Oxidation & reduction in terms of oxygen

• The reactions of metals with oxygen, such as in iron rusting can be classified as?oxidation
• Oxidation is any reaction in which a substance?gains oxygen
• The opposite of oxidation is?reduction
• Reduction is a reaction in which a substance?loses oxygen
• For example, the displacement reaction between zinc and copper(II)oxide can be classified as a?redox reaction

Zn? ? +? ? ?CuO? ? →? ? ZnO? ? +? ? Cu

zinc + copper(II) oxide → zinc oxide + copper

• Oxidation cannot occur without reduction happening simultaneously, hence these are called redox reactions
• The copper(II)oxide supplies the oxygen, so it is the?oxidising agent
• The zinc is the?reducing agent?because it removes the oxygen

Oxidation & Reduction in terms of electrons

• Displacement reactions can be analysed in terms 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:

Mg (s) + Cu²⁺?(aq) + SO₄^2-?(aq) → Mg²⁺?(aq) + SO₄^2-?(aq) + Cu (s)

• The sulfate ions, SO₄^2-, 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:

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

• This equation is an example of a balanced?ionic equation?which can be further split into two?half equations?illustrating oxidation and reduction individually:

Mg → Mg²⁺?+ 2e^–

Cu²⁺?+ 2e^–→ Cu

• The magnesium atoms are thus?oxidised?as they?lose?electrons
• The copper ions are thus?reduced?as they?gain?electrons
• These equations illustrate the broader definition of oxidation and reduction in terms of electron transfer:
  • Oxidation is the loss of electrons
  • Reduction is the gain of electrons

   

'OIL RIG' is a useful mnemonic to help remember the definitions of oxidation and reduction