Copper: Studies of Heavy Metals – Class 12 Chemistry

Unit 7: Studies of Heavy Metals: Copper

Introduction to Copper

Occurrence of copper

Copper occurs in native as well as combined states. Native copper is found in the USA, Mexico, Russia and China. The common ores of copper are.

1. Chalcocite or copper glance (Cu₂S).
2. Cuprite or Ruby copper (Cu₂O).
3. Chalcopyrite or copper pyrites (CuFeS₂).
4. Malachite green [CuCO₃.Cu(OH)₂].
5. Azurite (blue) [Cu(OH)₂.2CUCO₃]

In Nepal, copper occurs in free and as chalcopyrites in Chitwan, Makanpur, Udaypur, Chisapani Gadhi.

Extraction of copper from copper pyrites (CuFeS₂)

Copper is mainly extracted from copper pyrite ore. The various steps involved in the extraction of copper from the copper pyrites ore are described below.

Step 1: Crushing and pulverization:

The collected big lump of ore is crushed in jaw crushers and then pulverized in ball mills. The powdered ore is then taken for concentration.

Step 2: Concentration:

The powdered ore is concentrated by the froth flotation method. The powdered ore is agitated with a mixture of pine oil and water in a flotation tank by blowing compressed air. The pure ore particles come to the surface with froths which are the skimmed off and impurities gangue particles settle down at the bottom. In this process, copper content concentration is increased to 25-30 %.

Step 3: Roasting:

The concentrated ore is heated strongly in he presence of air on the hearth of reverberatory furnace. In this process impurities like arsenic, antimony, sulfur etc are removed as their volatile oxides. Moisture and organic matters are removed.

$$ 4As\;+\;3O_2\;\xrightarrow\triangle\;2As_2O_3 $$$$ 4Sb\;+\;3O_2\;\xrightarrow\triangle\;2Sb_2O_3 $$$$ S\;+\;O_2\;\xrightarrow\triangle\;SO_2 $$

The copper pyrite ore is partially converted in to sulfides of iron and copper. Further sulfides are partially oxidized into cuprous oxide and ferrous oxides.

$$ 2CuFeS_2\;+\;O_2\;\xrightarrow\triangle\;Cu_2S\;+\;2FeS\;+\;SO_2$$ $$2Cu_2S\;+\;3O_2\;\xrightarrow\triangle\;2Cu_2O\;+\:2SO_2$$ $$ 2FeS\;+\;3O_2\;\xrightarrow\triangle\;2FeO\;+\:2SO_2 $$

Therefore, roasted ore mainly contains a mixture of Cu₂O, Cu₂S, FeS and FeO.

Step 4: Smelting:

The roasted ore is then mixed with powdered coke and sand and heated strongly in the blast furnace about 4.5 -6 meter high and 2 meter in diameter. It is made of steel lined inside with fire clay brisk. Hot air at about 800oc is introduced from tuyeres near the base of the furnace. The coke burns and about 100° C is produced. Here, following changes occurs.

Ferrous sulphide and Cu2S is oxidized in to ferrous oxide $$2FeS + 3O_2 \xrightarrow\triangle 2 FeO + 2SO_2$$

Some of cuprous oxides get reduced by coke
$$Cu_2O + C \xrightarrow\triangle 2Cu + CO_2↑$$

Some cuprous oxide again reacts with FeS to give back Cu2S.
$$Cu_2O + FeS \xrightarrow\triangle Cu_2S + FeO$$

Alumina and iron oxide combine with silica to form fusible slag.
$$FeO + SiO_2(flug) \xrightarrow\triangle FeSiO_3 $$

ferrous silicate (fusible slag)

$$Al2O3 + 3SiO2 (slag) \xrightarrow\triangle Al2(SiO3)3$$

(fusible slag) aluminum silicate

The slag being lighter floats on the surface forming a layer which is removed through the slag hole from time to time. The molten mass containing about 40-45% of metal, Cu2S and some trace of FeS is called matte or coarse metal which forms lower layer in the blast furnace and is taken out from the tapping hole at the bottom.

Step 5: Bessemerization:

The matte is mixed with little silica and charged into a Bessemer converter. It is pear shaped steel furnace lined with refractory materials like silica, lime etc and is mounted on pivots so that it can be tilted. A blast of hot air is admitted through tuyeres from the base of the converter. FeS present in matte is oxidized to FeO which combine with silica to form slag.

2FeS + 3O₂ –^∆→ 2 FeO + 2SO₂
FeO + SiO₂(flug) –^∆→ FeSiO₃
(fusible slag)

Slag thus formed floats on the surface of the molten mass and removed. The copper sulfide undergoes oxidation to form cuprous oxide which reacts with copper sulfide to give metallic copper.
2Cu₂S + 3O₂ –^∆→ 2Cu₂O + 2SO₂
2Cu₂O + Cu₂S –^∆→ 6 Cu + SO₂

After completion of reaction, the converter is tilted and the molten metal is poured into moulds and cooled to escape dissolved gases. However, some of the gas bubbles are entrapped during solidification giving blister appearance. Therefore, metal thus obtained is called blister of copper and it is 98% pure copper.

