OxidatIon & Reduction in Terms of Electrons (OCR Gateway GCSE Chemistry)

• For reactions not involving oxygen, we can look at oxidation and reduction in terms of losing and gaining electrons
• Oxidation is the loss of electrons
• Reduction is the gain  of electrons 
• We can use half and ionic equations to determine which species has been oxidised and reduced in terms of electrons 
• A displacement reaction occurs between magnesium and copper sulfate: 

Mg (s) +  CuSO₄ (aq) →   MgSO₄ (aq) + Cu (s) 

• The  ionic equation for this reactions is:

Mg (s) + Cu²⁺ (aq)  → Mg²⁺ (aq)  + Cu (s)

• This can be split into two half equations which demonstrate oxidation and reduction individually:

Mg → Mg²⁺ + 2e^–

Cu²⁺ + 2e^–→ Cu

• The magnesium atoms are oxidised as they lose electrons
• The copper ions are reduced as they gain electrons

Answer:

• • Write the overall balanced symbol equation:

Zn (s) + CuSO₄ (aq)→ ZnSO₄ (aq) + Cu (s)

• • Write out the ions separately:

Zn (s) + Cu²⁺(aq) + SO₄^2- (aq) →Zn²⁺(aq) + SO₄^2-(aq) + Cu (s)

• • Eliminate ions that occur on both sides (spectator ions):

Zn (s) + Cu²⁺(aq) →  Zn²⁺(aq) + Cu (s)

• • Identify which species has lost or gained electrons
    • Zinc has lost electrons and been oxidised:

Zn →  Zn²⁺  +  2e^-

• • • Copper ions have gained electrons and been reduced:

Cu²⁺ +  2e^-  →  Cu