Theory of electrolytic dissociation. A simple explanation of complex processes

With the term "electrolytic dissociation" scientistswork since the late nineteenth century. His appearance is due 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 in the formation of melts. The mechanism of this phenomenon, he decided to explain the decomposition of molecules into ions, elements that have a positive or negative charge.

The theory of electrolytic dissociation explainselectrical conductivity of some solutions. For example, potassium chloride KCl is characterized by the decomposition of the molecule of this salt into a potassium ion, which has a charge with a plus sign (cation), and a chloride ion, a charge with a minus sign (anion). Hydrochloric acid HCl decomposes into a cation (hydrogen ion) and an anion (a chlorine ion), a solution of caustic soda NaHO leads to the appearance of sodium ions and anion in the form of a hydroxide ion. The basic theses 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.

Theory of electrolytic dissociation processThe formation of electrolytes in aqueous solutions is explained as follows. The appearance of free ions indicates the destruction of the crystal lattice of matter. This process when the substance is dissolved in water occurs under the influence of polar molecules of the solvent (in our example we consider water). They are able to so reduce the electrostatic attraction force that exists between ions in the lattice sites, which results in ions moving to a free movement in the solution. In this case, free ions fall into the environment of polar water molecules. This shell, formed around them, the theory of electrolytic dissociation calls hydration.

But the theory of electrolytic dissociation Arrheniusexplains the formation of electrolytes not only in solutions. The crystal lattice can also be destroyed under the influence of temperature. Heating the crystal, we get the effect of intense oscillation of ions 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, it follows separatelyconsider the property of a substance, which we call a solvent. The brightest representative of this family is water. The main feature is the presence of dipole molecules, i.e. when from one end the molecule is positively charged, and from the other it is negative. A water molecule completely satisfies these requirements, but water is not the only solvent.

The process of electrolytic dissociation canand also non-aqueous polar solvents, for example, liquid sulfur dioxide, liquid ammonia, etc. But it is water that occupies the main place in this series, since its property to weaken (dissolve) the electrostatic attraction and destroy the crystal lattices is particularly pronounced. Therefore, speaking of solutions, we mean liquids on a water basis.

Deep study of the properties of electrolytes allowedgo to the concept of their strength and degree of dissociation. The degree of dissociation of the electrolyte is the ratio of the number of dissociated molecules to their total number. In 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. Increasing 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 dissociationunder 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 a wide range of phenomena that are studied in the framework of physics, chemistry, physiology of plants and animals, and theoretical electrochemistry.