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
• 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

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