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CHEMISTRY : Metal Cation Identification


Information on COPPER




  1. General Information

  2. Occurence Uses and Properties

  3. History of the Metal

  4. Compounds
  5. Back to Main Metal List




General Information


Copper(Cu), chemical element, reddish, extremely ductile metal of Group Ib of the periodic table, unusually good conductor of electricity and heat. Copper is found in the free metallic state in nature; this native copper was first used (c. 8000 BC) as a substitute for stone by Neolithic man. Metallurgy dawned in Egypt as copper was cast to shape in molds (c. 4000 BC), was reduced to metal from ores with fire and charcoal, and was intentionally alloyed with tin as bronze (c. 3500 BC). The Roman supply of copper came almost entirely from Cyprus; it was known as aes Cyprium, "metal of Cyprus," shortened to cyprium and later corrupted to cuprum.

Copper is distributed widely in nature in the form of the free metal, sulfides, arsenides, chlorides, and carbonates. It is extracted by oxidative roasting and smelting, followed by electrodeposition from sulfate solutions, and it is technologically important, particularly in alloys, as an electroplated coating and as an exceptionally good conductor of heat and electricity. The pure metal is soft, tough, ductile, and characteristically reddish in colour and is second only to silver in thermal and electrical conductivity. Metallic copper is only superficially oxidized in air, sometimes acquiring a green coating that is a mixture of hydroxo-carbonate, hydroxosulfate, and small amounts of other compounds.

Copper is a moderately noble metal, being unaffected by nonoxidizing or noncomplexing dilute acids in the absence of air; it will, however, dissolve readily in nitric acid and in sulfuric acid in the presence of oxygen and is also soluble in aqueous ammonia or potassium cyanide in presence of oxygen, because of the formation of very stable cyano complexes upon dissolution. The metal will react at red heat with oxygen to give copper(II) oxide, CuO, and, at higher temperatures, copper(I) oxide, Cu2O. It reacts on heating with sulfur to give copper(I) sulfide, Cu2S.

Copper forms compounds in the oxidation states +1 and +2 in its normal chemistry, although under special circumstances some compounds of trivalent copper can be prepared.



Occurrence, uses, and properties.


Native copper is found at many loCATions as a primary mineral in basaltic lavas and also as reduced from copper compounds. The greatest known deposit of copper is in porphyries formed by volcanic activity in the Andean Mountains of Chile. (For mineralogical properties, see native elements [table].) Copper occurs combined in many minerals, such as chalcocite, chalcopyrite, bornite, cuprite, malachite, and azurite. It is present in the ashes of seaweeds, in many sea corals, in the human liver, and in many mollusks and arthropods. Copper plays the same role of oxygen transport in the hemocyanin of blue-blooded mollusks and crustaceans as iron does in the hemoglobin of red-blooded animals. The copper present in humans as a trace element helps CATalyze hemoglobin formation.

Copper is commercially produced mainly by smelting or leaching, usually followed by electrolytic refining or recovery. For a detailed treatment of the production of copper, see Industries, Extraction and Processing.

The major portion of copper produced in the world is used by the electrical industries; most of the remainder is combined with other metals to form alloys. Important series of alloys in which copper is the chief constituent are brasses (copper and zinc), bronzes (copper and tin), and nickel silvers (copper, zinc, and nickel, no silver). There are many useful alloys of copper and nickel, including Monel; the two metals are completely miscible. Copper also forms an important series of alloys with aluminum, called aluminum bronzes. Beryllium copper (2 percent Be) is an unusual copper alloy in that it can be hardened by heat treatment. Copper is a part of nearly all coinage metals. Long after the Bronze Age passed into the Iron Age, copper remained the metal second in use and importance to iron; but, by the 1960s, cheaper and much more plentiful aluminum had moved into second place in world production.

Copper is one of the most ductile metals, not especially strong or hard. Strength and hardness are appreciably increased by cold-working because of the formation of elongated crystals of the same face-centred cubic structure that is present in the softer annealed copper. Common gases, such as oxygen, nitrogen, carbon dioxide, and sulfur dioxide are soluble in molten copper and greatly affect the mechanical and electrical properties of the solidified metal. Natural copper is a mixture of two stable isotopes: copper-63 (69.17 percent) and copper-65 (30.83 percent).

