CBSE 2023 · Region 4 · Set 1 · Q34 · 5 marks
(i)Account for the following :(1)$\displaystyle \mathrm{Zn}^{2+}$ salts are colourless while $\displaystyle \mathrm{Ni}^{2+}$ salts are coloured.(2)$\displaystyle \mathrm{Cr}^{2+}$ is a strong reducing agent.(3)Transition metals and their compounds show catalytic activities.(ii)Write the ionic equations for the oxidizing action of $\displaystyle \mathrm{MnO}_{4}^{-}$in acidic medium with(1)$\displaystyle \mathrm{I}^{-}$ion, and(2)$\displaystyle \mathrm{Fe}^{2+}$ ion.(i)Name two oxometal anions of the 3d series of the transition metals in which the metal exhibits the oxidation state equal to its group number.(ii)What is the effect of increasing pH on a solution of $\displaystyle \mathrm{K}_{2} \mathrm{Cr}_{2} \mathrm{O}_{7}$ ?(iii)Why is $\displaystyle \mathrm{Cu}^{+}$not stable in aqueous solution ?(iv)Name a member of Lanthanoid series which is well-known to exhibit +$\displaystyle 4$ oxidation state.(v)Name two elements of 3d series which show anomalous electronic configuration.
(i)
Account for the following :
(1)
$\displaystyle \mathrm{Zn}^{2+}$ salts are colourless while $\displaystyle \mathrm{Ni}^{2+}$ salts are coloured.
(2)
$\displaystyle \mathrm{Cr}^{2+}$ is a strong reducing agent.
(3)
Transition metals and their compounds show catalytic activities.
(ii)
Write the ionic equations for the oxidizing action of $\displaystyle \mathrm{MnO}_{4}^{-}$in acidic medium with
(1)
$\displaystyle \mathrm{I}^{-}$ion, and
(2)
$\displaystyle \mathrm{Fe}^{2+}$ ion.
(i)
Name two oxometal anions of the 3d series of the transition metals in which the metal exhibits the oxidation state equal to its group number.
(ii)
What is the effect of increasing pH on a solution of $\displaystyle \mathrm{K}_{2} \mathrm{Cr}_{2} \mathrm{O}_{7}$ ?
(iii)
Why is $\displaystyle \mathrm{Cu}^{+}$not stable in aqueous solution ?
(iv)
Name a member of Lanthanoid series which is well-known to exhibit +$\displaystyle 4$ oxidation state.
(v)
Name two elements of 3d series which show anomalous electronic configuration.
Marking-scheme solution
(a) (i)
(1) Because of no unpaired electron in d-orbitals in \(\displaystyle \mathrm{Zn}^{2+}\) whereas, \(\displaystyle \mathrm{Ni}^{2+}\) has $\displaystyle 2$ unpaired electrons in d-orbitals / \(\displaystyle \mathrm{Ni}^{2+}\) shows d-d transition while \(\displaystyle \mathrm{Zn}^{2+}\) does not.
(2) Because Cr is more stable in + $\displaystyle 3$ oxidation state due to stable \(\displaystyle \mathrm{t}_{2 \mathrm{~g}}{ }^{3}\) configuration.
(3) Because of their ability to show multiple or variable oxidation states / ability to form complex / provide larger surface area for the reactants.
(1) \(\displaystyle \mathbf{2 M n O}_{\mathbf{4}}^{-}+10 \mathrm{I}^{-}+16 \mathrm{H}^{+} \longrightarrow 2 \mathrm{Mn}^{2+}+5 \mathrm{I}_{2}+8 \mathrm{H}_{2} \mathrm{O}\)
(2) \(\displaystyle \mathbf{M n O}_{\mathbf{4}}^{-} \boldsymbol{+} \mathbf{5 ~ F e}^{\mathbf{2}+} \boldsymbol{+} \mathbf{8 ~ H}^{+} \longrightarrow \mathbf{M n}^{\mathbf{2}+}+\mathbf{5 ~ F e}^{\mathbf{3}+}+\mathbf{4 ~ H}_{\mathbf{2}} \mathbf{O}\)
The d-and f-Block ElementsGeneral Properties of the Transition Elements (d-Block)Understandlong_answermedium
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CBSE Class 12 Chemistry past-paper question from the 2023board exam, with the answer as CBSE’s own marking scheme gives it. Where our answers come from.