Explain the Liquid junctions?
Some galvanic cells contain two electrolyte solutions with different compositions. These solutions must be separated by a porous barrier or some other kind of junction in order to prevent rapid mixing. At this liquid junction in the zero-current cell, there is in general a liquid junction potential caused by diffusion of ions between the two bulk electrolyte phases. To understand this phenomenon, imagine the situation that would exist at the junction if both solution phases had the same electric potential. An ion species with different chemical potentials in the two solutions would spontaneously diffuse across the junction in the direction of lower chemical potential. Different ions would diffuse at different rates, resulting in a net charge transfer across the junction and an electric potential difference. It is this electric potential difference in the equilibrium state of the cell that prevents further net charge transfer under zero-current conditions. The liquid junction may consist of a bridging solution in a salt bridge. A commonly used kind of salt bridge is a glass tube filled with gel made from agar and concentrated aqueous KCl or KNO3; this type of liquid junction is believed to reduce the liquid junction potential to several millivolts or less.