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2. Electrochemistry — Chemistry STD 12 Science — Question

Gujarat BoardEnglish MediumSTD 12 ScienceChemistry2. Electrochemistry1 Mark
MCQ
What is the standard reduction potential $(E^o)$ for $Fe^{3+} \to Fe$ ?  ............... $\mathrm{V}$

Given that :

$F{e^{2 + }} + 2{e^ - } \to Fe;$      ${E^o}_{F{e^{2 + }}/Fe} =  - 0.47\,V$

$F{e^{3 + }} + {e^ - } \to F{e^{2 + }};$   ${E^o}_{F{e^{3 + }}/F{e^{2 + }}} =  + 0.77\,V$

  • ✓
    $-0.057$
  • B
    $+0.057$
  • C
    $+0.30$
  • D
    $-0.30$
✓

Answer

Correct option: A.
$-0.057$
a
$\Delta {G^o}\, = \, - nF{E^o}$

$(i)\,F{e^{2 + }}\, + \,2{e^ - }\, \to \,Fe;$                    ${E^o}\, = \, - 0.47\,\,V;$

$(ii)\,F{e^{3 + }}\, + \,{e^ - }\, \to \,F{e^{2 + }};$          ${E^o}\, = \, + 0.77\,\,V;$

$(iii)\,F{e^{3 + }}\, + \,3{e^ - }\, \to Fe$

$(i)\,\Delta {G^o}\, = \, - nF{E^o}\, = \, - \,2\,( - 0.47)F\, = \,0.94\,F$

$(ii)\,\Delta {G^o}\, = \, - nF{E^o}\, = \, - \,1\,( + 0.77)F\, = \, - 0.77\,F$

$(iii)$ on adding $:\,\Delta {G^o}\, = \, + \,0.17\,F$

$\Delta {G^o}\, = \, - nF{E^o}\,{E^o}$ for

$(F{e^{3 + }} \to Fe)\, = \,\frac{{\Delta {G^o}}}{{ - nF}}\,$ $ = \,\frac{{0.17F}}{{ - 3F}}\, = \, - \,0.057\,V$

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