Amphoteric materials are metals that are chemically vulnerable in both acidic and alkaline environments and can be affected at the cathode in a galvanic corrosion cell.

• A. Amphoteric materials
• B. Passive metals
• C. Noble metals
• D. Nonconductive metals

Answer: (A)

Amphoteric behavior means a metal’s oxide or hydroxide can dissolve in both acidic and basic environments. That makes the protective film on these metals unstable across a wide pH range, so the metal tends to corrode whether the solution is strongly acidic or strongly alkaline. In a galvanic couple, the environment that dissolves the film can expose the surface, and the metal at the cathode can also be attacked if the protective layer isn’t stable there. For example, aluminum or zinc form films that dissolve to aluminate or other complexes in base, and dissolve to solvated ions in acid, removing protection. Because the protective layer isn’t robust in either extreme, amphoteric metals are vulnerable in both environments and can be affected at the cathode in galvanic corrosion as well.