$Pt _{( s )}\left| H _2( g , 1\,atm )\right| H ^{+}( aq , 1 M )|| Fe ^{3+}( aq ), Fe ^{2+}( aq ) \mid Pt ( s )$
$298\,K$ પર જયારે કોષ નો પોટેન્શિયલ $0.712\,V$ હોય તો $\left[ Fe ^{2+}\right] /\left[ Fe ^{3+}\right]$ નો ગુણોત્તર $.......$ છે.
આપેલ:$Fe ^{3+}+ e ^{-}= Fe ^{2+}, E ^{\circ} Fe ^{3+}, Fe ^{2+} \mid Pt =0.771$
$\frac{2.303 RT }{ F }=0.06\,V$
$\text { at anode } H _2 \longrightarrow 2 H ^{+}+2 e ^{-}$
$\text {At cathode } Fe _{ aq }^{3+}+ e ^{-} \longrightarrow Fe _{ aq }^{2+}$
$E ^{\circ}= E _{ H _2 / H ^{+}}^{\circ}+ E _{ Fe ^{3+} Fe ^{2+}}^{\circ}=0 \cdot 771\,V$
$E = E ^{\circ}-\frac{0 \cdot 06}{1} \log \frac{ Fe ^{2+}}{ Fe ^{3+}}$
$0 \cdot 712=(0+0 \cdot 771)-\frac{0 \cdot 06}{1} \log \frac{ Fe ^{2+}}{ Fe ^{3+}}$
$\log \frac{ Fe ^{2+}}{ Fe ^{3+}}=\frac{0 \cdot 059}{0 \cdot 06} \approx 1$
$\frac{ Fe ^{2+}}{ Fe ^{3+}}=10$
$Z{n^{2 + }}\,(aq)\, + \,2e\, \rightleftharpoons \,Zn\,(s)\,;\, - \,0.762\,V$
$C{r^{3 + }}\,(aq)\, + \,3e\, \rightleftharpoons \,Cr(s)\,;\, - \,0.740\,\,V$
$2{H^ + }\,(aq)\, + \,2e\, \rightleftharpoons \,{H_2}(g)\,;\,\,\,0.00\,\,\,V$
$F{e^{3 + }}\,(aq)\, + \,e\, \rightleftharpoons \,F{e^{2 + }}(aq)\,;\,\,\,0.770\,\,\,V$
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