Question

The above Lassaigne's extract on treatment with $F{e}^{2+}$ does not give a blood red colour because of the

• A. Absence of $S$ in the organic compound
• B. Presence of halogen in the organic compound
• C. Dissociation of $NaSCN$ into $N{a}_{2}S$ and $NaCN$
• D. Conversion of $NaSCN$ into $HSCN$

Answer 1

The correct option is C Dissociation of $NaSCN$ into $N{a}_{2}S$ and $NaCN$

If the Lassaigne's extract gives a violet coloured complex, it clearly confirms the presence of Sulphur.

The formation of a Prussian blue coloured complex confirms the presence of Nitrogen.

If Lassaigne's extract does not give a blood red coloured complex, it means that the excess of $Na$ metal caused dissociation of $NaSCN$ into $N{a}_{2}S$ and $NaCN$
$2Na+NaSCN\stackrel{\Delta }{\to }N{a}_{2}S+NaCN$