Step 6: Refining:

The metal crude metal is refined in following steps.

a) Bessemerisation: The molten metal is retaken in a Bessemer converter. The impurities are converted into slag and thus formed slag is removed.

b) Poling: Remaining cuprous oxide is reduced back to copper by stirring the molten metal green poles of wood. The hydrocarbons present in these poles reduce the cuprous oxide to metallic copper. Copper thus obtained is 99.5 %.

c) Electrolytic refining: In this method, a thin sheet of pure metal is made cathode and the block of crude metal is made anode. When an electric current is passed , impure copper from the anode goes in to solution and pure copper from solution gets deposited at cathode.The impurities like zinc, nickel, iron etc get collected below the anode as anode mud.

$$ CuSO4\;\rightleftharpoons Cu^{+2}\;\;+\;SO4^{-2} $$

At Anode Cu →Cu⁺² + 2e

At cathode Cu⁺² + 2e → Cu.

Chemical Properties

1. Action with Air

a. Reaction in Dry Air

On heating copper in dry air, it forms cuprous oxide (Cu₂O) and cupric oxide (CuO) depending on the temperature:

Formation of Cuprous Oxide: $$ 4Cu+O2 \xrightarrow{> 1100^\circ \text{C}} 2\text{Cu}_2\text{O}$$

Formation of Cupric Oxide: $$ 2Cu+O2 \xrightarrow{< 1100^\circ \text{C}} 2\text{CuO}$$

b. Reaction in Moist Air

In the presence of moist air, copper reacts to form green basic copper carbonate:

$$2Cu+H_2O+CO_2+O_2→CuCO3⋅Cu(OH)_2$$

This compound is known as basic copper carbonate.

2. Action with Acids

a) Reaction with Hot and Concentrated H₂SO₄

When heated with concentrated sulfuric acid, copper reacts to form copper sulfate, water, and sulfur dioxide: $$\text{Cu} + 2\text{H}_2\text{SO}_4 \xrightarrow{\Delta} \text{CuSO}_4 + 2\text{H}_2\text{O} + \text{SO}_2$$

With dilute sulfuric acid in the presence of air (oxygen), copper reacts to form copper sulfate and water: $$\text{Cu} + 2\text{H}_2\text{SO}_4 + \text{O}_2 \xrightarrow{\Delta} 2\text{CuSO}_4 + 2\text{H}_2\text{O}$$

b) Reaction with Hydrochloric Acid (HCl)

When hydrogen chloride gas is passed over heated copper, cuprous chloride (Cu₂​Cl₂) and hydrogen are formed: $$2\text{Cu} + 2\text{HCl} \xrightarrow{\Delta} \text{Cu}_2\text{Cl}_2 + \text{H}_2$$

In the presence of oxygen, the reaction forms cuprous chloride and water: $$2\text{Cu} + 2\text{HCl} + \text{O}_2 \xrightarrow{\Delta} \text{Cu}_2\text{Cl}_2 + \text{H}_2\text{O}$$

c) Reaction with Nitric Acid (HNO₃​)

With Hot and Concentrated Nitric Acid: Copper reacts with hot and concentrated nitric acid to form copper nitrate, water, and nitrogen monoxide: 3$$3\text{Cu} + 8\text{HNO}_3 \rightarrow 3\text{Cu(NO}_3\text{)}_2 + 4\text{H}_2\text{O} + 2\text{NO}$$

With Dilute Nitric Acid: Copper reacts with dilute nitric acid to form copper nitrate, water, and nitrous oxide: $$4\text{Cu} + 10\text{HNO}_3 \rightarrow 4\text{Cu(NO}_3\text{)}_2 + 5\text{H}_2\text{O} + \text{N}_2\text{O} $$

3. Action with Metal Ions

Copper can reduce some metal ions in their aqueous solutions. It can displace metals lying below it in the electrochemical series. For example:

$$ \text{Cu} + 2\text{AgNO}_3 \rightarrow 2\text{Ag} + \text{Cu(NO}_3\text{)}_2$$

This reaction shows copper displacing silver from silver nitrate solution, forming copper(II) nitrate and metallic silver.

4. Action with Ammonia

Copper dissolves in aqueous ammonia in the presence of air to form a deep blue complex compound:

$$ 2\text{Cu} + 8\text{NH}_3 + 2\text{H}_2\text{O} + \text{O}_2 \rightarrow 2[\text{Cu(NH}_3\text{)}_4](\text{OH})_2$$

The product is tetra amine copper(II) dihydroxide.

