STUDY OF SOME IMPORTANT COMPOUNDS

(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.
 

            2Cu + 2H₂SO₄ + O₂ → 2CuSO₄ + 2H₂O     
Properties

1. Action of heat

In CuSO₄.5H₂O, four H₂O molecules are coordinated to the central Cu²⁺ ion. While the 5^th 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

    CuSO₄ + 2NaOH ——→ Cu(OH)₂ + Na₂SO₄

    With NH₄OH it forms tetraamminecopper (II) sulphate

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

    CuSO₄ + 2KI ——→ CuI₂ + K₂SO₄

    2Cul₂ ——→ 2Cul + l₂

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.

(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.