Compounds of Copper

Blue vitrol (CuSO₄.5H₂O)

The synonyms of blue vitrol are:

• copper sulphate pentahydrate
• copper(II) sulphate 5-water
• Roman vitriol
• Salzburg vitriol
• blue vitriol
• copper sulfate 5-water
• copper sulfate pentahydrate
• copper sulphate 5-water
• copper(II) sulfate 5-water
• cupric sulfate 5-water
• cupric sulphate 5-water

The oxidation number of copper in copper sulphate pentahydrate is 2.

• Formula: CuSO₄.5H₂O
• Hill system formula: Cu₁H₁₀O₉S₁
• Formula weight: 249.686

• Colour: blue, greenish blue
• Melting point: 30°C and 110°C (dehydrates)
• Density: 2286 kg m^-3

Preparation

• It is prepared by treating copper turnings with dilute sulphuric acid (H₂SO₄) in the presence of air.

2Cu + 2H₂SO₄ + O₂ → 2CuSO₄ + 2H₂O

• It is also prepared by treating CuO, Cu(OH)₂, CuCO₃ with dilute sulphuric acid (H₂SO₄).

CuO + H₂SO₄ → CusO₄ + H₂O

CuCO₃ + H₂SO₄ → CuSO₄ + CO₂

CuOH₂ + H₂SO₄ → CuSO₄ + 2H₂O

The blue solution of copper sulphate after crystallization gives crystal of blue vitriol.

CuSO₄ + 5H₂O → CuSO₄∙5H₂O

Physical properties

• It is crystalline and contains five molecules of water of crystallization.
• It is soluble in water.

• Its aqueous solution is acidic due to hydrolysis.

Chemical properties

• Action with heat: blue vitrol on heating loses it’s water of crystallization and finally turns into black oxide of copper.

CuSO₄∙5H₂O → CuSO₄∙H₂O → CuSO₄ → CuO + SO₃

Blue vitrol at 100 loses four water of crystallizations to form the bluish white compound and further when heated above 100 loses another water of crystallization to form white copper sulphate and when further heated at 750 forms a black oxide of copper.

• Action with ammonia solution:ammonia solution reacts with blue vitrol to form bluish white cupric hydroxide and with excess ammonia, tetraamine copper sulphate is formed which is deep blue in colour.

CuSO₄ + NH₄OH → Cu(OH)₂ + (NH₄)SO₄

Cu(OH)₂ + NH₄OH + (NH₄)SO₄ → {Cu(NH₃)₄}SO₄ + 4H₂O

• Action with KI: When copper sulphate combines with potassium iodide, a violet coloured ppt. of cuprous iodide and iodine is formed.

2CuSO₄ + 4KI → Cu₂I₂ + 2I₂ + 2K₂SO₄

• Action with potassium ferrocyanide: The copper sulphate solution reacts with potassium ferrocyanide solution to give chocolate brown ppt of cupric ferro cyanide.

CuSO₄ + K₄{Fe(CN)₆} → Cu₂{Fe(CN)₆} + 2K₂SO₄

• Reaction with H₂S: On passing H₂S gas in copper sulphate solution black ppt. of cupric sulphide is obtained.

CuSO₄ + H₂S → CuS + H₂SO₄

Uses

• Used in electroplating, electrorefining of metal.
• Used as germicide and fungicide in agriculture.
• Used as weedicide in swimming pool, water reservoir tank.
• Used as the laboratory reagent.

Cupric oxide or Black oxide (CuO)

The synonym of black oxide are:

• copper oxide
• copper(II) oxide
• cupric oxide

The oxidation number of copper in the copper oxide is 2.

• Formula: CuO
• Hill system formula: Cu₁O₁
• Formula weight: 79.545
• Class: oxide

• Colour: black or brown-black
• Appearance: crystalline solid
• Melting point: l336°C (under 1-atmosphere oxygen)

Preparation

• It is prepared by heating copper in presence of air below 1100

2Cu + O₂ → 2CuO

• It is also prepared by heating CuCO₃, Cu(OH)₂, CuSO₄

CuCO₃ → CuO +CO₂

Cu(OH)₂ → CuO + H₂O

CuSO₄ → CuO + SO₂

Physical properties

• It is an amorphous black oxide.
• It is insoluble in water.

Chemical properties

• Action with heat: when the cupric oxide is heated at 1000 , it decomposes to cuprous oxide (Cu₂O).

4CuO → 2Cu₂O + O₂

• Action with HCl: when the cupric oxide is treated with HCl cupric chloride is obtained.

CuO + HCl → CuCl₂ + H₂O

• Action with hydrogen (H₂): CuO acts as oxidizing agent

CuO + H₂ → Cu + H₂O

Uses

• Used as the oxidizing agent.
• Used to make black colored glass.

Cuprous oxide (Cu₂O)

The synonyms of cuprous oxide are:

• dicopper oxide
• copper(I) oxide
• copper oxide
• cuprous oxide
• dicopper oxide
• red copper oxide

The oxidation number of copper in dicopper oxide is 1.

• Formula: Cu₂O
• Hill system formula: Cu₂O₁
• Formula weight: 143.091

• Colour: yellow, red, or brown
• Appearance: crystalline solid
• Melting point: 1230°C
• Boiling point: 1800°C
• Density: 6000 kg m^-3

Preparation

• Cuprous oxide is obtained by heating copper in the presence of air above 1100 .

Cu + O₂ → Cu₂O

• It is also prepared by treating cupric oxide with glucose.

CuO + C₆H₁₂O₆ → Cu₂O + C₆H₁₇O₇

Physical properties

• It is red colored amorphous solid.
• It is also insoluble in water.

Chemical properties

• Action with heat: it changes to cupric oxide on heating in the presence of air.

Cu₂O + O₂ → CuO

• Action with acid:

Cu₂O + HCl → CuCl₂ + H₂O +Cu (concentrated HCl)

Cu₂O + H₂SO₄ → CuSO₄ + H₂O + Cu (concentrated sulphuric acid)

Cu₂O + HNO₃ → Cu(NO₃)₂ + H₂O + Cu (concentrated nitric acid)

Uses

• Used as anti-rusting pigment
• Used in making ruby red glass.

Reference

poulse, tracy. Introduction to chemistry. u.s.a: flexbook, 2010.

Pathak, Sita Karki. The Text Book of Chemistry. kathmandu: Vidhyarthi Pustak Bhandar, 2012.