The oxidation is a reaction where an atom, ion or molecule loses electrons while the reduction corresponds to the gain of electrons from an atom, ion or molecule. Both oxidation and reduction depend on the change in the oxidation state of the atom, that is, on the difference in the charge of the atom in a reaction.
Oxidation and reduction reactions always occur simultaneously for what are generally known as oxidation-reduction reactions or redox reactions . For example, combustion and corrosion are oxidation-reduction reactions.
| Oxidation | Reduction | |
|---|---|---|
| Definition | Semi reaction where an atom, ion or molecule loses electrons. | Semi reaction where an atom, ion or molecule gains electrons. |
| Key concept | Oxidation is loss of electrons. | Reduction is gain of electrons. |
| Partial equation | Zn→ Zn 2+ + 2e – | Cu 2+ + 2e – → Cu |
| Oxidation state | Increases | Decreases |
| Agents involved | The oxidizing agent is the one that traps the electrons. The oxidized agent is the one that loses the electrons. | The reducing agent is the one that provides the electrons. The reduced agent is the one that gains the electrons. |
| Examples | Oxidation of methanol to formaldehyde: CH3OH→ CH2O +H2 Change from the Mg magnesium atom to the Mg 2+ magnesium ion | Silver formation from silver ions. Transition of molecular oxygen O 2 to oxide O -2 |
Index
What is oxidation?
Oxidation is the loss of electrons by a molecule, atom, or ion. An element oxidizes when it loses electrons in a reaction; this is verified by the increase in the oxidation state of the atom. The higher the oxidation state of an atom, the higher the degree of oxidation.
The word “oxidation” was used for the first time in the 18th century thanks to the work of the French chemist Antoine Lavoisier when he identified oxygen in the air. At that time, any reaction in which oxygen was a reactant was described as oxidation reactions. Today we know that not all oxidation reactions involve the participation of oxygen.
Partial oxidation equation
A partial oxidation equation is the part of the general reaction where the element that undergoes oxidation and the amount of electrons that are withdrawn on the right side of the products are present. For example, in the corrosion reaction of aluminum:
4Al + 3O 2 → 2Al 2 O 3
The partial oxidation equation for aluminum is:
Al 0 → Al +3 + 3e –
In this case, the oxidation state of aluminum in its elemental state is 0 (zero) and it is oxidized to aluminum ion with an oxidation state +3; that is, the oxidation state of aluminum increases.
Oxidizing and oxidizing agents
An oxidizing agent is one that causes another chemical to be oxidized. For example, when magnesium reacts with oxygen to form magnesium oxide:
2Mg(s) + O2(g)→ 2MgO(s),
oxygen causes magnesium to lose electrons, therefore oxygen is the oxidizing agent and magnesium is the oxidized chemical. Metals, such as iron, copper, and magnesium are easily oxidized.
Examples of oxidation reactions
- Dehydrogenation of methanol to formaldehyde:
CH3OH → H2C=O
- The magnesium atom loses two electrons and becomes the magnesium ion:
Mg(s)→Mg2+(s) +2e–
- The transformation of alcohol into vinegar is an oxidation reaction:
CH 3 CH 2 OH → CH 3 COOH
What is reduction?
Reduction is the gain of electrons by a molecule, atom, or ion. An element is reduced when in a reaction it gains electrons. This is verified by the decrease in the oxidation state . The lower the oxidation state of an atom, the greater the degree of reduction.
For example, the change of copper ion, with oxidation state 2+, becomes solid copper, with oxidation state 0:
Cu 2+ (ac) + 2e – → Cu (s)
The word “reduction” comes from the Latin reduco which means “to restore”. The metal extraction process was seen as the recovery of metal from its mineral compounds, such as iron from iron oxide or copper from copper (II) oxide.
Partial reduction equation
A partial reduction equation is the part of the general reaction where the element that undergoes reduction and the amount of electrons it receives on the left side of the reactants appear. For example, in the corrosion reaction of aluminum:
4Al + 3O 2 → 2Al 2 O 3
the partial oxygen reduction equation is:
O 0 + 2e -2 → O -2
In this case, the oxidation state of oxygen in its molecular state is 0 (zero) and it is reduced to an oxide ion with an oxidation state -2; that is, the oxidation state of oxygen goes from 0 to -2, it decreases.
Reducing and reducing agents
A reducing agent causes another chemical to be reduced. For example, when magnesium reacts with oxygen to form magnesium oxide:
2Mg(s) + O2(g)→ 2MgO(s),
magnesium causes oxygen to gain electrons, so magnesium works as a reducing agent while oxygen is reduced.
Metals tend to lose electrons so they act as reducing agents.
Examples of reduction reactions
- Molecular oxygen gains four electrons to transform into an oxide ion:
O 2 (g) + 4e – → 2O 2-
- The formation of silver from silver ions:
Ag + (ac) + e – → Ag (s)
You may also be interested in:
