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2.1.2Organic Chemistry

Types of Reduction and Oxidation — Edexcel AS Chemistry Revision Notes & Topical Questions

5 min read 5 parts Lesson 2 of 42

📚 Edexcel AS Chemistry Hub / Topical Revision
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Curriculum Equation Key معادلة تفاعل تكوين الإستر (الأسترة) - Esterification Reaction EquationFast Exam Solution
R-COOH + R2-OH ⇌ (conc. H₂SO₄) R-COO-R2 + H₂O
Word Equation & Conditions: حمض كربوكسيلي + كحول (في وجود حمض الكبريتيك المركز كعامل حفاز ونازع للماء) ⇌ إستر + ماء
Location & Specifications: الكيمياء العضوية للثانوية العامة والتحصيلي و Edexcel Chemistry.
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Part 1 of 5Electron Transfer

Oxidation
  • Oxidation Oxidation is loss of electrons, and the oxidation number of the element increases.
Reduction
  • Reduction Reduction is gain of electrons, and the oxidation number of the element decreases.
Memory aid
  • Memory aid OIL RIG stands for Oxidation Is Loss, Reduction Is Gain of electrons.
Simultaneous
  • Simultaneous Oxidation and reduction always occur together in a redox reaction.
Both together
  • Both together Oxidation and reduction cannot happen alone, because electrons lost by one species must be gained by another.

Part 2 of 5Other Definitions

Other Definitions
Oxygen
  • Oxygen Gain of oxygen is oxidation and loss of oxygen is reduction.
Hydrogen
  • Hydrogen Loss of hydrogen is oxidation and gain of hydrogen is reduction.
Oxidation number
  • Oxidation number An increase in oxidation number means oxidation; a decrease means reduction.
Best method
  • Best method Use oxidation numbers or electrons in exams because they apply to every type of reaction.
ChangeOxidationReduction
ElectronsLostGained
Oxidation numberIncreasesDecreases
OxygenGainedLost

Part 3 of 5Oxidising and Reducing Agents

1
An oxidising agent takes electrons from another species, so it is itself reduced.
2
A reducing agent gives electrons to another species, so it is itself oxidised.
3
In Mg + Cl₂ → MgCl₂, magnesium loses two electrons and is oxidised, so it is the reducing agent.
4
Chlorine gains electrons and is reduced, so it is the oxidising agent.
5
Always identify the species that changes, not the whole compound.
6
In Zn + Cu²⁺ → Zn²⁺ + Cu, zinc is the reducing agent and the copper ion is the oxidising agent.

Part 4 of 5Half-Equations

Oxidation half-equation
  • Oxidation half-equation Mg → Mg²⁺ + 2e⁻ shows electrons on the product side.
Reduction half-equation
  • Reduction half-equation Cl₂ + 2e⁻ → 2Cl⁻ shows electrons on the reactant side.
Balancing electrons
  • Balancing electrons Multiply half-equations so that electrons lost equal electrons gained before adding them.
Spectator ions
  • Spectator ions Ions that remain unchanged do not appear in the half-equations.
Halogens
  • Halogens Chlorine is a strong oxidising agent because it readily gains electrons to form chloride ions.

Part 5 of 5Exam Checklist & Tips

2.1.2 – Key Points for the Exam

  • Oxidation Loss of electrons or increase in oxidation number.
  • Reduction Gain of electrons or decrease in oxidation number.
  • Oxidising agent A species that accepts electrons and is reduced.
  • Reducing agent A species that donates electrons and is oxidised.

Common Mistakes

  • Mixing up the oxidising agent with the species oxidised; they are opposites.
  • Writing electrons on the wrong side of a half-equation.
  • Using only oxygen gain as the definition of oxidation.
  • Failing to state that both processes happen at the same time.

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