JEE Main & Advanced Sample Paper JEE Main Sample Paper-7

  • question_answer
    Given that \[{{E}^{o}}=\,+0.897\,V,\] calculate \[E\] at \[{{25}^{o}}C\] for  \[Pb(s)|P{{b}^{2+}}(0.040\,M)||F{{e}^{3+}}(0.20\,M),\] \[F{{e}^{2+}}(0.010M)|Pt(s)\]

    A)  \[+0.779\,V\]                   

    B)  \[+0.935\,V\]

    C)  \[+1.015\,V\]                   

    D)  \[+1.134\,V\]

    Correct Answer: C

    Solution :

    At anode, \[P{{b}_{(s)}}\xrightarrow{\,}\,P{{b}^{2+}}+2{{e}^{-}}\] At cathode, \[\left( F{{e}^{3+}}+1{{e}^{-}}\xrightarrow{\,}F{{e}^{2+}} \right)\times 2\] Cell reaction: \[Pb+2F{{e}^{3+}}\xrightarrow{\ }\,P{{b}^{2+}}+2F{{e}^{2+}}\] \[{{E}_{cell}}=E_{cell}^{0}-\frac{0.0591}{2}\log \,\frac{[P{{b}^{2+}}]{{[F{{e}^{2+}}]}^{2}}}{{{[F{{e}^{3+}}]}^{2}}}\] \[=+0.897-\frac{0.0591}{2}\log \frac{(0.040){{(0.010)}^{2}}}{{{(0.20)}^{2}}}\] \[=0.897-0.0295\log \frac{0.04\times 0.01\times 0.01}{0.2\times 0.2}\] \[=0.897-0.0295\log {{10}^{-4}}\] \[=0.897-0.0295\times -4\log \,10\] \[=0.897-0.0295\times -4\] \[=1.015\,V\]


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