Using the standard electrode potential, find out the pair between…

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MCQ

Using the standard electrode potential, find out the pair between which redox reaction is not feasible:

$\text{E}^{\ominus}\text{values:}$ $\text{Fe}^{3+}/\text{ Fe}^{2+}=+0.77;\text{I}_2/\text{I}^{-}=+0.54;$

$\text{Cu}^{2+}/\text{Cu}=+0.34;\text{Ag}^+/\text{Ag}=+0.80\text{V}$

A
$\text{Fe}^{3+} \text{and}\text{ I}^-$
B
$\text{Ag and Cu}$
C
$\text{Fe}^{3+}\text{ and Cu}$
D
$\text{Ag and Fe}^{3+}$

✓

Answer

$\text{Ag and Fe}^{3+}$

Explanation:

Using the standard electrode potential, find out the pair between which redox reaction is not feasible.

$2\text{Fe}^{3+}+2\text{e}^-\xrightarrow[]{\ \ \ \ \ \ \ \ \ \ \ }2\text{Fe}^{2+};\ \text{E}^0=+0.77\text{V}\\\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ 2\text{I}^-\xrightarrow[]{\ \ \ \ \ \ \ \ \ \ \ }\text{I}_2+2\text{e}^-;\text{E}^0=-0.54\text{V (sign of E}^{\text{0}}\text{is reversed})\\\underline{\\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ }\\ \ \ \ \ \ \ 2\text{Fe}^{3+}2\text{I}^-\xrightarrow[]{\ \ \ \ \ \ \ \ \ \ \ \\ }2\text{Fe}^{2+}+\text{I}_2;\text{E}^0_{\text{cell}}=+0.23\text{V}\\ \text{This reaction is feasible since E}^0_\text{cell}=+0.23\text{V}$
$\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \text{Cu}\xrightarrow[]{\ \ \ \ \ \ \ \ \ \ \ }\text{Cu}^{2+}+2\text{e}^-;\text{E}^0=-0.34\text{V(sing of E}^0\text{is reversed)}\\\ 2\text{Ag}^++2\text{e}^-\xrightarrow[]{\ \ \ \ \ \ \ \ \ \ \ }2\text{Ag};\text{E}^0=+0.80\text{V}\\\underline{\\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ }\\ \ \text{Cu}+2\text{Ag}^+\xrightarrow[]{\ \ \ \ \ \ \ \ \ \ \ }\text{Cu}^{2+}+2\text{Ag;}\text{E}^0=+0.46\text{V} \\ \text{This reaction is feasible since E}^0_\text{cell}=+\text{Ve.}$
$2\text{Fe}^{3+}+2\text{e}^-\xrightarrow[]{\ \ \ \ \ \ \ \ \ \ \ }2\text{Fe}^{2+};\ \text{E}^0=+0.77\text{V}\\\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \text{Cu}\xrightarrow[]{\ \ \ \ \ \ \ \ \ \ \ }\text{Cu}^{2+}+2\text{e}^-;\text{E}^0=-0.34\text{V (sign of E}^{\text{0}}\text{is reversed})\\\underline{\\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ }\\ \ \ \ \ \ \ 2\text{Fe}^{3+}\text{Cu}\xrightarrow[]{\ \ \ \ \ \ \ \ \ \ \ \\ }2\text{Fe}^{2+}+\text{Cu}^{2+};\text{E}^0=+0.43\text{V}\\ \text{This reaction is feasible since E}^0_\text{cell}=+0.43\text{V}$
$ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \text{Ag}\xrightarrow[]{\ \ \ \ \ \ \ \ \ \ \ }\text{Ag}^+\text{e}^-;\text{E}^0=-0.80\text{V(sing of E}^0\text{is reversed}\\\ \text{Fe}^{3+}+2\text{e}^-\xrightarrow[]{\ \ \ \ \ \ \ \ \ \ \ }\text{Fe}^{2+};\text{E}^0+0.77\text{V}\\\underline{\\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ }\\ \ \ \ \text{Ag}+\text{Fe}^{3+}\xrightarrow[]{\ \ \ \ \ \ \ \ \ \ \ \\ }\text{Ag}^+\text{Fe}^{2+};\text{E}^0=-0.03\text{V}\\ \text{This reaction is not feasible since E}^0_\text{cell}=-\text{ve.}$

Thus, option (d) is correct.