Core Chemistry - Topic 4 Obtaining and Using Metals

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  • Created by: Katie
  • Created on: 10-04-13 16:00


  • Metals found as elements
    • Gold, platinum, silver (very few)
    • Very unreactive
    • Have never reacted with oxygen
  • Metals found in compounds
    • If metal is reactive, it easily forms compounds with other substances
    • Most metals are obtained from their compounds by chemical reactions
    • Most compounds are oxides
    • Found in rocks that are called ores if metal can be profitably extracted
  • Examples of ores
    • Bauxite – Aluminium
    • Cinnabar – Mercury
    • Galena – Lead
    • Haemaitte – Iron
    • Malachite – Copper
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Ores Continued

  • Extraction – chemical reaction process of getting metal from a compound in a rock
    • Some extracted by heating their compounds with carbon
    • Others extracted through electrolysis of a molten compound
    • Electrolysis decomposes some compounds into their elements
  • Method of metal extraction depends on its reactivity
    • More reactive – harder to extract 
  • Electrolysis of a molten compound – Most reactive
    • Potassium, sodium, calcium, magnesium, aluminium
  • Heat an ore with carbon – Medium reactive
    • Zinc, iron, tin, lead, copper
  • Found as the uncombined element – Least reactive
    • Silver, gold, platinum
  • Electrolysis is more expensive than heating with carbon (cost of electricity)
    • Reactive metals are harder and more expensive to extract
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Oxidation and Reduction

  • Metal extraction is reduction
    • To obtain a metal from its compound (usually oxide), oxygen must be removed
    • When removed, its reduced and called reduction
  • Corrosion of metals is oxidation
    • Most metals corrode – metal becoming oxidised
    • Surface of the is metal changed by reacting with oxygen and sometimes water
    • Oxidation is the addition of oxygen to a substance
  • High reactivity – more rapid corrosion
  • Low reactivity – more resistant to corrosion
    • BUT Aluminium - the surface oxides quickly forming a protective layer of aluminium oxide, stops further corrosion
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Recycling Metals

  • Many metals can be recycled
    • Melted down to make something new
  • Advantages
    • Natural reserves of metal ores will last longer
    • For most metals, less energy is required to recycle than to extract from their ores
      • therefore also cheaper
    • Reduces the need to mine ores and damage the landscape/create noise and dust pollution
    • Produces less pollution than fossil fuelled electrolysis and gases from extracting
    • Less waste metals are filling up landfill sites
  • Separated by magnetism (steel, iron) or by hand (others)
  • Melted into blocks and sold to manufacturers
  • % of metal used that is recycled
    • aluminium – 40%
    • copper –     30%
    • lead –         75%
    • iron/steel –  40%
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Properties of Metals

  • Many useful properties
    • Shiny when polished
    • Conduct heat and electricity
    • Malleable (hammered into shape)
    • Ductile (stretched into wires)
    • Different metals useful for different things
  • Aluminium
    • Low density
    • Does not corrode
    • Used to make aeroplanes and many cars
  • Copper
    • Extremely good electrical conductor
    • Low reactivity
    • Does not react with water
    • Used to make electrical cables, water pipes
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Properties of Metals Continued

  • Gold
    • Very unreactive
    • Does not corrode – remains shiny
    • Very attractive in appearance
    • Worked easily into shapes
    • Best electrical conductor
    • Used for jewellery, most electronic devices, printed circuit boards, connection strips, contacts in switches
  • Iron and steel
    • Used more than any other metal
    • Cheap to extract by heating with carbon
    • Iron is soft, so it’s mixed into steel with carbon
    • Steel is strong and hard
    • Magnetic
    • Rust – reacts with oxygen and water
    • Used for bridges, cars, electrical products, machinery, frames of buildings
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Alloy - Metals mixed with other metals to improve properties for specific applications

  • In a pure metal, atoms are the same size
    • Layers of atoms can slide over each other
    • This makes them soft
  • In alloys, some atoms of other elements are different sizes
    • Layers are prevented from moving past each other so easily
    • This makes them much harder and stronger


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Alloys Continued

  • Many different alloy steels
    • small amounts of other metals mixed with iron
    • stronger than iron (more force to break them)
    • some resist corrosion
      • stainless steel - alloy of iron, chromium and nickel doesn't corrode at al
  • Pure gold is too soft to use in jewellery successfully
    • copper or silver are added to make it harder and stronger
    • the purity is measured in carats or as a fineness

Carats      % of gold/fineness

24              100%       1000

22               91.7%       917

18               75%          750

12               50%          500

  9               37.5%       375

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