Question

Which of the following reactions occurs when iron is immersed in (oxygenated) sea water?

(a) Fe==>Fe^+2+2e, 2H^++2e==>H2

(b) Fe==>Fe^+2+2e, O2+2H2O+4e==>4OH^–

(c) Fe^+2+2e==>Fe^+2, 4H^++O2+4e==>2H2O

(d) Fe^+2+2e==>Fe^+2, 2H^++2e==>H2

This question was posed to me in an interview for internship.

Question is taken from Corrosion Principles topic in division Corrosion Principles of Corrosion Engineering

Answer 1

Correct choice is (b) Fe==>Fe^+2+2e, O2+2H2O+4e==>4OH^–

The explanation is: Iron dissolution (anodic reaction) Fe==>Fe^+2+2e. Oxygenated hydrogen reaction (cathodic reaction) in a neutral solution (pH=7) is O2+2H2O+4e==>4OH^–.