JEE Advance - Chemistry (1979 - No. 14)
The precipitation of second group sulphides in qualitative
analysis is carried out with hydrogen sulphide in the presence
of hydrochloric acid but not in nitric acid. Explain.
Hydrochloric acid acts as a catalyst in the precipitation reaction.
Nitric acid is a weaker acid than hydrochloric acid.
Nitric acid oxidizes H2S to elemental sulfur, preventing sulfide precipitation.
Hydrochloric acid prevents the formation of unwanted hydroxides.
Nitric acid forms soluble complexes with the group II cations.
Uitleg
As nitric acid is an oxidising agent, it oxides H2S to S.