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

Common oxidants and reductants

What makes a good oxidant?

A chemical that is easily reduced will normally be a good oxidant. When chemists need to oxidise a substance, there is a range of oxidants that can be used. The one thing that these oxidants have in common is the ability to gain electrons. Oxidants could, therefore, be regarded as substances that 'soak up electrons'. In the process they will form new substances where one of the elements will have a lower oxidation number.

Below is a list of common oxidants:

• oxygen (O₂)
• chlorine (Cl₂)
• permanganate (MnO₄^-)
• dichromate (Cr₂O₇^2-)
• hypochlorite (ClO^-)
• concentrated sulfuric acid (H₂SO₄)
• nitric acid (HNO₃)

In this activity three of these oxidants are shown in their original and reduced forms.

Activity: Oxidants

You are required to calculate the drop in oxidation number of the element mentioned. Type in the answer and check your response before moving to the next oxidant.

1	Permanganate ion MnO4- converts to Mn2+ when it acts as an oxidant. What is the drop in oxidation number of the manganese? Well done!The oxidation number drops from +7 to +2.Your answer has been saved.

2	Dichromate Cr2O72- converts to Cr3+ when it acts as an oxidant. What is the drop in oxidation number of the manganese? Well done!The oxidation number drops from +6 to +3.Your answer has been saved.

3	Nitric acid HNO3 converts to NO when it acts as an oxidant. What is the drop in oxidation number of the nitrogen? Well done!The oxidation number drops from +5 to +2.Your answer has been saved.

Reductants

Reductants work in the opposite way – they are oxidised when they act as reducing agents. The following gives a list of common reductants. In the activity match the oxidised form of the species to the original form.

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Common reductants Select the oxidised form of the reactants from the drop down list. a) zinc metal (Zn) Choose... CO2 H+ Zn2+ Fe3+ b) carbon (C) Choose... CO2 H+ Zn2+ Fe3+ c) hydrogen gas (H2) Choose... CO2 H+ Zn2+ Fe3+ d) iron(II) salts (Fe2+) Choose... CO2 H+ Zn2+ Fe3+ e) oxalic acid (HOOCCOOH) Choose... CO2 H+ Zn2+ Fe3+ Well done.Some of the answers do not match, please try again.Your answer has been saved.

In the next section you will see some of the applications of these oxidants and reactants.