Rocks, minerals and ores☄️
Most metals are found in the Earth as part of a chemical compound. Naturally occuring compounds are called minerals. Rocks are mixtures of different minerals. Some rocks are metal ores. Very unreactive metals like gold can be found in the Earth as elements. Metal ores contain metal compounds and unwanted rock. The metal must be extracted from the ore.
The cost of the metal is higher if:
- The ore is difficult to obtain
- The method of extraction is expensive
- The ore contains a low percentage of the metal
Iron is cheap as iron ore (haematite) is plentiful and inexpensive to extract. Gold has a high price because the ore is rare. Aluminium ore (bauxite) is plentiful but aluminium is expensive as it costs a lot to extract.
Some metals can be extracted by heating with Carbon, e.g. extracting iron.
iron oxide + carbon --> carbon dioxide + iron
Other metals must be extracted by electrolysis, e.g. extracting aluminium
aluminium oxide ----electricity-------> aluminium + oxygen
Electrolysis is expensive because of the high cost of electricity.
Methods Of Extraction🔨
Metal ores often contain metal oxides. To extract the metal, oxygen must be removed from the oxide. The method of extraction chosen depends on how reactive the metal is. The reactivity series shows which metals are more reactive than carbon and must be extracted by electrolysis, and which are less reactive and can be extracted with carbon.
Oxidation and Reduction🧪
Metals can gain oxygen and become oxides. This is called oxidation.
e.g. iron + oxygen --> iron oxide
This is what happens when iron rusts. Oxidation of metals is called corrosion.
Metal oxides can lose oxygen and become metals. This is called reduction. Reduction takes place when the iron is extracted from its ore. The equation for reduction of iron ore with carbon is:
2Fe2O3 (s) + 3C (s) --> 4Fe (s) + 3CO2 (g)
iron oxide +carbon --> iron + carbon dioxide
Carbon is oxidised and iron oxide is reduced. If iron is not protected, then it will corrode by reacting with oxygen from the air.
4Fe (s) + 3O2 (g) --> 2Fe2O3 (s)
iron + oxygen --> iron oxide
Reactivity and Corrosion💨
The more reactive a metal is, the more rapidly it becomes oxidised. Many metals form an impermeable layer of metal oxide, which creates a barrier between oxygen and the metal underneath. They do not continue to corrode. Iron corrodes when it comes into contact with water and oxygen.
In I/GCSE Chemistry, you have to explain how to prevent the corrosion of metals.
This is mainly done in 2 ways: Galvanising and Sacrificial Protection. Galvanising is when iron is coated with zinc, a more reactive metal. The zinc corrodes first, protecting the iron. This process is called sacrificial protection.
Drafted by Catrina Lee (Chemistry)