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Copper and its Properties

The major ores of copper are copper pyrites (CuFeS₂), cuprite (Cu₂O), copper(I) sulphide (Cu₂S), and malachite (CuCO₃.Cu(OH)₂).

Copper is very stable in air, it can therefore be found freely as a metal in a few places.

The ore from which copper is commonly extracted is copper pyrites, CuFeS₂. It is initially concentrated by a process of floatation, and then roasted in air to produce copper(I)sulphide.

2CuFeS_2(s) + 4O_2(g) → Cu2S_(s) + 3SO_2(g) + 2FeO_(s)

The addition of SiO₂ and heating in the absence of air removes the iron(II) oxide as slag of iron(II) trioxosilicate(IV), FeSiO₃. Copper(I)sulphide, Cu₂S is then left.

Copper is extracted from the Cu₂S by heating it in a regulated supply of air.

Cu₂S_(s) + O_2(g) → 2Cu_(s) + SO_2(g)

Note:

*The supply of air has to be regulated because copper could react with oxygen to form oxides.

*The copper produced is very impure, hence, it is purified by using electrolytic means. The impure copper is made the anode, while the cathode is a strip of pure copper.

The electrolyte is a solution of CuSO₄ - see more details for this process here: Electrolytic Cells

Copper shows the following physical and chemical properties:

Physical Properties

1. Copper is a soft, red solid with a lustre.

2. It has density of 8.95 g/cm³.

3. It is very malleable and ductile.

4. It has relatively high tensile strength.

5. Its melting point is 1080^oC.

6. It is a very good conductor of heat and electricity.

Chemical Properties

Copper, silver and gold are often called the coinage elements because they are used to make the world’s coins, due to the fact that they are not reactive and are resistant to corrosion.

1. Exposure to air - copper is very stable in pure air (recall that copper is less reactive, being much lower in the reactivity series).

If exposed to moist air, it gradually becomes covered with a green coating of basic copper(II)sulphate(VI), CuSO₄.3Cu(OH)₂ and carbonate. If exposed to moist sea air, a coating of basic chloride is formed on it.

Copper, when heated in air is readily oxidized to give copper(II)oxide (black).

2Cu_(s) + O_2(g) → 2CuO_(s)

2. With acids - copper will not displace the hydrogen of dilute acids (being lower than hydrogen in the activity series).

Therefore, it does not react with dilute HCl or H₂SO₄. However, copper reacts with solutions of the oxidizing acids, such as HNO₃ and hot conc. H₂SO₄. With HNO₃ - the concentration of the acid will determine the products formed.

With hot conc. HNO₃ - nitrogen(IV)oxide and copper(II)trioxonitrate(V) salt are formed.

Cu_(s) + 4HNO_3(aq) → Cu(NO₃)_2(aq) + 2H₂O_(l) + 2NO_2(g)

With dilute HNO₃ - nitrogen(II)oxide and copper(II)trioxonitrate(V) salt are formed.

3Cu_(s) + 8HNO_3(aq) → 3Cu(NO₃)_2(aq) + 4H₂O_(l) + 2NO_(g)

With hot conc. H₂SO₄ - CuSO₄ is formed and SO₂ is liberated.

Cu(s) + 2H₂SO_4(aq) → CuSO_4(aq) + 2H2O_(l) + SO_2(g)

The salt, CuSO₄ crystallizes as blue pentahydrate - CuSO₄.5H₂O

Note: the reaction between metallic copper and H₂SO₄ only occurs when the acid is hot and concentrated.

With alkalis - copper do not react with alkalis.

CuSO₄ can be used in the following ways:

(1). As fungicide for spraying vines, citrus trees and potatoes.

(2). In the manufacture of certain pigments.

(3). In making washes, such as ‘Bordeaux mixture.’

(4). In electroplating.

(5). In dyeing.

(6). In the preparation of other copper compounds.

(7). To preserve timber.

Solutions of copper(II) salts are usually blue in colour. The following tests will identify and confirm them:

1. Flame Test - Copper(II) salts burn in a non luminous flame, producing bluish - green colour.

2. With sodium hydroxide - a blue gelatinous precipitate is formed when a few drops of NaOH is added to a solution of Cu²⁺ salt.

The precipitate is insoluble in excess of NaOH.

Cu²⁺_(aq) + 2NaOH_(aq) → Cu(OH)_2(s) + 2Na⁺_(aq)

3. With aqueous ammonia - a blue precipitate is given. The blue precipitate is infact copper(II) hydroxide, Cu²⁺_(aq) + 2OH^-_(aq) → Cu(OH)_2(s) which will dissolve in excess of aqueous ammonia to give a deep blue solution.

 Cu(OH)_2(s) + 4NH₄⁺_(aq) + 4OH^-_(aq) → Cu(NH₃)₄²⁺_(aq) + 2OH^-_(aq) + 4H₂O_(l)

(1). Copper being a very good conductor of electricity, and also being ductile is used for making electric wires.

(2). It is used in metal works, plumbing and roofing.

(3). In making various alloys of immense usage.

(4). Used in making coins.