Chemistry - Topic taught 20 April

Electrochemistry is the branch of chemistry which deals with the relationship between electrical energy and chemical energy and inter-conversion of one form into another.
2. An electrochemical cell consists of two metallic electrodes dipped in electrolytic solutions. The cells are of two types:
(a) Electrolytic cells (b) Galvanic cells
3. A galvanic cell consists of two half cells. Each half cell contains an electrolytic solution and a metallic electrode.The electrode at which- oxidation takes place is called an anode and the electrode at which reduction takes place is called the cathode. The half-cells are separated from each other by means of a porous pot or a salt bridge.

What is Salt Bridge?

A salt bridge is a device used in an electrochemical cell for connecting its oxidation and reduction half cells wherein a weak electrolyte is used. In other words, a salt bridge is a junction that connects the anodic and cathodic compartments in a cell or electrolytic solution.

The salt bridge usually consists of a strong electrolyte which is further made up of ions. For example, AgNO3, KCl, etc. Salt bridges are generally used in a galvanic cell such as a voltaic cell or Daniel cell.

Salt Bridge Function

The main function of a salt bridge is to help maintain the electrical neutrality within the internal circuit. It also helps in preventing the cell from taking its reaction to equilibrium. If salt bridges are absent or if they are not used then the reaction will likely continue and the solution in one-half electrodes will gather a negative charge. Similarly, in the other half, electrodes would accumulate a positive charge. This will further result in the stoppage of the reaction and no electricity will be produced.

Therefore, a salt bridge basically helps in preventing the accumulation of positive and negative charges around the respective electrodes and further allowing a smooth reaction to take place. It also helps in the continual flow of electrons. However, the purpose of a salt bridge is not to move electrons from the electrolyte; rather it’s to maintain charge balance because the electrons are moving from one-half cell to the other.

Salt bridge prevents the diffusion or mechanical flow of solution from one-half cell to another.

It prevents or minimizes the liquid-liquid junction potential. (Potential arises between two solutions when they are in contact with each other).

Salt bridge acts as an electrical contact between two half cells.