Between a metal with a higher standard reduction potential and a metal with a lower one, which is reduced at the cathode?

• A. The metal with higher standard reduction potential
• B. The metal with lower standard reduction potential
• C. The metal that is more reactive
• D. The metal that is anode

Answer: (A)

The key idea is that the cathode is the site of reduction. A metal with a higher standard reduction potential is more eager to gain electrons than one with a lower potential. When two metals compete for reduction at the cathode, the one with the higher E°red will accept electrons and be deposited or stayed in its reduced form at the cathode. The other metal, with the lower E°red, is less favored to gain electrons and is more likely to be oxidized at the anode, or simply not reduced at the cathode under the same conditions.

So, the metal with the higher standard reduction potential is reduced at the cathode. For context, in a Daniell-type cell, the species with the more positive E°red reduces at the cathode while the other serves as the anode and is oxidized. The idea that it’s simply the more reactive metal or the metal that is the anode doesn’t fit the instruction about where reduction occurs.