Question:
In the ring test of NO3– ion, Fe2+ ion reduces nitrate ion to nitric oxide, which combines with Fe2+ (aq) ion to form the brown complex. Write the reactions involved in the formation of a brown ring.
Solution:
NO3– + 3Fe2+ + 4H+ → NO + 3Fe2+ 2H2O
[Fe(H2O)6]SO4 + NO → [Fe(H2O)5NO]SO4
Thus the complex formed is brown.