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3.5.6Movement and Interactions

Electron Transfer Reactions (HT Only) — AQA GCSE Combined Science Synergy 8465 - Physical Sciences Revision Notes & Topical Questions

5 min read 7 parts Lesson 59 of 59

📚 AQA GCSE Combined Science Synergy 8465 - Physical Sciences Hub / Topical Revision
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Part 1 of 5Oxidation and reduction (HT only)

Oxidation
  • Oxidation A substance is oxidised when it loses electrons.
Reduction
  • Reduction A substance is reduced when it gains electrons.
Redox
  • Redox Both happen in the same reaction, so it is called a redox reaction.
  • Memory aidOIL RIG, oxidation is loss, reduction is gain.

Part 2 of 5Splitting a redox reaction

1
Write the full equation: Fe + CuSO4 → FeSO4 + Cu.
2
Write it as an ionic equation, showing the ions: Fe + Cu2+ + SO42− → Fe2+ + SO42− + Cu.
3
Cross out spectator ions that appear unchanged on both sides, here sulfate: Fe + Cu2+ → Fe2+ + Cu.
4
Write a half equation for each change: Fe → Fe2+ + 2e− and Cu2+ + 2e− → Cu.
5
Label them: the iron loses electrons so it is oxidised; the copper ion gains electrons so it is reduced.

Part 3 of 5Electrolysis as redox

Electrolysis
At the cathode
  • At the cathode Positive ions gain electrons, so reduction happens here. Example: Pb2+ + 2e− → Pb.
At the anode
  • At the anode Negative ions lose electrons, so oxidation happens here. Example: 2Br− → Br2 + 2e−.
Electron flow
  • Electron flow Electrons are pushed by the power supply from the anode round the circuit to the cathode.

Part 4 of 5Identifying what is oxidised and reduced

ChangeElectronsProcess
Zn → Zn2+Lost: 2e−Oxidation
Cu2+ → CuGained: 2e−Reduction
Fe3+ → Fe2+Gained: 1e−Reduction
V3+ → V4+Lost: 1e−Oxidation

Part 5 of 5Displacement as electron transfer

1More reactive metal
  • More reactive metal Its atoms lose electrons easily to become ions.
2Electrons transferred
  • Electrons transferred The electrons pass to the less reactive metal ion.
3Less reactive metal forms
  • Less reactive metal forms The ions are reduced to atoms and appear as a solid.

Key terms

TermMeaning
OxidationThe loss of electrons by a substance.
ReductionThe gain of electrons by a substance.
Redox reactionA reaction in which oxidation and reduction occur together.
Spectator ionAn ion present in the reaction mixture that does not change and takes no part in the reaction.
Half equationAn equation showing only the loss or gain of electrons by one species.

Avoid these mistakes

1
Reversing OIL RIG, and saying that oxidation is gain of electrons.
2
Leaving spectator ions in the ionic equation instead of cancelling them.
3
Forgetting that half equations must balance in both atoms and charge.
4
Writing electrons on the wrong sideelectrons appear on the right in oxidation and on the left in reduction.
5
Saying the metal ion is oxidised when it forms a metal atom; it is reduced.

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