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Edexcel A Level Chemistry

Topic 3
Redox I

Topic 3 introduces oxidation number as a way to classify redox reactions, identify oxidation and reduction, write ionic half-equations and construct full ionic equations. Students build the language needed for redox chemistry across both inorganic and organic contexts.

Exam Papers
Paper 1 & 2
9CH0/01 and 9CH0/02
Specification Points
3.1 – 3.13
13 points covered
Topic Parts
4 parts
Revision notes available
Exam Board
Edexcel
Pearson 9CH0

Revision Notes

Work through each part of Edexcel Topic 3 in a structured sequence.

Oxidation state
Oxidation
Numbers
+, -, 0 and Roman numerals
1

Oxidation Numbers

Assigning oxidation numbers in elements, compounds and ions, including Roman numeral notation.

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Electron flow
Half
Equations
2

Electron Transfer and Half-Equations

Oxidation, reduction, oxidising agents, reducing agents and constructing ionic half-equations.

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Two changes
Disproportion
ation
oxidised and reduced
3

Disproportionation

Reactions where one element in a single species is oxidised and reduced at the same time.

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Classifying reactions
Redox
Classification
identify the chemical change
4

Redox Classification

Using oxidation numbers and electron transfer to classify reactions as redox or non-redox.

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Summary map

Download, print and revise the key facts of this topic at a glance.

Summary map · PDF

Redox Map

Edexcel A Level Chemistry · Topic 3 Redox I

The whole topic on one A4 page: oxidation number rules, Roman numerals, half-equations, disproportionation and a table of polyatomic ions with their charges.

Download the map6 key ideas + 16 ions · A4 portrait · print ready

© 2026 Online Learning System. For personal study: printing is allowed; editing, copying and redistribution are not.

Specification Coverage

Topic 3 Redox I – Edexcel A Level Chemistry

The following specification points outline the knowledge and skills students are expected to demonstrate for Topic 3.

3.1
know what is meant by the term oxidation number
3.2
be able to calculate the oxidation number of elements in compounds and ions. The use of oxidation numbers in peroxides and metal hydrides is expected.
3.3
understand oxidation and reduction in terms of electron transfer and changes in oxidation number, applied to reactions of s- and p-block elements
3.4
understand oxidation and reduction in terms of electron loss or electron gain
3.5
know that oxidising agents gain electrons
3.6
know that reducing agents lose electrons
3.7
understand that a disproportionation reaction involves an element in a single species being simultaneously oxidised and reduced
3.8
know that oxidation number is a useful concept in terms of the classification of reactions as redox and as disproportionation
3.9
be able to indicate the oxidation number of an element in a compound or ion, using a Roman numeral
3.10
be able to write formulae given oxidation numbers
3.11
understand that metals, in general, form positive ions by loss of electrons with an increase in oxidation number
3.12
understand that non-metals, in general, form negative ions by gain of electrons with a decrease in oxidation number
3.13
be able to write ionic half-equations and use them to construct full ionic equations
Specification Coverage

Topic 3 Redox I – Edexcel A Level Chemistry

The following specification points outline the knowledge and skills students are expected to demonstrate for Topic 3.

3.1
know what is meant by the term oxidation number
3.2
be able to calculate the oxidation number of elements in compounds and ions. The use of oxidation numbers in peroxides and metal hydrides is expected.
3.3
understand oxidation and reduction in terms of electron transfer and changes in oxidation number, applied to reactions of s- and p-block elements
3.4
understand oxidation and reduction in terms of electron loss or electron gain
3.5
know that oxidising agents gain electrons
3.6
know that reducing agents lose electrons
3.7
understand that a disproportionation reaction involves an element in a single species being simultaneously oxidised and reduced
3.8
know that oxidation number is a useful concept in terms of the classification of reactions as redox and as disproportionation
3.9
be able to indicate the oxidation number of an element in a compound or ion, using a Roman numeral
3.10
be able to write formulae given oxidation numbers
3.11
understand that metals, in general, form positive ions by loss of electrons with an increase in oxidation number
3.12
understand that non-metals, in general, form negative ions by gain of electrons with a decrease in oxidation number
3.13
be able to write ionic half-equations and use them to construct full ionic equations