In a salt-bridge–compatible cell, which direction do ions move in the salt bridge during a galvanic reaction?

• A. Anions migrate toward the anode compartment and cations toward the cathode.
• B. Anions move toward the cathode and cations toward the anode.
• C. Anions migrate to the cathode and cations to the anode.
• D. Ions do not move in a salt bridge.

Answer: (C)

The key idea is charge balance through the salt bridge. As the galvanic cell operates, oxidation at the anode releases positive charge into that compartment (for example, metal atoms become metal ions in solution). To prevent a buildup of positive charge, negative ions from the bridge migrate into the anode side to neutralize that excess positive charge. At the cathode, reduction removes positive charge from the solution (positive metal ions are pulled out as metal is plated), which makes the cathode side relatively more positive in needing balance; therefore positive ions from the bridge move into the cathode compartment to compensate. In short, anions move toward the anode, and cations move toward the cathode, to maintain electrical neutrality as the redox reaction proceeds.