Because copper lies below hydrogen in the electromotive series, it is not soluble in acids with the evolution of hydrogen, though it will react with oxidizing acids, such as nitric and hot, concentrated sulfuric acid. Copper resists the action of the atmosphere and seawater; exposure for long periods to air, however, results in the formation of a thin protective coating of green, basic copper carbonate (patina)



History


Copper was discovered and first used during the Neolithic Period, or New Stone Age. Though the exact time of this discovery will probably never be known, it is believed to have been about 8000 BC. Copper is found in the free metallic state in nature; this native copper is the material that humans employed as a substitute for stone. From it they fashioned crude hammers and knives and, later, other utensils. The malleability of the material made it relatively simple to shape implements by beating the metal. Pounding hardened the copper so that more durable edges resulted; the bright reddish colour of the metal and its durability made it highly prized.

The search for copper during this early period led to the discovery and working of deposits of native copper. Sometime after 6000 BC the discovery was made that the metal could be melted in the campfire and cast into the desired shape. Then followed the discovery of the relation of metallic copper to copper-bearing rock and the possibility of reducing ores to the metal by the use of fire and charcoal. This was the dawn of the metallic age and the birth of metallurgy.

The early development of copper probably was most advanced in Egypt. As early as 5000 BC, copper weapons and implements were left in graves for the use of the dead. Definite records have been found of the working of copper mines on the Sinai Peninsula about 3800 BC, and the discovery of crucibles at these mines indiCATes that the art of extracting the metal included some refining. Copper was hammered into thin sheets, and the sheets were formed into pipes and other objects. During this period bronze first appeared. The oldest known piece of this material is a bronze rod found in the pyramid at Maydum (Medum), near Memphis in Egypt, the date of origin being generally accepted as about 3700 BC.

Bronze, an alloy of copper and tin, is both harder and tougher than either; it was widely employed to fashion weapons and objects of art. The period of its extensive and characteristic use has been designated the Bronze Age. From Egypt the use of bronze rapidly spread over the Mediterranean area: to Crete in 3000 BC, to Sicily in 2500 BC, to France and other parts of Europe in 2000 BC, and to Britain and the Scandinavian area in 1800 BC.

About 3000 BC copper was produced extensively on the island of Cyprus. The copper deposits there were highly prized by the successive masters of the island--Egyptians, Assyrians, Phoenicians, Greeks, Persians, and Romans. Cyprus was almost the sole source of copper to the Romans, who called it aes cyprium ("ore of Cyprus"), which was shortened to cyprium and later corrupted to cuprum. From this name comes the English name copper. The first two letters of the Latin name constitute the chemical symbol Cu.

When copper and bronze were first used in Asia is not known. The epics of the Shu ching mention the use of copper in China as early as 2500 BC, but nothing is known of the state of the art at that time or of the use of the metal prior to that time. Bronze vessels of great beauty made during the Shang dynasty, 1766-1122 BC, have been found, indiCATing an advanced art. The source of the metals, however, is unknown.

The Copper Age in the Americas probably dawned between AD 100 and 200. Native copper was mined and used extensively and, though some bronze appeared in South America, its use developed slowly until after the arrival of Columbus and other European explorers. Both North and South America passed more or less directly from the Copper Age into the Iron Age.

As man learned to fashion his weapons from iron and steel, copper began to assume another role. Being a durable metal and possessed of great beauty, it was used extensively for household utensils and water pipes and for marine uses and other purposes that required resistance to corrosion. The unusual ability of this metal to conduct electric current accounts for its greatest use today.



Chemical compounds


Copper forms compounds in the oxidation states +1 and +2 in its normal chemistry, although under special circumstances some compounds of trivalent copper can be prepared. It has been shown that trivalent copper survives no more than a few seconds in an aqueous solution.

