Why is a sacrificial zinc block (galvanization) effective in preventing the oxidative corrosion of an underground steel (iron) pipeline?
Answer and explanation
Correct answer: C. Zinc is more easily oxidized than iron (more negative reduction potential), acting as a sacrificial anode
The standard reduction potential of Zn2+/Zn is -0.76 V, which is more negative than that of Fe2+/Fe (-0.44 V). Because zinc has a greater tendency to lose electrons (higher oxidation potential), it oxidizes preferentially when electrically coupled to iron: Zn(s) -> Zn2+ + 2 e-. The electrons flow to the iron, maintaining it in a reduced cathodic state (cathodic protection).
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