Question

The standard reduction potentials of $Z{n}^{2+}\left|Zn,C{u}^{2+}\right|Cu$ and $A{g}^{+}\mid Cu$ and $A{g}^{+}\mid Ag$ are respectively $-0.76,0.34$ and $0.8V$. The following cells were constructed :
(1) $Zn\left|Z{n}^{2+}\Vert C{u}^{2+}\right|Cu$
(2) $Zn\left|Z{n}^{2+}\Vert A{g}^{+}\right|Ag$
(3) $Cu\left|C{u}^{2+}\Vert A{g}^{+}\right|Ag$
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 $Z{n}^{2+}⟶Zn{E}^{\circ }=-0.78V$
$C{u}^{2+}⟶Cu{E}^{\circ }=0.34V$
$A{g}^{+}Ag{E}^{\circ }=0.8V$
Cell reaction of $(1)$ is
$Zn+C{u}^{2+}⟶Z{n}^{2+}+Cu$
$E_{\text{cell }}^{\circ }=E_{\text{oxidation }}+E_{\text{reduction }}$
$=+0.78+0.34$
$=+1.12V$
Cell reaction of $(2)$ is
$Zn+A{g}^{+}⟶Z{n}^{2+}+Ag$
$E_{\text{cell }}^{\circ }=0.78+0.8$
$=+1.58V$
Cell reaction of $(3)$ is :
$Cu+A{g}^{+}⟶C{u}^{2+}+Ag$
$E_{\text{cell }}^{\circ }=-0.34+0.8$
$=+0.46$
So, the correct order of $E_{\text{cell }}^{\circ }$ of these cell is -
$b>a>c$