The essence of the process of electrolytic dissociation lesson. The essence of the process of electrolytic dissociation. Showing the teacher's presentation

1. General provisions

1.1. In order to maintain business reputation and ensure compliance with federal legislation, the Federal State Institution State Research Institute of Technology "Informika" (hereinafter referred to as the Company) considers the most important task to be ensuring the legitimacy of the processing and security of personal data of subjects in the Company's business processes.

1.2. To solve this problem, the Company has introduced, operates and undergoes periodic review (monitoring) of a personal data protection system.

1.3. The processing of personal data in the Company is based on the following principles:

The legality of the purposes and methods of processing personal data and integrity;

Compliance of the purposes of processing personal data with the goals predetermined and stated when collecting personal data, as well as with the powers of the Company;

Correspondence of the volume and nature of the processed personal data, methods of processing personal data to the purposes of processing personal data;

The reliability of personal data, their relevance and sufficiency for the purposes of processing, the inadmissibility of processing personal data that is excessive in relation to the purposes of collecting personal data;

The legitimacy of organizational and technical measures to ensure the security of personal data;

Continuous improvement of the level of knowledge of Company employees in the field of ensuring the security of personal data during their processing;

Striving for continuous improvement of the personal data protection system.

2. Purposes of processing personal data

2.1. In accordance with the principles of processing personal data, the Company has determined the composition and purposes of processing.

Purposes of processing personal data:

Conclusion, support, amendment, termination of employment contracts, which are the basis for the emergence or termination of labor relations between the Company and its employees;

Providing a portal, personal account services for students, parents and teachers;

Storage of learning results;

Fulfillment of obligations provided for by federal legislation and other regulatory legal acts;

3. Rules for processing personal data

3.1. The Company processes only those personal data that are presented in the approved List of personal data processed in the Federal State Autonomous Institution State Research Institute of Technology "Informika"

3.2. The Company does not allow the processing of the following categories of personal data:

Race;

Political Views;

Philosophical beliefs;

About the state of health;

State of intimate life;

Nationality;

Religious Beliefs.

3.3. The Company does not process biometric personal data (information that characterizes the physiological and biological characteristics of a person, on the basis of which one can establish his identity).

3.4. The Company does not carry out cross-border transfer of personal data (transfer of personal data to the territory of a foreign state to an authority of a foreign state, a foreign individual or a foreign legal entity).

3.5. The Company prohibits making decisions regarding personal data subjects based solely on automated processing of their personal data.

3.6. The Company does not process data on subjects' criminal records.

3.7. The company does not publish the subject’s personal data in publicly available sources without his prior consent.

4. Implemented requirements to ensure the security of personal data

4.1. In order to ensure the security of personal data during its processing, the Company implements the requirements of the following regulatory documents of the Russian Federation in the field of processing and ensuring the security of personal data:

Federal Law of July 27, 2006 No. 152-FZ “On Personal Data”;

Decree of the Government of the Russian Federation of November 1, 2012 N 1119 “On approval of requirements for the protection of personal data during their processing in personal data information systems”;

Decree of the Government of the Russian Federation dated September 15, 2008 No. 687 “On approval of the Regulations on the specifics of processing personal data carried out without the use of automation tools”;

Order of the FSTEC of Russia dated February 18, 2013 N 21 “On approval of the composition and content of organizational and technical measures to ensure the security of personal data during their processing in personal data information systems”;

Basic model of threats to the security of personal data during their processing in personal data information systems (approved by the Deputy Director of the FSTEC of Russia on February 15, 2008);

Methodology for determining current threats to the security of personal data during their processing in personal data information systems (approved by the Deputy Director of the FSTEC of Russia on February 14, 2008).

4.2. The company assesses the harm that may be caused to personal data subjects and identifies threats to the security of personal data. In accordance with identified current threats, the Company applies necessary and sufficient organizational and technical measures, including the use of information security tools, detection of unauthorized access, restoration of personal data, establishment of rules for access to personal data, as well as monitoring and evaluation of the effectiveness of the measures applied.

4.3. The Company has appointed persons responsible for organizing the processing and ensuring the security of personal data.

4.4. The Company's management is aware of the need and is interested in ensuring an adequate level of security for personal data processed as part of the Company's core business, both in terms of the requirements of regulatory documents of the Russian Federation and justified in terms of assessing business risks.

