Topic 4 Metals and Equilbria

• Oxidation


  Reaction with oxygen
• Oxygen reduction


  Removal of oxygen
• Combustion reactions


  Involve oxidation
• Reactivity Series


  • Potassium
  • Sodium
  • Calcium
  • Magnesium
  • Aluminium
  • Carbon
  • Zinc
  • Iron
  • Hydrogen
  • Copper
  • Silver
  • Gold
• Metals at the top of the reactivity series

  • Most reactive and easily lose electrons to form cations (positive ions)
  • Easily oxidised
• Metals at the bottom of the reactivity series

  • Less reactive and more resistant to oxidation
• Reactivity of metals


  The more easily a metal atom loses its outer electrons and forms a positive ion, the more reactive it will be
• Experiment to show reactivity of metals

  1. Place pieces of various metals into dilute hydrochloric acid

  2. Observe speed of reaction based on rate of hydrogen bubbles given off
• Faster hydrogen bubbles


  Faster reaction and more reactive the metal
• Reaction of very reactive metals with water

  Metal + water → metal hydroxide + hydrogen
• Pure gold is found on the ground because gold is unreactive
• Oxidation


  Loss of electrons
• Reduction


  Gain of electrons
• A more reactive element


  Displaces and takes the place of a less reactive element
• During displacement reactions


  The more reactive metal is oxidised and the less reactive metal is reduced
• Metal ore


  • A rock which contains enough metal to make it worthwhile extracting the metal from it
• Some unreactive metals such as gold and platinum are present in the Earth's crust as uncombined elements
• Extracting metals using carbon

  1. Metal ore is reduced, oxygen is removed

  2. Metals higher than carbon in the reactivity series have to be extracted using electrolysis

  3. Metals below carbon in the reactivity series can be extracted by reduction using carbon
• Carbon can only take the oxygen away from metals which are less reactive than carbon
• Extracting metals more reactive than carbon


  Using electrolysis
• Electrolysis


  An electric current is passed through the molten metal ore, the metal is discharged at the cathode and the non-metal at the anode
• Extracting metals using reduction with carbon is much cheaper than electrolysis as carbon is cheap and acts as a fuel
• Biological method of extracting metals

  1. Bioleaching: uses bacteria to separate metals from their ores, the bacteria get energy from the bonds between the atoms in the ore

  2. The leachate (solution produced) contains metal ions which can be extracted with a more reactive metal
• The demand for lots of metals is growing which may lead to shortages in the future, so scientists are looking for ways of extracting metals from low grade ores or waste
• Phytoextraction


  Involves growing plants that contain metal compounds
• The plants can't use or get rid of the metals so they gradually build up in the leaves
• Phytoextraction process


  1. Plants can be harvested

  2. Dried

  3. Burned in a furnace

  4. Ash contains metal compounds

  5. Metal can be extracted from ash by electrolysis or displacement reactions
• Traditional mining methods


  • Damaging to the environment
• New extraction methods


  • Smaller environmental impact
  • Slow
• Redox reactions


  Oxidation and reduction take place at the same time
• Oxidation


  A substance loses electrons
• Reduction


  A substance gains electrons
• When a metal reacts with an acid, a redox reaction takes place
• The metal ions have lost electrons so have been oxidised
• The hydrogen ions have gained electrons so have been reduced
• A spectator ion is one that does not take part in the reaction
• Extracting metals and using metals

  1. Sustainable development approach to human and environmental needs

  2. Recycling raw materials

  3. Extracting raw materials can take large amounts of energy, which comes from burning fossil fuels

  4. Fossil fuels are running out, so it's important to conserve them but burning them contributes to acid rain and climate change

  5. Recycling saves energy as this process often only uses a small fraction of the energy needed to extract raw materials

  6. Extracting metals also impacts the environment, mines are damaging to the environment and destroy habitats

  7. Recycling means no mining is needed, it also cuts down the amount of rubbish that gets sent to landfill

  8. It's particularly beneficial to the economy to recycle metals that are expensive to extract or buy

  9. Recycling also a massive industry and creates a lot of jobs, the materials being recycled need to be transported and processed at recycling centres, then need to be reprocessed to be sold

  10. Two processes avoided when manufacturing cans from recycled aluminium: separating the aluminium using electrolysis, mining the aluminium ore from the ground
• Recycling saves energy as this process often only uses a small fraction of the energy needed to extract raw materials
• Extracting metals also impacts the environment, mines are damaging to the environment and destroy habitats
• Recycling means no mining is needed, it also cuts down the amount of rubbish that gets sent to landfill