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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Solution:

  1. $Zn _2\left[Fe(CN) _6\right], K _3\left[Co\left(NO _2\right) _6\right]$ 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.

Spectrochemical series

$I^{-}<Br^{-}<S^{2-}<SCN^{-}<Cl^{-}<NO _3^{-}<N _3^{-}<F^{-}<OH^{-}$

$<C _2 O _4^{2-} \approx H _2 O<NCS^{-}<CH _3 CN<$ py $<NH _3<$ en

$<$ bipy $<$ Phen $<NO _2^{-}<PPh _3<CN^{-} \approx CO$



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