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Chemistry · 2023 · 2 marks
The d-and f-Block ElementsGeneral Properties of the Transition Elements (d-Block)2 marksUnderstandvery short answer
CBSE 2023 · Region 1 · Set 2 · Q21
How would you account for: (a) The E^° value for the Mn^3+ / Mn^2+ couple is much more positive than that for Cr^3+ / Cr^2+ couple or Fe^3+ / Fe^2+…
How would you account for:
(a)
The $\displaystyle \mathrm{E}^{\circ}$ value for the $\displaystyle \mathrm{Mn}^{3+} / \mathrm{Mn}^{2+}$ couple is much more positive than that for $\displaystyle \mathrm{Cr}^{3+} / \mathrm{Cr}^{2+}$ couple or $\displaystyle \mathrm{Fe}^{3+} / \mathrm{Fe}^{2+}$ couple.
(b)
Complete the following equation: \[2 \mathrm{MnO}_{4}^{-}+16 \mathrm{H}^{+}+5 \mathrm{C}_{2} \mathrm{O}_{4}^{2-} \longrightarrow \]
Marking-scheme solution
(a) \(\displaystyle \mathrm{Mn}^{3+}\) changes to \(\displaystyle \mathrm{Mn}^{2+}\) stable half-filled \(\displaystyle \mathrm{d}^{5}\) configuration / much larger third ionization enthalpy of Mn whereas \(\displaystyle \mathrm{Cr}^{3+}\) and \(\displaystyle \mathrm{Fe}^{3+}\) have stable configuration.
(b) \[2\,\mathrm{MnO}_4^{-} + 16\,\mathrm{H}^{+} + 5\,\mathrm{C}_2\mathrm{O}_4^{2-} \longrightarrow 2\,\mathrm{Mn}^{2+} + 10\,\mathrm{CO}_2 + 8\,\mathrm{H}_2\mathrm{O}\]
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CBSE Class 12 Chemistry past-paper question from the 2023 board exam, with the answer as CBSE’s own marking scheme gives it. Where our answers come from.