Skip to content
Dabour HubLEARN · PRACTICE · EXPLORESign inStudent

6.3Chemical Reactions

Redox — Combined Science 0653 - Chemistry Revision Notes & Topical Questions

5 min read 16 parts Lesson 10 of 10 1 quiz

📚 Combined Science 0653 - 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
Lesson summary

6.3 Redox — COMBINED SCIENCE (CHEMISTRY) notes: Define oxidation, reduction and redox in terms of oxygen and electrons and identify oxidising and reducing agents.Roman numeral — in a name it shows the charge and oxidation number of the metal ion.Fe2+ is iron(II) and Fe3+ is iron(…

  • Oxidation state
  • Redox reaction
  • Memory aid
  • Displacement
  • Charge versus number
  • Acidified potassium manganate(VII)

Section 1 of 16Oxidation numbers and Roman numerals

Roman numeral
  • Roman numeral in a name it shows the charge and oxidation number of the metal ion.
  • Fe2+ is iron(II) and Fe3+ is iron(III).
  • FeO is iron(II) oxide and Fe2O3 is iron(III) oxide.
  • CoCl2 is cobalt(II) chloride.
Oxidation state
  • Oxidation state the terms oxidation number and oxidation state are used interchangeably at this level.

Section 2 of 16Redox in terms of oxygen

Oxidation
  • = addition of oxygen to an element or compound.
Reduction
  • = removal of oxygen from an element or compound.
Redox reaction
  • = oxidation and reduction happening together in the same reaction.
  • In zinc oxide + carbon, zinc oxide is reduced and carbon is oxidised.
  • In Fe2O3 + 3CO → 2Fe + 3CO2, iron(III) oxide is reduced and carbon monoxide is oxidised.

Section 3 of 16Redox in terms of electrons (supplement)

Oxidation
  • = loss of electrons, and the oxidation number increases.
  • Ag → Ag+ + e-.
Reduction
  • = gain of electrons, and the oxidation number decreases.
  • O2 + 4e- → 2O2-.
Memory aid
  • OIL RIGOxidation Is Loss, Reduction Is Gain.
  • Displacement
    • Fe + Cu2+ → Fe2+ + Cu: iron is oxidised and copper ions are reduced.
    • Sulfate ions are spectator ions.

Section 4 of 16Rules for oxidation numbers (supplement)

RuleOxidation number
Uncombined element0
Monatomic ionEqual to its charge
Group 1 / Group 2 in compounds+1 / +2
Fluorine−1
Hydrogen+1 (−1 in hydrides)
Oxygen−2 (−1 in peroxides)
CompoundSum is 0
IonSum equals the charge
Charge versus number
  • Charge versus number charge is written as number then sign, oxidation number as sign then number.
Redox
  • Redox a change in oxidation number during a reaction shows redox.

Section 5 of 16Colour tests for redox (supplement)

1Acidified potassium manganate(VII)
  • Acidified potassium manganate(VII) is an oxidising agent that turns from purple to colourless with a reducing agent.
2Potassium iodide
  • Potassium iodide is a reducing agent that turns red-brown, forming iodine, with an oxidising agent such as chlorine or hydrogen peroxide.

Section 6 of 16Oxidising and reducing agents (supplement)

Oxidising agent
  • = substance that oxidises another and is itself reduced, gaining electrons.
  • Examples are hydrogen peroxide, fluorine and chlorine.
Reducing agent
  • = substance that reduces another and is itself oxidised, losing electrons.
  • Examples are carbon and hydrogen.
Example
  • Example in CuO + H2 → Cu + H2O hydrogen is the reducing agent and copper oxide is the oxidising agent.
Industry
  • Industry reduction is used to extract metals from their ores.

Section 7 of 16More from the specification

1Precipitation and oxidized product
  • Precipitation and oxidized product electron loss converts metal atoms into aqueous cations, yielding a soluble or insoluble oxidized product during redox reactions.
2Oxidation (OIL)
  • The chemical process in which a reacting chemical species loses electrons or increases its oxidation state.
3Reduction (RIG)
  • The chemical process in which a chemical species gains electrons or decreases its oxidation state.
4Oxidising and reducing agents
  • An oxidising agent gains electrons by oxidising other species, while a reducing agent donates electrons and is oxidized.
5Redox displacement
  • A reactive metal displaces less reactive metal ions, such as copper reacting with aqueous silver ions (Cu + 2Ag+ → Cu2+ + 2Ag).
6Formula
  • Symbols and numbers showing the atoms in a compound.

Section 8 of 16Identifying redox by oxidation number

Method
  • Method find the species whose oxidation number rises or falls between reactants and products.
  • Oxidation number increasesthe species is oxidised (loses electrons).
  • Oxidation number decreasesthe species is reduced (gains electrons).
Memory aid
  • OIL RIGOxidation Is Loss, Reduction Is Gain.