This chemistry lesson is studied according to O.S. Gabrielyan’s teaching materials (2 hours per week) in the chapter “Dissolution. Solutions. Properties of electrolyte solutions" in the 4th quarter of 8th grade. Lesson type – learning new material. During the lesson, students consolidate knowledge about the types of chemical bonds; get acquainted with the essence and mechanism of electrolytic dissociation.

Increasing cognitive motivation in the lesson is facilitated by demonstration of experiments on the electrical conductivity of solids and electronic presentation.

The study of new material occurs through demonstration experiments, analysis of diagrams and drawings, as well as the use of an electronic presentation of the Microsoft Power Point program. During the lesson, students develop the following skills: observe, compare, analyze, and draw conclusions. When studying new material, interdisciplinary connections with physics are used.

The training session combines frontal and individual work.

The result of the work is: intensification of the work of the teacher and students in the lesson; Students consolidate their understanding of the types of chemical bonds, master the concepts of electrolyte and non-electrolyte, and study the essence and mechanism of electrolytic dissociation.

Lesson reflection is carried out in the form of a chemical dictation.

Download:

Preview:

Municipal educational institution

"Basic secondary school No. 12"

Chemistry lesson

8th grade

ELECTROLYTIC DISSOCIATION

Chemistry teacher

Kharitonova M.V.

Moore

2012-2013 academic year

Explanatory note

Increases cognitive motivation in the classroomdemonstration of experiments on the electrical conductivity of solids and electronic presentation.

The training session combines frontal and individual work.

Lesson reflection is carried out in the form of a chemical dictation.

Objective of the lesson: studying the essence of the new concept “electrolytic dissociation”

Tasks:

Educational objectives:

Ensure that students learn new concepts: electrolyte, non-electrolyte, electrolytic dissociation.
Establish the dependence of the electrical conductivity of solutions on the type of chemical bond and crystal structure of the substances.
Reveal the essence and mechanism of the process of electrolytic dissociation using the example of substances with ionic and polar covalent bonds.
To deepen students' knowledge about ionic and covalent polar bonds, the properties of the main classes of inorganic substances.

Developmental tasks:

Developing the ability to observe experiments, analyze diagrams and drawings, and take notes.

Development of cognitive experience of schoolchildren.

Continue to form a worldview about the dependence of the properties of substances on composition and structure.

Educational tasks:

Continue building motivation for learning activities.

Continue to form ideas about the positive role of chemistry to explain ongoing processes in nature.

Lesson type : a lesson in learning new material.

Technologies used: The lesson is built using modern information technologies - Microsoft Power Point.

Forms of training organization: a combination of frontal and individual work.

Interdisciplinary connections: physics (two types of charges).

Lesson equipment:

Multimedia equipment;electrical conductivity tester substances.

Basic concepts:electrolyte, non-electrolyte, electrolytic dissociation.

Expected results: intensification of the work of the teacher and students in the lesson; Students consolidate their understanding of the types of chemical bonds, master the concepts of electrolyte and non-electrolyte, and study the essence and mechanism of electrolytic dissociation.

LESSON PLAN

STAGE I - MOTIVATIONAL-ORIENTATION

Introduction to a new topic. Repetition of types of chemical bonds.

STAGE II - OPERATIONAL AND EXECUTIVE

1. Electrolytes and non-electrolytes.

2. The structure of the water molecule.

3. The mechanism and essence of electrolytic dissociation.

4. Svante Arrhenius - message from a student.

5. Degree of dissociation. Strong and weak electrolytes.

STAGE III - EVALUATIVE-REFLECTIVE.

Students complete assignments.

LESSON SUMMARY.

Today we are starting to study a new topic: “Electrolytic dissociation.” The purpose of the lesson will be to reveal the essence of a new concept for you - electrolytic dissociation.

You already know that chemical bonds between atoms can be of two types: ionic and covalent. Give examples of substances with these types of bonds. What is the type of chemical bond in compounds of atoms from three or more different elements: salts of oxygen-containing acids and bases?

