An oxidizing agent or oxidising agent (also called an oxidant, oxidizer or oxidiser) can be defined as either:
In both cases, the oxidizing agent becomes reduced in the process.
In simple terms:
A mnemonic for differentiating the reactions is "OIL RIG": Oxidation Is Loss, Reduction Is Gain (of electrons) or "LEO the lion says GER" (Lose Electrons: Oxidation, Gain Electrons: Reduction)
In the above equation, the Iron (Fe) has an oxidation number of 0 before and 3+ after the reaction. For oxygen (O) the oxidation number began as 0 and decreased to 2−. These changes can be viewed as two "half-reactions" that occur concurrently:
Iron III (Fe) has been oxidized because the oxidation number increased and is the reducing agent because it gave electrons to the oxygen (O). Oxygen (O) has been reduced because the oxidation number has decreased and is the oxidizing agent because it took electrons from iron (Fe)
One definition, an oxidizing agent receives - or accepts - electrons from a reagent. In this context, the oxidizing agent is called an electron acceptor. A classic oxidizing agent is the ferrocenium ion [Fe(C5H5)2]+ which accepts an electron to form Fe(C5H5)2. Of great interest to chemists are the details of the electron transfer event, which can be described as inner sphere or outer sphere.
In another more colloquial usage, an oxidizing agent transfers oxygen atoms to the substrate. In this context, the oxidizing agent can be called an oxygenation reagent or oxygen-atom transfer agent. Examples include [MnO4]− permanganate, [CrO4]2− chromate, OsO4 osmium tetroxide, and especially [ClO4]− perchlorate. Notice that these species are all oxides, and in fact, polyoxides. In some cases, these oxides can also serve as electron acceptors, as illustrated by the conversion of [MnO4]− to [MnO4]2−, manganate.
The strict dangerous goods definition of an oxidizing agent are substances that, while in themselves not necessarily combustible, may, generally by yielding oxygen, cause, or contribute to, the combustion of other material. (Australian Dangerous Goods Code 6th Edition) By this definition some materials that are classified as oxidizing agents by analytical chemists are not classified as oxidizing agents in a dangerous goods sense. An example is potassium dichromate which does not pass the dangerous goods test of an oxidizing agent.
|O2 oxygen||Various, including the oxides H2O and CO2|
|O3 ozone||Various, including ketones, aldehydes, and H2O; see ozonolysis|
|I2 iodine||I−, I3−|
|OCl− hypochlorite||Cl−, H2O|
|ClO3− chlorate||Cl−, H2O|
|HNO3 nitric acid||NO nitric oxide|
NO2 nitrogen dioxide
CrO3 chromium trioxide
|Mn2+ (acidic) or MnO2 (basic)|
|H2O2, other peroxides||Various, including oxides and H2O|