Question

The standard reduction potentials of $Ag , Cu$ Co and $Zn$ are $0.799,0.337,-0.277,-0.762\, V$ respectively. Which of the following cells will have maximum cell emf?

• A. $ Zn|Z{{n}^{2+}}(1M)||C{{u}^{2+}}(1M)|Cu $
• B. $ Zn|Z{{n}^{2+}}(1M)||A{{g}^{+}}(1M)|Ag $
• C. $ Cu|C{{u}^{2+}}(1M)||A{{g}^{+}}(1M)|Ag $
• D. $ Zn|Z{{n}^{2+}}(1M)||C{{o}^{2+}}(1M)|Co $

Answer 1

Answer: (B)

$E_{\text {cell }}=E_{\text {cell }}^{\circ}-\frac{0.0591}{n} \log \frac{\text { [oxidised species] }}{[\text { reduced species] }}$
Since, concentration of all the ions is equal, higher the value of $E_{\text {cell }}^{\circ}$, higher is the $E_{\text {cell }}$.
(a) $E_{\text {cell }}^{\circ}=E_{\text {cathode }}-E_{\text {anode }}$
$=0.337-(-0.762)=1.09$
(b) $E_{\text {cell }}^{\circ}=0.799-(-0.762)=1.56\, V$
(c) $E_{\text {cell }}^{\circ}=0.799-0.337=0.46\, V$
(d) $E_{\alpha \in 11}^{\circ}=-0.227-(-0.762)=0.53\, V$
Thus, emf is maximum for the cell given in option