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3.2Reaction Types

Oxidation and reduction — EST 2 Chemistry Revision Notes & Topical Questions

5 min read 8 parts Lesson 2 of 4 1 quiz

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Lesson summary

Oxidation and reduction EST Chemistry notes: Assign oxidation numbers.OIL RIGOxidation Is Loss, Reduction Is Gain.Oxidation always occurs at the anode; reduction at the cathode (An Ox, Red Cat).E°cell = E°cathode − E°anode.A salt bridge keeps each half-cell electrically neutral.C…

  • Disproportionation
  • Find the oxidation number of Mn in KMnO4
  • Zn + Cu2+ → Zn2+ + Cu. Identify the agents
  • Oxidation and reduction EST Chemistry: what to do next
  • Oxidizing agent
  • Reducing agent

Part 1 of 8Key ideas

OIL RIG
Oxidation Is Loss, Reduction Is Gain.
Oxidation always occurs at the anode; reduction at the cathode (An Ox, Red Cat).
What the symbols mean:
E°cell = E°cathode − E°anode.
What the symbols mean: Ecell = standard cell potential (V) · Eright = electrode potential of the positive (reduction) half-cell · Eleft = potential of the negative half-cell (V)
A salt bridge keeps each half-cell electrically neutral.
Corrosion of iron is an oxidation process; zinc coating (galvanising) protects it.

Part 2 of 8Learning objectives

Learning objectives
Assign oxidation numbers.
Identify oxidizing and reducing agents.
Balance redox reactions and describe cells.

Part 3 of 8Essential knowledge

Combustion and respiration are redox reactions.
Disproportionation
Disproportionation one element is both oxidised and reduced.
Electrons flow anode → cathode in the external wire.
Electrolysis of brine produces Cl2, H2 and NaOH.
Higher E° means stronger oxidizing agent.

Part 4 of 8Process & sequence

1
Assign oxidation numbers to every atom.
2
Find the atom whose number rises (oxidised) and falls (reduced).
3
Split into half-reactions.
4
Balance atoms, then O with H2O, H with H+, charge with e−.
5
Equalise electrons and add the halves.

Balancing a redox equationwrite these steps in this order; each step is a marking point.

1
Assign oxidation numbers
2
Split half-reactions
3
Balance atoms, O, H
4
Balance charge with e−
5
Combine and check

Part 5 of 8Worked examples

1Find the oxidation number of Mn in KMnO4.
  • +1 + Mn + 4(−2) = 0, so Mn = +7.
2Zn + Cu2+ → Zn2+ + Cu. Identify the agents.
  • Zn is oxidised (reducing agent); Cu2+ is reduced (oxidizing agent).

Part 6 of 8Summary

Summary
Oxidation = loss; reduction = gain.
Oxidizing agent is reduced.
Anode: oxidation.

Part 7 of 8Keep going

Oxidation and reduction EST Chemistry: what to do next

These Oxidation and reduction EST Chemistry notes covered the key ideas, worked examples and exam technique for this topic. Check your Oxidation and reduction EST Chemistry understanding with the practice questions below, then reread any Oxidation and reduction EST Chemistry point you were unsure about before moving on.

1
Practice: Oxidation and reduction EST Chemistry practice questions
2
Previous lesson: 3.1 Acids and bases
3
Next lesson: 3.3 Redox & Electrochemistry — EST II Notes
4
Course: EST 2 Chemistry — all units
5
Official syllabus: OpenStax free science textbooks

Oxidation and reduction EST Chemistry revision notes

Part 8 of 8Compare: Compare

Oxidation number rules
RuleExample
Free element = 0O2, Na, Fe
Monatomic ion = its chargeCl− = −1
O is usually −2 (−1 in peroxides)H2O2
H is +1 (−1 in metal hydrides)NaH
Sum = overall chargeSO42−: S = +6
Voltaic vs electrolytic cells
FeatureVoltaicElectrolytic
EnergyChemical → electricalElectrical → chemical
Spontaneous?Yes (E° > 0)No
AnodeOxidation, negativeOxidation, positive
CathodeReduction, positiveReduction, negative

Key terms

Command terms

Command terms
Identify / Describe (FRQ)
A short, specific statement; describing requires relevant characteristics, not a single word.
Explain / Justify (FRQ)
Give the cause-and-effect reasoning or evidence; a restated fact does not score.
Calculate
Show setup, substitution and the answer with units.
Predict
State the expected outcome; add a reason only if asked to justify.
MCQ technique
Read every option; eliminate distractors that are true statements but do not answer the question; watch for NOT/EXCEPT.

Exam technique

Keywords the mark scheme looks for in this lesson

Keywords the mark scheme looks for in this lesson
Oxidation · Reduction · Oxidizing agent · Reducing agent · Oxidation number · Half-reaction · Voltaic cell · Electrolysis
Learn each definition in the Key words tab exactly; a missing keyword in a definition usually loses the mark.

How to get full marks (examiner guidance)

1
Answer exactly what is asked; extra correct material does not earn credit, and contradictory statements can cancel credit (AP FRQ).
2
Use precise vocabulary (e.g. “active site”, “concentration gradient”, “allele”), never “it/stuff/things”.
3
Show units and working in calculations.
4
In MCQs, predict the answer before reading the options, then eliminate.

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