Copper sulphate penta hydrate (CuSO4 5H2O)

Copper sulphate penta hydrate is known as blue vitirol and is the most common oxosalt of copper(2)
Preparation
Copper sulphate is prepared industrially by blowing a current of air through copper scrap and dilute sulphuric acid.

2Cu + 2H2O + O2 --------> 2CuSO4 + 2H2O

The crude copper(2) sulphate solution obtained contain iron(2) sulphates as impurity Dilute nitric acid is added to oxidize iron(2) to iron(3) sulphate which remains in solution after crystallization and CuSO4 5H2O crystallizes out.

The crystalline copper(2) sulphate, CuSO4 5H2O has the structure in which four water molecules are coordinated to the central copper cation in square planar structure. The fifth water molecule is held by hydrogen bonds between a sulphate anion and a coordinated water molecule. The fifth hydrogen bonded water molecule is deeply embedded in the crystal lattice and hence not easily removed.

Properties

1. Copper sulphate penta hydrate is a blue coloured crystalline solid, soluble in water.

2. Action of heat
On heating, copper sulphate penta hydrate gives trihydrate at 305 kelvin, monohydrate at 373 kelvin. On further heating it forms white anhydrous copper sulphate at 573 kelvin. The white anhydrous copper sulphate decomposes to give copper oxide and sulphur trioxide on heating to 673 kelvin.

At 3o5 kelvin CuSO4 5H2O ---------> CuO + SO2

At 373 kelvin CuSO4 3H2O ---------> CuO + SO2

At 573 kelvin CuSO4 H2O ---------> CuO + SO2

At 673 kelvin CuSO4 ---------> CuO + SO2

3. Copper(2) sulphate forms well defined crystalline double salts with sulphates of strongly electropositive metals of the type M2SO4.CuSO4 6H2O like (NH4)2SO4. CUSO4 6H2O. These double salts are isomorphous with the double salts of bivalent metals, Fe, Co, Ni.

4. If an aqueous solution of copper(2)sulphate is saturated with ammonia, the blue compound [Cu (NH3)4]SO4 H2O crystallizes on evaporation.

Uses of CuSO4 5H20
Copper(2)sulphate is used in copper plating and electro refining of metals. It is used as a mordant in dyeing and in electroplating. It is also used as germicide and fungicide under the name Bordeaux mixture which is a mixture of CuSO4 and Ca(OH)2.

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