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Element Fact
Iridium is the most corrosion-resistant metal known. Together with platinum, it is used to make the international prototype of the kilogram, which is the standard definition for the unit of mass.

Copper, Cu

copper sample

Atomic number: 29
Atomic mass: 63.546(3)
Natural abundance: 68 ppm
63Cu (62.929601) - 69.17%
65Cu (64.927794) - 30.83%

History and Production

From Latin cuprum, the island of Cyprus. The metal has been known since ancient times. It is one of the man's most important metal. As early as 3500 BC it was already obtained by charcoal reduction of its ores. By 3000 BC knowledge of adding tin to copper to make bronze was already appreciated in Mesopotamia and Greece (the Bronze age). Nowadays it is extracted from the oxide ores using coke as the source of carbon. However, the metal can also be obtained from sulfide ores which require more complicated treatments. Copper is mainly used in the electrical industry as an electrical conductor (copper wire, for example). It is also used for making alloys such as brass (with zinc), bronze (with tin) and Monel(with nickel). One of the most important compound is the blue vitriol or copper sulfate which is used as fungicide and agricultural poison.

Physical Data

Copper is reddisd-brown in color with bright metallic lustre. It is malleable, ductile and a good conductor of heat and electricity. Relative abundance in the earth's crust is 68 ppm and can be found in a variety of minerals such as copper pyrite (CuFeS2), cuprite (Cu2O) and malachite (Cu2CO3(OH)2).

Interatomic distance: 255.6 pm
Melting point: 1084.62C
Boiling point: 2562C
Thermal conductivity/Wm-1K-1: 401 (27C)
Density/kgm-3: 8960 (20C), 7940 (m.p.)

Standard Thermodynamic Data (atomic gas)

Enthalpy of formation: 337.4 kJ/mol
Gibbs free energy of formation: 297.7 kJ/mol
Entropy: 166.4 J/mol K
Heat capacity: 20.8 J/mol K

Electronic data

Electronic configuration: [Ar] 3d10 4s1
Term symbol: 2S1/2
Electron affinity: 119.1595 kJ/mol   Electronegativity (Pauline): 1.90
Ionization energy (first, second, third): 745.483, 1957.92, 3554.62 kJ/mol

Chemical properties

Very slowly attack by cold concentrated hydrochloric acid or dilute sulfuric acid. However, it is readily attacked by dilute nitric acid (to form soluble copper(II) nitrate) and by both hot concentrated sulfuric acid and hydrobromic acid.

Water-soluble copper(II) salts yield bluish-green precipitate of copper(II) hydroxide when sodium hydroxide is added. The precipitate gives black copper(II) oxide when heated.

In moist air copper corrodes to produce greenish basic copper carbonate. This is the green coloration associated with copper roofing and bronze statues:

copper carbonate

Test for copper:
(1) Flame test: green.
(2) Borax bead test: blue in oxidizing flame.
(3) Fusion with sodium carbonate on charcoal block gives a reddish-brown residue of copper.

Test for copper(II) ions
(1) Sodium hydroxide solution gives a pale blue precipitate of copper(II) hydroxide. It turns black on boiling.
(2) Ammonia solution gives a pale blue precipitate the dissolves in excess ammonia to give a clear blue solution.
(3) Hydrogen sulfide precipitates the black copper(II) sulfide.
(4) A brown precipitate of copper(II) hexacyanoferrate(II) form when potassium ferrocyanide is added.

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