Transition and InnerTransition Elements - Result Question 19
20. Which of the following compounds is not yellow coloured?
(2015 Main)
(a) $Zn _2\left[Fe(CN) _6\right]$
(b) $K _3\left[Co\left(NO _2\right) _6\right]$
(c) $\left(NH _4\right) _3\left[As\left(Mo _3 O _{10}\right) _4\right]$
(d) $BaCrO _4$
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Answer:
Correct Answer: 20. (a)
Solution:
$Zn _2\left[Fe(CN) _6\right], K _3\left[Co\left(NO _2\right) _6\right]$ and $\left(NH _4\right) _3$ As $\left[Mo _3 O _{10}\right] _4$ show colour due to $d$ - $d$ transition while $BaCrO _4$ is coloured due to charge transfer phenomenon.
Further according to spectrochemical series the strong ligand possessing complex has higher energy and hence lower wavelength. Therefore, complexes containing $NO _2, NH _4^{+}, O^{2-}$ etc., ligands show yellow colour while $CN^{-}$forces the complex to impart white colour.
$I^{-} < Br^{-} < S^{2-} < SCN^{-} < Cl^{-} < NO _3^{-} < N _3^{-} < F^{-} < OH^{-}$
$ < C _2 O _4^{2-} \approx H _2 O < NCS^{-} < CH _3 CN < $ py $ < NH _3 < $ en
$ < $ bipy $ < $ Phen $ < NO _2^{-} < PPh _3 < CN^{-} \approx CO$
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