Redox, Rusting and Iron

• Redox reactions are reactions in which oxidation and reduction occur at the same time (reduction-oxidation)
• Oxidation

  Gain of oxygen, loss of hydrogen or loss of electrons
• Reduction

  Loss of oxygen, gain of hydrogen or gain of electrons
• Rust is hydrated iron(III) oxide
• Recognising oxidation and reduction in terms of loss or gain of oxygen or hydrogen


  1. Choose and state the appropriate definition of oxidation or reduction

  2. Name the species that is being oxidised or reduced
• The burning of magnesium in air is an oxidation reaction because magnesium has gained oxygen and is therefore oxidised
• The burning of sulfur in air is an oxidation reaction
• H2 + Cl2 → 2HCl is a reduction reaction
• The reduction of copper (II) oxide

  1. Copper (II) oxide is heated in a stream of hydrogen

  2. Observations: colour change, formation of copper
• Redox reaction

  A reaction in which both oxidation and reduction occur
• The reaction of aluminium and iron(III) oxide is a redox reaction because aluminium is oxidised (gains oxygen) and iron(III) oxide is reduced (loses oxygen)
• Oxidation is the loss of electrons, reduction is the gain of electrons
• Cl2 + 2e- → 2Cl- is a reduction reaction because the chlorine molecules gain electrons
• Rust is hydrated iron(III) oxide formed when iron reacts with oxygen and water
• Rusting is an oxidation reaction because iron gains oxygen
• The conditions needed for rusting are oxygen (air) and water
• Barrier methods to prevent rusting

  • Paint
  • Plastic
  • Oil
  • Zinc (galvanising)
  • Chromium
  • Tin
• Sacrificial protection

  A more reactive metal like magnesium or zinc is attached to the iron object, and this more reactive metal corrodes instead of the iron
• If a zinc plated object is scratched, the iron below will not rust, but if a tin plated object is scratched, the iron below will rust
• Extraction of iron from haematite in the blast furnace

  1. Production of reducing agent (carbon monoxide)

  2. Reduction of haematite (iron(III) oxide) to iron

  3. Removal of acidic impurities (silicon dioxide) using limestone
• Iron is used in many structures and bridges due to its strength
• Removal of acidic impurities

  1. Limestone (calcium carbonate) is added

  2. Limestone thermally decomposes to give calcium oxide and carbon dioxide

  3. Calcium oxide reacts with acidic silicon dioxide to produce calcium silicate (slag)

  4. Molten slag floats on top of molten iron and is tapped off separately
• Thermal decomposition

  The breaking down of a substance using heat
• Iron is a cheap metal because the ore is abundant. It is used in many structures and bridges due to its strength
• The reaction between iron(III) oxide and carbon monoxide is a redox reaction
• Reduction

  The loss of oxygen
• Oxidation


  The gain of oxygen
• The chemical name for rust is hydrated iron(III) oxide
• Galvanised


  Coated with a layer of zinc
• Sacrificial protection

  A method of protecting iron from rusting by attaching blocks of a more reactive metal like zinc to it
• The two conditions necessary for rusting to occur are the presence of oxygen and water
• Oxidation is the gain of oxygen or the removal of hydrogen from a substance
• Reduction is the reverse of oxidation, the loss of oxygen or the addition of hydrogen to a substance
• Rusting is an oxidation reaction
• Boiling the water removes dissolved oxygen, preventing rusting
• Anhydrous calcium chloride absorbs water, preventing rusting
• Methods to prevent iron from rusting

  • Galvanising
  • Painting
  • Greasing
  • Chrome plating
  • Oiling
• Hydrogen gas reacts with copper(II) oxide


  Colour changes from black to red
• Reaction between hydrogen gas and copper(II) oxide

  Copper(II) oxide + hydrogen → copper + excess hydrogen
• The common name for the iron ore used in the Blast Furnace is haematite