GCSE Chemistry Rock and Metals

C1a 2.1 Extracting Metals

  • Metals are found in the Earth’s crust, and most of them are combined with other elements, usually oxygen, so they must be chemically separated from their compounds
  • A rock containing a reasonable amount of a metal is a metal ore
  • Some metals are so unreactive that they do not combine with other elements (e.g. gold, silver, platinum) and so are found in their native state
  • The way in which we extract metals depends on its place in the reactivity series

    – A more reactive metal will displace a less reactive metal from its compound in general

    – Carbon (a non-metal) will also displace a less reactive metal from its oxide

    – We use carbon to extract metals from their ores commercially

  • Many metals are found in their metal oxide form, like copper, lead and zinc. Because carbon is more reactive than these metals, we

    can use it to extract them from their ores

  • When you heat the metal oxide with the carbon, the carbon removes the oxygen to form carbon dioxide, leaving the pure element behind:
  • metal oxide + carbon → metal + carbon dioxide

lead oxide + carbon → lead + carbon dioxide 2PbO + C → 2Pb + CO2

  • We call the removal of oxygen this way a reduction reaction

     

     

 

 

C1a 2.2 Extracting Iron – The Blast Furnace

 

Iron is the second most common ore in the crust, and iron ore contains oxygen. As iron is less reactive than carbon, we can remove oxygen from the ore using carbon

  • We extract iron using a blast furnace
  • In the blast furnace, we enter three substances:

    – haematite, which is the most common iron ore, containing mostly iron(III) oxide and some sand – written as Fe2O3

    – a substance made from coal which is almost pure carbon called coke

    – and limestone

  • Hot air is blown into the furnace, making the furnace heat up, forming carbon dioxide as the coke reacts with the oxygen

    C + O2 → CO2

  • The carbon dioxide reacts with the coke a second time, forming carbon monoxide

    CO2 + C → 2CO

  • The carbon monoxide reacts with the iron oxide, removing its oxygen and reducing it to molten iron, which flows out of the bottom of the furnace

    Fe2O3 + 3CO → 2Fe + 3CO2

     

    C1a 2.3 Iron and Steels

    • The iron produced by the blast furnace is only about 96% iron, and is called pig iron
    • Pig iron contains carbon, but we can treat it to remove this carbon
    • Removing all the carbon and other impurities makes pure iron, which is soft and bendy, and not that useful, so to make sure it is really useful, we ensure it has tiny amounts of other elements in it, including carbon and certain metals
    • We call a metal containing other elements an alloy
    • We call iron which has had other elements alloyed to it a steel
    • There are many different steels, the most common of which being carbon steels, containing from 0.03% to 1.50% carbon. Carbon steels are the cheapest steels to make and can be used for a variety of things, including car bodies and building
    • Low-alloy steels contain 1% – 5% of many other elements, and are more expensive than carbon steels
    • High-alloy steels contain between 12% and 15% of other elements, and are even more expensive to make. An example of a high-alloy steel is chromium-nickel steel, more commonly known as stainless steel, often used for cooking utensils and cutlery

      C1a 2.4 Alloys

    • Copper is a useful metal which we have used for thousands of years
    • Bronze, probably the first alloy made, is formed by alloying copper with tin – but we can also add a range of other elements to give the bronze different properties
    • More workable than bronze is brass, made by alloying copper with zinc
    • Aluminium is a metal with over 300 alloys, as it can be alloyed with many elements
    • If we bend (or deform) alloys and heat them, some will return to their original shape. T

      C1a 2.5 Aluminium and Titanium

    • Aluminium is a metal with many uses. Some of its most useful properties are that it is a reactive metal, but it does not corrode easily
    • The most common aluminium ore is named bauxite, and it is mined using open-cast mining
    • Because carbon is less reactive than aluminium, carbon will not reduce aluminium oxide to aluminium, but instead we need to use electrolysis
    • Electrolysis requires a lot of electricity. The aluminium oxide must be in liquid form, so high temperatures are needed. During the process, aluminium forms at the negative electrode and the oxygen forms at the positive electrode. The oxygen reacts with the carbon electrode and lots of carbon dioxide (and some carbon monoxide) are formed. The aluminium is released from the electrolysis cell as a liquid