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(I) Copper (II) Sulphate pentahydrate or blue vitriol, CuSO4.5H2O

Preparation

In the laboratory, it is prepared by dissolving cupric oxide, cupric hydroxide or carbonate in dilute H2SO4.

CuO + H2SO4 -> CuSO4 + H2O

Cu(OH)2 + H2SO4 -> CuSO4 + 2H2O

CuCO3 + H2SO4 -> CuSO4 + H2O + CO2

The solution of CuSO4 thus obtained is concentrated and cooled when crystals of blue vitriol, CuSO4.5H2O separates out. Commercially it is prepared by the action of hot dilute sulphuric acid on scrap copper in the presence of air.

Properties

1.   Action of heat

       

In CuSO4.5H2O, four H2O molecules are coordinated to the central Cu2+ ion. While the 5th one is attached between   and H2O molecule by hydrogen bonding. This fifth H2O molecule is thus deep inside the crystal lattice and is not easily lost.

2.   Action of alkalis

     

With NH4OH it forms tetraamminecopper (II) sulphate

3.   Reaction with KI

      

      

The liberation of iodine in this reaction is quantitative. Therefore, this reaction is used to estimate copper volumetrically.

Uses

(i) It is used as an electrolyte in electroplating, electrotyping and refining of copper.

(ii) It is used in reservoirs and swimming pools to prevent the growth of weeds.

(iii) It is used as a fungicide under the name Bordeaux mixture, which is a mixture of CuSO4 and slaked lime Ca(OH)2.

(iv) Anhydrous CuSO4 is used for detection of moisture in organic liquids such as alcohol, ether etc

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