Question

The standard reduction potentials of $Zn ^{2+}\left| Zn , Cu ^{2+}\right| Cu$ and $Ag ^{+} \mid Cu$ and $Ag ^{+} \mid Ag$ are respectively $-0.76,0.34$ and $0.8\, V$. The following cells were constructed :
(1) $Zn \left| Zn ^{2+} \| Cu ^{2+}\right| Cu$
(2) $Zn \left| Zn ^{2+} \| Ag ^{+}\right| Ag$
(3) $Cu \left| Cu ^{2+} \| Ag ^{+}\right| Ag$
What is the correct order of $E_{\text {cell }}^{\circ}$ of these cells?

• A. 2 > 3 > 1
• B. 2 > 1 > 3
• C. 1 > 2 > 3
• D. 3 > 1 > 2

Answer 1

Answer: (B)

Given $Zn ^{2+} \longrightarrow Zn \,\,\,E^{\circ}=-0.78 \,V $
$ Cu ^{2+} \longrightarrow Cu \,\,\, E^{\circ}=0.34 \, V $
$ Ag ^{+} Ag\,\,\,\, E^{\circ}=0.8 \, V $
Cell reaction of $(1)$ is
$Zn + Cu ^{2+} \longrightarrow Zn ^{2+}+ Cu$
$ E_{\text {cell }}^{\circ} =E_{\text {oxidation }}+E_{\text {reduction }} $
$=+0.78+0.34 $
$=+1.12 \,V$
Cell reaction of $(2)$ is
$Zn + Ag ^{+} \longrightarrow Zn ^{2+}+ Ag$
$E_{\text {cell }}^{\circ} =0.78+0.8$
$=+1.58 \, V$
Cell reaction of $(3)$ is :
$Cu + Ag ^{+} \longrightarrow Cu ^{2+}+ Ag$
$E_{\text {cell }}^{\circ} =-0.34+0.8 $
$=+0.46$
So, the correct order of $E_{\text {cell }}^{\circ}$ of these cell is -
$b > a > c$