Consider the passage of electric current through solutions of acids, salts and alkalis.

Pure distilled water is almost an insulator. This can be shown with the following experience: if in series with the lamp filament to connect the bath with distilled water, which lowered the metal plate, and to turn on the light and a bath in the network, the lamp is not lit. It turns out, the solution of sugar in water also does not conduct current. If using a pipette to enter into the bath water with a few drops of acid, the lamp illuminates brightly. So, a solution of acid in water is a good conductor of current. Consider the causes of these phenomena.

Water molecules are natural dipoles. Suppose, that the input is a molecule of hydrochloric acid HC1. This molecule consists of ion H⁺ ion and CL^‒, held the Coulomb force of attraction. Remember, that water greatly weakens the interaction of electric charges (about 80 time), and randomly moving water molecules hit from all sides, the molecule of hydrochloric acid; as a result, the molecule of Hcl splits into ions. You can say, the dipoles of the water molecule surround the acid and as its pulled apart into ions (rice. 19.1). Note, that being in water oppositely charged ions are attracted to meeting up again to form molecules. So, when the acid hits the water, there is not only the process of disintegration of the molecules into ions, but the process of formation of neutral molecules from ion:

(arrows show, what process occurs in both directions).

The breakdown of molecules into ions under the action of the solvent is called electrolytic dissociation. The number, showing, what fraction of all the molecules of the solute are molecules, apart into ions, called the degree of dissociation.

So, mobile charge carriers in solutions are the ions. In the dissociation of hydrogen ions and all metals are positively charged. Ions in solution often represent a group of several atoms.

Notice, the dissociation of molecules into ions can cause not only solvent. For example, a strong heating of the substance and its molecules, composed of ions, can dissociate into separate ions. Therefore, the molten salts are also conductors of electric current.

Thus, according to the theory of electrolytic dissociation, in solutions of salts, acids and bases there are always free ions, as they appear at the time of dissolution of the substance in water or in another solvent.