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
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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
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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 .