Question

A common method to retard rusting is to have a significant amount of a second metallic element in electrical contact, usually connected by a wire, with the bridge, building, ship, etc. This second metallic element is oxidized in preference to the iron in the building or other structure. Which of these metallic elements are good choices to use on an iron structure as a preferred oxidation site?

A. Mg, Au, Zn

B. Zn

C. Au

D. Cu

E. Al, Cu

F. Mg, Al, Zn

G. Al

H. Mg

Answer 1

answer: (F) Mg, Al, Zn

metallic elements whose reduction potential is lower than Iron must help and act as a first preferred oxidation site than iron. Because tendency of that metallic to get oxidized is more than the iron.

Cathodic protection is a technique used to prevent rusting and is often used in concrete-encased steel and storage tanks by supplying an electrical charge that suppresses the electrochemical reaction that causes rusting. A sacrificial anode that can be more easily corroded – commonly made of zinc, aluminum or magnesium – is attached, making the steel or iron act as the cathode in the electrochemical reaction.

Element Electrode Reaction (Reduction) Standard Electrode Reduction potential E^o, volt

Mg Mg²⁺ + 2e^- Mg   -2.37

Al Al³⁺ + 3e^- Al -1.66

Zn Zn²⁺ + 2e^- Zn -0.7628

Fe Fe²⁺ + 2e^- Fe -0.44

so reduction potential of iron is greater than other three so they can be used as sacrificing metallic elements or preferred oxidation site