We explain what oxidation is and how it occurs. Also, the types of oxidation, oxidation number and reduction.
What is oxidation?
It is commonly called oxidation to chemical reactions in which oxygen combines with other substances, forming molecules called oxides. This is particularly prevalent in the world of metals, although by no means exclusive to them. In chemistry oxidation is called the chemical phenomenon in which a atom, molecule or ion loses one or more electrons, thus increasing its positive charge.
As oxygen is an element that usually accepts these electrons, this type of reaction was called reduction-oxidation reactions, oxide-reduction reactions or redox reactions, but it is also important to clarify that there may be redox reactions in which oxygen does not participate. Take into account that the name oxygen comes from the Greek oxys, "Acid"; Y genos, "Producer": that is, oxygen is so named because it corrodes the metals, just as he does acid.
Most cases of oxidation involve oxygen, but it can also occur in its absence. And similarly, oxidation and reduction always occur together and simultaneously.
Two elements that exchange electrons always participate in them:
- The oxidizing agent. It is the chemical element that captures the electrons transferred, that is, it receives them and increases its negative charge. This is called having a lower oxidation state, or in other words, being reduced.
- The reducing agent. Is he chemical element that gives up or loses the transferred electrons, increasing their positive charge. This is called having a higher oxidation state, or in other words, being oxidized.
So: the oxidizing agent is reduced by the reducing agent, while the reducing agent is oxidized by the oxidizing agent. Thus, we have to to oxidize is to lose electrons, while to reduce is to gain electrons.
These processes are common and everyday, in fact they are essential for the life: the living creatures we obtain chemical energy thanks to similar reactions, such as the oxidation of glucose.
Types of oxidation
There are two known types of oxidation:
- Slow oxidation. It is produced by the oxygen contained in the air or in the Water, the one that makes metals lose their shine and suffer corrosion being exposed to too long environment.
- Fast oxidation. It occurs in violent chemical reactions such as combustion, generally exothermic (they release energy in the form of heat), and is produced mainly in organic elements (containing carbon and hydrogen).
Oxidation number
Chemical elements have an oxidation number, which represents the number of electrons that this element puts into play when it comes to associating with others to form a given compound.
This number is almost always integer, and can be positive or negative, depending on whether the element in question loses or gains electrons during the reaction, respectively.
For example: an element with oxidation number +1 tends to lose an electron when reacting with others, while one with number -1 tends to gain an electron when it reacts with others to form a compound. These oxidation numbers can have values as high as electrons involved in the process, and in some cases they usually depend on what elements they are reacting with.
Free elements, that is, that are not combined with others, have oxidation number 0. On the other hand, some examples of oxidation numbers are:
The oxidation number of oxygen is -2 (O-2), except for peroxides that have -1 (O2-2) and superoxides that have -½ (O2–).
The oxidation number of metallic elements is positive. For example: sodium ion (Na +), magnesium ion (Mg2 +), iron ions (Fe2 +, Fe3 +)
The oxidation number of hydrogen is +1 (H +), except for metal hydrides which has -1 (H–).
Oxidation and reduction
Oxidation and reduction are inverse and complementary processes, always occurring at the same time. In the first, electrons are lost and in the second they are gained, thus varying the electric charges of the elements.
These reactions are often used in industrial and metallurgical processes, for example, to reduce minerals obtaining pure metallic elements such as iron or aluminum; or in the combustion of organic matter, as in electricity generation plants or even in jet engines.