What is the role of a salt bridge?

The role of a salt bridge is to maintain electrical neutrality by allowing the flow of ions between two half-cells in an electrochemical cell. In electrochemistry, a salt bridge is an important device used in galvanic or voltaic cells. Without a salt bridge, the reaction would stop because charges would build up and prevent further flow of electrons.

Definition

A salt bridge is a U-shaped tube filled with an electrolyte solution such as potassium chloride (KCl) or potassium nitrate (KNO₃), which connects the two half-cells of a galvanic cell.

Functions of a Salt Bridge

• Maintains Electrical Neutrality: Prevents the buildup of positive or negative charges.
• Allows Ion Flow: Completes the circuit by allowing ions to move between half-cells.
• Prevents Mixing: Stops the two solutions from mixing directly, which could destroy the cell.
• Ensures Continuous Reaction: Without it, the redox reaction would stop quickly.

Working Example

In a Daniell cell:

• Zinc (Zn) oxidizes to Zn²⁺ ions in one half-cell.
• Copper (Cu²⁺) reduces to copper metal in the other half-cell.
• The salt bridge allows Cl^- and K⁺ ions to flow, balancing the charge.