Q. The standard reduction potential of Zn and Ag in water at 298 K are, ${Zn}^{2 +}\ + {2e}^{-}\ \ \rightleftharpoons \ \ Zn;\ E^{{^\circ}}\ = \ - 0.76\ V$ and ${Ag}^{+}\ + \ e^{-}\ \ \rightleftharpoons \ Ag\ ;\ \ \ \ \ E^{{^\circ}}\ = \ + 0.80\ V$. Which of the following reactions take place?
A) ${Zn}^{2 +}\ (aq)\ + \ 2Ag\ (s)\ \rightarrow \ {2Ag}^{+}(aq)\ + \ Zn\ (s)$
B) $Zn\ (s)\ + \ {2Ag}^{+}\ (aq)\ \rightarrow \ {Zn}^{2 +}\ (aq)\ + \ 2Ag\ (s)$
C) ${Zn}^{2 +}\ (aq)\ + \ {Ag}^{+}\ (aq)\ \rightarrow \ Zn\ (s)\ + \ Ag\ (s)$
D) $Zn\ (s)\ + \ Ag\ (s)\ \rightarrow \ {Zn}^{2 +}\ (aq)\ + \ {Ag}^{+}\ (aq)$
Explanation
(b)
As the reduction potential of Zn is less than that of Ag, hence Zn will act as anode when Acell is made using them.
Hence , the correct reaction will be
$\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ Zn(s)\ \rightarrow \ {Zn}^{2 +}\ (aq)\ + {2e}^{-}$ (oxidation)
$\ \ \ \ \ {2Ag}^{+}\ (aq) + \ {2e}^{-}\ \rightarrow 2Ag\ (s$)
[table] $Zn\ (s) + \ {2Ag}^{+}\ (aq) \rightarrow \ {Zn}^{2 +}\ (aq) + \ 2Ag\ (s)$ [/table]
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.