Qualitative Analysis of Ammonium Ion
On warming with NaOH solution, a colourless gas with pungent smell of ammonia is evolved.
NH4+ + OH- → NH3 + H2O
Confirmatory Test
On passing the gas through Nessler reagent, a reddish brown precipitate is obtained.
K2HgI4 → 2KI + HgI2
HgI2 + 2NH3 → Hg(NH2)I + NH4I
2Hg(NH2)I + 2H2O → Reddish brown precipitate