The oxidation is a reaction where an atom, ion or molecule loses electrons, while the reduction corresponds to the electron gain of an atom, ion, or molecule. Both oxidation and reduction depend on the change in the oxidation state of the atom, that is, the difference in charge of the atom in a reaction.
Oxidation and reduction reactions always occur simultaneously, so they are generally known as oxide-reduction reactions or redox reactions. For example, combustion and corrosion are oxide-reduction reactions.
|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 electron gain.|
|Partial equation||Zn → Zn2+ + 2e–||With2++ 2e–→ Cu|
|Oxidation state||It increases||It decreases|
The oxidizing agent is the one that traps the electrons.
The rusty agent is the one that loses electrons.
The reducing agent is what provides the electrons.
The reduced agent is the one that gains the electrons.
Oxidation of methanol to formaldehyde:
CH3OH → CH2O + H2
Passage of the Mg magnesium atom to Mg magnesium ion2+
Silver formation from silver ions.
Molecular oxygen passage O2 to oxide O-2
What is oxidation?
Oxidation is the loss of electrons by a molecule, atom, or ion. An element oxidizes when in a reaction it loses electrons; this is verified by increase in oxidation state of the atom. The higher the oxidation state of an atom, the higher the degree of oxidation.
The word “oxidation” was first used in the 18th century thanks to the work of French chemist Antoine Lavoisier when he identified oxygen in the air. By that time, any reaction where 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 is presented and the amount of electrons that are removed from the right side of the products. For example, in the corrosion reaction of aluminum:
4Al + 3O2 → 2Al2O3
the partial oxidation equation of aluminum is:
In the0→ Al+3 + 3e–
In this case, the oxidation state of aluminum in the elemental state is 0 (zero) and it is oxidized to aluminum ion with an oxidation state of +3; that is, it increases the oxidation state of aluminum.
Oxidizing and oxidizing agents
An oxidizing agent is one that causes another chemical to rust. For example, when magnesium reacts with oxygen to form magnesium oxide:
2Mg (s) + O2(g) → 2MgO (s),
oxygen causes magnesium to lose electrons, so oxygen is the oxidizing agent and magnesium is the rusty chemical. Metals, such as iron, copper, and magnesium, are easily corroded.
Examples of oxidation reactions
- The dehydrogenation of methanol to formaldehyde:
CH3OH → H2C = O
- The magnesium atom loses two electrons and is transformed into the magnesium ion:
Mg (s) → Mg2+(s) + 2e–
- The transformation of alcohol into vinegar is an oxidation reaction:
CH3CH2OH → CH3COOH
What is reduction?
The reduction is the electron gain by a molecule, atom, or ion. An element is reduced when in a reaction it gains electrons. This is verified by the decrease in oxidation state. The smaller the oxidation state of an atom, the greater the degree of reduction.
For example, the change of copper ion with oxidation state 2+ changes to solid copper with oxidation state 0:
With2+(ac) + 2e– → Cu (s)
The word “reduction” comes from Latin I reduce which means “restore.” The process of extracting metals was considered the recovery of the 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 undergoing reduction is presented and the amount of electrons it receives on the left side of the reactants. For example, in the corrosion reaction of aluminum:
4Al + 3O2 → 2Al2O3
the partial oxygen reduction equation is:
O0 + 2e-2 → O-2
In this case, the oxidation state of oxygen in the molecular state is 0 (zero) and is reduced to oxide ion with an oxidation state -2; that is, the oxidation state of oxygen goes from 0 to -2, decreases.
Reducing and reduced 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 acts 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:
O2(g) + 4e–→ 2O2-
- The formation of silver from silver ions:
Ag+(ac) + e–→ Ag (s)
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