Hydrogen sulphide (H2S)

Hydrogen sulphide is prepared in laboratory by the action of dilute HCl or dilute H2SO4 on ferrous sulphide in Kipp’s apparatus.

FeS + H2SO4 ---------->4 + H2S

Physical properties

It is colourless gas with the smell of rotten eggs. It is denser than air and is soluble in water.

Chemical properties

1. Combustibility

Hydrogen sulphide burns in limited supply of oxygen to form sulphur. In presence of excess of oxygen, it gives sulphur dioxide.

2. Acidic property

H2S is a weak dibasic acid and forms two types of salts namely bisulphides and sulphides

NaOH + H2S ----------> NaHS + H2O

2NaOH + H2S ----------> Na2S + 2H2O

3. Action with metals

When H2S is passed over hot metals the sulphides and hydrogen are formed

Cu + H2S -----------> CuS + H2

4. Hydrogen sulphide in qualitative analysis

H2S precipitates metal sulphides having characteristic colours from metal salt solutions in acidic or alkaline medium. Therefore H2S is used in qualitative analysis to identify metal ions belonging to different classes.

In acidic solution, it precipitates group 2 cations (Hg2+, Cu2+, Pb2+, Bi3+, Sb2+, Sn2+, As3+, Cd2+ and Sn4+) as their sulphides with characteristic (Co2+, Ni2+,Zn2+ and Mn2+) as their sulphides with characteristic colours.

Related article Sulphur

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