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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 3 · Set 1 · Q4
Account for the following: (i) Cu^2+ salts are coloured while Zn^2+ salts are white. (ii) E^° value for the Mn^3+ / Mn^2+ couple is much more…
Account for the following :
(i)
$\displaystyle \mathrm{Cu}^{2+}$ salts are coloured while $\displaystyle \mathrm{Zn}^{2+}$ salts are white.
(ii)
$\displaystyle \mathrm{E}^{\circ}$ value for the $\displaystyle \mathrm{Mn}^{3+} / \mathrm{Mn}^{2+}$ couple is much more positive than that for $\displaystyle \mathrm{Cr}^{3+} / \mathrm{Cr}^{2+}$.
(iii)
Transition metals form alloys.
Marking-scheme solution
(i) Because \(\displaystyle \mathrm{Cu}^{2+}\) has one unpaired electron in 3d-orbital whereas \(\displaystyle \mathrm{Zn}^{2+}\) has no unpaired electron \(\displaystyle / \mathrm{Cu}^{2+}\) shows d-d transition whereas \(\displaystyle \mathrm{Zn}^{2+}\) does not.
(ii) Because Mn is more stable in +$\displaystyle 2$ due to stable \(\displaystyle 3 d^{5}\) configuration whereas Cr is more stable in +$\displaystyle 3$ due to stable \(\displaystyle t_{2 g}^{3}\) configuration / Much larger third ionization energy of Mn as compared to Cr.
(iii) Because of similar atomic radii.
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