JEE Main & Advanced JEE Main Paper (Held on 08-4-2019 Afternoon)

  • question_answer
    Calculate the standard cell potential in(V) of the cell in which following reaction takes place:
    \[F{{e}^{2+}}(aq)+A{{g}^{+}}(aq)\to F{{e}^{3+}}(aq)+Ag(s)\]
    Given that
    \[E_{A{{g}^{+}}/Ag}^{o}=xV\]
    \[E_{F{{e}^{2+}}/Fe}^{o}=yV\]
    \[E_{F{{e}^{3+}}/Fe}^{o}=zV\]
    [JEE Main 8-4-2019 Afternoon]

    A) \[x+2y-3z\]     

    B) \[x-z\]

    C) \[x-y\]  

    D)   \[x+y-z\]

    Correct Answer: A

    Solution :

    \[F{{e}^{+2}}(aq)+A{{g}^{+}}(aq)\to F{{e}^{+3}}(aq)+Ag(s)\] Cell reaction             anode :\[F{{e}^{+2}}(aq)\to F{{e}^{+3}}(aq)+{{e}^{\Theta }};\] \[E_{F{{e}^{+2}}/F{{e}^{+3}}}^{o}=mV\] cathode :\[A{{g}^{+}}(aq)+{{e}^{\Theta }}\to Ag(s);\] \[E_{A{{g}^{+}}/Ag}^{o}=xV\] \[\Rightarrow \]cell standard potential \[=(m+x)V\] \[\therefore \]to find ?m?; \[F{{e}^{+2}}+2{{e}^{\Theta }}\to Fe;\] \[E_{1}^{o}=yV\Rightarrow \Delta _{1}^{o}G=-(2Fy)\] \[F{{e}^{+3}}+3{{e}^{\Theta }}\to Fe;\] \[E_{2}^{o}=zV\Rightarrow \Delta _{2}^{o}G=-(3Fz)\] \[F{{e}^{+2}}(aq)\to F{{e}^{+3}}(aq)+{{e}^{\Theta }};\] \[E_{3}^{0}=mV\Rightarrow \Delta _{3}^{o}G=-(1Fm)\] \[\Delta _{3}^{o}G=\Delta G_{1}^{o}-\Delta G_{2}^{o}=(-2Fy+3Fz)=-Fm\] \[\Rightarrow \]\[m=(2y-3z)\] \[\Rightarrow \]\[E_{cell}^{o}=(x+2y-3z)V\]          


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