Thus, salt crystals are composed of ions: “+” charge for the metal and “-” charge for the acid residue Na+ Cl - , K + NO - 3 , Na + 3 PO 3- 4

Solid bases also have a crystal lattice with “+” charged metal ions and “-” charged hydroxy ions: NaOH, Ca(OH) 2

If the compound contains only non-metal atoms (O, H, C), then all bonds are covalent. Such substances as glucose, sugar, alcohol, etc. contain neutral molecules - there are no ions.

II. 1. Differences in the nature of the chemical bond affect the behavior of substances in solutions, since most reactions occur in solutions.

From your physics course, you know that the ability of solutions to conduct electric current is determined by the presence of electrical charge carriers - ions. To do this, use a device for testing electrical conductivity (brief description of the device).

Demonstration of experiments on the electrical conductivity of solids and their solutions, followed by their discussion.

Thus, a salt solution, unlike pure water and solid salt, conducts an electric current, since it contains freely moving ions. Like salt solutions, alkali solutions conduct electric current. Salts and alkalis conduct electric current not only in solutions, but also in melts: upon melting, the crystal lattice is destroyed into ions and they begin to move freely, transferring an electric charge.

SUBSTANCES

ELECTROLYTES NON-ELECTROLYTES

“SUBSTANCES, SOLUTIONS OR MELTS OF WHICH CONDUCT ELECTRIC CURRENT ARE CALLED ELECTROLYTES.”

These are salts, acids, alkalis (electric current is transmitted in them due to the movement of “+” and “-” ions).

Now let’s test solutions of substances with covalent bonds - sugar, alcohol - for electrical conductivity. The light bulb does not light, which means that solutions of these substances do not conduct electric current.

“SUBSTANCES IN WHICH SOLUTIONS DO NOT CONDUCT ELECTRICITY ARE CALLED NON-ELECTROLYTES.

CONCLUSION: charge is carried by free ions that have the ability to move. This means that the behavior of substances in an aqueous solution depends on their structure.

2. Let us remember the structure of the water molecule. In a water molecule there is a polar covalent bond between the O and H atoms. The electron pairs connecting the atoms are shifted to O, where a partially “-” charge is formed, and H has a partially “+” charge. The bonds of each H atom with O in water form an angle of 104.5 with each other 0 , due to which the water molecule has an angular shape. A polar water molecule is depicted as dipoles

3. Let us consider the mechanism of dissociation using the example of a NaCl salt solution. When salt dissolves, the water dipoles are oriented with oppositely charged ends around the “+” and “-” ions of the electrolyte. Mutual attractive forces arise between the ions of the electrolyte and the water dipole. As a result, the connection between the ions weakens, and the ions move from the crystal to the solution (Fig. 42 of the textbook). The sequence of the dissociation process of substances with ionic bonds (salts and alkalis) will be as follows:

a) orientation of molecules - water dipoles near crystal ions

b) hydration (interaction) of water molecules with ions of the surface layer of the crystal

c) dissociation (decay) of the electrolyte crystal into hydrated ions.

The ongoing processes can be reflected in a simplified way using the equation: NaСl = Na+ + Cl -

Electrolytes, in whose molecules there is a covalent polar bond (for example, HCl), dissociate similarly, only in this case, under the influence of water dipoles, the covalent polar bond is converted into an ionic one and the sequence of processes will be as follows.

a) orientation of water molecules around the poles of an electrolyte molecule

b) hydration (interaction) of water molecules with electrolyte molecules

c) ionization of electrolyte molecules (conversion of a covalent polar bond into an ionic one).

d) dissociation (decay) of electrolyte molecules into hydrated ions.

A simplified equation for the dissociation of hydrochloric acid looks like this:

HCl = H + + Cl -

An ion surrounded by a hydration shell (water molecules) is calledhydrated.The presence of a hydration shell prevents the transition of ions into the crystal lattice. The formation of hydrated ions is accompanied by the release of energy, which is spent on breaking the bonds between the ions in the crystal.

Thus, when salts, alkalis and acids are dissolved, these substances break down into ions.

“The process of an electrolyte breaking down into ions when it is dissolved in water or melted is called electrolytic dissociation.”

The theory that explains the special behavior of electrolytes in a molten or dissolved state by decomposition into ions is calledtheory of electrolytic dissociation.

