Extracting iron and copper

Ores

Unreactive metals such as gold are found in the Earth's crust as the uncombined elements. However, most metals are found combined with other elements to form compounds.

Most metals are extracted from ore found in the Earth's crust. An ore is a rock that contains enough of a metal or a metal compound to make extracting the metal worthwhile.

Extraction methods

The extraction method used depends upon the metal's position in the reactivity 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(II) 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)

Copper oxide is reduced as carbon is oxidised, so this is an example of a redox reaction.

The table summarises the extraction methods used for different metals.

List of metals and their extraction methods and reactivity, listen from most to least reactive.

Although an unreactive metal is found as the metal itself, chemical reactions are often needed to remove other elements that might contaminate it.

Extracting iron

Iron(III) oxide is reduced to molten iron when it reacts with carbon. One of the products is carbon monoxide:

iron(III) oxide + carbon → iron + carbon monoxide

Fe2O3(s) + 3C(s) → 2Fe(l) + 3CO(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.

Question

In the reaction of iron(III) oxide with carbon, state which substance is reduced and which substance is oxidised.

Carbon gains oxygen, so it is oxidised. Iron(III) oxide loses oxygen, so it is reduced.