Laboratory preparation, properties and uses of hydrogen sulphide

Formula of Hydrogen sulphide: H₂S

Relative Molecular Mass: 34

Vapour Density: 17

Preparation of hydrogen sulphide

Hydrogen sulphide is prepared by the action of sulphuric acid on metal sulphides.

It is collected by the upward displacement of air.

Chemical properties of hydrogen sulphide

Acidic Nature

Hydrogen sulphide turns wet blue litmus paper red. It is a weak dibasic acid.

Combustibility

It is a combustible gas, and burns with a blue flame. In a limited supply of oxygen or air, the products are water and sulphur. In excess of air or oxygen, the products are water and sulphur dioxide.

Reducing Property

Hydrogen sulphide acts as a powerful reducing agent.

a) With concentrated sulphuric acid

When passed through concentrated sulphuric acid, it reduces the acid to sulphur.

b) With sulphur dioxide

Hydrogen sulphide reduces sulphur dioxide to sulphur.

Precipitation of Sulphides

When hydrogen sulphide is passed through aqueous solutions of metallic salts, the sulphides of the respective metals get precipitated. These sulphides have characteristic colours.

Uses of hydrogen sulphide

1. In the laboratory, hydrogen sulphide acts as a reagent to detect the presence of certain anions and cations present in a given salt.

2. Hydrogen sulphide is used in the preparation of metallic sulphides.