4. In electrolyte solutions, along with ions, there are also molecules. Therefore, electrolyte solutions are characterizeddegree of dissociation, which is denoted by the Greek letter α (“alpha”).

The degree of dissociation is the ratio of the number of particles disintegrated into ions (N d ), to the total number of dissolved particles (N P):

α=N d /N P

The degree of electrolyte dissociation is determined experimentally and is expressed in fractions or percentages. If α=0, then there is no dissociation, and if α=1, or 100%, then the electrolyte completely disintegrates into ions. Different electrolytes have different degrees of dissociation, that is, the degree of dissociation depends on the nature of the electrolyte. It also depends on the concentration: as the solution is diluted, the degree of dissociation increases.

Based on the degree of electrolytic dissociation, electrolytes are divided into strong and weak.

Strong electrolytes –electrolytes that, when dissolved in water, almost completely dissociate into ions. For such electrolytes, the degree of dissociation tends to unity.

Strong electrolytes include:

1) all soluble salts;

2) strong acids, for example: H 2 SO 4, HCl, HNO 3;

3) all alkalis, for example: NaOH, KOH.

Weak electrolytes- these are electrolytes that, when dissolved in water, almost do not dissociate into ions. For such electrolytes, the degree of dissociation tends to zero.

Weak electrolytes include:

weak acids – H 2 S, H 2 CO 3, HNO 2;
aqueous ammonia solution NH 3 *H 2 O;
water.

III. CONCLUSIONS and CONCLUSION.

What substances are called electrolytes? Give examples. Why do these substances conduct electricity?

What substances are called non-electrolytes? Give examples.

What is meant by electrolytic dissociation?

What does the degree of dissociation indicate?

How are electrolytes classified according to the degree of dissociation?

Chemical dictation

Write down the substances. Underline electrolytes with one line, non-electrolytes with two lines. Arrange the charges.

Liquid ammonia, calcium chloride solution, sulfuric acid, potassium nitrate, potassium hydroxide, acetone, calcium phosphate, benzene, sugar solution, nitric acid, calcium carbonate, hydrogen iodide.

Students will complete the assignment followed by a test.

Classification of substances SUBSTANCES ELECTROLYTES NON-ELECTROLYTES NaCl, NaOH, KNO 3 Sugar, glucose, alcohol SUBSTANCES, SOLUTIONS OR MELTS OF WHICH CONDUCT ELECTRIC CURRENT ARE CALLED ELECTROLYTES. SUBSTANCES IN WHICH SOLUTIONS DO NOT CONDUCT ELECTRICITY ARE CALLED NON-ELECTROLYTES.

Structure of the water molecule O H H - + 104.5 0

Scheme of electrolytic dissociation of a polar hydrogen chloride molecule H + CL - + + + + + + H + + - + + + + + + CL - + + + + + H + + - + + + + C L - + - + + + + +

“The process of an electrolyte breaking down into ions when it is dissolved in water or melted is called electrolytic dissociation.” 1887 Svante Arrhenius

Classification of electrolytes ELECTROLYTES STRONG WEAK NaCl, NaOH, KNO 3 NH 4 OH, HNO 2

Chemical dictation Write down the substances. Underline electrolytes with one line, non-electrolytes with two lines. Arrange the charges. Liquid ammonia, calcium chloride solution, sulfuric acid, potassium nitrate, potassium hydroxide, acetone, calcium phosphate, benzene, sugar solution, nitric acid, calcium carbonate, hydrogen iodide.

Kazakhstan, North Kazakhstan region, district named after Gabit Musrepov, Sokologorovka village

KSU "Sokologorovskaya Secondary School"

Lesson in 9th grade

Topic: “The essence of the dissociation process”

Lesson Plan

Subject: The essence of the electrolytic dissociation process

Lesson objectives: deepen and generalize knowledge, basic concepts of electrolytic dissociation; teach how to use them in composing dissociation equations; give an idea of the universality of the theory of electrolytic dissociation and its application to inorganic chemistry.

Basic concepts: electrolytes, non-electrolytes, dissociation, hydrates, crystalline hydrates.

Lesson structure

1) Organizational moment

2) Checking homework

3) Learning new material

4) Consolidation of new material

5) Homework, grading

Lesson progress

1) Organizational moment (3-5 min.)

