Scientists have been working with the term “electrolytic dissociation” since the end of the nineteenth century. We owe his appearance to the Swedish chemist Arrhenius. Working on the problem of electrolytes in 1884-1887, he introduced it to describe the phenomenon of ionization in solutions and during the formation of melts. He decided to explain the mechanism of this phenomenon by the decay of molecules into ions, elements having a positive or negative charge.
The theory of electrolytic dissociation explains the electrical conductivity of some solutions. For example, potassium chloride KCl is characterized by the decay of a molecule of this salt into a potassium ion having a charge with a plus sign (cation), and into a chlorine ion, a charge with a minus sign (anion). Hydrochloric acid HCl decomposes into a cation (hydrogen ion) and anion (chlorine ion), a solution of sodium hydroxide NaHO leads to the appearance of sodium ions and anion in the form of a hydroxide ion. The main principles of the theory of electrolytic dissociation describe the behavior of ions in solutions. According to this theory, they move completely freely within the solution, and even in a small drop of the solution, a uniform distribution of oppositely charged electric charges is maintained.
The theory of electrolytic dissociation explains the process of formation of electrolytes in aqueous solutions as follows. The appearance of free ions indicates the destruction of the crystal lattice of the substance. This process when a substance is dissolved in water occurs under the influence of polar solvent molecules (in our example, we consider water). They are able to reduce the electrostatic attraction between the ions located in the nodes of the crystal lattice so much that, as a result, the ions transfer to free movement in the solution. In this case, free ions are surrounded by polar water molecules. The theory of electrolytic dissociation calls this shell, which forms around them, hydrated.
But the theory of electrolytic dissociation of Arrhenius explains the formation of electrolytes not only in solutions. The crystal lattice can also be destroyed under the influence of temperature. By heating the crystal, we get the effect of intense ion vibrations at the lattice sites, which gradually leads to the destruction of the crystal and the appearance of a melt completely consisting of ions.
Returning to solutions, we should separately consider the property of a substance, which we call a solvent. The most striking representative of this family is water. The main sign is the presence of dipole molecules, i.e. when the molecule is positively charged at one end and negatively charged at the other. A water molecule fully satisfies these requirements, but water is not the only solvent.
Non-aqueous polar solvents, for example, liquid sulfur dioxide, liquid ammonia, etc. can also cause the process of electrolytic dissociation. But it is water that occupies the main place in this series, since its ability to weaken (dissolve) electrostatic attraction and destroy crystal lattices is especially pronounced. Therefore, speaking of solutions, we mean water-based liquids.
A deep study of the properties of electrolytes allowed us to move on to the concept of their strength and degree of dissociation. Under the degree of dissociation of the electrolyte is meant the ratio of the number of dissociated molecules to their total number. For potential electrolytes, this coefficient is in the range from zero to unity, and the degree of dissociation equal to zero indicates that we are dealing with non-electrolytes. An increase in the degree of dissociation is positively affected by an increase in the temperature of the solution.
The strength of electrolytes is determined by the degree of dissociation under the condition of constant concentration and temperature. Strong electrolytes have a degree of dissociation approaching unity. These are well soluble salts, alkalis, acids.
The theory of electrolytic dissociation made it possible to explain an extensive series of phenomena that are studied in the framework of physics, chemistry, plant and animal physiology, and theoretical electrochemistry.