What is the purpose of a salt bridge in an electrochemical cell?

The purpose of a salt bridge in an electrochemical cell is to connect the two half-cells and maintain electrical neutrality within them. In an electrochemical cell, oxidation occurs at the anode and reduction occurs at the cathode, resulting in the flow of electrons through an external circuit. As the reaction proceeds, ions are produced or consumed, which can lead to an imbalance of charge in the two half-cells.

The salt bridge contains an electrolyte, often a salt solution, that allows ions to move between the two half-cells. This movement of ions compensates for the charge imbalance, preventing the buildup of excess positive charge in one half-cell and excess negative charge in the other. By maintaining charge neutrality, the salt bridge ensures the continued flow of electrons through the external circuit. Without it, the cell would quickly reach a state of equilibrium, halting the electrochemical reaction and the generation of electrical energy.