To understand how the hydrolysis of salts proceeds in their aqueous solutions, we begin by defining the process.
This process involves chemical actionions of water with ions of salt, as a result a weak base (or acid) is formed, and the reaction of the medium also changes. Any salt can be represented as a product of the chemical interaction of a base and an acid. Depending on what their strength is, several variants of the process flow are singled out.
In chemistry, three varieties are consideredthe course of the reaction between the cations of salt and water. Each process is carried out with a change in the pH of the medium, therefore, it is assumed that different types of indicators are used to determine the hydrogen index. For example, violet litmus is used for acidic medium, phenolphthalein is suitable for an alkaline reaction. Let us analyze in more detail the features of each hydrolysis variant. Strong and weak bases can be determined from the solubility table, and the strength of acids is determined from the table.
В качестве примера такой соли рассмотри хлорид iron (2). Ferric hydroxide (2) is a weak base, and hydrochloric acid is strong. During the interaction with water (hydrolysis), the formation of the basic salt (iron hydroxochloride 2) occurs, and hydrochloric acid also forms. An acidic medium appears in the solution, it can be determined with the help of blue litmus (pH less than 7). In this case, hydrolysis itself proceeds through the cation, since a weak base is used.
Let us give one more example of the course of hydrolysis fordescribed case. Consider the salt of magnesium chloride. Magnesium hydroxide is a weak base, and hydrochloric acid is a strong base. In the process of interaction with water molecules, magnesium chloride is converted to the basic salt (hydroxochloride). Magnesium hydroxide, the formula of which is generally represented in the form of M (OH)2, slightly soluble in water, but strong hydrochloric acid gives the solution an acidic medium.
The next variant of hydrolysis is characteristic for the salt, which is formed by a strong base (alkali) and a weak acid. As an example for this case, consider sodium carbonate.
В данной соли есть сильное основание натрия, а also a weak carbonic acid. Interaction with water molecules proceeds with the formation of an acid salt - sodium hydrogencarbonate, that is, hydrolysis proceeds by anion. In addition, sodium hydroxide is formed in the solution, which gives the solution an alkaline medium.
Let us give one more example for this case.Potassium sulphite is a salt that is formed by a strong base - caustic potassium, and also weak sulfuric acid. In the process of interaction with water (during hydrolysis), potassium hydrosulfite (acid salt) and potassium hydroxide (alkali) form. The medium in the solution will be alkaline, it can be confirmed with phenolphthalein.
The salt of a weak acid and a weak base undergoes complete hydrolysis. Let's try to find out what its peculiarity is, and what products will be formed as a result of this chemical reaction.
Analyze the hydrolysis of a weak base andweak acid on the example of aluminum sulfide. This salt is formed by aluminum hydroxide, which is a weak base, as well as weak hydrogen sulfide acid. When interacting with water, complete hydrolysis is observed, as a result of which gaseous hydrogen sulfide is formed, and also aluminum hydroxide as a precipitate. Such interaction proceeds both along the cation and along the anion; therefore, this hydrolysis variant is considered complete.
Also as an example of the interactionThis type of salt with water can be given magnesium sulfide. The composition of this salt is magnesium hydroxide, its formula is Mg (OH) 2. It is a weak base, insoluble in water. In addition, inside the magnesium sulfide there is hydrogen sulphide acid, which is weak. When interacting with water, complete hydrolysis occurs (by cation and anion), as a result of which magnesium hydroxide forms as a precipitate, and hydrogen sulfide is released as a gas.
Если рассматривать гидролиз соли, которая formed by a strong acid and a strong base, it should be noted that it does not leak. The medium in solutions of salts such as sodium chloride, potassium nitrate, remains neutral.
Strong and weak bases, acids that form salts, affect the result of hydrolysis, the reaction of the medium in the resulting solution. Similar processes are widespread in nature.
Hydrolysis is of particular importance in chemicaltransformation of the earth's crust. It contains sulfides of metals, poorly soluble in water. As they hydrolyze, hydrogen sulfide is formed, released in the process of volcanic activity on the surface of the earth.
Silicate rocks in the transition to hydroxides, cause the gradual destruction of rocks. For example, such a mineral as malachite, is a product of the hydrolysis of copper carbonates.
Intensive hydrolysis also occurs.in the oceans. Hydrocarbons of magnesium and calcium, which are removed by water, have a weak alkaline environment. Under such conditions, the process of photosynthesis in marine plants is excellent, and marine organisms develop more intensively.
In oil there are impurities of water and calcium salts andmagnesium. In the process of heating the oil, they interact with water vapor. In the course of hydrolysis, hydrogen chloride is formed, when interacting with the metal, the destruction of equipment occurs.
