GCSE Combined Science (AQA)

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Redox Reactions

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Chemical changes Reactions of acids

Redox Reactions

9:33 Acid Reactions and Salt Formation
Spec 4.4.2.1
Previous Displacement Reactions of Metals Next Neutralisation and Naming Salts
  • A redox reaction involves both oxidation and reduction.
  • Oxidation and reduction can describe the gain or loss of oxygen or the transfer of electrons.
  • Acronym "OIL RIG": Oxidation Is Loss (of electrons), Reduction Is Gain (of electrons).
  • Example reaction: Metal + Acid ��� Salt + Hydrogen.
  • Magnesium reacts with sulfuric acid to form magnesium sulfate and hydrogen gas.
  • Magnesium (metal) loses electrons and is oxidized.
  • Hydrogen ions gain electrons and are reduced.
  • Half equations:
  • Mg(s) ��� Mg�����(aq) + 2e���
  • 2H���(aq) + 2e��� ��� H���(g)
  • Redox reactions involve the transfer of electrons between species.
  • Example reaction: Iron + Hydrochloric acid ��� Iron chloride + Hydrogen.
  • Iron (metal) loses electrons and is oxidized.
  • Hydrogen ions gain electrons and are reduced.
  • Half equations:
  • Fe(s) ��� Fe�����(aq) + 2e���
  • 2H���(aq) + 2e��� ��� H���(g)
  • For exams, analyze reactions involving magnesium, iron, zinc, hydrochloric acid, and sulfuric acid.
  • Worked example: Zinc + Hydrochloric acid ��� Zinc chloride + Hydrogen.
  • Zinc is oxidized (loses electrons).
  • Hydrogen ions are reduced (gain electrons).
  • Steps to identify oxidation and reduction:
  • 1. Identify species forming a compound.
  • 2. Determine if electrons are gained or lost.
  • 3. Identify if the species is oxidized or reduced.
  • 4. Identify species starting in a compound and becoming an atom/molecule.
  • 5. Determine if electrons are lost or gained.
  • 6. Identify if the species is oxidized or reduced.

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