Measurement of electrode potential in a cell
o Salt bridge is an inverted U-tube like structure.
o The tube is filled with concentrated solution of an inert electrolyte.
o The electrolyte does not undergo any sort of chemical reaction nor does it reacts with concentrated solution in the two half cells.
o Most of the time salts like KCl, KNO3, NH4NO3 are used as electrolyte. o
Salt bridge is constructed by filing the U-tube with a mixture prepared by mixing agar-agar or gelatine with a hot concentrated solution of the electrolyte. o
The apparatus is then cooled and consequently the solution fixes within the U-tube in the form of gel.
o This prevents the intermixing of fluids. o
o
o
The either ends of the tube are then sealed using cotton wool in order to reduce diffusion.
The main advantage of suing this bridge is that it prevents the arousal of potential difference( also called liquid junction potential) when two solutions are in contact with each other.
It completes the electrical circuit as it connects the electrolytes in the two half cells.
o It avoids the chances of diffusion of solutions between the half cells. o
It maintains electrical neutrality by providing a path for the movement of ions.
Measurement of electrode potential in a cell
o
o
The electrode is connected to a standard hydrogen electrode( SHE) to constitute a cell.
The electrode forming the negative terminal of the cell is allotted negative value of electrode potential whereas the electrode forming the positive terminal of the cell is allotted a positive value of electrode potential.