Chemical Properties of H2S

1. It reacts with oxygen to form water and sulphur (iv) oxide but in limited supply of oxygen, it forms water and sulphur.
2H₂S_(g) + 3O_2(g) → 2H₂O_(L) + 2SO_2(g)

2H₂S_(g) + O_2(g)  →  2H₂O_(L)+ 2S_(s)

2. It acts as an acid – It acts as acid to form a weak, dibasic acid.
2NaOH_(aq) + H₂S_(g) →  Na₂S_(aq) + 2H₂O_(L)

3. As a reducing agent – It reduces oxidizing agents leaving traces of yellow deposits of sulphur.
KMnO_4(aq) + 3H₂SO_4(aq) + 5H₂S_(g) →  K₂SO_4(aq) + 2MnSO_4(aq) + 8H₂O_(L) + 5S_(s)

4. As a precipitating agent – It reacts with lead (ii) trioxonitrate (v) salts to precipitate block lead (ii) Sulphide.
Pb(NO₃)_2(aq) + H₂S_(g) →  PbS_(s) + 2HNO_3(aq)

NB: This is a test for hydrogen sulphide.