Why rapid corrosion of iron (Fe) occurs in dilute nitric acid and not inconcentrated nitric acid?
Question
Why rapid corrosion of iron (Fe) occurs in dilute nitric acid and not inconcentrated nitric acid?
Solution
The corrosion of iron in nitric acid is a redox reaction. In dilute nitric acid, the iron is oxidized to Fe2+ ions, while the nitric acid is reduced to nitrogen monoxide (NO).
The reaction is as follows:
3Fe(s) + 8HNO3(aq) → 3Fe(NO3)2(aq) + 2NO(g) + 4H2O(l)
However, in concentrated nitric acid, the situation is different. The concentrated nitric acid is a powerful oxidizing agent and it oxidizes the iron to Fe3+ ions and itself gets reduced to nitrogen dioxide (NO2).
The reaction is as follows:
4Fe(s) + 10HNO3(aq) → 4Fe(NO3)3(aq) + NO2(g) + H2O(l)
In this case, a layer of Fe(NO3)3 forms on the surface of the iron, which protects the iron from further corrosion. This is why iron does not corrode rapidly in concentrated nitric acid.
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