9.6 Extraction of metals

2026 Syllabus Objectives

Core:

  1. Describe the ease in obtaining metals from their ores, related to the position of the metal in the reactivity series
  2. Describe the extraction of iron from hematite in the blast furnace, limited to:
    • (a) the burning of carbon (coke) to provide heat and produce carbon dioxide
    • (b) the reduction of carbon dioxide to carbon monoxide
    • (c) the reduction of iron(III) oxide by carbon monoxide
    • (d) the thermal decomposition of calcium carbonate/limestone to produce calcium oxide
    • (e) the formation of slag
    • Symbol equations are not required
  3. State that the main ore of aluminium is bauxite and that aluminium is extracted by electrolysis

Supplement: 4. State the symbol equations for the extraction of iron from hematite:

  • (a) C+O2→CO2\mathrm{C} + \mathrm{O}_2 \rightarrow \mathrm{CO}_2
  • (b) C+CO2→2CO\mathrm{C} + \mathrm{CO}_2 \rightarrow 2\mathrm{CO}
  • (c) Fe2O3+3CO→2Fe+3CO2\mathrm{Fe}_2\mathrm{O}_3 + 3\mathrm{CO} \rightarrow 2\mathrm{Fe} + 3\mathrm{CO}_2
  • (d) CaCO3→CaO+CO2\mathrm{CaCO}_3 \rightarrow \mathrm{CaO} + \mathrm{CO}_2
  • (e) CaO+SiO2→CaSiO3\mathrm{CaO} + \mathrm{SiO}_2 \rightarrow \mathrm{CaSiO}_3
  1. Describe the extraction of aluminium from purified bauxite/aluminium oxide, including:
    • (a) the role of cryolite
    • (b) why the carbon anodes need to be regularly replaced
    • (c) the reactions at the electrodes, including ionic half-equations
    • Details of the purification of bauxite are not required

Metal Extraction and the Reactivity Series

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🔑 Key Concepts

Some metals exist naturally as pure metals (native metals) in the Earth's crust, while others are found combined with other elements in compounds called ores. An ore is a naturally occurring mineral from which a metal can be extracted.

Occurrence of Metals

Metals that do not occur uncombined in the ground are usually found as:

  • Metal oxides, or
  • Compounds that can easily be converted to oxides

To extract the metal from its oxide, we need to carry out reduction - the removal of oxygen from the metal.

Position of Carbon in the Reactivity Series

The method used to extract a metal from its ore depends on the position of the metal in the reactivity series. Carbon is a very important element in metal extraction because it acts as a strong reducing agent.

Practical experiments have shown that carbon sits between aluminium and zinc in the reactivity series.

Reactivity Series with Carbon:

PositionElement
Most reactivePotassium (K)
Sodium (Na)
Calcium (Ca)
Magnesium (Mg)
Aluminium (Al)
↑Carbon (C)
Zinc (Zn)
Iron (Fe)
Copper (Cu)
Silver (Ag)
Least reactiveGold (Au)

Extraction Methods Based on Reactivity:

  • Metals above carbon in the reactivity series → Must be extracted by electrolysis
  • Metals below carbon in the reactivity series → Can be extracted by heating with carbon (reduction)

Why This Works

For metals below carbon:

  • The oxygen in the metal oxide forms covalent bonds more easily with carbon than remaining as oxide ions
  • Carbon acts as the reducing agent, removing oxygen from the oxide
  • This is a relatively cheap and straightforward process

For metals above carbon (more reactive than carbon):

  • The metal is held too strongly in its oxide compound
  • Carbon cannot remove the oxygen
  • Reduction must be achieved by electrolysis - the metal ions gain electrons at the cathode to produce free metal
  • This is an expensive process requiring large amounts of electrical energy

💡 Important Principle: The more reactive a metal is, the more difficult (and expensive) it is to extract from its ore.

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