CBSE 2023 · Region 5 · Set 1 · Q35 · 5 marks
(a)Why is chemistry of actinoids complicated as compared to lanthanoids ? \[\](b)Complete the following reaction and justify that it is a disproportionation reaction : $\displaystyle 3 \mathrm{MnO}_{4}{ }^{2-}+4 \mathrm{H}^{+} \rightarrow$ + $\displaystyle +2 \mathrm{H}_{2} \mathrm{O}$.(c)The given graph shows the trends in melting points of transition metals :
Explain the reason why Cr has highest melting point and manganese (Mn) a lower melting point.
(a)
Why is chemistry of actinoids complicated as compared to lanthanoids ? \[\]
(b)
Complete the following reaction and justify that it is a disproportionation reaction : $\displaystyle 3 \mathrm{MnO}_{4}{ }^{2-}+4 \mathrm{H}^{+} \rightarrow$ + $\displaystyle +2 \mathrm{H}_{2} \mathrm{O}$.
(c)
The given graph shows the trends in melting points of transition metals :
Explain the reason why Cr has highest melting point and manganese (Mn) a lower melting point.
Marking-scheme solution
(a)
Actinoids show wide range of oxidation states / most of them are radioactive elements.
\[\text { (b) } 3 \mathrm{MnO}_{4}^{2-}+4 \mathrm{H}^{+} \longrightarrow+2 \mathrm{MnO}_{4}^{-}+\mathrm{MnO}_{2}+2 \mathrm{H}_{2} \mathrm{O}
\]
Oxidation state of Mn increases from +$\displaystyle 6$ to + $\displaystyle 7$ (oxidation) and decreases from + $\displaystyle 6$ to + $\displaystyle 4$ (reduction) / Mn undergoes increase and decrease in oxidation state simultaneously.
(c)
Due to the presence of a greater number of unpaired electrons which leads to strong interatomic metal-metal bonding whereas Mn with a stable half-filled \(\displaystyle \mathrm{d}^{5}\) configuration has a weaker metallic bond.
The d-and f-Block ElementsThe ActinoidsUnderstandlong_answerhard
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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.