Chemicals are a collection of atoms that are linked to each other by a certain law, or more precisely, each of which is a system consisting of nuclei and electrons.If the system is composed of one type of atoms, then it can be called a single core if different types of atoms, the neodnoyadernoy.These systems are electrically neutral.As a result of external influences (temperature, light, radiation, or a polar solvent molecules with dipole polarization) decomposes chemical substances.The cations and anions, which under the action of the molecules of the polar solvent (water) separate molecules of the substance (electrolyte) are not electrically neutral.Any system tend to equilibrium.In weak electrolytes example shows that reversible dissociation reaction.For strong electrolytes, this statement is not suitable, since virtually all the molecules dissociate into ions.The tendency of the system to equilibrium is described by electrolytic dissociation Khao ↔ x • To + from A- and • indicates the dissociation constant Kd = [K +] • x [A] v / [Khao].
seen from the above equation: the more undissociated molecules, the smaller the dissociation constant and vice versa.However, this does not apply to strong electrolytes have been found that with an increase in their concentration does not Kd increases and decreases.This is due not decrease the number of broken molecules, and an increase between oppositely charged particles the forces of mutual attraction due to the reduction of the distance between them is due to the increased concentration of the solution.Therefore, the ability of strong electrolytes dissociate into ions measured indicators such as the apparent degree of dissociation, and the CD is not used because it is meaningless.To a solution of a weak electrolyte has no sense to apply, and the degree of dissociation, because with decreasing concentration ratio of dissociated molecules to the total number of decay is increased, but it does not characterize the effect of the electrolyte.Their ability to dissociate into ions indicates the dissociation constant, since it depends only on the temperature of the solution and the nature of the solvent, that is, Kd is a constant for a particular substance Khao.
Plain water (out of natural sources, or the one that flows from the tap) is not clean.Pure well water contains hydronium ions [H3O + 1] and hydroxide ions [OH-1].They are formed from two molecules of water: H2O + H2O ↔ H3O + + 1 OH-1.It rarely happens, because the water is practically dissolves into ions, as a weak electrolyte.At equilibrium, the concentration of hydroxide ions and hydronium ions are: [H3O + 1] = [OH-1].The process is reversible.Water generally exists as a mixture of molecules, hydroxide ions and hydronium ions dominated by water molecules and ions present in only trace.The dissociation constant of water is expressed by the equation: Kd = [H3O + 1] • [OH-1] / [H2O] • [H2O].
dissociation of acid in the solution is the decay into protons H + and acid residue.Dissociation polybasic acid proceeds in several steps (which cleaved only one hydrogen cation), each stage is characterized by the value of the constant Kd.In the first step hydrogen ion cleaved easier than in subsequent stages, so constant from stage to stage, reduced.Acid dissociation constant Kd is an indicator of acid strength: the strong acids have a higher Kd and vice versa.Upon reaching equilibrium of the decay rate and the rate of formation of molecules are equal.For strong acids can be used (taking into account only the ion-ion interaction forces in solutions of strong electrolytes) the laws of chemical equilibrium to calculate Kd at 25 ° C.For hydrochloric acid (HCl) Kd = 10000000, hydrogen bromide (HBr) Kd = 1000000000, yodovodorodnoy (HJ) Kd = 100000000000, sulfuric acid (H2SO4) Kd = 1000, nitric acid (HNO3) Kd = 43.6, acetate (CH3COOH) Kd =0.00002, tsianovodorodnoy (HCN) Kd = 0.0000000008.Knowing the properties of acids and comparing with given values of Kd, one can argue that the dissociation constant of the higher, the stronger the acid.
