Question

Compounds containing both nitrogen and sulphur sometimes give red colouration with fecl3

Answer 1

In case, N & S both are present in the organic compound, sodium thiocyanate is formed. It gives blood red colour.

$Na + N + C + S \overset{Fuse}{\longrightarrow} Na^+CNS^-$

$F^{3+} + 3CNS^- \longrightarrow Fe(CNS)_3$

                              Ferric sulphocyanide

                             (blood red colouration)