# Chemistry of Copper Sulphate and Blue Vitriol

Copper sulphate: Copper sulphate is the inorganic compound of copper with the chemical formula CuSO4. It has many hydrous as well as non hydrous form. The common hydrous form of copper sulphate is blue vitriol (CuSO4.5H2O).

Preparation:

1. On dissolving copper scrap in concentrated sulphuric acid, Copper sulphare will be obtained, which on heating upto crystallization point, crystals of blue vitriol will be obtained. It is the commercial method for the preparation of blue vitriol.
$$\ce{Cu + conc.H2SO4->[\Delta]CuSO4 SO2 + H2O}$$
$$\ce{CuSO4 + 5H2O->[\text{crystallization point}]CuSO4.5H2O}$$
2. It is also prepared by the action of dilute sulphuric acid upon copper hydroxide.
$$\ce{Cu(OH)2 + dil. 2H2SO4->CuSO4 + 2H2O}$$

Physical properties:

• It is a blue colored crystalline solid substance.
• It is insoluble in water but soluble in ethanol.

Chemical properties:

1.  Action of heat: Blue vitriol when exposed to air loses 2 molecules of water. When it is heated to 100 oC, it lose two more molecules of water. Heating upto the temperature of 250oC, blue vitriol loses all of its water molecule and further heating on more than 700oC decomposes to cuprous oxide and oxygen.
$$\ce{CuO.5H2O->[air]CuSO4.3H2O->[{100^{\circ}C}]CuSO4.H2O->[{230^{\circ}C}]CuSO4->[{700^{\circ}C}]SO3 ^ + CuO}$$
2. Action with sodium hydroxide: Copper sulphate when reacted with sodium hydroxide gives blue precipitate of copper hydroxide. $$\ce{CuSO4 + 2NaOH->Na2SO4 + \underset{\text{Blue ppt.}}{\ce{Cu(OH)2}}}$$
3. Action with Ammonia: When CuSO4 solution is treated with ammonium hydroxide, bluish white precipitate is fromed. When excess of ammonium hydroxide is added, deep blue coloration of tetra-amine copper (II) sulphate is produced. The product obtained is also called Schwitzer’s reagent.  $$\ce{CuSO4 + 2NH4OH ->Cu(OH)2 + \underset{\text{Bluish white precipitate}}{\ce{(NH4)SO4}}}$$ $$\ce{Cu(OH)2 + (NH4)2SO4 + 2NH4OH->\underset{\text{Blue ppt.}}{\ce{[Cu(NH3)4]SO4}} + 4H2O}$$
4. Action with hydrogen sulphide: CuSO4 when reacted with ammonia gives black precipitate of copper sulphide. $$\ce{CuSO4 + H2S-> \underset{\text{black}}{\ce{CuS v}} + H2SO4}$$
5. Action with potassium cynide: With potassium cynide, copper sulphate gives yellow ppt of potassium sulphate. $$\ce{CuSO4 + 2KCN->CuCN2 + \underset{\text{yellow ppt.}}{\ce{K2SO4}}}$$

Uses:

• It is used in copper plating and electro refiining of copper.
• It is used for detecting moisture.
• It is used as a laboratory reagent.

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