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Chemistry · 2026 · 3 marks
CBSE 2026 · Region 4 · Set 1 · Q25
(a) When a coordination compound CoCl_3 · 6 NH_3 is mixed with excess of AgNO_3 solution, 3 moles of AgCl are precipitated per mole of the compound.…
When a coordination compound $\displaystyle \mathrm{CoCl}_{3} \cdot 6 \mathrm{NH}_{3}$ is mixed with excess of $\displaystyle \mathrm{AgNO}_{3}$ solution, $\displaystyle 3$ moles of AgCl are precipitated per mole of the compound. Write the structural formula of the complex, IUPAC name, its hybridisation and magnetic behaviour on the basis of valence bond theory.
(i)
How many geometrical isomers are possible in each of the following complexes?
(I)
$\displaystyle \left[\mathrm{Cr}\left(\mathrm{C}_{2} \mathrm{O}_{4}\right)_{3}\right]^{3-}$
(II)
$\displaystyle \left[\mathrm{Co}\left(\mathrm{NH}_{3}\right)_{3} \mathrm{Cl}_{3}\right]$
(ii)
$\displaystyle \left[\mathrm{Co}\left(\mathrm{NH}_{3}\right)_{6}\right]^{3+}$ is an inner orbital complex whereas $\displaystyle \left[\mathrm{Ni}\left(\mathrm{NH}_{3}\right)_{6}\right]^{2+}$ is an outer orbital complex. Why ? [Atomic number : $\displaystyle \mathrm{Co}=27, \mathrm{Ni}=28$ ]
(iii)
Write the formula of Wilkinson catalyst and its use.
Marking-scheme solution
•
[Co(NH3)$\displaystyle 6$]Cl3
• Hexaamminecobalt(III) chloride
•
d2sp3
• diamagnetic
(i)
(I)
Nil / zero
(II)
$\displaystyle 2$
(ii)
NH3 being a strong field ligand pair up the unpaired electrons in Co3+ leaving two
d-orbitals empty for d2sp3 hybridization forming inner orbital complex.
Whereas it cannot pair up in Ni2+ as only one ‘d’ orbital is left empty after pairing
which is not possible and hence outer d-orbital is used. / Diagrammatic representation
(iii)
[(Ph3P)3RhCl]
Used for hydrogenation of alkene
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