Question

The standard emf of the cell $Zn | Zn^{2+} || Ag^+ | Ag$ is $1.56\, V$. If the standard reduction potential of $Ag$ is $0.8\, V$, the standard oxidation potential of $Zn$ is

• A. $- 0.76\, V$
• B. $+ 0.76\, V$
• C. $- 2.36\, V$
• D. $+ 2.36\, V$

Answer 1

Answer: (B)

For the cell,
$Zn | Zn^{2+} || Ag^+ | Ag$
$E^{^\circ}_{cell} = E^{\circ}_{cathode} = E^{\circ}_{anode}$
$1.56 \,V = E^{^\circ}_{Ag^+ /Ag} - E^{^\circ}_{Zn^{2+} /Zn} $
$1.56\, V = 0.8\, V - E^{^\circ}_{Zn^{2+} /Zn} $
$ E^{^\circ}_{Zn^{2+} /Zn} $ = - 0.76\, V
$\therefore \:\:\: E^{^\circ}_{Zn^{2+} /Zn} = + 0.76\, V$