Section 9 of 16Identifying redox with half-equations

1
Write half-equations to see which species gains and which loses electrons.
2
Use OIL RIG to decide which is oxidised and which is reduced.
3
The reducing agent is the species that is oxidised.
4
The oxidising agent is the species that is reduced.

Section 10 of 16Examples of redox reactions

ReactionOxidisedReduced
Mg + CuSO4 → MgSO4 + CuMg (0 to +2)Cu2+ (+2 to 0)
Fe + Br2 → FeBr2FeBr2
Cl2 + 2KI → 2KCl + I2I- (−1 to 0)Cl2 (0 to −1)
  • Link
    • electrons lost by one species are gained by the other, so oxidation and reduction always happen together.

Section 11 of 16Oxidising and reducing agents

Oxidising agent
  • Oxidising agent oxidises another substance and is itself reduced, gaining electrons.
  • Hydrogen peroxide, fluorine and chlorine.
Reducing agent
  • Reducing agent reduces another substance and is itself oxidised, losing electrons.
  • Carbon and hydrogen.

Section 12 of 16Colour tests

1Acidified potassium manganate(VII)
  • Acidified potassium manganate(VII) is an oxidising agent;
    • its purple colour turns colourless when added to a reducing agent.
2Potassium iodide
  • Potassium iodide is a reducing agent used to test for oxidising agents.
  • With acidified chlorine or hydrogen peroxide it turns red-brown as iodine forms.
  • Iodide is oxidised and the oxidising agent is reduced.

Section 13 of 16Oxygen and electron definitions together

Oxygen definition
  • Oxygen definition oxidation is gain of oxygen and reduction is loss of oxygen.
Electron definition
  • Electron definition works for all redox reactions, including those with no oxygen.

Section 14 of 16More from the specification

More from the specification
Oxidation numbers and Roman numerals
  • In chemical nomenclature, a Roman numeral in parentheses (e.g. copper(II) sulfate or silver(I) nitrate) indicates the formal oxidation state of the transition metal element in the compound.
Redox as oxidation number change
  • In a redox reaction, oxidation corresponds to an increase in oxidation state and reduction corresponds to a decrease in oxidation state (gain of electrons).
    • (loss of electrons)
Displacement reactions of transition metals
  • When zinc metal reacts with aqueous copper(II) sulfate (CuSO4), copper ions gain electrons to form metallic copper,
  • while zinc is oxidised: Zn + Cu2+ → Zn2+ + Cu.
Determining formula from ionic charge
  • The chemical formula of an ionic compound is deduced by balancing the total positive charge of metal cations against the total negative charge of non-metal anions.
Oxidation numbers and Roman numerals
  • In chemical nomenclature, a Roman numeral in parentheses (e.g. copper(II) sulfate or silver(I) nitrate) indicates the formal oxidation state of the transition metal element in the compound.
Redox as oxidation number change
  • In a redox reaction, oxidation corresponds to an increase in oxidation state and reduction corresponds to a decrease in oxidation state (gain of electrons).
    • (loss of electrons)
Displacement reactions of transition metals
  • When zinc metal reacts with aqueous copper(II) sulfate (CuSO4), copper ions gain electrons to form metallic copper,
  • while zinc is oxidised: Zn + Cu2+ → Zn2+ + Cu.
Determining formula from ionic charge
  • The chemical formula of an ionic compound is deduced by balancing the total positive charge of metal cations against the total negative charge of non-metal anions.
Element
  • A substance made of only one type of atom.
Compound
  • Two or more elements chemically combined in a fixed ratio.
Charge
  • Q = It, measured in coulombs.
    What the symbols mean: Q = charge (C) · I = current (A) · t = time (s)
Formula
  • Symbols and numbers showing the atoms in a compound.
Roman numeral
  • The numeral in a name showing the oxidation number of the metal.

Section 15 of 16Key terms

TermMeaning
OxidationGain of oxygen or loss of electrons.
ReductionLoss of oxygen or gain of electrons.
RedoxOxidation and reduction in the same reaction.
Oxidation numberNumber showing electrons lost, gained or shared.
Oxidising agentSubstance that is reduced and oxidises another.
Reducing agentSubstance that is oxidised and reduces another.
TermMeaning
RedoxOxidation and reduction occurring together.
Oxidising agentSubstance that gains electrons and is reduced.
Reducing agentSubstance that loses electrons and is oxidised.
Oxidation numberNumber showing electrons lost, gained or shared.
Half-equationEquation showing only the electron gain or loss.
OIL RIGOxidation Is Loss, Reduction Is Gain.

Section 16 of 16Exam technique

1
Saying oxidation is gain of electrons — it is loss.
2
Saying the oxidising agent is oxidised — it is reduced.
3
Confusing oxidation number with charge.
4
Forgetting that oxidation and reduction occur together.
1
Confusing the oxidising agent with the species oxidised — the oxidising agent is reduced.
2
Saying oxidation is gain of electrons.
3
Forgetting to acidify the potassium iodide or manganate(VII) test.
4
Describing iodine in water as purple — it is brown (vapour is purple).

Last updated: