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) + 3O2(g) → 2H2O(L) + 2SO2(g)

2H2S(g) + O2(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.
KMnO4(aq) + 3H2SO4(aq) + 5H2S(g) →  K2SO4(aq) + 2MnSO4(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) + 2HNO3(aq)

NB: This is a test for hydrogen sulphide.

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