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  4. In the detection of nitrogen of an organic compound by Lassaigne's test, Prussian blue colour is obtained. This is due to the formation of which of the following complexes?

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Q. In the detection of nitrogen of an organic compound by Lassaigne's test, Prussian blue colour is obtained. This is due to the formation of which of the following complexes?

AP EAMCETAP EAMCET 2019

Solution:

In Lassaigne's test for detection of nitrogen in organic compounds Prussian blue colour is obtained due to the formation of iron (III) hexacyanoferrate (II) complex. The reaction is as follows:

$6CN^- + Fe^{2+} \rightarrow \underset{\text{Hexacyanoferrate}}{[Fe(CN)_6]^{4-}}$

$3[ Fe(CN)_6]^{4-} + 4Fe^{3+} \ce{->[xH_2O]} \underset{\text{Iron (III) hexacyanoferrate (II) (Prussian blue)}}{Fe_4[Fe(CN)_6]_3 \cdot xH_2O}$