Why is concentrated HNO3 not used in the preparation of H2S?

Answer: Concentrated HNO3 is not used in H2S preparation as concentrated HNO3 is an oxidising agent. H2S produced by the reaction of HNO3 with ferrous sulphide is oxidized by concentrated HNO3 to sulfur and HNO3, which itself is reduced to produce nitrogen dioxide (NO2).

H2S + 2HNO3 = S ↓ + 2NO2 ↑ + 2H20