In a galvanic couple, which factor primarily determines which metal corrodes preferentially?

• A. Electrode potential difference
• B. Temperature
• C. Flow rate
• D. Color

Answer: (A)

In a galvanic couple, a potential difference between the two metals in an electrolyte creates the driving force for corrosion. The metal with the lower electrode potential is the one that tends to oxidize, so it becomes the anode and corrodes preferentially. The other metal, with the higher potential, acts as the cathode and is protected from corrosion by the flow of electrons. The size of that potential difference sets how strong the driving force is, so a larger difference leads to faster preferential corrosion of the anodic metal. Temperature and flow rate can affect the overall rate of corrosion but do not determine which metal corrodes; color has no relevance here. For example, in a zinc–copper pair in an electrolyte, zinc (the less noble metal) corrodes while copper remains relatively protected.