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.
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