CBSE 2022 · Region 4 · Set 1 · Q5 · 3 marks
(i)Write the electronic configuration of $\displaystyle d^{5}$ on the basis of crystal field splitting theory if $\displaystyle \Delta_{0}<\mathrm{P}$.(ii)$\displaystyle \left[\mathrm{Fe}(\mathrm{CN})_{6}\right]^{3-}$ is weakly paramagnetic whereas $\displaystyle \left[\mathrm{Fe}(\mathrm{CN})_{6}\right]^{4-}$ is diamagnetic. Give reason to support this statement. [Atomic no. : $\displaystyle \mathrm{Fe}=26$ ](iii)Write the number of ions produced from the complex $\displaystyle \left[\mathrm{Co}\left(\mathrm{NH}_{3}\right)_{6}\right] \mathrm{Cl}_{2}$ in solution.(i)Calculate the spin only magnetic moment of the complex $\displaystyle \left[\mathrm{CoF}_{6}\right]^{3-}$. (Atomic no. of $\displaystyle \mathrm{Co}=27$ )(ii)Write the IUPAC name of the given complex : \[\left[\mathrm{CrCl}_{2}\left(\mathrm{H}_{2} \mathrm{O}\right)_{4}\right] \mathrm{Cl} \](iii)Which out of the two complexes is more stable and why ? \[\left[\mathrm{Fe}\left(\mathrm{H}_{2} \mathrm{O}\right)_{6}\right]^{3+},\left[\mathrm{Fe}\left(\mathrm{C}_{2} \mathrm{O}_{4}\right)_{3}\right]^{3-} \]
(i)
Write the electronic configuration of $\displaystyle d^{5}$ on the basis of crystal field splitting theory if $\displaystyle \Delta_{0}<\mathrm{P}$.
(ii)
$\displaystyle \left[\mathrm{Fe}(\mathrm{CN})_{6}\right]^{3-}$ is weakly paramagnetic whereas $\displaystyle \left[\mathrm{Fe}(\mathrm{CN})_{6}\right]^{4-}$ is diamagnetic. Give reason to support this statement. [Atomic no. : $\displaystyle \mathrm{Fe}=26$ ]
(iii)
Write the number of ions produced from the complex $\displaystyle \left[\mathrm{Co}\left(\mathrm{NH}_{3}\right)_{6}\right] \mathrm{Cl}_{2}$ in solution.
(i)
Calculate the spin only magnetic moment of the complex $\displaystyle \left[\mathrm{CoF}_{6}\right]^{3-}$. (Atomic no. of $\displaystyle \mathrm{Co}=27$ )
(ii)
Write the IUPAC name of the given complex : \[\left[\mathrm{CrCl}_{2}\left(\mathrm{H}_{2} \mathrm{O}\right)_{4}\right] \mathrm{Cl} \]
(iii)
Which out of the two complexes is more stable and why ? \[\left[\mathrm{Fe}\left(\mathrm{H}_{2} \mathrm{O}\right)_{6}\right]^{3+},\left[\mathrm{Fe}\left(\mathrm{C}_{2} \mathrm{O}_{4}\right)_{3}\right]^{3-} \]
Marking-scheme solution
(a) (i) \(\displaystyle \mathrm{t}_{2 \mathrm{~g}}{ }^{3} \mathrm{e}_{\mathrm{g}}{ }^{2}\)
(ii) \(\displaystyle \left[\mathrm{Fe}(\mathrm{CN})_{6}\right]^{3-}\), it has one unpaired electron and hence is paramagnetic. In \(\displaystyle \left[\mathrm{Fe}(\mathrm{CN})_{6}\right]^{4-}\), all electrons are paired so diamagnetic.
(iii) 3.
(b)
No. of unpaired electrons $\displaystyle (n) = 4$
$\displaystyle \mu = \sqrt{n(n+2)} = \sqrt{4(4+2)} = \sqrt{24} = 4.9\ \mathrm{BM}$
(ii)
Tetraaquadichloridochromium (III) chloride
(iii)
$\displaystyle \left[\mathrm{Fe}\left(\mathrm{C}_{2} \mathrm{O}_{4}\right)_{3}\right]^{3-}$, due to chelate effect / cyclic structure
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CBSE Class 12 Chemistry past-paper question from the 2022board exam, with the answer as CBSE’s own marking scheme gives it. Where our answers come from.