To understand how hydrolysis of salts proceeds in their aqueous solutions, we first give a definition of this process.
Definition and features of hydrolysis
This process involves the chemical action of water ions with salt ions, 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 base and acid. Depending on what their strength is, there are several options for the process.
Types of Hydrolysis
In chemistry, three types of the reaction between salt and water cations are considered. Each process is carried out with a change in the pH of the medium; therefore, it is supposed to use different types of indicators to determine the hydrogen index. For example, violet litmus is used for an acidic environment, phenolphthalein is suitable for an alkaline reaction. Let us analyze in more detail the features of each variant of hydrolysis. Strong and weak bases can be determined by the solubility table, and the strength of acids is revealed by the table.
Cation hydrolysis
As an example of such a salt, consider iron chloride (2). Iron hydroxide (2) is a weak base, and hydrochloric acid is strong. In the process of interaction with water (hydrolysis), the formation of the basic salt (iron hydroxochloride 2) occurs, and hydrochloric acid is also formed. An acidic medium appears in the solution, it can be determined using a blue litmus (pH less than 7). In this case, the hydrolysis itself proceeds along the cation, since a weak base was used.
We give one more example of hydrolysis for the described case. Consider the magnesium chloride salt. Magnesium hydroxide is a weak base, and hydrochloric acid is strong. In the process of interaction with water molecules, magnesium chloride turns into a basic salt (hydroxochloride). Magnesium hydroxide, the formula of which is generally represented as M (OH) 2 , is slightly soluble in water, but strong hydrochloric acid gives the solution an acidic environment.
Anion hydrolysis
The next variant of hydrolysis is characteristic of salt, which is formed by a strong base (alkali) and weak acid. As an example for this case, consider sodium carbonate.
This salt has a strong sodium base, as well as a weak carbonic acid. Interaction with water molecules proceeds with the formation of an acid salt - sodium bicarbonate, that is, anion hydrolysis occurs. In addition, sodium hydroxide is formed in the solution , which gives the solution an alkaline environment.
We give one more example for this case. Potassium sulfite is a salt that is formed by a strong base - caustic potassium, as well as weak sulfuric acid. In the process of interaction with water (during hydrolysis), potassium hydrosulfite (acid salt) and potassium hydroxide (alkali) are formed. The medium in the solution will be alkaline; it can be confirmed using phenolphthalein.
Complete hydrolysis
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.
Let us analyze the hydrolysis of a weak base and a weak acid using aluminum sulfide as an example. This salt is formed by aluminum hydroxide, which is a weak base, as well as a weak hydrogen sulfide acid. When interacting with water, complete hydrolysis is observed, resulting in the formation of gaseous hydrogen sulfide, as well as aluminum hydroxide in the form of a precipitate. Such an interaction proceeds along both the cation and the anion; therefore, this variant of hydrolysis is considered complete.
Also, magnesium sulfide can be cited as an example of the interaction of this type of salt with water. The composition of this salt contains magnesium hydroxide, its formula is Mg (OH) 2. It is a weak base, insoluble in water. In addition, within the magnesium sulfide there is hydrogen sulfide, which is weak. When interacting with water, complete hydrolysis occurs (along the cation and anion), as a result of which magnesium hydroxide is formed as a precipitate, and hydrogen sulfide is released as a gas.
If we consider the hydrolysis of a salt that is formed by a strong acid and a strong base, it should be noted that it does not leak. The environment in solutions of salts such as sodium chloride , potassium nitrate , remains neutral.
Conclusion
Strong and weak bases, acids with which salts are formed, 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 the chemical transformation of the earth's crust. It contains metal sulfides, sparingly soluble in water. As they are hydrolyzed, hydrogen sulfide is formed and released during volcanic activity onto the surface of the earth.
Silicate rocks during the transition to hydroxides cause gradual destruction of rocks. For example, a mineral such as malachite is a product of the hydrolysis of copper carbonates.
An intensive process of hydrolysis also occurs in the oceans. Hydrocarbonates of magnesium and calcium, which are carried out by water, have a slightly alkaline environment. Under such conditions, the process of photosynthesis in marine plants is excellent, and marine organisms are developing more intensively.
In oil there are impurities of water and salts of calcium and magnesium. In the process of heating oil, they interact with water vapor. During hydrolysis, hydrogen chloride is formed, during the interaction of which with metal, equipment is destroyed.