Uses of Copper

1. Electrical Applications:
   • Electrical Cables: Copper is widely used in electrical wiring and cables due to its excellent electrical conductivity.
   • Electrical Appliances: Used in various electrical appliances and electronics for efficient transmission of electricity.
2. Household Items:
   • Utensils and Containers: Copper is used in making utensils, cookware, and containers due to its good thermal conductivity and antimicrobial properties.
3. Industrial Applications:
   • Electroplating: Copper is used in electroplating to provide a protective and decorative coating on other metals.
4. Agricultural Uses:
   • Insecticide: Copper compounds, such as copper sulfate, are used as insecticides and fungicides in agriculture to protect crops.

Compounds of Copper

• Copper Sulphate CuSO₄.5H₂O
• Black oxide of copper (CuO, cupric oxide)
• Red oxide of copper (Cu₂O)

Blue Vitriol (Copper(II) Sulfate Pentahydrate)

Chemical Formula: CuSO₄.5H₂O
Other Names: Blue vitriol, Nilo tutho (Nepali)

Preparation

1. Laboratory Preparation:
   • Copper sulfate can be prepared by reacting copper oxide, hydroxide, or carbonate with dilute sulfuric acid.
     • CuO+H₂​SO_4​ → CuSO_4​+H₂​O
     • Cu(OH)₂​+H₂​SO₄ ​→ CuSO_4​+2H₂​O
     • CuCO₃​+H₂​SO₄​ → CuSO₄​+H₂​O+CO₂​
   • The resulting copper sulfate solution is then evaporated to form crystals of copper sulfate.
2. Preparation from Copper Metal:
   • Copper reacts with hot and concentrated sulfuric acid to produce copper sulfate, water, and sulfur dioxide.
     • $$ \text{Cu} + 2\text{H}_2\text{SO}_4 \xrightarrow{\Delta} \text{CuSO}_4 + 2\text{H}_2\text{O} + \text{SO}_2$$
3. Industrial Manufacture:
   • Copper sulfate is manufactured on a large scale by heating scrap copper with dilute sulfuric acid in the presence of air.
     • $$2\text{Cu} + 2\text{H}_2\text{SO}_4 + \text{O}_2 \rightarrow 2\text{CuSO}_4 + 2\text{H}_2\text{O} $$
   • From the solution of copper sulfate, crystals are obtained by concentrating and cooling.
     • $$ \text{CuSO}_4 + 5\text{H}_2\text{O} \xrightarrow{\Delta} \text{CuSO}_4 \cdot 5\text{H}_2\text{O}$$

Properties

Physical Properties:

1. Appearance: Blue crystalline solid.
2. Solubility: Readily soluble in water.
3. Nature of Aqueous Solution: Slightly acidic.
4. Action with Heat:
   • On heating, it loses water of crystallization in stages:

• The color changes from blue to pale blue to bluish white to white.

Chemical Properties:

1. Action with Ammonia:
   • When ammonia is added to copper sulfate solution, a bluish white precipitate of copper(II) hydroxide is formed, which dissolves in excess ammonia to form a deep blue solution of tetraamine copper(II) sulfate.
     • CuSO₄+2NH₄OH→Cu(OH)₂↓+(NH₄)₂SO₄
     • Cu(OH)₂+4NH₄OH+(NH₄)₂SO₄→[Cu(NH3)₄]SO₄+6H₂O
2. Formation of Double Salts:
   • Copper sulfate forms double salts such as potassium sulfate copper sulfate hexahydrate and ammonium sulfate copper sulfate hexahydrate.
     • K₂​SO₄​+CuSO₄​+6H₂​O→K₂SO₄​⋅CuSO₄​⋅6H₂​O
3. Action with Alkali:
   • Copper sulfate reacts with sodium hydroxide or potassium hydroxide to give a bluish white precipitate of copper(II) hydroxide.
     • CuSO₄​+2NaOH→Cu(OH)₂​↓+Na₂​SO₄​
4. Action with Potassium Iodide (KI):
   • Copper sulfate reacts with potassium iodide to form a dark brown precipitate of copper(I) iodide.
     • 2CuSO₄​+4KI→Cu₂​I₂+I₂​+2K₂​SO₄​

Uses

1. Medicine:
   • Used as an antiseptic.
2. Agriculture:
   • Employed as a fungicide and germicide.
3. Electroplating:
   • Used in electroplating baths.
4. Dyeing:
   • Used in the manufacture of dyestuffs and as a mordant in dyeing.

Black Oxide of Copper (Cupric Oxide, CuO)

Common Name: Black oxide of copper
Chemical Formula: CuO

Uses:

1. Oxidizing Agent: Used as an oxidizing agent in various chemical reactions.
2. Colored Glass Production: Used to prepare colored glass.
3. Organic Compound Analysis: Used to estimate the carbon and hydrogen content in organic compounds.

Red Oxide of Copper (Cuprous Oxide, Cu₂O)

Chemical Formula: Cu_2​O

Uses:

1. Glass Industry: Used to make red glass.
2. Protective Paint: Used as a protective paint to prevent rusting.
3. Preparation of Cuprous Chloride: Used to prepare cuprous chloride (CuCl).