow{{}}Al\] In \[AgN{{O}_{3}},\] \[\underset{1\,mol}{\mathop{A{{g}^{+}}}}\,+\underset{1\,F}{\mathop{{{e}^{-}}}}\,\xrightarrow{{}}Ag\] Thus, the ratio of amounts of electricity  required is 2 : 3 : 1


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