Salt Bridge
Definition and meaning of Salt Bridge in chemistry.
A salt bridge is a laboratory device that connects the oxidation and reduction half-cells of a galvanic cell, allowing spectator ions to flow and maintain overall electrical neutrality.
In more detail
Without a functioning salt bridge, the rapid buildup of positive charge at the anode and negative charge at the cathode would quickly halt the flow of electrons through the external electrical circuit. It typically consists of an inverted U-shaped glass tube filled with a highly concentrated solution of an inert electrolyte, such as potassium chloride or potassium nitrate, often suspended in a rigid agar gel. The mobile ions in the bridge migrate into the respective half-cells to neutralize the local charges generated by the ongoing redox reactions.
Key facts
| Field | Analytical Chemistry |
|---|---|
| Formula | KNO3 or KCl |
| Function | Maintains electrical neutrality |
In a classic Daniell cell, a salt bridge containing a gelled KNO3 solution continuously connects the zinc sulfate and copper(II) sulfate solutions to keep the battery operating.
Frequently asked questions
Why are potassium chloride and potassium nitrate commonly selected as electrolytes in salt bridges?
Their specific cations and anions possess very similar ionic mobilities, which heavily minimizes unwanted liquid junction potentials at the interfaces.