2.34     describe the conditions under which iron rusts

Iron rusts in the presence of oxygen (air) and water.  Both of these substances need to be present.

Like any other reaction, this is speeded up if the temperature is raised.  Salt (sodium chloride) also speeds up the rusting process.

Note that “iron” here can refer to all types of steel except stainless steel.

5.5        explain the uses of aluminium and iron, in terms of their properties

Aluminium has a high strength for its low density. This makes it suitable for aircraft manufacture. It is also malleable and resistant to corrosion as it is covered in an oxide layer. This makes it suitable for making drinks cans.  Aluminium is an excellent conductor of heat and can be used for saucepans and cooking foil.  It is an excellent conductor of electricity and is used for overhead power cables.

Iron is generally used in the form of steel (iron with a small amount of carbon). Steel is strong and relatively cheap, so it is suitable for construction of buildings and bridges, car bodies, railway lines, tools and machinery, etc.

5.4        describe and explain the main reactions involved in the extraction of iron from iron ore (haematite), using coke, limestone and air in a blast furnace

The raw materials needed to make iron in a blast furnace are the iron ore itself, coke (which is an impure form of carbon made from coal), limestone and air.  The main ore of iron is called haematite and contains the compound iron (III) oxide, Fe2O3.

The ore contains other impurities like sand and clay.  Sand is silicon dioxide.  This would clog up the furnace if it were not removed.  Limestone (which is calcium carbonate) is used to react with the sand inside the furnace and remove it as slag (calcium silicate).

1)   The carbon (coke) burns to provide the heat required in the blast furnace

C(s) + O2(g) → CO2(g)

2)   The carbon dioxide reacts with more carbon to produce the reducing agent, carbon monoxide

CO2(g) + C(s) → 2CO(g)

3)   The reducing agent, carbon monoxide, removes the oxygen from the iron oxide (haematite)

Fe2O3(s) + 3CO(g) → 2Fe(l) + 3CO2(g)

4)   Meanwhile the calcium carbonate (limestone) decomposes in the high temperatures

CaCO3(s) → CaO(s) + CO2(g)

5)   Calcium oxide is a basic oxide (see Section 2.3) and reacts with the acidic silicon dioxide (sand impurity) in a neutralisation reaction. This forms calcium silicate (slag) which is easily removed from the iron, because it floats on top of it at the bottom of the furnace.

CaO(s) + SiO2(s) → CaSiO3(l)