4.2 - Redox

Oxidation and reduction as oxygen transfer

• Oxidation is the gain of oxygen by a substance.
• Reduction is the loss of oxygen from a substance.

Examples

• When magnesium burns in oxygen to form magnesium oxide, the magnesium gains oxygen, so it has been oxidised:
  • 2Mg + O₂ → 2MgO
• When copper(II) oxide reacts with carbon, the copper(II) oxide loses oxygen and is reduced, while the carbon gains oxygen and is oxidised:
  • 2CuO + C → 2Cu + CO₂
• A reaction where oxidation and reduction happen together is a redox reaction.

Following hydrogen instead

• Losing hydrogen is oxidation, gaining hydrogen is reduction.
• When hydrogen and chlorine react, the chlorine gains hydrogen, so it has been reduced:
  • H₂ + Cl₂ → 2HCl