Chemistry - Electrochemistry Question with Solution | TestHub

The given standard reduction potentials of $\mathrm{Zn}, \mathrm{Cu}, \mathrm{Ag}$ and $\mathrm{Fe}$ are;

$$\begin{gathered} \mathrm{E}{°}_{\raisebox{1ex}{${\mathrm{Zn}}^{2+}$}\!\left/ \!\raisebox{-1ex}{$\mathrm{Zn}$}\right.}=-0.76 \mathrm{V}, \mathrm{E}{°}_{\raisebox{1ex}{${\mathrm{Cu}}^{2+}$}\!\left/ \!\raisebox{-1ex}{$\mathrm{cu}$}\right.}=0.34 \mathrm{V} \\ \mathrm{E}{°}_{\raisebox{1ex}{${\mathrm{Ag}}^{+}$}\!\left/ \!\raisebox{-1ex}{$\mathrm{Ag}$}\right.}=0.80 \mathrm{V}, \mathrm{and} \mathrm{E}{°}_{\raisebox{1ex}{${\mathrm{Fe}}^{2+}$}\!\left/ \!\raisebox{-1ex}{$\mathrm{Fe}$}\right.}=-0.44 \mathrm{V} \end{gathered}$$

The condition for reaction to occur, $\mathrm{E}{°}_{\mathrm{Cell}}={\left(\mathrm{E}{°}_{\mathrm{SRP}}\right)}_{\mathrm{reduction} \mathrm{reaction}}-{\left(\mathrm{E}{°}_{\mathrm{SRP}}\right)}_{\mathrm{oxidation} \mathrm{reaction}}$ must have the positive value.

$\left(\mathrm{A}\right) {\mathrm{Cu}}^{2+}\left(\mathrm{aq}\right)+\mathrm{Fe}\to \mathrm{Cu} +{\mathrm{Fe}}^{2+}\left(\mathrm{aq}\right)$

$$\begin{gathered} \mathrm{E}{°}_{\mathrm{Cell}}=0.34+0.44 \\ \mathrm{E}{°}_{\mathrm{Cell}}=0.78 \mathrm{V} \end{gathered}$$

$\left(\mathrm{B}\right) \mathrm{Zn} +{\mathrm{Fe}}^{2+}\left(\mathrm{aq}\right)\to {\mathrm{Zn}}^{2+}\left(\mathrm{aq}\right)+\mathrm{Fe}$

$$\begin{gathered} \mathrm{E}{°}_{\mathrm{Cell}}=-0.44+0.76 \\ \mathrm{E}{°}_{\mathrm{Cell}}=+0.32 \mathrm{V} \end{gathered}$$

$\left(\mathrm{C}\right) {\mathrm{Cu}}^{2+}\left(\mathrm{aq}\right)+2\mathrm{Ag}\to 2{\mathrm{Ag}}^{+}\left(\mathrm{aq}\right)+\mathrm{Cu}$

$$\begin{gathered} \mathrm{E}{°}_{\mathrm{Cell}}=0.34-0.80 \\ \mathrm{E}{°}_{\mathrm{Cell}}=-0.46 \mathrm{V} \end{gathered}$$

$\left(\mathrm{D}\right) \mathrm{Zn}+{\mathrm{Cu}}^{2+}\left(\mathrm{aq}\right)\to {\mathrm{Zn}}^{2+}\left(\mathrm{aq}\right)+\mathrm{Cu}$

$$$$\begin{gathered} \mathrm{E}{°}_{\mathrm{Cell}}=0.34+0.76 \\ \mathrm{E}{°}_{\mathrm{Cell}}=+1.10 \mathrm{V} \end{gathered}$$

Hence, the reaction given in $\mathrm{C}$ option is not possible.