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8.4.1The Periodic Table

Oxidation and Reduction in Terms of Oxygen — Cambridge IGCSE Chemistry 0620 Revision Notes & Topical Questions

5 min read 4 parts Lesson 13 of 23 Unit quiz

📚 Cambridge IGCSE Chemistry 0620 Hub / Topical Revision
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Curriculum Equation Key قوانين الرقم الهيدروجيني والاتزان الأيوني - pH & Acid-Base Equilibrium FormulasFast Exam Solution
pH = -log[H⁺] | pOH = -log[OH⁻] | pH + pOH = 14 | [H⁺][OH⁻] = 10⁻¹⁴
Word Equation & Conditions: الرقم الهيدروجيني = -لوغاريتم تركيز أيون الهيدروجين | pH + pOH = 14
Location & Specifications: الاتزان الأيوني، كيمياء 3 ثانوي، التحصيلي، و AP Chemistry.
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Part 1 of 4Oxygen Definitions

Redox reactions are defined by the gain and loss of oxygen.

Oxidation
  • Oxidation Oxidation is a reaction in which oxygen is added to an element or a compound.
Reduction
  • Reduction Reduction is a reaction in which oxygen is removed from an element or a compound.
Redox
  • Redox Oxidation and reduction always take place together in the same reaction, and such a reaction is called a redox reaction.
Identifying
  • Identifying Check which species gains oxygen and which loses it, because the species oxidised and the species reduced are different.

Part 2 of 4Worked Examples

Two examples show how to identify the change in each species.

1
Zinc oxide reacts with carbon: ZnO + C → Zn + CO. Zinc oxide loses oxygen, so it is reduced.
2
In the same reaction, carbon gains oxygen to form carbon monoxide, so the carbon is oxidised.
3
In the blast furnace, Fe₂O₃ + 3CO → 2Fe + 3CO₂, the iron(III) oxide loses oxygen and is reduced to iron.
4
The carbon monoxide gains oxygen to form carbon dioxide, so it is oxidised, and the overall change is a redox reaction.

Part 3 of 4Common Errors

Precise language avoids losing marks in exams.

Common Errors
Reduced substance
  • Reduced substance In the blast furnace it is the iron(III) oxide that is reduced, not the iron.
Gain or loss
  • Gain or loss Oxidation adds oxygen and reduction removes it, so identify the species changing before naming the process.
Both occur
  • Both occur If one substance is oxidised in a reaction, another must be reduced in the same reaction.
Vocabulary
  • Vocabulary Use precise terms such as gains oxygen or loses oxygen rather than vague words such as burnt.

Part 4 of 4Exam Checklist & Tips

8.4.1 – Key Points for the Exam

  • Oxidation A reaction in which a substance gains oxygen.
  • Reduction A reaction in which a substance loses oxygen.
  • Redox reaction A reaction in which oxidation and reduction occur together.
  • Blast furnace A furnace in which iron(III) oxide is reduced to iron using carbon monoxide.

Common Mistakes

  • Saying the iron is reduced in the blast furnace; it is the iron(III) oxide that is reduced.
  • Describing a reaction as oxidation simply because a new substance forms; oxidation is defined by oxygen gain.
  • Saying that oxidation and reduction can happen separately; they always occur together in a redox reaction.
  • Stating that carbon is reduced in the zinc oxide reaction; carbon gains oxygen, so it is oxidised.

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