IB Chemistry Topic R3.2.1 Oxidation and Reduction Definitions Revision Notes (SL/HL)

IB Chemistry Topic R3.2.1 Oxidation and Reduction Definitions Revision Notes (SL/HL) | RevisionDojo

Written by official IB examiners

Oxidation and Reduction: More Than Just Electron Transfer

Redox reactions involve two simultaneous processes: oxidation and reduction.
These terms can be understood in different ways depending on the context.

Oxidation

Electron Loss: When an atom or ion loses electrons, it undergoes oxidation.
Oxygen Gain: Oxidation can also refer to the addition of oxygen.
Hydrogen Loss: Oxidation may involve the loss of hydrogen.

Example

Sodium loses an electron and is oxidized: $$
\text{Na(s)} \rightarrow \text{Na⁺(aq)} + e⁻
$$
Magnesium gains oxygen and is oxidized: $$
2\text{Mg(s)} + \text{O₂(g)} \rightarrow 2\text{MgO(s)}
$$
Methane loses hydrogen during combustion: $$
\text{CH₄(g)} + 2\text{O₂(g)} \rightarrow \text{CO₂(g)} + 2\text{H₂O(g)}
$$

Note

While oxygen gain and hydrogen loss are traditional definitions of oxidation, they are less commonly used today compared to the electron transfer definition.
Always consider the context of the reaction.

Reduction

Electron Gain: Reduction occurs when an atom or ion gains electrons.
Oxygen Loss: Reduction can also mean the removal of oxygen.
Hydrogen Gain: Reduction may involve the addition of hydrogen.

Example

Chlorine gains electrons and is reduced: $$
\text{Cl₂(g)} + 2e⁻ \rightarrow 2\text{Cl⁻(aq)}
$$
Copper(II) oxide loses oxygen and is reduced: $$
\text{CuO(s)} + \text{H₂(g)} \rightarrow \text{Cu(s)} + \text{H₂O(g)}
$$
Ethene gains hydrogen in this reaction: $$
\text{C₂H₄(g)} + \text{H₂(g)} \rightarrow \text{C₂H₆(g)}
$$

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Oxidation and Reduction: More Than Just Electron Transfer

Redox reactions involve two simultaneous processes: oxidation and reduction.
These terms can be understood in different ways depending on the context.

Oxidation

Electron Loss: When an atom or ion loses electrons, it undergoes oxidation.
Oxygen Gain: Oxidation can also refer to the addition of oxygen.
Hydrogen Loss: Oxidation may involve the loss of hydrogen.

Example

Sodium loses an electron and is oxidized: $$
\text{Na(s)} \rightarrow \text{Na⁺(aq)} + e⁻
$$
Magnesium gains oxygen and is oxidized: $$
2\text{Mg(s)} + \text{O₂(g)} \rightarrow 2\text{MgO(s)}
$$
Methane loses hydrogen during combustion: $$
\text{CH₄(g)} + 2\text{O₂(g)} \rightarrow \text{CO₂(g)} + 2\text{H₂O(g)}
$$

Note

While oxygen gain and hydrogen loss are traditional definitions of oxidation, they are less commonly used today compared to the electron transfer definition.
Always consider the context of the reaction.

Reduction

Electron Gain: Reduction occurs when an atom or ion gains electrons.
Oxygen Loss: Reduction can also mean the removal of oxygen.
Hydrogen Gain: Reduction may involve the addition of hydrogen.

Example

Chlorine gains electrons and is reduced: $$
\text{Cl₂(g)} + 2e⁻ \rightarrow 2\text{Cl⁻(aq)}
$$
Copper(II) oxide loses oxygen and is reduced: $$
\text{CuO(s)} + \text{H₂(g)} \rightarrow \text{Cu(s)} + \text{H₂O(g)}
$$
Ethene gains hydrogen in this reaction: $$
\text{C₂H₄(g)} + \text{H₂(g)} \rightarrow \text{C₂H₆(g)}
$$

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Structure 1. Models of the particulate nature of matter5 subtopics

Structure 2. Models of bonding and structure4 subtopics

Structure 3. Classification of matter2 subtopics

Reactivity 1. What drives chemical reactions?4 subtopics

Reactivity 2. How much, how fast and how far?3 subtopics

Reactivity 3. What are the mechanisms of chemical change?4 subtopics

IB Chemistry R3.2.1 Oxidation and Reduction Definitions Notes

Structure 1. Models of the particulate nature of matter5 subtopics

Structure 2. Models of bonding and structure4 subtopics

Structure 3. Classification of matter2 subtopics

Reactivity 1. What drives chemical reactions?4 subtopics

Reactivity 2. How much, how fast and how far?3 subtopics

Reactivity 3. What are the mechanisms of chemical change?4 subtopics

Oxidation and Reduction: More Than Just Electron Transfer

Oxidation

Reduction

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Oxidation and Reduction: More Than Just Electron Transfer

Oxidation

Reduction

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