2) Checking homework (10 min.)

a) Identify covalent polar and nonpolar bonds in the following molecules: N 2, CO 2, NH 3, SO 2, HBr.

b) What is electronegativity?

c) How are σ-bonds and π-bonds formed?

d) What is the reason for the sharp difference in the physical properties of CO 2 and SiO 2?

e) List the types of chemical bonds.

3) Studying new material (15-20 min.)

Electrolytes and non-electrolytes. You can get acquainted with the characteristics of the dissolution of substances with different types of chemical bonds in water experimentally by studying the electrical conductivity of solutions of these substances using a device for testing the electrical conductivity of solutions.

If you immerse the electrodes of the device, for example, in dry table salt, the light bulb will not light up. The same result will be obtained if the electrodes are immersed in distilled water. However, when the electrodes are immersed in an aqueous solution of sodium chloride, the light bulb begins to glow. This means that the sodium chloride solution conducts electric current. Other soluble salts, alkalis and acids behave similarly to sodium chloride. Salts and alkalis conduct electric current not only in aqueous solutions, but also in melts. Aqueous solutions, for example, sugar, glucose, alcohol, oxygen, nitrogen, do not conduct electric current. Based on these properties, all substances are divided into e electrolytes And non-electrolytes.

The mechanism of dissolution of substances with different types of chemical bonds in water. Of the examples considered, why do salts, alkalis and acids conduct electric current in an aqueous solution? To answer this question, it is necessary to remember that the properties of substances are determined by their structure. For example, the structure of sodium chloride crystals differs from the structure of oxygen and hydrogen molecules.

To correctly understand the mechanism of dissolution of substances with ionic bonds in water, one should also take into account that in water molecules there are covalent highly polar bonds between the hydrogen and oxygen atoms. Therefore, water molecules are polar. As a result, for example, when sodium chloride is dissolved, water molecules are attracted by their negative poles to the positive poles - to the negatively charged chloride ions. As a result, the bond between the ions is weakened and the crystal lattice is destroyed. This process is also facilitated by a large dielectric constant of water, which at 20ºС is equal to 81. The chemical bond between ions in water is weakened 81 times compared to vacuum.

When substances with a covalent highly polar bond, such as hydrogen chloride HCl, are dissolved in water, the nature of the chemical bond changes, i.e. under the influence of polar water molecules, the covalent polar bond turns into an ionic bond and then the process of separation of particles.

When electrolytes melt, the oscillatory movements of particles increase, which leads to a weakening of the connection between them. As a result, the crystal lattice is also destroyed. Consequently, when salts and alkalis are dissolved, these substances disintegrate into ions.

The process of an electrolyte breaking down into ions when it is dissolved in water or melted is called electrolytic dissociation.

Basic theoretical principles of electrolytic dissociation formulated in 1887 by the Swedish scientist Svante Arrhenius. However, S. Arrhenius failed to fully reveal the complexity of the process of electrolytic dissociation. He did not take into account the role of solvent molecules and believed that there were free ions in the aqueous solution. The concept of electrolytic dissociation was further developed in the works of Russian scientists I. A. Kablukov and V. A. Kistyakovsky. To understand the essence of the ideas of these scientists, let us familiarize ourselves with the phenomena that occur when substances dissolve in water.

When solid sodium hydroxide NaOH or concentrated sulfuric acid H 2 SO 4 is dissolved in water, strong heating occurs. Particular care must be taken when dissolving sulfuric acid, since due to an increase in temperature, some of the water can turn into steam and, under its pressure, can throw the acid out of the vessel. To avoid this, sulfuric acid is poured into water in a thin stream (but not vice versa!) with constant stirring.

If, for example, ammonium nitrate (ammonium nitrate) is dissolved in water in a thin-walled glass placed on a wet board, then such strong cooling is observed that the glass even freezes to it. Why, when substances dissolve, in some cases there is heating, and in others - cooling?

When solids dissolve, their crystal lattices are destroyed and the resulting particles are distributed between the solvent molecules. At the same time the necessary energy is absorbed from outside and cooling occurs. According to this feature, the dissolution process should be attributed to physical phenomena.

Why does heating occur when some substances dissolve?

