The concept of hydrolysis. Numerical characteristics of the process: the hydrolysis constant and the degree of hydrolysis

Under the hydrolysis of salts , the processes of reactions between water molecules and the molecules of salts dissolved in it are implied. As a result of this reaction, malodisociated compounds are formed. The process can occur not only with the participation of salts, but also in the presence of other dissolved substances - carbohydrates, proteins, fats or esters. Two quantities are applied numerically to the reaction: the degree of hydrolysis (β) and the salt hydrolysis constant (K [g]).

As a result of the reaction, as a rule, a change in the acidity of the initial solution is observed. Instead of an organic solvent (water), a different type of solvent can be used. However, in this case, the reaction between the solvent and the salt is called solvolysis.

It is important to know that only salts that are derivatives of weak bases and acids are involved in the hydrolysis. Salts obtained from strong bases and acids, hydrolytic reaction are not affected.

To give a characteristic of the completeness of the process, a special definition is used-the degree of hydrolysis (β). The degree of hydrolysis determines the ratio of the concentration of molecules that undergo hydrolysis (C [hydr]) to the original (initial) concentration of the already dissolved salt (C [ref]). Mathematically, this can be expressed by the following equation: β = C [hydr] / C [ref.].

The degree of reaction directly depends on three factors:

- the nature of the ions, of which the salt is composed;

- concentration of salt ions;

- the temperature of the solution.

The degree of hydrolysis has the property of increasing as the dissociation constant of a weak base or acid decreases, as well as a decrease in the degree of salt concentration and an increase in temperature.

The reaction can occur to a significant extent only in dilute solutions. Therefore, if the quantity C [H20] has approximately constant value, then it becomes possible to calculate the derivative K [r] (or the hydrolysis constant). Depending on the relative properties of the acid and the base from which the salts are formed, hydrolysis can occur in one of three schemes, and therefore the salt hydrolysis constant is calculated in different ways.

Hydrolysis of salts, which are the derivatives of a strong acid and a weak base (another process name is hydrolysis by a cation)

The hydrolysis constant is determined by the following formula: K [r] = K [W] / K [base], where K [W] is the result of the ion product of water (C [H] + C [OH (-)]).

It is seen from the expression for the hydrolysis constant that when the strength of the base decreases, an increase in the value of the hydrolysis constant, and, consequently, of the degree of hydrolysis is observed. In turn, the degree of hydrolysis has the property of increasing with a decrease in the strength of the base and the degree of concentration of salts in the solution. An increase in the reaction temperature also leads to an increase in the hydrolysis constant and an increase in the degree of hydrolysis.

Hydrolysis of salts that are derivatives of a strong base and a weak acid (another name for the process is hydrolysis by anion)

The hydrolysis constant is calculated by the following formula: K [r] = K [W] / K [acid], where K [acid] is the dissociation constant for the weak acid.

Hydrolysis of salts, which are derivatives of a weak base and a weak acid (also called hydrolysis by cation and anion)

In this case, the hydrolysis constant will be determined by the values of the dissociation constant of a weak base and a weak acid. It is calculated by the following formula: K [r] = K [W] / K [acid] * K [base].

The significance of the hydrolysis process

Reactions occurring in the hydrolysis process are widely used in modern production processes. For example, this reaction is used to purify water from harmful impurities of a colloidal and coarsely dispersed series. For this purpose, special precipitates of iron and aluminum hydroxides, obtained by hydrolysis of iron sulfates, iron chlorides and aluminum sulfates, are used.

Hydrolysis is an important part of the process of digestion of living organisms on Earth. Most of the energy necessary for the existence of the body is stored as an adenosine triphosphate (ATP). The release of energy is due to the hydrolysis process involving ATP.