These electrodes are coated with finely divided electrodeposited platinum black. It is the resistance that is measured with an alternating current to minimize electrolysis. The catalytic properties of the platinum black allow what ever electrolysis there is to occur so rapidly in both directions that there is no buidup of products. The cell constant is not measured geometrically but by measuring the resistance of a sample solution of known conductivity, usually potassium chloride. With respect to this behavior there are two classes, strong and weak electrolytes, that have different characteristics.
Weak electrolytes vary in a non-linear manner.
They dissociate to a greater extent with increasing dilution. C. The dissociation constant can be expressed as where a is the degree of dissociation. Arrhenius showed that a can be given as Combining the last two equations gives Independent migration of ions Each individual ion of an electrolyte contributes independently to molar conductivity. It is written in terms of infinite dilution because it is only under such conditions, with minimum ion-ion interaction, that the law strictly holds. It then applies to both strong and weak electrolytes.