Question 59. Appearance of blood red colour on treatment of the sodium fusion extract of an organic compound with {\mathrm{FeSO}}_4 in the presence of concentrated {\mathrm H}_2{\mathrm{SO}}_4 indicates the presence of element or elements:
(1) Br
(2) N
(3) N and S
(4) S
Answer: (3)
Explanation:
In the sodium fusion test, nitrogen and sulphur present in the organic compound form thiocyanate ion.
Ferrous ion is oxidised in acidic medium.
\mathrm{Fe}^{2+}\xrightarrow[\text{conc. }\mathrm{H}{2}\mathrm{SO}{4}]{\mathrm{H}^{+}}\mathrm{Fe}^{3+}Ferric ion reacts with thiocyanate ion to form ferric thiocyanate, which is blood red in colour.
\mathrm{Fe}^{3+}+\mathrm{SCN}^{-}\rightarrow\mathrm{Fe}(\mathrm{SCN})_{3}Hence, appearance of blood red colour indicates the presence of both nitrogen and sulphur.