What is corrosion? Write the chemistry behind the formation of rust

1.	What is corrosion? Write the chemistry behind the formation of rust
Answer» (i) The slow and steady destruction of a metal by chemical or electro chemical reaction with the environment. (ii) When the surface of iron is exposed to moisture and other gases present in the atmosphere, the following chemical reaction takes place. Fe → Fe²⁺ + 2e^- O₂ + 2H₂O + 4e^- → 4OH^- O₂ + 4H⁺ + 4e^- → 2H₂O The Fe²⁺ ions are oxidised to Fe³⁺ ions. The Fe³⁺ ions combine OH^- ions to form Fe(OH)₃ . This becomes rust which is hydrated ferric oxide with the formula Fe₂O₃.xH₂O. It is a reddish brown substance.

Answer»

(i) The slow and steady destruction of a metal by chemical

or electro chemical reaction with the environment.

(ii) When the surface of iron is exposed to moisture and other gases present in the atmosphere, the following chemical reaction takes place.

Fe → Fe²⁺ + 2e^-

O₂ + 2H₂O + 4e^- → 4OH^-

O₂ + 4H⁺ + 4e^- → 2H₂O

The Fe²⁺ ions are oxidised to Fe³⁺ ions.

The Fe³⁺ ions combine OH^- ions to form Fe(OH)₃ . This becomes rust which is hydrated ferric oxide with the formula Fe₂O₃.xH₂O. It is a reddish brown substance.

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