Oxidising agents and reducing agents
In this section we will concentrate more on the chemicals that are causing the oxidation or reduction reactions.
Substances that cause another substance to be oxidised are called oxidising agents, or oxidants.
Substances that cause another substance to be reduced are called reducing agents, or reductants.
An example of an oxidant is hydrogen peroxide (H2O2). This is used in bleaches and disinfectants. Hydrogen peroxide will cause a range of other chemicals to be oxidised. The hydrogen peroxide will itself be reduced as it causes oxidation to occur. This can be shown by the following half-equation.
H2O2(aq) + 2 H+(aq) + 2 e- → 2 H2O(l)
As you can see, the reduction of the hydrogen peroxide requires electrons. It is these electrons that are removed from the chemical that the hydrogen peroxide is oxidising.
This is the case for any substance acting as an oxidising agent. By acting as an oxidant, it will be reduced.
Likewise, any substance acting as a reductant will itself be oxidised.
In the next section you will use these ideas to identify oxidants and reductants in chemical reactions.
Antioxidants are substances that will prevent or slow down oxidation reactions. They are present naturally in a number of foods, for example vitamin C (C6H8O6) is an antioxidant.
Click here to view the structure of vitamin C 
Antioxidants are also used to control chemical processes, for example sulfur dioxide (SO2) is used in the wine industry to prevent unwanted oxidation reactions.
The video below explains about the role of sulfur dioxide in the production of wine and how the amount of sulfur dioxide in wine can be measured.
Text alternative to sulfur dioxide in wine production video
Video explaining the role of sulfur dioxide in the production of wine. The main points covered include the use of sulfur dioxide as an antioxidant which prevents the spoilage of the wine. It can do this because it has the ability to react with oxygen, thus removing unwanted oxygen from the wine. It also shows how the level of sulfur dioxide is analysed in the laboratory by driving out the sulfur from the wine and titrating the sulfuric acid produced using sodium hydroxide.
Click here to open the video in a new window.
