Chemistry Edexcel GCSE Extracting Metals

• Very unreactive metals such as gold and platinum are found in the Earth's crust as uncombined elements. We say they exist in their native state. However, most metals occur as compounds (such as oxides, chlorides and carbonates) in rocks.
• An ore is a rock that contains enough of a metal or a metal compound to make extracting the metal worthwhile.
• Low-grade ores contain a small percentage of the metal or its compound.
• High-grade ores contain a larger percentage of the metal or it's compound.
• Most metals are extracted from high-grade ores found in the Earth's crust.
• Most metals are extracted from high-grade ores found in the Earth's crust.
• The ore (compound) must be reduced in some way to extract the metal. The method used to extract a metal from its ore depends on its position in the reactivity series.
• Ores are non-renewable resources. The reserves of high-grade ores in the Earth's crust is decreasing.
• List some factors that contribute to the price of a metal

  The abundance of the ore in the Earth's crust. The mining costs. The energy costs in the process of extracting the metal from its ore. The demand for the metal.
• Give some advantages of recycling metals.

  1. Natural reserves of metal ores will last longer.
  2. Less energy is needed to recycle metals than to extract the metal from its ore, for some metals.
  3. The need to mine ores is reduced.
  4. There is less waste in landfill sites.
  5. There will be less damage to the landscape/There is less dust or noise from mining ores.
• Give some disadvantages of recycling metals.

  1. There are costs and energy is needed to collect, transport and sort the metals. 2. More energy is needed to recycle the metal than to extract it from its ore, for some metals 3. A large amount of energy is needed to melt the used metal items.
• Gold occurs native in the Earth's crust. Explain.

  Gold is found as an element in the Earth's crust because it is very unreactive.
• Titanium is extracted from its ore rutile by electrolysis. Rutile contains titanium dioxide. Give reasons why titanium is much more expensive than iron.

  Electrolysis is expensive because it uses large amounts of electricity. Iron is obtained from its ore by reduction by heating the ore with carbon. This process is cheaper than electrolysis because carbon is easily available.
• The method used to extract a metal from its ore depends on its position in the reactivity series. I fa metal is more reactive than carbon it is extracted by electrolysis of the molten ore. If a metal is less reactive than carbon it is extracted by heating the ore with carbon.
• In principle, any metal could be extracted from its compound using electrolysis. However, electrolysis is an expensive process because it uses large amounts of electricity. Therefore, electrolysis is only used for the reactive metals (above carbon).
• How would you extract the ore of these metals: K Na Ca Mg Al ?

  In metals more reactive than carbon, Electrolysis of the molten ore is used. (molten means in the liquid state). e.g. Aluminium is produced by electrolysis of molten found in the ore called bauxite. Al³+ + 3e- -> Al
• How would you extract the ore of these metals: Zn Fe Cu Ag ?

  In metals less reactive than carbon, Heat the ore with carbon. e.g. Copper can be produced by heating copper (II) oxide with carbon.

  2CuO + C -> Cu + CO2
• Gold and Platinum are found as pure elements so they do not need to be extracted from their ore.
• The method of extraction depends on the reactivity of the metal. The more reactive the metal, the more difficult it is to extract the metal from its compound because, the more reactive the metal, the more difficult it is to reduce the compound (ore).
• As aluminium is more reactive than iron, it is more difficult to reduce aluminium oxide than to reduce iron (1) oxide. A greater amount of energy is needed to break the bonds in aluminium oxide. Therefore electrolysis is used to extract aluminium from aluminium oxide.
• Electrolysis is the most powerful way to reduce a metal compound Electrolysis is an expensive process because it uses large amounts of electricity. Therefore, electrolysis is only used to extract very reactive metals that cannot be obtained by heating their oxides with carbon.
• Why are different methods of extraction used for aluminium and iron?


  As aluminium is more reactive than iron, it is more difficult to extract aluminium from its oxide than to extract iron from its oxide. Aluminium is extracted from its oxide by electrolysis of the molten oxide. Aluminium cannot be extracted by heating its oxide with carbon because carbon is less reactive than aluminium.
• Why is aluminium more expensive than iron even though they are both extracted from their oxides?

  Aluminium is produced by electrolysis of molten aluminium oxide. Iron is produced by heating iron (II) oxide with carbon. The process of extracting Al from AlO; is expensive because a high temperature is needed to melt the aluminium oxide and electrolysis uses large amounts of electricity.
• Metals that are more reactive than carbon, such as aluminium, are extracted by electrolysis of the molten compound. A high temperature is needed to melt the aluminium oxide and electrolysis uses large amounts of electricity. This makes the process of extraction expensive.
• Aluminium extraction

  1. Electrolysis of a molten mixture of aluminium oxide and cryolite

  2. Aluminium oxide is melted and dissolved in molten cryolite

  3. Mixture has a lower melting point than aluminium oxide

  4. Cryolite lowers the temperature required to melt aluminium oxide, so reduces the cost of melting aluminium oxide

  5. Electrodes are made of carbon
• Aluminium ions

  Attracted to the negative electrode where they gain electrons and are reduced
• Oxide ions

  Attracted to the positive electrode where they lose electrons and are oxidised
• Aluminium formation

  Al³+ + 3e- -> Al
• Oxygen formation

  2O²- -> O2 + 4e-
• Oxygen formed at positive electrode

  Reacts with carbon due to high temperature to form carbon dioxide
• Carbon dioxide formation

  C + O2 -> CO2
• this is the aluminium extraction diagram

  
• Suggest why the anodes disappear and have to be replaced frequently.

  The anodes are made of carbon, so the oxygen reacts with carbon due to the high temperature in the cell to form carbon dioxide which escapes as a gas.
• Suggest why the aluminium is produced in the electrolysis cell as a liquid.

  The melting point of aluminium is lower than 950°C.
• In this electrolysis, aluminium and oxygen gas are produced from the aluminium oxide. Suggest why most of the waste gas is carbon dioxide and not oxygen.

  The anodes are made of carbon, so the oxygen reacts with carbon due to the high temperature in the cell to form carbon dioxide. C + O2 -> CO2
• There is a greater percentage of bauxite in the Earth's crust as compared to haematite. Why is aluminium more expensive than iron?

  Aluminium is obtained from its ore by electrolysis. Electrolysis is an expensive process because it uses large amounts of electricity/energy. Iron is obtained from its ore by reduction using carbon which is easily available.
• There is a greater percentage of bauxite in the Earth's crust as compared to haematite. Why is aluminium more expensive than iron?

  Aluminium is obtained from its ore by electrolysis. Electrolysis is an expensive process because it uses large amounts of electricity/energy. Iron is obtained from its ore by reduction using carbon which is easily available.
• Bauxite is the ore of aluminium Al2O3
• haematite is the ore of iron Fe2O3
• reasons for recycling aluminium

  It saves energy. Natural reserves of bauxite will last longer.

  There is less mining of the ore.