Oxidation & Reduction (CIE IGCSE Chemistry)

Redox reactions

• Oxidation and reduction take place together at the same time in the same reaction
• These are called redox reactions
• Oxidation is a reaction in which oxygen is added to an element or a compound
• Reduction is a reaction in which oxygen is removed from an element or compound

Example: Identifying the loss and gain of oxygen in an equation

zinc oxide + carbon → zinc + carbon monoxide

ZnO + C → Zn + CO

• • In this reaction, the zinc oxide has been reduced since it has lost oxygen
  • The carbon atom has been oxidised since it has gained oxygen

Names using oxidation numbers

• Transition elements can bond in different ways by forming ions with different charges
• When naming, the charge on the ion is shown by using a Roman numeral after the element's name
  • e.g. iron can form ions with a 2+ charge, called iron(II) ions or a 3+ charge, called iron(III) ions
• The Roman numeral is the oxidation number of the element
• When iron reacts with oxygen to form iron oxide, the formula depends on the oxidation state of the iron ions
  • The compound where iron has a 2+ charge has the formula FeO and is called iron(II) oxide
  • The compound where iron has a 3+ charge has the formula Fe₂O₃ and is called iron(III) oxide