Final answer:
The purpose of a salt bridge in galvanic cells is to complete the electrical circuit and to maintain electrical neutrality by enabling the flow of ions between compartments, thus preventing charge buildup and allowing the redox reaction to continue.
Step-by-step explanation:
The salt bridge plays a vital role in galvanic cells by allowing the electrical circuit to be completed and ensuring that electrical neutrality is maintained in the solutions involved in the redox reactions. It consists of a nonreactive electrolyte solution through which ions move, balancing the charges in the separate compartments of the cell. For example, in a Cu-Ag galvanic cell, as oxidation occurs at the anode, the metal loses electrons and the solution becomes positively charged. Similarly, reduction at the cathode absorbs cations from the solution making it negatively charged. The salt bridge compensates for these changes by allowing the migration of anions into the anode compartment and cations into the cathode compartment, thereby preventing charge buildup and permitting the reaction to continue undisturbed.
The electrolyte in the salt bridge can be of any inert ion pair that will not react under the cell's conditions. This setup is crucial in applications like cathodic protection, where a more active metal is connected to the metal needing protection; the salt bridge here can be natural, like seawater or groundwater, completing the circuit and enabling oxidation to occur at the anode and not the protected metal.