2.3.5Chemical Bonding, Application Of Chemical Reactions and Organic Chemistry
Oxidation and Reduction
5 min read 6 parts Lesson 29 of 54 1 quiz
Section 1 of 6Three ways to define the terms
| Definition | Oxidation | Reduction |
|---|---|---|
| Oxygen | Gain of oxygen | Loss of oxygen |
| Hydrogen | Loss of hydrogen | Gain of hydrogen |
| Electrons | Loss of electrons | Gain of electrons |
Section 2 of 6Remembering and using the electron definition
OIL RIG
- OIL RIG Oxidation Is Loss of electrons; Reduction Is Gain of electrons.
- The electron definition is the most general and works for reactions that involve no oxygen at all.
Always together
- Always together Whenever one substance is oxidised another is reduced, so these reactions are called redox reactions.
- Electrons lost by one species are gained by another.
Examples
- Examples Magnesium burning: 2Mg + O2 → 2MgO.
- Magnesium gains oxygen and loses electrons (Mg → Mg2+ + 2e-), so it is oxidised.
- Oxygen gains those electrons (O2 + 4e- → 2O2-), so it is reduced.
Section 3 of 6Oxidising and reducing agents
Redox agents
Oxidising agent
- Oxidising agent A substance that oxidises another by taking electrons or giving oxygen. It is itself reduced.
Reducing agent
- Reducing agent A substance that reduces another by giving electrons or removing oxygen.
- It is itself oxidised.
Example: iron(III) oxide and carbon monoxide
- Example: iron(III) oxide and carbon monoxide Fe2O3 + 3CO → 2Fe + 3CO2.
- The iron oxide loses oxygen, so it is reduced;
- carbon monoxide gains oxygen, so it is oxidised and is the reducing agent.
- The iron oxide loses oxygen, so it is reduced;
Example: displacement
- Example: displacement Zn + Cu2+ → Zn2+ + Cu.
- Zinc loses electrons (oxidised) and copper ions gain them (reduced).
Section 4 of 6Colour tests for redox
1
To show that a substance is a reducing agent, add it to acidified potassium manganate(VII). The purple solution turns colourless as the manganate(VII) is reduced.
2
To show that a substance is an oxidising agent, add it to potassium iodide solution. The colourless solution turns brown as iodide ions are oxidised to iodine.
3
In each case, record the colour before and after, and state which species lost or gained electrons.
Section 5 of 6Key terms
| Term | Meaning |
|---|---|
| Oxidation | Gain of oxygen, loss of hydrogen or loss of electrons. |
| Reduction | Loss of oxygen, gain of hydrogen or gain of electrons. |
| Redox reaction | A reaction in which oxidation and reduction occur together. |
| Oxidising agent | A substance that causes oxidation and is itself reduced. |
| Reducing agent | A substance that causes reduction and is itself oxidised. |
Section 6 of 6Exam technique
1
Mixing up the directionloss of electrons is oxidation, not reduction.
2
Saying an oxidising agent is oxidised. It is the reducing agent that is oxidised.
3
Using only the oxygen definition for reactions where no oxygen is involved, such as metal displacement.
4
Forgetting that oxidation and reduction always happen at the same time in one reaction.