Explain how rusting of iron is envisaged as setting up of an electrochemical cell.

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Solution

Rusting of iron
In process of rusting, water molecules present at the layer of iron react with oxides of the like $C O_{2}, S O_{2}$ etc. to form acids which dissociate to give $H^{+}$ ions.

$H_{2} O + C O_{2} \to H_{3} C O_{3}$

$H_{2} C O_{3} ⇌ 2 H^{+} + C O_{3}^{2 -}$

Reaction at anode:

In presence of $H^{+} ions,$ iron converts to $F e^{2 +}$ , so this part acts as anode.

$2 F e (s) \to 2 F e^{2 +} (a q) + 4 e^{-}$

Reaction at Cathode:

Electrons released at anodic spot move through the metals and go to another spot on the metal and reduce oxygen.
This spot acts as cathode.

$O_{2} (g) + 4 H^{+} (a q) + 4 e^{+}$

Reaction at Cathode:
Electrons released at anodic spot move through the metals and go to another spot on the metal and reduce oxygen.
This spot acts as cathode.

$O_{2} (g) + 4 H^{+} (a q) + 4 e^{+} (a q) \to 2 H_{2} O (l)$

The overall reaction:

$2 F e (s) + O_{2} (g) + 4 H^{+} (a q) \to 2 H_{2} O (l) + 2 F e^{2 +} (a q)$

As shown above, we can see that rusting of iron sets up an electrochemical cell.

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Explain how rusting of iron is envisaged as setting up of an electrochemical cell. 1 marks.

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