KVPY Sample Paper KVPY Stream-SX Model Paper-24

  • question_answer
    \[E{{{}^\circ }_{F{{e}^{3+}}/Fe}}=-0.336V,\]\[E{{{}^\circ }_{F{{e}^{2+}}/Fe}}=-0.439V\]The value of standard electrode potential for the charge, \[F{{e}^{3+}}\left( aq \right)+{{e}^{-}}\xrightarrow{{}}F{{e}^{2+}}\left( aq \right)\]will be

    A) \[-0.072V\]

    B) \[0.385V\]

    C) \[0.770V\]

    D) \[-0.270V\]

    Correct Answer: C

    Solution :

    Given,\[F{{e}^{3}}+3{{e}^{-}}\xrightarrow{{}}Fe;\]
    \[{{E}_{1}}{}^\circ =-0.336V\]?? (i)
    \[F{{e}^{2+}}+2{{e}^{-}}\xrightarrow{{}}Fe;\,\,\,\,\,\,\,\,{{E}_{2}}{}^\circ =-0.439V\] ? (ii)
    We need to calculate
    \[F{{e}^{3+}}+{{e}^{-}}\xrightarrow{{}}F{{e}^{2+}},{{E}_{3}}{}^\circ =?\] ?. (iii)
    We can obtain the Eq. (iii) by subtracting Eq. (ii) from Eq. (i), but \[{{E}_{3}}{}^\circ \], cannot be obtained by this method because electrode potential is intensive property. Thus we can it by determine
    \[\Delta {{G}_{3}}=\Delta {{G}_{1}}-\Delta {{G}_{2}}\]
    (\[\Delta G\] is an extensise property)
    \[\Delta {{G}_{3}}=3\times 0.336V-2\times 0.439V\]
    \[\Delta {{G}_{3}}=0.108V-0.878V\]\[-1\times V\times E_{3}^{{}^\circ }\]\[=-0.770\,\,V\]\[\Rightarrow E_{3}^{{}^\circ }=0.770V\]


You need to login to perform this action.
You will be redirected in 3 sec spinner