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Chemistry · 2022 · 3 marks
The d-and f-Block ElementsGeneral Properties of the Transition Elements (d-Block)3 marksUnderstandshort answer
CBSE 2022 · Region 2 · Set 2 · Q5
From the given E^ values of the first row transition elements, answer the following questions: (i) Why is E_Mn^2+ / Mn^ value highly negative as…
| $\displaystyle \mathrm{E}_{\mathrm{M}^{2+} / \mathrm{M}}^{\ominus}$ | Cr | Mn | Fe | Co | Ni | Cu | Zn |
| -$\displaystyle 0.91$ | -$\displaystyle 1.18$ | -$\displaystyle 0.44$ | -$\displaystyle 0.28$ | -$\displaystyle 0.25$ | + $\displaystyle 0.34$ | -$\displaystyle 0.76$ |
(i)
Why is $\displaystyle \mathrm{E}_{\mathrm{Mn}^{2+} / \mathrm{Mn}}^{\ominus}$ value highly negative as compared to other elements?
(ii)
What is the reason for the irregularity in the above $\displaystyle \mathrm{E}^{\Theta}$ values ?
(iii)
Why is $\displaystyle \mathrm{E}_{\mathrm{Cu}^{2+} / \mathrm{Cu}}^{\ominus}$ value exceptionally positive ?
Marking-scheme solution
(i) Because of the stable half-filled \(\displaystyle 3 d^{5}\) configuration in \(\displaystyle \mathrm{Mn}^{2+}\).
(ii) Because of the irregular sum of ( \(\displaystyle \Delta_{i} H_{1}+\Delta_{i} H_{2}\) ) values and much less sublimation enthalpies for Mn and V.
(iii) Because of high \(\displaystyle \Delta_{a} H^{0}\) and low \(\displaystyle \Delta_{\text {hyd }} H^{0}\)
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CBSE Class 12 Chemistry past-paper question from the 2022 board exam, with the answer as CBSE’s own marking scheme gives it. Where our answers come from.