As we know, the release of heat is a sign of a chemical reaction. Hence, when dissolved, chemical reactions also take place. For example, sulfuric acid molecules react with water molecules and compounds of the composition H 2 SO 4 ·H 2 O (sulfuric acid monohydrate) and H 2 SO 4 ·2H 2 O (sulfuric acid dihydrate) are formed, i.e. a sulfuric acid molecule attaches one or two water molecules.

The interaction of sulfuric acid molecules with water molecules is referred to as hydration reactions, and the substances that are formed in this case are called hydrates.

From the above examples it is clear that when solids are dissolved in water, both physical and chemical processes occur. If, as a result of hydration, more energy is released than is spent on the destruction of crystals of a substance, then dissolution is accompanied by heating, if, on the contrary, cooling.

Hence, dissolution is a physicochemical process.

This explanation of the essence of the dissolution process and the nature of solutions was first theoretically substantiated by the great Russian scientist D.I. Mendeleev. he developed hydration theory of solutions.

When studying hydration processes, scientists had a question: what particles does water react with?

I.A. Kablukov and V.A. Kistyakovsky independently suggested that electrolyte ions react with water molecules, i.e. is happening hydration of ions. This

4) Consolidating new material (5-7 min.)

a) When did research into air composition begin?

b) What substances are contained in air?

c) Which scientist first established the composition of French air in 1774?

5) Homework, grading (3 min.)

§26 retelling p.70-72; exercises No. 3, 4.5 p.72

This lesson is devoted to the study of the topic “Electrolytic dissociation”. In the process of studying this topic, you will understand the essence of some amazing facts: why solutions of acids, salts and alkalis conduct electric current; Why is the boiling point of an electrolyte solution higher than that of a non-electrolyte solution.

Topic: Chemical bond.

Lesson:Electrolytic dissociation

The topic of our lesson is “ Electrolytic dissociation" We will try to explain some amazing facts:

Why do solutions of acids, salts and alkalis conduct electric current?

Why does the boiling point of an electrolyte solution always be higher than the boiling point of a non-electrolyte solution of the same concentration?

Svante Arrhenius

In 1887, the Swedish physicist chemist Svante Arrhenius, While studying the electrical conductivity of aqueous solutions, he suggested that in such solutions substances disintegrate into charged particles - ions, which can move to the electrodes - a negatively charged cathode and a positively charged anode.

This is the reason for the electric current in solutions. This process is called electrolytic dissociation(literal translation - splitting, decomposition under the influence of electricity). This name also suggests that dissociation occurs under the influence of an electric current. Further research showed that this is not the case: ions are onlycharge carriers in solution and exist in it regardless of whether it passes throughcurrent solution or not. With the active participation of Svante Arrhenius, the theory of electrolytic dissociation was formulated, which is often named after this scientist. The main idea of this theory is that electrolytes spontaneously disintegrate into ions under the influence of a solvent. And it is these ions that are charge carriers and are responsible for the electrical conductivity of the solution.

Electric current is the directed movement of free charged particles. You already know that solutions and melts of salts and alkalis are electrically conductive, since they consist not of neutral molecules, but of charged particles - ions. When melted or dissolved, the ions become free carriers of electric charge.

The process of a substance breaking down into free ions when it dissolves or melts is called electrolytic dissociation.

Rice. 1. Scheme of decomposition into sodium chloride ions

The essence of electrolytic dissociation is that ions become free under the influence of a water molecule. Fig.1. The process of decomposition of an electrolyte into ions is represented using a chemical equation. Let us write the dissociation equation for sodium chloride and calcium bromide. When one mole of sodium chloride dissociates, one mole of sodium cations and one mole of chloride anions are formed. NaCl⇄ Na + + Cl -

When one mole of calcium bromide dissociates, one mole of calcium cations and two moles of bromide anions are formed.

CaBr 2 ⇄ Ca 2+ + 2 Br -

Please note: since the formula of an electrically neutral particle is written on the left side of the equation, the total charge of the ions must be equal to zero.

Conclusion: upon dissociation of salts, metal cations and anions of the acid residue are formed.

Let us consider the process of electrolytic dissociation of alkalis. Let us write the dissociation equation in a solution of potassium hydroxide and barium hydroxide.

