At 298 K, the standard electrode potentials of Cu2+ / Cu, Zn2+ / Zn, Fe2+ / Fe and Ag+ / Ag are 0.34 V, 0.76 V, 0.44 V V and 0.80 V, respectively.
On the basis of standard electrode potential, predict which of the following reaction cannot occur?
- ACuSO4(aq) + Zn(s) ZnSO4(aq) + Cu(s)
- BCuSO4(aq) + Fe(s) FeSO4(aq) + Cu(s)
- CFeSO4(aq) + Zn(s) ZnSO4(aq) + Fe(s)
- D2CuSO4(aq) + 2Ag(s) 2Cu(s) + Ag2SO4(aq)
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Correct answer: D
For a reaction to be spontaneous, E$_{cell}^o$ must be positive.
$\bullet$ For, FeSO4(aq) + Zn(s) $\to$ ZnSO4(aq) + Fe(s)
E$_{cell}^o$ = E$_{cathode}^o$ $-$ E$_{anode}^o$
= $-$0.44 V $-$ ($-$0.76 V)
= 0.32 V
$\bullet$ For, 2CuSO4(aq) + 2Ag(s) $\to$ 2Cu(s) + Ag2SO4(aq)
E$_{cell}^o$ = 0.34 V $-$ 0.80 V
= $-$0.46 V
$\bullet$ For, CuSO4(aq) + Zn(s) $\to$ ZnSO4(aq) + Cu(s)
E$_{cell}^o$ = 0.34 V $-$ ($-$0.76 V)
= 1.1 V
$\bullet$ For, CuSO4(aq) + Fe(s) $\to$ FeSO4(aq) + Cu(s)
E$_{cell}^o$ = 0.80 V $-$ ($-$0.44 V)
= 1.24 V
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