Oxidation & Reduction in Terms of Electrons | Chemistry for Grade 10 PDF Download

Higher Tier Only

• Displacement reactions can be analysed in terms of redox reactions by studying the transfer of electrons
• For the example of magnesium and copper sulfate, a balanced equation can be written in terms of the ions involved:
  
• The sulfate ions, SO42-, appear on both sides of the equation unchanged hence they are spectator ions and do not participate in the chemistry of the reaction so can be omitted:
  
• This equation is an example of a balanced ionic equation which can be further split into two half equations illustrating oxidation and reduction individually:
  
• The magnesium atoms are thus oxidised as they lose electrons
• The copper ions are thus reduced as they gain electrons

Exam Tip

Remember: OIL RIG - Oxidation Is Loss, Reduction Is Gain of electrons

Identifying Oxidised & Reduced Species

Solved Example

• Write the full equation
  • Zn (s) + CuSO₄ (aq) → ZnSO₄ (aq) + Cu (s)
• Write the ionic equation
  • Zn (s) + Cu²⁺ (aq) + (aq) → Zn²⁺ (aq) +  (aq) + Cu (s)
• Use the ionic equation to rule out / ignore spectator ions that are present as reactants and products
  • is present as a reactant and a product so it can be ignored
• Use the ionic equation to identify the species that is oxidised (OIL)
  • Zn (s) → Zn²⁺ (aq) + 2_e^– 
• Use the ionic equation to identify the species that is reduced (RIG)
  • Cu²⁺ (aq) + 2e^– → Cu (s)

Exam Tip

After writing half equations, you can see if they are correct by checking that the number of electrons on either side is the same, which should combine to give 0 charge.