- - chemical reference table.
From the standpoint of the theory of electrolytic dissociation of acid - a compound which, upon dissociation in water splits into positive hydrogen ions and negatively charged substrate.The definition implies that the degree of dissociation determines force acid .
degree of dissociation depends on the concentration and is given by the equation: a = Cdis / Sobsch%;where Sdis - molar concentration of dissociated molecules Sobsch - the total molar concentration of the substance taken for solu
tion.Strong acid dissociates almost completely, acid medium strength - from 3 to 30%, weak - less than 3%.As seen from the equation, the greater the concentration of substances in solution, and the smaller the value.Knowing the degree of dissociation, you can judge the strength acid .
Force acid also characterizes the dissociation constant or acidity constant.It is given by: K = [A +] * [B -] / [AB] = const, where [A +], [B-] - equilibrium concentrations of dissociated ions, [AB] - equilibrium concentration of dissociated molecules.Of the total molar concentration of the substance does not depend on the dissociation constant.With increasing temperature, the degree and the dissociation constant increases.
To determine the effect acid , get its dissociation constant in the reference tables.The larger it is, the stronger the acid.Strong acid are constant from 43,6 (HNO3) and above.The strengths of the mineral acids include acids: chlorine, hydrochloric acid, sulfuric acid and others.By weak acids include organic acids (acetic, malic et al.) And some minerals (coal, cyanide).
Along with the constant use the acidity pK, which is equal to the negative decimal logarithm of the constant: pK = - lgK.In strong acids it is negative.
But how to determine which of more strong acids, if their degree of dissociation in water tend to infinity?Such acid called superacids.To compare with each other, they are considered by the Lewis theory of electron acceptors.Superacids force measured in other environments having them in contact with a weak base properties.The media attributed the hydrogen protons acid .