Solutions of different concentrations, or containing
different substances, when in contact develop a potential across the interface
called a junction potential. This ‘potential’ results from different ions
having different migrating rates due to size, weight and shape differences in
the respective ions. Such potentials develop across all solution interfaces and
depend on ionic mobility’s and the concentration gradient.
Although junction potentials cannot be eliminated, they can be minimized by employing a concentrated electrolyte solution, or salt bridge, between the two cells. A saturated potassium chloride solution (>4M) has only a 4%difference between the mobility of the potassium ion and that of the chloride ion. Most liquid junction potentials can be reduced in this manner to less than 4mv and sometimes less than 1 mv.