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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.

Extraction of Copper

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.

2CuFeS2(s) + 4O2(g) → Cu2S(s) + 3SO2(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) + O2(g) → 2Cu(s) + SO2(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

Properties of Copper (Physical and Chemical)

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 1080oC.

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) + O2(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) + 4HNO3(aq) → Cu(NO3)2(aq) + 2H2O(l) + 2NO2(g)

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

3Cu(s) + 8HNO3(aq) → 3Cu(NO3)2(aq) + 4H2O(l) + 2NO(g)

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

Cu(s) + 2H2SO4(aq) → CuSO4(aq) + 2H2O(l) + SO2(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.

Uses of CuSO4

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.

Test for Copper(II) Ion, Cu2+

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)

Uses of Copper

(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.
 

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