Question

# 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)

Hint: We are given with the standard reduction potential of both the metals, i.e Zn, and Ag. Identify the reactions occurring at anode, and at the cathode on the basis of reduction potential. Then, the reaction could be known.

The reaction of zinc at anode is Zn $\rightarrow$ Zn$^{2+}$ + 2e$^{-}$
Now, the reaction of silver at cathode is Ag$^{+}$ + e$^{-}$ $\rightarrow$ Ag(s), But the silver will gain two electrons, then the reaction will be 2Ag$^{+}$ + 2e$^{-}$ $\rightarrow$ 2Ag(s)
Then, the cell reaction is Zn (s) +2Ag$^{+}$ (aq) $\rightarrow$ Zn$^{2+}$ (aq) + 2Ag(s).