Oxidation is a reaction where an atom, ion, or molecule loses electrons while reduction corresponds to an atom, ion or molecule gaining electrons. 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 so they are generally known as oxidation-reduction reactions or redox reactions. For example, combustion and corrosion are oxidation-reduction reactions.
Difference between Oxidation and Reduction in tabular form
|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|
|agents involved||The oxidizing agent is the one that traps the electrons. |
The oxidized agent is the one that loses 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: |
CH 3 OH→ CH 2 O +H 2
Passage of the magnesium atom Mg to magnesium ion Mg 2+
|Silver formation from silver ions. |
Passage of molecular oxygen O 2 to oxide O -2
What is oxidation?
Oxidation is the loss of electrons by a molecule, atom, or ion. An element is oxidized 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 greater 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. At that time, all reactions where oxygen was a reactant were 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 overall reaction where the element undergoing oxidation is presented and the number of electrons removed from it on the right hand side of the products. 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 the aluminum ion with a +3 oxidation state; 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) + O 2 (g)→ 2MgO(s),
oxygen causes magnesium to lose electrons, therefore oxygen is the oxidizing agent and magnesium is the chemical being oxidized. Metals, such as iron, copper and magnesium are easily oxidized.
Examples of oxidation reactions
- The dehydrogenation of methanol to formaldehyde:
CH3OH → H2C = O
- The magnesium atom loses two electrons and becomes the magnesium ion:
Mg(s)→Mg 2+ (s) +2e –
- The transformation of alcohol into vinegar is an oxidation reaction:
CH3CH2OH → CH3COOH _ _ _ _
What is reduction?
Reduction is the gain of electrons by a molecule, atom, or ion. An element is reduced when it gains electrons in a reaction. 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 exchange of copper ion, with oxidation state 2+, passes to solid copper, with oxidation state 0:
Cu 2+ (aq) + 2e – → Cu(s)
The word “reduction” comes from the Latin reduco, which means “to restore.” The metal extraction process was considered as 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 overall reaction where the element undergoing reduction and the number of electrons it receives on the left hand side of the reactants are presented. For example, in the corrosion reaction of aluminum:
4Al + 3O 2 → 2Al 2 O 3
the partial oxygen reduction equation is:
OR 0 + 2e -2 → OR -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 of -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) + O 2 (g)→ 2MgO(s),
magnesium causes oxygen to gain electrons, so magnesium comes to function 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 become an oxide ion:
O 2 (g) +4e – →2O 2-
- The formation of silver from silver ions:
Ag + (aq) +e – →Ag(s)
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