The Chemistry of Copper, the Transition Metal
Copper is a transition element, and has the symbol Cu and the atomic number 29. It is a reddish-coloured metal, is malleable and ductile, is resistant to corrosion and is a good conductor of heat and electricity. It has a wide variety of applications in modern life, domestically, in industry and biologically. It is extensively mined across the world, but it has been estimated that available reserves will only last for up to 60 years before being exhausted.The History of Copper
Copper has been used by humans for at least 10,000 years, artefacts having been discovered in what is now northern Iraq which date back to 8700 BC. It came into its own, however, during the Bronze Age, from about 3000 BC, when its alloy with tin, called bronze, became the material of choice across much of the world.
It was known to the Romans as Cyprium, because so much of it was mined in Cyprus, although this was simplified to Cuprum, from which came the English word, Copper, and the chemical symbol, Cu. It was always highly valued, although behind gold and silver, and hence became a constituent of currency. In the modern period the uses of copper have greatly multiplied, and it is estimated that 95 percent of all copper ever mined and smelted has been extracted since 1900.
Extraction of Copper
Copper is mined as the yellow copper-iron sulfide known as chalcopyrite, or the green copper carbonate known as malchite. The ore is first crushed into a fine powder, and the lighter particles containing copper are separated using froth flotation. The metal is then extracted by roasting with carbon in air, followed by purification in a reduction furnace. The molten metal is then cooled into slabs which are then purified further by electrolysis.
Compounds of Copper
Copper is not very reactive, however, it does react with nitric acid to form a nitrate and tarnishes in air to form the oxide. Copper has two oxidation states, the most common is copper (II), but it also forms some copper (I) compounds, such as copper (I) oxide which is red in colour, while copper (II) oxide is black.
Most other copper (II) compounds are blue, and copper salts give a green flame test. Copper salts in solution form a pale blue precipitate of copper hydroxide when sodium hydroxide solution is added. Adding ammonia solution initially gives the same pale blue precipitate, but this becomes a clear, deep inky blue solution when more ammonia is added.
Applications of Copper
98 percent of all applications of copper involve the metal. It is often used as part of an alloy to create a harder metal for many uses, especially intricate parts such as threaded components. It is used in electrical wire, electromagnets, electronic components and printed circuit boards. It is also used as a roofing materials and in statues, including the Statue of Liberty. Alloyed with nickel it is used in many shipbuilding applications.
As a metal, it is used for many hospital applications because bacteria will not grow on its surface. The element is, however, an essential trace element to all living organisms, especially in the liver, muscle and bone. Interestingly, octopus, snail and spider blood is blue because its oxygen-carrying system uses copper in place of the iron used by mammals.
J. Emsley, Molecules at an Exhibition, 1998, Oxford University Press, p49-51
C. Johnson, Chemistry for GCSE, 1987, Heinemann
Copper article in ChemistryDaily.com (accessed 5th Febraury 2011)