AQA GCSE Chemistry

Revision Notes

4.1.4 Oxidation & Reduction in Terms of Electrons

Higher Tier Only

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) + SO42- (aq) → Mg2+ (aq) + SO42- (aq) + Cu (s)

  • The sulfate ions, SO42-, 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
Higher Tier Only

Identifying Oxidised & Reduced Species

  • Using the principles of electron loss and gain it is possible to identify which species undergo oxidation and reduction in redox reactions

Worked Example

Zinc displaces copper from a solution of copper(II)sulfate. Using ionic equations, determine which species undergoes oxidation and which species undergoes reduction.


Identifying Oxidation and Reduction WE, downloadable IGCSE & GCSE Chemistry revision notes

Exam Tip

After writing half equations, you can see if they are correct by checking that the number of electrons on either side is the same, which should combine to give 0 charge.

Author: Francesca

Fran has taught A level Chemistry in the UK for over 10 years. As head of science, she used her passion for education to drive improvement for staff and students, supporting them to achieve their full potential. Fran has also co-written science textbooks and worked as an examiner for UK exam boards.

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