The half-reaction 2H+ + 2e- → H2 occurs at which electrode?

• A. Anode
• B. Cathode
• C. Either electrode
• D. Neither electrode

Answer: (B)

At the cathode. The half-reaction given involves hydrogen ions gaining electrons to form hydrogen gas, which is a reduction process (electrons are being added). In electrochemical cells, reduction occurs at the cathode, while oxidation happens at the anode. So the site where this proton-to-hydrogen conversion happens is the cathode, regardless of whether the cell is galvanic or electrolytic. Hydrogen gas commonly evolves at the cathode in acidic solutions because protons are reduced there.