In a pit cell, the surrounding surfaces act as which electrode?

• A. The interior pit surfaces
• B. The surrounding surfaces
• C. The bottom of the pit
• D. The electrolyte solution

Answer: (B)

In a pit cell, a small galvanic couple forms: metal dissolves at the pit interior (anodic behavior) while the surrounding metal surfaces serve as the site for reduction reactions (cathodic behavior). The surrounding surfaces provide the cathodic electrode where electrons flow to from the pit and reduction (often oxygen reduction) occurs. So, the surrounding surfaces act as the cathode in the pit cell, completing the circuit through the electrolyte that carries ions between the pit and the surrounding metal.