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Redox Reactions

Chemistry: AQA GCSE Higher, topic 4.3.2

Redox Reactions

Redox reactions involve a reduction reaction (one reactant gains electrons) and an oxidation reaction (one reactant loses electrons). Here, we will look at the example of reacting magnesium with hydrochloric acid.

Magnesium + hydrochloric acid

Magnesium + hydrochloric acid

  • Mg(s) + 2HCl(aq) → MgCl2(aq) + H2(g)
  • Mg(s) + 2H+(aq) + 2Cl-(aq) → Mg2+(aq) + 2Cl-(aq) + H2(g)
Magnesium

Magnesium

  • Magnesium atoms are oxidised (loses electrons) to become Mg2+ ions.
Chlorine

Chlorine

  • Cl- ions are unchanged.
  • They are spectator ions and aren't included in the ionic equation.
Hydrogen

Hydrogen

  • H+ ions are reduced (gains electrons) to become hydrogen atoms.
  • The atoms join together to form H2(g).

Test yourself on Redox Reactions

  • Mg(s) + 2H+(aq) + 2Cl-(aq) → Mg2+(aq) + 2Cl-(aq) + H2(g)
    What happens in this redox reaction?

  • Mg(s) + 2H+(aq) + 2Cl-(aq) → Mg2+(aq) + 2Cl-(aq) + H2(g)
    Why is the Cl- ion left out of this ionic equation?

  • What types of reaction take place during a redox reaction?

  • Why is the reaction between magnesium and hydrochloric acid a redox reaction?

  • Why does the ionic equation show hydrogen ions changing into hydrogen gas, but not show the chloride ions changing?

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