When one mole of potassium hydroxide dissociates, one mole of potassium cations and one mole of hydroxide anions are formed. KOH⇄ K + + OH -

When one mole of barium hydroxide dissociates, one mole of barium cations and two moles of hydroxide anions are formed. Ba(OH) 2 ⇄ Ba 2+ + 2 OH -

Conclusion: During the electrolytic dissociation of alkalis, metal cations and hydroxide anions are formed.

Water-insoluble bases practically are not exposed electrolytic dissociation, since they are practically insoluble in water, and when heated they decompose, so it is not possible to obtain a melt.

Rice. 2. Structure of hydrogen chloride and water molecules

Consider the process of electrolytic dissociation of acids. Acid molecules are formed by polar covalent bonds, which means that acids consist not of ions, but of molecules.

The question arises: how then does the acid dissociate, that is, how do free charged particles form in acids? It turns out that ions are formed in acid solutions precisely during dissolution.

Let's consider the process of electrolytic dissociation of hydrogen chloride in water, but for this we will write down the structure of the molecules of hydrogen chloride and water. Fig.2.

Both molecules are formed by a polar covalent bond. The electron density in a hydrogen chloride molecule is shifted towards the chlorine atom, and in a water molecule - towards the oxygen atom. A water molecule is able to abstract a hydrogen cation from a hydrogen chloride molecule, resulting in the formation of a hydronium cation H 3 O + .

The equation for the reaction of electrolytic dissociation does not always take into account the formation of the hydronium cation - usually they say that a hydrogen cation is formed.

Then the dissociation equation for hydrogen chloride looks like this:

HCl⇄ H + + Cl -

When one mole of hydrogen chloride dissociates, one mole of hydrogen cation and one mole of chloride anions are formed.

Stepwise dissociation of sulfuric acid

Consider the process of electrolytic dissociation of sulfuric acid. Sulfuric acid dissociates stepwise, in two stages.

I-stage of dissociation

At the first stage, one hydrogen cation is removed and a hydrogen sulfate anion is formed.

II - stage of dissociation

At the second stage, further dissociation of hydrogen sulfate anions occurs. HSO 4 - ⇄ H + + SO 4 2-

This stage is reversible, that is, the resulting sulfate ions can attach hydrogen cations and turn into hydrogen sulfate anions. This is shown by the reversibility sign.

There are acids that do not dissociate completely even at the first stage - such acids are weak. For example, carbonic acid H 2 CO 3.

We can now explain why the boiling point of an electrolyte solution will be higher than the boiling point of a non-electrolyte solution.

When dissolving, the molecules of the solute interact with the molecules of the solvent, for example, water. The more particles of a solute there are in one volume of water, the higher its boiling point will be. Now imagine that equal amounts of an electrolyte substance and a non-electrolyte substance were dissolved in equal volumes of water. The electrolyte in water will disintegrate into ions, which means the number of its particles will be greater than in the case of dissolution of a non-electrolyte. Thus, the presence of free particles in the electrolyte explains why the boiling point of an electrolyte solution will be higher than the boiling point of a non-electrolyte solution.

Summing up the lesson

In this lesson, you learned that solutions of acids, salts and alkalis are electrically conductive, since when they dissolve, charged particles - ions are formed. This process is called electrolytic dissociation. When salts dissociate, metal cations and anions of acidic residues are formed. When alkalis dissociate, metal cations and hydroxide anions are formed. When acids dissociate, hydrogen cations and anions of the acid residue are formed.

1. Rudzitis G.E. Inorganic and organic chemistry. 9th grade: textbook for general education institutions: basic level / G. E. Rudzitis, F.G. Feldman. M.: Enlightenment. 2009 119 p.: ill.

2. Popel P.P. Chemistry: 8th grade: textbook for general education institutions / P.P. Popel, L.S. Krivlya. -K.: IC “Academy”, 2008.-240 p.: ill.

3. Gabrielyan O.S. Chemistry. 9th grade. Textbook. Publisher: Bustard: 2001. 224s.

1. No. 1,2 6 (p.13) Rudzitis G.E. Inorganic and organic chemistry. 9th grade: textbook for general education institutions: basic level / G. E. Rudzitis, F.G. Feldman. M.: Enlightenment. 2009 119 p.: ill.

2. What is electrolytic dissociation? What classes of substances belong to electrolytes?

3. Substances with what type of bond are electrolytes?