An ore is a rock that contains enough of a metal or a metal compound to make extracting the metal worthwhile:
Most metals are extracted from ores found in the Earth’s crust. It is more expensive and wasteful to extract a metal from a low grade ore, but a lot of the high grade ores have already been used.
The extraction method used depends upon the metal's position in thereactivity series. In principle, any metal could be extracted from its compounds using electrolysis. However, large amounts of electrical energy are needed to do this, so electrolysis is expensive.
If a metal is less reactive than carbon, it can be extracted from its compounds by heating with carbon. Copper is an example of this. Copper mostly occurs as sulfide ores, which are heated in air to convert them to copper oxide. Molten copper can be produced from copper oxide by heating with carbon:
copper oxide + carbon → copper + carbon dioxide
2CuO(s) + C(s) → 2Cu(l) + CO2(g)
The table summarises the extraction methods used for different metals.
Although an unreactive metal is found as the uncombined element, chemical reactions are often needed to remove other elements that might contaminate it.
Iron is extracted from iron ore in a large container called a blast furnace. Iron(III) oxide is reduced to molten iron when it reacts with carbon. For example:
iron(III) oxide + carbon → iron + carbon monoxide
Fe2O3(s) + 3C(s) → 2Fe(l) + 3CO(g)
In the high temperatures of a blast furnace, carbon monoxide also reduces iron(III) oxide:
iron(III) oxide + carbon monoxide → iron + carbon dioxide
Fe2O3(s) + 3CO(s) → 2Fe(l) + 3CO2(g)
This method of extraction works because carbon is more reactive than iron, so it can displace iron from iron compounds.
Extracting a metal by heating with carbon is cheaper than using electrolysis.
Write a balanced equation for the reaction between iron(III) oxide and carbon, forming molten iron and carbon dioxide.
2Fe2O3(s) + 3C(s) → 4Fe(l) + 3CO2(g)