How to write down the equation of hydrolysis of s alts? This topic often causes difficulties for graduates of secondary schools who choose chemistry for the exam. Let's analyze the main types of hydrolysis, consider the rules for compiling molecular and ionic equations.
Definition
Hydrolysis is a reaction between a substance and water, accompanied by the combination of components of the original substance with it. This definition indicates that this process occurs not only in inorganic substances, it is also characteristic of organic compounds.
For example, the hydrolysis reaction equation is written for carbohydrates, esters, proteins, fats.
Hydrolysis value
All chemical interactions that are observed in the hydrolysis process are used in various industries. For example, this process is used to remove coarse and colloidal impurities from water. For these purposes, special precipitates of aluminum and iron hydroxides are used, which are obtained by hydrolysis of sulfates and chlorides of these metals.
What else does it matterhydrolysis? The equation of this process indicates that this reaction is the basis of the digestive processes of all living beings. The main part of the energy that the body needs is focused as ATP. The release of energy is possible due to the hydrolysis process, in which ATP takes part.
Process Features
The molecular equation of s alt hydrolysis is written as a reversible reaction. Depending on which base and acid the inorganic s alt is formed, there are various options for the course of this process.
The s alts that are formed enter into such an interaction:
- mild hydroxide and active acid (and vice versa);
- volatile acid and active base.
It is impossible to write the ionic hydrolysis equation for s alts that are formed by an active acid and a base. The reason is that the essence of neutralization comes down to the formation of water from ions.
Process characteristic
How can hydrolysis be described? The equation of this process can be considered using the example of a s alt, which is formed by a monovalent metal and a monobasic acid.
If an acid is represented as HA and a base is MON, then the s alt they form is MA.
How can hydrolysis be written? The equation is written in molecular and ionic form.
For dilute solutions, the hydrolysis constant is used, which is defined as the ratio of the number of moless alts involved in hydrolysis, to their total number. Its value depends on which acid and base form the s alt.
Anion hydrolysis
How to write the molecular hydrolysis equation? If the s alt contains an active hydroxide and a volatile acid, the result of the interaction will be an alkali and an acidic s alt.
Typical is the sodium carbonate process, which produces an alkali and an acid s alt.
Given that the solution contains anions of the hydroxyl group, the solution is alkaline, the anion is hydrolyzed.
Process example
How to write down such hydrolysis? The process equation for ferrous sulfate (2) assumes the formation of sulfuric acid and ferrous sulfate (2).
The solution is acidic, created by sulfuric acid.
Total hydrolysis
Molecular and ionic equations for the hydrolysis of s alts, which are formed by an inactive acid and the same base, suggest the formation of the corresponding hydroxides. For example, for aluminum sulfide formed by amphoteric hydroxide and volatile acid, the reaction products will be aluminum hydroxide and hydrogen sulfide. The solution is neutral.
Sequence of actions
There is a certain algorithm, following which high school students will be able to accurately determine the type of hydrolysis, identify the reaction of the medium, and also record the products of the ongoing reaction. First you need to define the typeprocess and record the process of ongoing s alt dissociation.
For example, for copper sulfate (2), the decomposition into ions is associated with the formation of a copper cation and an anion of sulfate.
This s alt is formed by a weak base and an active acid, so the process takes place along the cation (weak ion).
Next, the molecular and ionic equation of the ongoing process is written.
To determine the reaction of the medium, it is necessary to compose an ionic view of the ongoing process.
The products of this reaction are: copper hydroxosulfate (2) and sulfuric acid, so the solution is characterized by an acid reaction of the medium.
Hydrolysis has a special place among the various exchange reactions. In the case of s alts, this process can be represented as a reversible interaction of substance ions with a hydration shell. Depending on the strength of this impact, the process can proceed with different intensity.
Donor-acceptor bonds appear between cations and water molecules that hydrate them. The oxygen atoms contained in water will act as a donor, since they have unshared electron pairs. Acceptors will be cations that have free atomic orbitals. The charge of the cation determines its polarizing effect on water.
