account for the following:- 1) Alkaline medium inhibts the rusting of iron? 2) Iron does not rust even if the zinc coating is broken in a galvanized iron pipe ? 3) Can we use Al in place of Zn for cathodic protection of iron against rusting .comment?

Asked by rohit varshney | 4th Mar, 2011, 06:53: PM

Expert Answer:

Dear Student
In order that rust should be formed iron must go into solution and hydrogen must be given off in the presence of oxygen or certain oxidizing agents. This presumes electrolytic action, as every iron ion that appears at a certain spot demands the disappearance of a hydrogen ion at another, with a consequent formation of gaseous hydrogen. The gaseous hydrogen is rarely visible in the process of rusting, owing to the rather high solubility and great diffusive power of this element. Substances which increase the concentration of hydrogen ions, such as acids and acid salts, stimulate corrosion, while substances which increase the concentration of hydroxyl ions inhibit it.
(ii) According to the elctrochemical series Zn2+ (-0.76v) has more reducing power than Fe2+(-0.44v). So, Fe will not loose electron in the presence of zinc.
(iii)  No,  Al cant be used in place of Zn for cathodic protection of iron rusting.
We hope that clarifies your query.

Answered by  | 5th Mar, 2011, 01:02: PM

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