Oxidising and reducing agents

Table of Contents

1. Oxidising agents and reducing agents
2. Redox reactions
   1. Oxidation numbers
3. Oxidising agents and reducing agents
   1. Oxidants and reductants
   2. Common oxidants and reductants
4. Half-equations
   1. Writing half-equations
   2. Combining half-equations
5. Reduction potentials
   1. Source of reduction potentials
   2. Using standard electrode potentials
   3. Predicting reaction tendencies
6. Redox reactions in action

1. Additional resources:
   1. Glossary
   2. Print content

Redox reactions

Oxidation can be described as the reaction with oxygen. Respiration is an example of an oxidation reaction. The reaction is shown below.

C₆H₁₂O₆ + 6 O₂ → 6 CO₂ + 6 H₂O

From your earlier studies, you should know some other definitions of oxidation and reduction. Write down any definitions that you know, discussing your ideas with others or your teacher if you have the opportunity. Click the link below to reveal more.

Oxidation and reduction

You have seen that oxidation and reduction are the reverse of each other, and one cannot occur without the other. In a redox reaction there is always a substance being oxidised and a substance being reduced. The best way to investigate redox reactions at this stage is by considering the transfer of electrons.

In the following reactions, identify the substances being oxidised.

Text alternative to the burning magnesium video

Magnesium ribbon burns in air with bright white flame.

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1

Reaction 1: Burning magnesium 2 Mg + O2 → 2 MgO a) oxygen b) magnesium c) neither Please select an answerIncorrect, oxygen is being reduced because it is gaining electrons to form an oxide (O2-) ion.Correct, magnesium is being oxidised because it is losing electrons to form a positive ion (Mg2+) ion.Incorrect, the magnesium is losing electrons and the oxygen is gaining electrons.

Text alternative to the forming silver video

Silver forms on a copper wire which is placed in a blue solution of copper(II) sulfate.

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2

Reaction 2: Forming silver Cu + 2 AgCl → CuCl2 + 2 Ag a) copper b) silver ions c) chloride ions d) none of the above Please select an answerCorrect, copper is being oxidised because it is losing electrons as it converts from copper (Cu) to copper(II) ions (Cu2+).Incorrect, silver is being reduced from silver ions (Ag+) to silver metal (Ag).Incorrect, chlorine remains as chloride ions (Cl-). Incorrect, there is a redox reaction occurring.

Text alternative to the copper hydroxide video

A blue precipitate is formed in a solution.

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3

Reaction 3: Forming copper(II) hydroxide CuSO4 + 2 NaOH → Cu(OH)2 + Na2SO4 a) copper(II) ions b) sodium ions c) sulfur d) none of the above Please select an answerIncorrect, copper remains as copper(II) ions (Cu2+).Incorrect, sodium remains as sodium ions (Na+).Incorrect, sulfur remains in the form of sulfate ions (SO42-).Correct, this is not a redox reaction.

Half-equations

You should recall that we can use half-equations to show the oxidation and reduction processes occurring in redox reactions. Write half-equations in your notes for the reactions in the above activity that were redox reactions.

Once you have done this, click the link below.

Half equations

Sometimes it is helpful to use the concept of oxidation number to determine whether a redox reaction is occurring, and to identify what is being oxidised and reduced in the process. The next section will revise the idea of oxidation number and use oxidation numbers to reveal the changes occurring in more redox reactions.