GCSEScienceAQACombined Science: TrilogyChemistryRevision NotesChemical ChangesReactions of AcidsMetal & Acid Reactions as Redox Reactions

Metal & Acid Reactions as Redox Reactions (AQA GCSE Combined Science: Trilogy): Revision Note

Exam code: 8464

Stewart Hird

Written by: Stewart Hird

Updated on

AQA Combined Science: Trilogy: ChemistryAQA Chemistry

Metals & acid reactions as redox reactions

Higher tier only

  • Metal-acid reactions are redox reactions

  • Redox means reduction and oxidation at the same time

  • If we analyse the ionic equation for the reaction between zinc and hydrochloric acid:

Zn + 2HCl ⟶ ZnCl2 + H2

  • The ionic equation is:

Zn + 2H+⟶ Zn2+ + H2

  • This equation can be further split into two half equations illustrating oxidation and reduction individually:

Zn → Zn2+ + 2e–

  • The zinc atoms are oxidised as they lose electrons

2H+ + 2e–→ H2

  • The hydrogen ions are reduced as they gain electrons

  • Both reactions are occurring at the same time, in the same reaction chamber

    • This means that it is a redox reaction

Worked Example

Magnesium reacts with sulfuric acid according to the equation:

Mg (s) + H2SO4 (aq) → MgSO4 (aq) + H2 (g)

Write the ionic equation for this reaction, construct the two half equations, and identify which species is oxidised and which is reduced.

Answer:

  • Step 1: Write the ionic equation, omitting spectator ions

    • SO42- ions are spectator ions and are not included

Mg + 2H+ → Mg2+ + H2

  • Step 2: Write the oxidation half equation

Mg → Mg2+ + 2e-

  • Step 3: Write the reduction half equation

2H+ + 2e- → H2

  • Step 4: Identify oxidation and reduction

    • Magnesium loses 2 electrons, so it is oxidised

    • Hydrogen ions gain electrons, so they are reduced

Examiner Tips and Tricks

Remember metal atoms tend to lose electrons and in these reactions are usually the species that undergoes oxidation

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Stewart Hird

Author: Stewart Hird

Expertise: Chemistry Content Creator

Stewart has been an enthusiastic GCSE, IGCSE, A Level and IB teacher for more than 30 years in the UK as well as overseas, and has also been an examiner for IB and A Level. As a long-standing Head of Science, Stewart brings a wealth of experience to creating Topic Questions and revision materials for Save My Exams. Stewart specialises in Chemistry, but has also taught Physics and Environmental Systems and Societies.