Theory of electrolytic dissociation. A simple explanation of complex processes

With the term "electrolytic dissociation" scientists have been working 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 explains the electrical conductivity of certain 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 sodium hydroxide 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.

The theory of electrolytic dissociation, the process of the formation of electrolytes in aqueous solutions, explains 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 force of electrostatic attraction that exists between ions located in the nodes of the crystal lattice, that as a result, ions pass to free movement in solution. In this case, free ions fall into the environment of polar water molecules. This shell, formed around them, the theory of electrolytic dissociation is called hydrated.

But the theory of electrolytic dissociation Arrhenius explains the formation of electrolytes not only in solutions. The crystal lattice can also be destroyed under the influence of temperature. Heating the crystal, we obtain 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, we should separately consider 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 charged positively, 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 can also be caused by 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) electrostatic attraction and destroy crystal lattices is particularly pronounced. Therefore, speaking of solutions, we mean liquids on a water basis.

A profound study of the properties of electrolytes made it possible to proceed 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 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 a wide range of phenomena that are studied in the framework of physics, chemistry, physiology of plants and animals, and theoretical electrochemistry.