Question

How are redox reactions involved in corrosion?

Answer 1

Hint: Corrosion involves chemical change that occurs when the metal is exposed to any external conditions which affects the surface. Redox reaction involves a transfer of electrons between two species.

Complete answer:
- Corrosion is a naturally occurring process which involves changes in the physical and chemical properties of the refined metal which converts to a more stable form that is either oxides, sulfides or may be hydroxides.
- Corrosion occurs due to prolonged exposure to air which consists of a mixture of several gases.
- Rusting of iron is a common example of corrosion we see in our daily lives.
- Redox reaction is a type of reaction where oxidation and reduction both take place simultaneously.
- Rusting of iron is an example of a redox reaction. During the process of rusting, iron metal reacts with atmospheric oxygen in presence of moisture and forms iron oxide which is also called rust.
- This is an oxidation reaction where oxygen acts as an oxidizing agent.
- Since oxygen molecules in the process also combine henceforth with the iron, this is a reduction reaction, where iron acts as a reducing agent.
- The rusting process decreases the quality of iron.
- In the process of corrosion, in galvanic cells, iron is acting at anode where it gets oxidized to iron ions. Here, oxygen is at the cathode and is being reduced to water.
At cathode-
$O_{2}+4H^{+}+4e^{-}\rightarrow 2H_{2}O$
$E^{\circ }=1.23V$
At anode-
$Fe\rightarrow Fe^{2+}+2e^{-}$
$E^{\circ }=-0.45V$
The overall reaction would be-
$2Fe+O_{2}+4H^{+}\rightarrow 2Fe^{2+}+2H_{2}O$
$E^{\circ }=1.68V$
- Hence, corrosion involves redox reactions.

Note:
Corrosion is a process that occurs due to external factors and thus the inside of the object is not affected but the physical and chemical change occurs on the surface of the metal.