Home

Chemistry

Atoms, equations and reactions

Oxidation, reduction and redox reactions

Select Lesson

Exam Board

Select an option

Practical skills

The scientific method

How to plan experiments

Improving repeatability and reproducibility

Presenting results using tables and graphs

Analysing results: anomalies and correlation

Evaluating experiments

Analysis

Testing for functional groups

Chromatography

NMR spectroscopy

Proton NMR spectroscopy

Combining analytical techniques

Synthesis

Carbon-Carbon bond formation

Nitrile reactions and synthetic routes

Practical techniques

Synthetic routes

Amines and polymers

Aliphatic and aromatic amines

Reactions of amines

Forming amides

Optical isomers and chirality

Condensation polymers

Acid and base hydrolysis of polymers

Aromatic chemistry and carbonyls

Benzene: structure and combustion

Electrophilic substitution

Friedel-Crafts reactions

Phenols

Aldehydes and ketones

Carboxylic acids: properties and reactions

Acyl chlorides: formation and reactions

Esters: formation, properties and uses

Transition metals

Transition metals: electron configuration and oxidation number

Complex ions: formation, shape and isomerism

Colours of inorganic ions and complexes

Ligand substitution reactions

Redox reactions of complex ions

Transition metals as catalysts

Redox and cells

Redox titrations

Electrochemical cells and redox

Electrode potentials and calculations

The electrochemical series

Energy storage cells and hydrogen fuel cells

Enthalpy and entropy

Lattice enthalpies and Born-Haber cycles

Polarisation and the Pauling scale

Enthalpy change in solution

Entropy and calculating entropy change

Gibbs free energy change

Acids and bases

pH calculations

The ionic product of water

Buffer solutions and calculations

pH curves and indicators

Rates and equilibrium

Measuring rates of reaction

Determining reaction orders

The initial rates method

Rate equations and the rate constant

The rate determining step

Activation energy and the Arrhenius equation

Equilibrium constant calculations

Partial pressure and gas equilibria

Le Chatelier's principle and equilibrium constants

Organic synthesis and analysis

Mass spectrometry

IR spectroscopy

Organic techniques

Alcohols and haloalkanes

Alcohol: classification and reactions

Oxidation of alcohols

Halogenoalkanes and their reactions

Haloalkanes and the environment

The greenhouse effect and global warming

Organic chemistry - the basics

Basic concepts of organic chemistry

Organic reactions and mechanisms

Structural isomerism

Alkanes and free radical substitution

Alkenes: bonding and reactivity

Stereoisomerism

Reactions of alkenes

Addition polymerisation

Enthalpy and reaction rates

Enthalpy changes and reaction profiles

Standard enthalpy changes

Calculating bond enthalpies

Hess's Law and enthalpy cycles

Collision theory and rates of reaction

Calculating the rate of reaction

Catalysts and the Maxwell-Boltzmann distribution

Reversible reactions

Le Chatelier's principle

The equilibrium constant

The periodic table

The arrangement of the periodic table

Ionisation energies

Ionisation energy trends

Periodicity

Giant covalent and metallic structures

Predicting structures and properties

Group 2: ionisation energy and properties

Chemical properties of Group 7

Reactions with halogens

Testing for ions

Bonding and structure

Electronic structure: shells and orbitals

Ionic bonding

Covalent bonding

Shapes of molecules

Electronegativity and polarisation

Intermolecular forces: types and examples

Hydrogen bonding

Atoms, equations and reactions

The atom: history, structure and isotopes

Relative masses and mass spectrometry

The mole and Avogadro's constant

Calculations involving gases

Empirical and molecular formulae

Balancing equations

Formulae for crystals and salts

Acid-base titrations

Atom economy and percentage yield

Calculating oxidation numbers

Oxidation, reduction and redox reactions

Explainer Video

Tutor: Alexander

Summary

Oxidation, reduction and redox reactions

In a nutshell

Redox reactions involve the transfer of electrons where both reduction and oxidation occurs. Metals typically behave as reducing agents.

What is a redox reaction?

A loss of electrons is known as oxidation and a gain of electrons is known as reduction. This can be remembered by the mnemonic OIL RIG, oxidation is loss and reduction is gain. These reactions occur simultaneously, hence the term redox.

An oxidising agent is reduced (gains electrons), and a reducing agent is oxidised (electrons lost).

Oxidation numbers and electrons

For each electron lost, the oxidation number will go up by one. For each electron gained, the oxidation number goes down by one.

To determine whether an element has been oxidised or reduced, the oxidation numbers before and after the reaction have to be compared. If the oxidation number has increased the element has been oxidised, as electrons have been lost. If the oxidation number has decreased the compound has been reduced, as electrons have been gained.

When metals form compounds, they generally form positive ions. They donate electrons and behave as reducing agents. When non-metals form compounds, they generally form negative ions. They receive electrons and behave as oxidising agents.

Example

Identify the reducing and oxidising agents in this reaction.

$Ca\ +\ Cl_2\ \rightarrow\ CaCl_2$

$Ca$ went from an oxidation number of $0$ to an oxidation number of $+2$ . Calcium lost two electrons. This means that the calcium atom has been oxidised. Therefore, calcium is a reducing agent.

$Cl$ went from an oxidation number of $0$ to an oxidation number of $-1$ . Each chlorine atom has gained an electron. This means that the chlorine atoms have been reduced. Therefore, chlorine is an oxidising agent.

Acids and metals

When acids react with metals, they produce a salt and hydrogen gas. The metal is oxidised (forms positive ions) and hydrogen is reduced (gains electrons).

Example

$2HCl\ + \ Mg\ \rightarrow \ MgCl_2\ +\ H_2$

Hydrogen went from an oxidation number of $+1$ to $0$ . It has been reduced.

Magnesium went from an oxidation number of $0$ to an oxidation number of $+2$ . The magnesium atom was oxidised.

Learn with Basics

Length:

Unit 1

Displacement reactions

Unit 2

Oxidation and reduction: redox reactions - Higher

Jump Ahead

Unit 3