Chemo

• Occurrence and Extraction


  At the end of this section, students should be able to explain properties, occurrence and extraction of Copper; describe the the applications of Copper
• Copper


  • Occasionally found as native copper
  • Found mainly in compounds such as sulphides, oxides and the carbonates
  • Most important sulphide ores are chalcopyrite (CuFeS,), chalcocite (Cu,S), covellite (CuS) and bornite (Cu, Fes)
  • Principal oxide ores are cuprite (Cu,O) and tenorite (CuO)
  • In the carbonate form, it exists as malachite (CUCO,.Cu(OH),)
• Copper extraction


  1. Crushed and ground sulphide ore is first concentrated by froth flotation

  2. Concentrated ore is then roasted with a limited supply of air (oxygen)

  3. Roasted mixture is smelted by adding limestone and sand to form a molten slog that removes many of the impurities

  4. Cu,S obtained by roasting chalcopyrite is then reduced by heating it in a limited supply of oxygen
• Blister copper


  Copper produced by the above process, has 98.5-99.5 % purity, contains iron, silver, gold and sometimes zinc as impurities
• Electrolytic refining of copper

  1. Anode: A thick block of impure copper

  2. Cathode: A thin strip of pure copper

  3. Electrolyte: An aqueous solution of copper sulphate, Small quantity of dilute sulphuric acid is also added to the salt solution to prevent hydrolysis

  4. When electric current is passed, the copper of the anode is oxidized to Cu2+ ions, which pass into solution

  5. At the cathode, Cu2+ ions are reduced and deposited as metallic copper

  6. Pure copper deposited at cathode is removed and used, Copper obtained by electrolytic refining is 99.99% pure
• Physical Properties of Copper

  • Soft, ductile, malleable, reddish-brown metal with a density of 8.96 g/cm³
  • Second to silver in electrical conductivity
  • Melts at 1086°C and boils at 2310°C
• Chemical Properties of Copper

  • Less reactive metal that is why it is found in the native state
  • Powdered copper, when heated in air forms a black powder of copper (I) oxide CuO
  • Does not react with dilute acids like HCI and H,SO, cannot displace hydrogen from acids
  • Can be oxidized by oxidizing acids such as dilute and concentrated nitric acid and hot concentrated sulphuric acid, H,SO
  • Corrodes in moist air over a long period of time as a result of oxidation caused by a mixture of water, oxygen and carbon dioxide, turns green due to the formation of verdigris: a basic copper carbonate (CuCO,.Cu(OH),) or Cu(OH).CO
  • Exists as cuprous (Cu+) and cupric (Cu2+) ions, compounds containing copper in the +2 oxidation state are stable, Cu+ is unstable and cannot exist in aqueous solution since it reduces and oxidizes [disproportionates) itself
  • Aqueous solutions of many copper (II) compounds are blue, thus copper forms coloured compounds in the oxidation state of +2
• Uses of Copper


  Used to manufacture alloys like bronze (copper and tin) and brass (copper and zinc), used to make coins, medals, bells, machinery parts, etc.