Extraction of Metals & Reduction (AQA GCSE Chemistry: Combined Science)

• The Earth’s crust contains metals and metal compounds such as gold, copper, iron oxide and aluminium oxide
• Useful metals are often chemically combined with other substances forming ores
  • A metal ore is a rock that contains enough of the metal to make it worthwhile extracting
• They have to be extracted from their ores through processes such as electrolysis, using a blast furnace or by reacting with more reactive material
• In many cases, the ore is an oxide of the metal
  • Therefore, the extraction of these metals is a reduction process since oxygen is being removed
• Common examples of oxide ores are iron and aluminium ores which are called haematite and bauxite respectively
• Unreactive metals do not have to be extracted chemically as they are often found as the uncombined element
• This occurs as they do not easily react with other substances due to their chemical stability
• They are known as native metals and examples include gold and platinum which can both be mined directly from the Earth’s crust

Extraction of metals and the reactivity series

• The most reactive metals are at the top of the series
• The tendency to become oxidised is thus linked to how reactive a metal is and therefore its position on the reactivity series
• Metals higher up are therefore less resistant to oxidation than the metals placed lower down which are more resistant to oxidation
• The position of the metal on the reactivity series determines the method of extraction
• Higher placed metals (above carbon) have to be extracted from their compounds using electrolysis as they are too reactive and cannot be reduced by carbon

Which element is used for extracting metals from their compounds by reduction?

• Lower placed metals can be extracted from their compounds by heating with carbon which reduces them
  • E.g. The oxides of metals which are below carbon can be reduced by heating them with carbon 
    • The carbon removes the oxygen from the metal oxide
    • Carbon dioxide is formed as well as the metal element:

metal oxide + carbon   →   metal   +   carbon dioxide

Metals extraction method table

Metal	Extraction method
Most reactive
Potassium	Extracted by electrolysis of the molten chloride or oxide Large amounts of electricity are required, which makes this an expensive process
Sodium
Lithium
Calcium
Magnesium
Aluminium
Zinc	Extracted by heating with a reducing agent such as carbon or carbon monoxide in a blast furnace A cheap process as carbon is cheap and can also be a source of heat
Iron
Copper
Silver	Found as pure elements
Gold
Least reactive

The extraction method depends on the position of a metal in the reactivity series