Physical chemistry and biochemistry are characterized by a general process in which particles of a substance - molecules, ions (positively charged particles called cations and negatively charged particles called anions), radicals decay into simpler particles. This process is called dissociation, which is translated from Latin as "dissociation" means "separation." It is characterized by an indicator such as the “degree of dissociation”, which shows the ratio of the number of dissociated particles to the total number of particles before decay, that is, the fraction of particles that decayed. The process of particle decay can occur as a result of certain effects on a substance; the nature of these effects determines the type of dissociation. There are thermal dissociation, photodissociation, dissociation under the influence of ionizing radiation, electrolytic dissociation. Dissociation is the opposite of association and recombination. This process is often confused with ionization.
Electrolytic dissociation is a type of dissociation, proceeds under the influence of polar solvent molecules and is chemical in nature. Substances that can dissociate into ions and conduct an electric current in a solvent are called electrolytes (acids, salts, bases). Substances that, when dissolved, do not decompose into ions (alcohols, esters, carbohydrates, etc.) are not electrolytes. The most important solvent for electrolytes is water. Water itself is characterized as a weak electrolyte. Polar solvents (e.g. ethanol, ammonia and acetic acid) are also capable of dissolving electrolytes. The dissociation of acids and alkalis, as well as the dissociation of salts, proceed in aqueous solutions. Salts are a class of chemical compounds whose molecules are composed of positively charged particles (metal cations) and negatively charged particles (anions of acid residues). Acid salts, unlike ordinary salts, consist of two types of cations (metal and hydrogen) and an anion of an acid residue. When dissolved in water, salt molecules decay into ions. Salt can be restored by evaporating water.
Distinguish between strong and weak electrolytes. In the classical theory of electrolytic dissociation, this process is considered to be reversible, however, this statement applies only to weak electrolytes in dilute solutions. The electrolytic dissociation of acids, bases, salts is an irreversible process, since salts (almost all but some complex ones), acids and bases (those formed by alkaline and alkaline earth metals) are strong electrolytes, and in weak solutions their molecules are completely (per 100 %) dissociate into ions. Strong electrolytes: NaCl (sodium chloride), HNO3 (nitric acid), HClO3 (chloric acid), CaCl2 (calcium chloride), NaOH (sodium hydroxide). Weak electrolytes: NH4OH (ammonium hydroxide), H2CO3 (carbonic acid), CH3COOH (acetic acid) and most organic acids and bases. When dissolved in water, they are able to partially dissociate (usually this value lies in the range from 1 to 10%).
Therefore, the statement is true that in a solution of strong electrolytes only ions are contained, and in a solution of weak electrolytes, mainly undecayed molecules of the substance. Dissociation of salts leads to the fact that the solution contains only metal ions and an acid residue (for example, sodium cation Na + and chlorine anion Cl-), and there are no undecayed molecules (NaCl). Dissociation of acid salts leads to the formation of a metal cation, a hydrogen cation and an anion of an acid residue in a solution. For example, the acid salt of NaHCO3 (sodium bicarbonate) dissociates into a sodium cation (Na +), a hydrogen cation (H-) and an anion of an acid residue of carbonic acid (CO3-).
If the electrolyte solution (melt) is placed in the electrolyzer (vessel with the cathode and anode), then when the voltage is applied, the directed movement of charged particles to the electrodes with the opposite charge will begin: positive cations - to the negatively charged cathode, and negative anions - to the positively charged anode. This property of electrolytes, in particular, the dissociation of salts, is widely used in technology. The electrolysis method is used for the industrial production of aluminum and copper (by the method of electrolytic refining). Electrolysis allows you to get the purest substances, such a degree of purity cannot be achieved by other methods (distillation, crystallization and others). Using electrolysis, metals extracted from ores are refined, since only a metal cation is deposited on the cathode, while impurities remain in solution or melt. Such a phenomenon as the dissociation of salts underlies the production of pure hydrogen and pure chlorine. In water , sodium chloride decomposes into ions: sodium cation and chlorine anion. Pure chlorine will be released at the anode, hydrogen by-product at the cathode, and another important by-product, sodium hydroxide, will form in the solution.