Copper Sulphate or Blue vitriol: Preparation, Properties and Uses

Copper Sulphate (CuSO4.5H2O); Blue vitriol

Preparation

In laboratory it is prepared by dissolving cupric oxide (or) cupric hydroxide (or) cupric carbonate in dilute H2SO4

CuO + H2SO4 ® CuSO4 + H2O

Cu(OH)2 + H2SO4 ® CuSO4 + 2H2O

CuCO3 + H2SO4          ® CuSO4 + H2O + CO2­

Properties

Physical properties

1.    The anhydrous salt is colourless but the hydrated salt is blue in colour.

2.    It readily dissolves in water but is insoluble in alcohol.

Chemical Properties

1.    Action of Heat

On heating CuSO4.5H2O loses its water of crystallization and decomposes at 720 o C to give cupric oxide and sulphur trioxide.

2.        Action of ammonia

Copper sulphate gives deep blue colour with NH4OH forming complex compound.

CuSO4 + 4NH4OH ® [Cu (NH3)4]SO4 + 4H2O

3.    Action of KI

When KI is added to a solution of CuSO4, a white precipitate of cuprous iodide is produced.

CuSO4 + 2KI ® Cu I2 + K2SO4

(unstable)

2CuI2 ® Cu2I2 + I2

(white ppt)

4.    Action with KCN

A yellow precipitate of cupric cyanide is first formed with KCN and it decomposes to give cyanogen gas.

CuSO4 + 2KCN ® Cu(CN)2 + K2SO4

2Cu(CN)2 ® Cu2(CN)2 + (CN)2

cyanogen

5. Action of alkalies

With alkalies, a pale blue precipitate of copper hydroxide is formed.

CuSO4 + 2NaOH ® Cu(OH)2 + Na2SO4

Pale blue precipitate

6. Action with H2S

With H2S it gives a black precipitate of copper sulphide.

CuSO4 + H2S ® CuS + H2SO4 (Black ppt)

Uses

1.    It is used as a germicide and insecticide in agriculture.

2.    A mixture of copper sulphate and lime, commonly known as Bordeaux

mixture, is used as fungicide.

3. It is used in electroplating, calicoprinting and in electrical batteries.