Coordination Compounds 2 Question 22
24. Two complexes $\left[Cr\left(H _2 O\right) _6\right] Cl _3(A)$ and $\left[Cr\left(NH _3\right) _6\right] Cl _3(B)$ are violet and yellow coloured, respectively. The incorrect statement regarding them is
(2019 Main, 9 Jan I)
(a) $\Delta _o$ value for $(A)$ is less than that of $(B)$
(b) both absorb energies corresponding to their complementary colours
(c) $\Delta _o$ values of $(A)$ and $(B)$ are calculated from the energies of violet and yellow light, respectively
(d) both are paramagnetic with three unpaired electrons
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Answer:
Correct Answer: 24. (c)
Solution:
- ’ $A$ ’ absorbs yellow light of less energy and emits violet light of high energy (complementary colour) because $H _2 O$ is a weak field ligand. But in case of ’ $B$ ‘, due to presence of strong field ligand $\left(NH _3\right)$, it absorbs high energy violet light and emits low energy complementary yellow colour.
$\Delta$ (CFSE) is measured with help of wavelength of the colour absorbed by the given coordination compound, as
$ \Delta _O=h v=h \times \frac{c}{\lambda} $
Both the complexes contain three unpaired electrons. Therefore, both are paramagnetic.
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