Hydrolysis of salts means the processes of reactions between water molecules and molecules of salts dissolved in it. As a result of such a reaction, slightly dissociated compounds are formed. The process can occur not only with the participation of salts, but also in the presence of other dissolved substances in the water - 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 may be used. However, in this case, the reaction between the solvent and the salt is called solvolysis.
It is important to know that only those salts that are derived components of weak bases and acids are involved in hydrolysis. Salts derived from strong bases and acids are not susceptible to hydrolytic reactions.
To characterize 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 initial (initial) concentration of the already dissolved salt (C [original]). Mathematically, this can be expressed by the following equation: β = C [hydr] / C [source].
The degree of reaction depends on three factors:
- the nature of the ions that make up the salt;
- concentration of salt ions;
- temperature of the solution.
The degree of hydrolysis tends to increase with decreasing dissociation constant of a weak base or acid, as well as with a decrease in the degree of concentration of salts and an increase in temperature.
The reaction can occur to a noticeable extent only in dilute solutions. Therefore, if the value of C [H20] has an approximately constant value, then it becomes possible to calculate the derivative value of K [g] (or the hydrolysis constant). Depending on the relative properties of the acid and base from which the salts are formed, hydrolysis can occur according to one of three schemes, therefore, the salt hydrolysis constant is calculated differently.
Hydrolysis of salts that are derivatives of a strong acid and a weak base (another name for the process is cation hydrolysis)
The hydrolysis constant is determined by the following formula: K [g] = K [W] / K [base], where K [W] is the result of the ionic product of water (C [H] + C [OH (-)]).
From the above expression of the hydrolysis constant, it can be seen that with a decrease in the strength of the base, an increase in the value of the hydrolysis constant, and, hence, the degree of hydrolysis, is observed. In turn, the degree of hydrolysis tends to increase 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 derived from a strong base and a weak acid (another name for the process is anion hydrolysis)
The hydrolysis constant is calculated by the following formula: K [g] = K [W] / K [acid], where the value of K [acid] is the dissociation constant for a weak acid.
Hydrolysis of salts derived from a weak base and a weak acid (another name is hydrolysis by cation and anion)
In this case, the hydrolysis constant will be determined by the values of the dissociation constant of the weak base and weak acid. It is calculated by the following formula: K [g] = K [W] / K [acid] * K [base].
The importance of the hydrolysis process
Reactions occurring in the hydrolysis process are widely used in modern manufacturing processes. For example, such a reaction is used to purify water from harmful impurities of the colloidal and coarsely dispersed series. For this, special precipitates of iron and aluminum hydroxides are used, obtained due to the hydrolysis of iron sulfates, iron chlorides and aluminum sulfates.
Hydrolysis is an important part of the digestion of living organisms on Earth. Most of the energy necessary for the existence of the body is stored as adenosine triphosphoric acid (ATP). The release of energy occurs due to the hydrolysis process with the participation of ATP.