Question

An iron storage tank is placed in the ocean with no cathodic protection. a. What is the electrolyte in this reaction? b. As the iron tank rusts, does it act as an anode or cathode? Explain.

Answer 1

Answer:

Iron is being oxidized at the anode and water is acting as the electrolyte.

Explanation:

When iron is exposed to oxygen and water , the rusting of iron takes place.

The reaction taking place at anode : Oxidation of iron.

${anode:}\;\text{Fe}(s)\;{\longrightarrow}\;\text{Fe}^{2+}(aq)\;+\;2\text{e}^{-}$

The reaction taking place at cathode : Reduction of oxygen in the air.

${cathode:}\;\text{O}_2(g)\;+\;4\text{H}^{+}(aq)\;+\;4\text{e}^{-}\;{\longrightarrow}\;2\text{H}_2\text{O}(l)$  

The overall reaction:

${overall:}\;2\text{Fe}(s)\;+\;\text{O}_2(g)\;+\;4\text{H}^{+}(aq)\;{\longrightarrow}\;2\text{Fe}^{2+}(aq)\;+\;2\text{H}_2\text{O}(l)$

The rust that is hydrated iron(III) oxide can form iron(II) ions which can react further with oxygen.

$4\text{Fe}^{2+}(aq)\;+\;\text{O}_2(g)\;+\;(4\;+\;2x)\;\text{H}_2\text{O}(l)\;{\longrightarrow}\;2\text{Fe}_2\text{O}_3{\cdot}x\text{H}_2\text{O}(s)\;+\;8\text{H}^{+}(aq)$

Thus, from the above reactions ,

Iron is being oxidized at the anode and water is acting as the electrolyte.