Copper(I) (cuprous) compounds are all diamagnetic and, with few exceptions, colourless. Among the important industrial compounds of copper(I) are cuprous oxide (Cu2O), cuprous chloride (Cu2Cl2), and cuprous sulfide (Cu2S). Cuprous oxide is a red or reddish brown crystal or powder that occurs in nature as the mineral cuprite. It is produced on a large scale by reduction of mixed copper oxide ores with copper metal or by electrolysis of an aqueous solution of sodium chloride using copper electrodes. The pure compound is insoluble in water but soluble in hydrochloric acid or ammonia. Cuprous oxide is used principally as a red pigment for antifouling paints, glasses, porcelain glazes, and ceramics and as a seed or crop fungicide.

Cuprous chloride is a whitish to grayish solid that occurs as the mineral nantokite. It is usually prepared by reduction of copper(II) chloride with metallic copper. The pure compound is stable in dry air; moist air converts it to a greenish oxygenated compound, and upon exposure to light it is transformed into copper(II) chloride. It is insoluble in water but dissolves in concentrated hydrochloric acid or in ammonia because of the formation of complex ions. Cuprous chloride is used as a CATalyst in a number of organic reactions, notably the synthesis of acrylonitrile from acetylene and hydrogen cyanide; as a decolourizing and desulfurizing agent for petroleum products; as a denitrating agent for cellulose; and as a condensing agent for soaps, fats, and oils.

Cuprous sulfide occurs in the form of black powder or lumps and is found as the mineral chalcocite. Large quantities of the compound are obtained by heating cupric sulfide (CuS) in a stream of hydrogen. Cuprous sulfide is insoluble in water but soluble in ammonium hydroxide and nitric acid. Its appliCATions include use in solar cells, luminous paints, electrodes, and certain varieties of solid lubricants.

Copper(II) compounds of commercial value include cupric oxide (CuO), cupric chloride (CuCl2), and cupric sulfate (CuSO4). Cupric oxide is a black powder that occurs as the minerals tenorite and paramelaconite. Large amounts are produced by roasting mixed copper oxide ores in a furnace at a temperature below 1,030 C (1,900 F). The pure compound can be dissolved in acids and alkali cyanides. Cupric oxide is employed as a pigment (blue to green) for glasses, porcelain glazes, and artificial gems. It is also used as a desulfurizing agent for petroleum gases and as an oxidation CATalyst.

Cupric chloride is a yellowish to brown powder that readily absorbs moisture from the air and turns into the greenish blue hydrate, CuCl22H2O. The hydrate is commonly prepared by passing chlorine and water in a contacting tower packed with metallic copper. The anhydrous salt is obtained by heating the hydrate to 100 C (212 F). Like cuprous chloride, cupric chloride is used as a CATalyst in a number of organic reactions--e.g., in chlorination of hydrocarbons. In addition, it serves as a wood preservative, mordant (fixative) in the dyeing and printing of fabrics, disinfectant, feed additive, and pigment for glass and ceramics.

Cupric sulfate is a salt formed by treating cupric oxide with sulfuric acid. It forms as large, bright-blue crystals containing five molecules of water (CuSO45H2O) and is known in commerce as blue vitriol. The anhydrous salt is produced by heating the hydrate to 150 C (300 F). Cupric sulfate is utilized chiefly for agricultural purposes, as a pesticide, germicide, feed additive, and soil additive. Among its minor uses are as a raw material in the preparation of other copper compounds, reagent in analytic chemistry, electrolyte for batteries and electroplating baths, and in medicine as a locally applied fungicide, bactericide, and astringent.

Other important copper(II) compounds include cupric carbonate [Cu2(OH)2CO3], which is prepared by adding sodium carbonate to a solution of copper sulfate and then filtering and drying the product. It is used as a colouring agent; with arsenic it forms cupric acetoarsenite (commonly known as Paris green), a wood preservative and insecticide.

atomic number 29 atomic weight 63.546 melting point 1,083 C (1,981 F) boiling point 2,567 C (4,653 F) density 8.96 (20 C) valence 1, 2 electronic config. 2-8-18-1 or (Ar)3d104s1

    Reference: Encyclopędia Britannica, Inc. 1994-2000 ©


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