Generally speaking, the classification of a substance as a non-clcctrolytc or as an clcctrolytc is based on the conductance of its aqueous solution. Aqueous solutions of non-clcctrolytcs do not conduct an electric current to any greater extent than pure water docs, whereas aqueous solutions of electrolytes conduct an clcctric current and undergo electrolysis. Weak clcctrolytcs give solutions which arc relatively poor conductors bccausc of a limited degree of ionization. On the other hand, aqueous solutions of strong clcctrolytcs readily conduct an clcctric current.
If a strong clcctrolytc is formed as a result of a chcmical reaction involving two weak clcctrolytcs, the conductancc of the resulting solution increases. If the ions of a strong clcctrolytc arc removed from solution as an insoluble prccipitatc, or from a weak clcctrolytc with the ions of another rcactant, the conductancc of a mixture of the rcactants is less than that of the strong clcctrolytc. After the reaction is complete, the conductancc will increase upon further addition of the second rcactant, provided the latter is a strong clcctrolytc.
Electrolysis always accompanies the passage of a dircct current through an aqueous solution. Cations are rcduccd to a lower oxidation state, some of them to the free state, at the cathodc; anions arc oxidized to ions with a higher oxidation state, or to the free state, at the anode.