Salt Bridge
Definition
The tube of salt solution connecting a battery's two halves: it lets ions flow to balance charge while keeping the solutions from mixing.
Technical definition
A salt bridge is an inverted U-tube or porous barrier containing an inert electrolyte, such as KNO3, that connects two half-cells. It maintains electrical neutrality by allowing ion migration while preventing bulk mixing of the half-cell solutions.
Example
In the Daniell cell, a KNO3 salt bridge lets K+ drift toward the copper half-cell and NO3- toward the zinc half-cell as the reaction proceeds.
Common confusion
The salt bridge carries IONS, not electrons. Electrons travel through the external wire; the bridge's job is charge balance so the reaction does not choke on its own charge buildup.