Skip to content
Dabour HubLEARN · PRACTICE · EXPLORESign inStudent

2.3.2Unit 2. Energetics, Group Chemistry, Halogenoalkanes and Alcohols

Oxidation and Reduction — IAL Edexcel Linear (Chemistry) Revision Notes & Topical Questions

5 min read 5 parts Lesson 22 of 53 Unit quiz

📚 IAL Edexcel Linear (Chemistry) Hub / Topical Revision
🩺
100% Curriculum Specification Match Lesson Doctor Verified
The only platform with 100% curriculum specification match and verified interactive question banks.
0%read

Part 1 of 5Three Ways to Define the Terms

2.3.2 Oxidation and Reduction

The same reaction can be described using oxygen, electrons or oxidation numbers, and the last two are the most general.

Oxygen and hydrogen
  • Oxidation is gain of oxygen or loss of hydrogen, while reduction is loss of oxygen or gain of hydrogen.
Electrons
  • Oxidation is loss of electrons and reduction is gain of electrons, remembered by OIL RIG.
Oxidation number
  • Oxidation is an increase in oxidation number and reduction is a decrease in oxidation number.
Redox
  • Oxidation and reduction always happen together, because electrons lost by one species are gained by another.

Part 2 of 5Oxidising and Reducing Agents

Oxidising and Reducing Agents
Oxidising agent
  • This species takes electrons from another, so it is itself reduced and its oxidation number falls.
Reducing agent
  • This species gives electrons to another, so it is itself oxidised and its oxidation number rises.
Common oxidising agents
  • Halogens, acidified potassium manganate(VII) and acidified potassium dichromate(VI) are typical oxidising agents.
Common reducing agents
  • Metals, iodide ions and iron(II) ions readily donate electrons and act as reducing agents.

Part 3 of 5Analysing a Redox Equation

1
Write the oxidation number of every element above its symbol on both sides of the equation.
2
Find the element whose oxidation number increases; that species has been oxidised and is the reducing agent.
3
Find the element whose oxidation number decreases; that species has been reduced and is the oxidising agent.
4
Check that the total increase in oxidation number equals the total decrease, which confirms electrons are conserved.
5
State the answer using the correct terms, for example that magnesium is oxidised from 0 to +2 as it loses electrons.

Part 4 of 5Worked Example

Question In the reaction MnO₂(s) + 4HCl(aq) → MnCl₂(aq) + Cl₂(g) + 2H₂O(l), identify what is oxidised, what is reduced and the oxidising agent.

  1. Manganese in MnO₂ is +4, because the two oxygens give -4.
  2. Manganese in MnCl₂ is +2, so the oxidation number falls and Mn is reduced.
  3. Chlorine in HCl is -1 and chlorine in Cl₂ is 0, so the oxidation number rises and Cl is oxidised.
  4. The species that gets reduced is MnO₂, so it takes electrons from the chloride ions.

Answer Chloride in HCl is oxidised (-1 to 0), manganese is reduced (+4 to +2), so MnO₂ is the oxidising agent and HCl is the reducing agent.

Part 5 of 5Exam Checklist & Tips

2.3.2 – Key Points for the Exam

  • Oxidation Loss of electrons, or an increase in oxidation number.
  • Reduction Gain of electrons, or a decrease in oxidation number.
  • Oxidising agent A species that accepts electrons and is itself reduced.
  • Reducing agent A species that donates electrons and is itself oxidised.
  • Redox reaction A reaction in which oxidation and reduction occur together.

Common Mistakes

  • Saying the oxidising agent is oxidised; it causes oxidation but is reduced itself.
  • Describing oxidation as gain of electrons because it sounds like gain; it is loss.
  • Deciding what is oxidised or reduced without comparing the oxidation numbers of the element on both sides of the equation.
  • Stating oxidation number changes without the sign, such as writing 0 to 2 instead of 0 to +2.

Last updated:

\n