A weak hydrogen bond is formed between anions and HOH dipoles. With a strong action of anions, a complete detachment of a proton from a molecule is possible, which leads to the formation of an acid or an anion of the HCO3‾ type. Hydrolysis is a reversible and endothermic process.
Types of impact on s altwater molecules
All anions and cations, having insignificant charges and significant sizes, have a slight polarizing effect on water molecules, so there is practically no reaction in an aqueous solution. As an example of such cations, hydroxyl compounds, which are alkalis, can be mentioned.
Let's single out the metals of the first group of the main subgroup of D. I. Mendeleev's table. Anions that meet the requirements are acidic residues of strong acids. S alts, which are formed by active acids and alkalis, do not undergo the process of hydrolysis. For them, the dissociation process can be written as:
H2O=H+ + OH‾
Solutions of these inorganic s alts have a neutral environment, therefore, during hydrolysis, the destruction of s alts is not observed.
For organic s alts formed by the anion of a weak acid and an alkali cation, hydrolysis of the anion is observed. As an example of such a s alt, consider potassium acetate CH3COOK.
The bonding of CH3COOCOO- acetate ions with hydrogen protons in molecules of acetic acid, which is a weak electrolyte, is observed. In the solution, the accumulation of a significant amount of hydroxide ions is observed, as a result of which it acquires an alkaline reaction of the medium. Potassium hydroxide is a strong electrolyte, so it cannot be bound, pH > 7.
The molecular equation of the ongoing process is:
CH3SOOK + H2O=KOH +CH3UN
In order to understand the essence of the interaction between substances, it is necessary to compose a complete and reduced ionic equation.
Na2S s alt is characterized by a stepwise process of hydrolysis. Taking into account that the s alt is formed by a strong alkali (NaOH) and a dibasic weak acid (H2S), the binding of the sulfide anion by water protons and the accumulation of hydroxyl groups are observed in the solution. In molecular and ion form, this process will look like this:
Na2S + H2O=NaHS + NaOH
The first step. S2− + HON=HS− + OH−
Second step. HS− + HON=H2S + OH−
Despite the possibility of a two-stage hydrolysis of this s alt under normal conditions, the second stage of the process practically does not proceed. The reason for this phenomenon is the accumulation of hydroxyl ions, which give the solution a weak alkaline environment. This contributes to a shift in chemical equilibrium according to Le Chatelier's principle and causes a neutralization reaction. In this regard, the hydrolysis of s alts, which are formed by alkali and weak acid, can be suppressed by an excess of alkali.
Depending on the polarizing effect of anions, it is possible to influence the intensity of hydrolysis.
For s alts containing strong acid anions and weak base cations, cation hydrolysis is observed. For example, a similar process can be considered on ammonium chloride. The process can be represented as followsform:
molecular equation:
NH4CL + H2O=NH4OH + HCL
short ionic equation:
NH4++HOH=NH4OH + H +
Due to the fact that protons accumulate in the solution, an acidic environment is created in it. To shift the equilibrium to the left, an acid is introduced into the solution.
For a s alt formed by a weak cation and anion, the course of complete hydrolysis is typical. For example, consider the hydrolysis of ammonium acetate CH3COONH4. In ionic form, the interaction has the form:
NH4+ + CH3COO−+ HOH=NH4OH + CH3COOH
In closing
Depending on which acid and base the s alt is formed, the process of reaction with water has certain differences. For example, when s alt is formed by weak electrolytes and when they interact with water, volatile products are formed. Complete hydrolysis is the reason why it is not possible to prepare some s alt solutions. For example, for aluminum sulfide, you can write the process as:
Al2S3 + 6H2O=2Al(OH) 3↓ + 3H2S↑
Such s alt can only be obtained by the “dry method”, using the heating of simple substances according to the scheme:
2Al + 3S=Al2S3
To avoid decomposition of aluminum sulfide, it is necessary to store it in airtight containers.
In some cases, the hydrolysis process is quite difficult, so the molecularthe equations of this process have a conditional form. In order to reliably establish the products of interaction, it is necessary to conduct special studies.
For example, this is typical for multinuclear complexes of iron, tin, beryllium. Depending on the direction in which this reversible process needs to be shifted, it is possible to add ions of the same name, change its concentration and temperature.
