Q24 / 160 · TS EAMCET 2022 (19 Jul Shift 1) · Chemistry
Given $\mathrm{E}^{\circ} \mathrm{Mn}^{7+} / \mathrm{Mn}^{2+}=1.51 \mathrm{~V}, \mathrm{E}_{\mathrm{Mn}^{\circ+} / \mathrm{Mn}^{2+}}=1.23 \mathrm{~V}$ Calculate $\mathrm{E}^{\circ} \mathrm{Mn}^{7+} / \mathrm{Mn}^{4+}$
- A$0.28 \mathrm{~V}$
- B$-0.28 \mathrm{~V}$
- Correct answerC$1.7 \mathrm{~V}$
- D$0.48 \mathrm{~V}$
Solution
$$
\begin{aligned}
& \mathrm{E}_1^{\circ}=1.51 \mathrm{~V}, \quad \mathrm{E}_3^{\circ}=1.23 \mathrm{~V} \\
& \Delta \mathrm{G}_1^{\circ}=\Delta \mathrm{G}_2^{\circ}+\Delta \mathrm{G}_3^{\circ}
\end{aligned}
$$
or, $\quad-\mathrm{n}_1 \mathrm{FE}_1^{\circ}=-\mathrm{n}_2 \mathrm{FE}_2^{\circ}-\mathrm{n}_3 \mathrm{FE}_3^{\circ}$
or, $5 \times 1.51=3 \times \mathrm{E}_2^{\circ}+2 \times 1.23$
or, $\quad E_2^{\circ}=1.696 \mathrm{~V} \simeq 1.70 \mathrm{~V}$
Hence, the correct answer is option: 'C'.