The purpose of the salt bridge is to keep the solutions electrically neutral and allow the free flow of ions from one cell to another. Without the salt bridge, positive and negative charges will build up around the electrodes causing the reaction to stop.

Does the salt bridge matter?

It is desirable to have a salt bridge that can overcome the possibility of a large charge buildup. To achieve this and not deplete the ions in the salt bridge over the course of the reaction, the KCl is typically at a high concentration, usually 4 M.

What does a salt bridge prevent?

Salt bridge prevents the mechanical flow or diffusion of a solution from one-half cell to another. It also minimizes or prevents the liquid-liquid junction potential. (Potential arises between the two solutions when they are in contact with each other) The bridge acts as an electrical contact between the two half cells.