Definitions of oxidation and reduction (REDOX)

Oxidation and reduction in terms of oxygen transfer
Definitions
- Oxidation is gain of oxygen.
- Reduction is loss of oxygen.
Oxidising and reducing agents
An oxidising agent is substance which oxidises -something else. In the above example, the iron(III) oxide is the oxidising agent.
A reducing agent reduces something else. In the equation, the carbon monoxide is the reducing agent.
- Oxidising agents give oxygen to another substance.
- Reducing agents remove oxygen from another substance.
Oxidation and reduction in terms of hydrogen transfer
These are old definitions which aren't used very much nowadays. The most likely place you will come across them is in organic chemistry.
Definitions
- Oxidation is loss of hydrogen.
- Reduction is gain of hydrogen.
Notice that these are exactly the opposite of the oxygen definitions.
You would need to use an oxidising agent to remove the hydrogen from the ethanol. A commonly used oxidising agent is potassium dichromate(VI) solution acidified with dilute sulphuric acid.
Ethanal can also be reduced back to ethanol again by adding hydrogen to it. A possible reducing agent is sodium tetrahydridoborate, NaBH4. Again the equation is too complicated to be worth bothering about at this point.
An update on oxidising and reducing agents
- Oxidising agents give oxygen to another substance or remove hydrogen from it.
- Reducing agents remove oxygen from another substance or give hydrogen to it.
Oxidation and reduction in terms of electron transfer: This is easily the most important use of the terms oxidation and reduction at A level.
Definitions
- Oxidation is loss of electrons.
- Reduction. is gain of electrons.
It is essential that you remember these definitions. There is a very easy way to do this. As long as you remember that you are talking about electron transfer: