Chemicals are a set ofatoms that are connected to each other according to a certain law, more precisely, each of them is a system consisting of nuclei and electrons. If the system consists of one type of atoms, then it can be called single-core, if from atoms of different types, then non-nuclear. These systems are electrically neutral. As a result of external exposure (temperature, light, radiation, or polar solvent molecules with dipole polarization), chemical substances decompose. Cations and anions into which molecules of a substance (electrolyte) break up under the action of molecules of a polar solvent (water) are no longer electrically neutral. Any systems tend to balance. On the example of weak electrolytes, it can be seen that dissociation reactions are reversible. For strong electrolytes, this statement is not suitable, since all molecules practically break up into ions. The tendency of the system to equilibrium is described by the electrolytic dissociation equation KxAu ↔ x • K + + y • A– and shows the dissociation constant Kd = [K +] x • [A−] y / [KhAu].
From the above equation shows:the more non-dissociated molecules, the smaller the dissociation constant, and vice versa. However, this does not apply to strong electrolytes, since it has been established that with an increase in their concentration, Cd does not increase, but decreases. This is due not to a decrease in the number of molecules that have broken apart, but to an increase in the forces of mutual attraction between oppositely charged particles due to the reduced distance between them due to an increase in the concentration of the solution. Therefore, the ability of strong electrolytes to decay into ions is estimated by such an indicator as apparent degree of dissociation, and Cd is not used, since it is devoid of meaning. It does not make sense to apply the degree of dissociation to solutions of weak electrolytes, because with a decrease in concentration, the ratio of the dissociated molecules to the total number increases to decay, but does not characterize the strength of the electrolyte. Their ability to dissociate into ions shows the dissociation constant, since it depends only on the temperature of the solution and the nature of the solvent, that is, Cd is a constant value for a particular substance KxAy.
Plain water (from naturalsources or the one that flows from the tap) is not clean. The purest water contains hydroxonium ions [H3O + 1] and hydroxide ions [OH-1]. They are formed from two water molecules: H2O + H2O ↔ H3O + 1 + OH-1. This rarely happens, since water practically does not decompose into ions, being a weak electrolyte. At equilibrium, the concentrations of hydroxide ions and hydroxonium ions are equal: [H3O + 1] = [OH-1]. The process is reversible. Water usually exists as a mixture of molecules, hydroxide ions, and hydroxonium ions, where water molecules dominate and only traces of ions are present. The water dissociation constant is expressed using the equation: Cd = [H3O + 1] • [OH-1] / [H2O] • [H2O].
Dissociation of acid in solution means decomposition into protons H+ и кислотный остаток.The dissociation of polybasic acids proceeds in several stages (where only one hydrogen cation is split off), each stage is characterized by its own value of the Cd constant. At the first stage, the hydrogen ion is cleaved more easily than at subsequent stages, therefore the constant from stage to stage decreases. The acid dissociation constant cd is an indicator of the strength of an acid: strong acids have a higher cd value and vice versa. When the process reaches equilibrium, the rate of decomposition and the rate of formation of molecules are equal. For strong acids, one can apply (only with allowance for the forces of interionic interaction in solutions of strong electrolytes) the laws of chemical equilibrium for calculating the Cd at 25 ° C. For hydrochloric acid (HCl) Kd = 10000000, hydrobromic (HBr) Kd = 1000000000, iodine hydrogen (HJ) Kd = 100000000000, sulfuric (H2SO4) Kd = 1000, nitrogen (HNO3) Kd = 43.6, acetic (CH3COOH) Kd = 0.00002, cyanide (HCN) Cd = 0.0000000008. Knowing the properties of acids and comparing with the given values of Cd, it can be argued that the dissociation constant is the higher, the stronger the acid.
