Lesson 5
Topic: Process Essence electrolytic dissociation
Goals and objectives:
Educational:to form the concepts of "electrolytes, non-electrolytes, solution, hydration, hydrates, crystalline hydrates, water of crystallization", to reveal the essence of the process of electrolytic dissociation, to consider the main provisions of the theory of electrolytic dissociation;
Developing: to develop the ability to work with text, to characterize the process of electrolytic dissociation;
Educational: to cultivate interest in chemistry, to form a scientific worldview.
Equipment: salt, water, table, textbook, notebooks, did. cards.
During the classes:
1) Org. moment
2) Checking d.z.
Frontal conversation: "The main classes of inorganic substances";
Individual letters. card survey
Option 1: Give definitions: salts, oxides. Give their classification.
Give examples
Option 2: Give definitions: bases, acids. Give their classification.
Give examples.
Dictation
Write the formulas of acids, their acid residues, indicate their valency.
3) Learning new material
1.Updating knowledge
I. Experiments with dry substances, solutions and melts to conduct electric current
Fig.1 p.3
Dry NaCl, soda
Distilled water - do not conduct electricity
Solutions of NaCl, alkalis, salts - conduct current
Solutions of glucose
Alcohol - do not conduct electricity
Sahara
Oxygen
nitrogen
II. Mechanism of dissolution in water
1) B-in with ionic bond
Fig. 2 Na + Cl - + H-O-H
In p-re ions are hydrated - surrounded by water molecules
2) In-in with a covalent polar bond
НCl H + + Cl - hydrated ions
Covalent bond becomes ionic
III. Substances
Electrolytes Non-electrolytes p.5
… …
Definitions
Salt oxygen
Alkali nitrogen
Hydrogen acids
With ionic or covalent with covalent non-polar / weakly polar bond
highly polar bond
IV. Electrolytic dissociation -the process of decomposition of an electrolyte into ions when dissolved in water or melted.
V. Dissolution is a physical and chemical process
V. Hydration of ions
Kablukov and Kistyakovsky suggested that when p-rhenium, water molecules attach to ions, forming hydrates
Definition p.6
VI. Crystal hydrates and water of crystallization
C.7 definition
VII.Basic Provisionstheories of electrolytic dissociation
Sam-but p.8-9 by heart
4) Fixing
B.1-6 p.13
5) Reflection
6) d.z.
P.1 retelling, definitions and provisions of the theory by heart
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Abstract
chemistry lesson in 8th grade
School No. 16 in Saransk
4th year students of the chemical department
Institute of Physics and Chemistry
Moscow State University N. P. Ogareva
Lesson topic: electrolytic dissociation.
Lesson Objectives:
Educational:to form basic concepts about electrolytes and non-electrolytes, about writing dissociation equations, to consider the mechanism of dissociation of substances with different types of bonds.
Educational: Formation of teamwork skills in combination with individual work, increasing the creative activity of students, cognitive interest to chemistry, a sense of responsibility to their comrades.
Developing: Development in students cognitive abilities, the formation of independent thinking, the ability to reason logically, generalize and draw conclusions from the knowledge gained.
Lesson type: combined.
Lesson methods:
General: explanatory and illustrative;
Private: verbally - visually - practical.
Equipment and reagents:distilled water, KCl (solution and solid), sucrose solution, alkali, HCl, CuSO 4 , a device for studying the electrical conductivity of solutions of these substances, a chemical beaker.
Lesson plan:
Organizing time 1 minute.
Checking homework 10 min
Learning new material 30 min
Generalization 3 min
Summing up 1min
(grading, homework)
Hello guys!
I am glad to welcome you to the lesson.
My dear friends!
I congratulate everyone on my own behalf.
Each of you is good in your own way:
For people, for business, it’s good for everyone.
Now guys don't be sad
And solve problems
Come on, feel free to fly
And get assignments.
Card: "Extra solution"
Name the “extra” (falling out of the row) solution out of the five proposed. Why do you think that he is redundant? What do the other four solutions have in common?
copper-zinc alloy (brass)
solution of iodine in alcohol (iodine tincture)
copper-tin alloy (bronze)
copper-nickel alloy (cupronickel)
aluminum alloy with copper (duralumin)
Card "Missing Solution"
Which of the following solutions (a - c) would you place instead of the question mark in point 5? Explain why you chose this solution? Why are other solutions not suitable?
solution of oxygen in water
sulfuric acid solution in water
sugar solution in water
nitric acid solution in water
but) carbon dioxide in air, b) a solution of sodium chloride in water,
c) an alloy of gold and silver.
At this time, the questions are asked frontally:
Let's remember the role of solutions in nature and the practical activities of people.
Explain the essence of the physical and chemical theory of solutions. Why do they need to be combined?
So what is a solution?
Give evidence chemical interaction solute with water?
What is: hydration, hydrates, crystalline hydrates?
What is the solubility of substances in water?
How are the concepts “highly soluble in water”, “slightly soluble”, “practically insoluble” defined quantitatively?
Let's play the "pass it on" game:
The question is written on the board: Is this substance classified as slightly soluble, highly soluble or practically insoluble? (work with the solubility table)
The class is divided into six groups (in rows). Each group receives an album sheet divided into four columns (the student's last name and answers to the question) and as many lines as there are players in the team.
The task is to come up with a connection that is not the same as that of the neighbors and complete the tasks.
If the student can immediately answer the question, then he writes the answer and quickly passes the sheet to the team member sitting behind. And the team whose sheet reaches the teacher first gets extra points.
Let me read you a poem:
There lived one ionic crystal,
For ions, the house is huge,
He was handsome and even.
But trouble happened to him.
A drop fell on him
And the crystal was gone in an instant:
Spread into ions
His clever water.
The whole family was surprised:
"What happened outside?"
And in order to answer this question today's topic "Electrolytic dissociation." will help you. (floppy disk No. 1: topic name.) And the purpose of our lesson is to introduce new concepts of this topic.
So, you know that there are substances that conduct well electricity- these are (conductors).
Conductors are divided into conductors of the first kind - metals and conductors of the second kind - electrolytes.
Remember what is electric current?(This is the directed motion of charged particles.)
Because We will work with an electrical apparatus, it is necessary to follow the safety regulations. What rules do you know? (do not touch bare wires, electrodes with your hands, especially with wet ones; when the device lights up, turn off the general switch, do not leave it plugged in; extinguish with sand)
Let's do an experiment to study the electrical conductivity of solutions of certain substances.
The device consists of a glass into which a solution of the test substance is poured. A plate of ebonite is placed on the glass with two carbon electrodes mounted in it, to the terminals of which wires are attached. One of them is connected to a light bulb. The output contact from the light bulb and the wire from the other terminal go to the current source.
We lower the electrodes into a glass with solid crystalline salt CuSO 4 (the light does not light up), then into the CuSO solution 4 (the bulb lights up), then into solutions of HCl, sucrose, alkali and into distilled water.
During the experiment, the guys fill out the table:
CuSO4 |
etc.
Tell me, why does a solution of table salt conduct an electric current, but a solution of sucrose does not?(this is due to the formation of ions.) And what is an ion? (these are the smallest charged particles of a substance that determine the chemical and physical properties of this substance).
Thus, according to the ability to conduct an electric current, substances are divided into electrolytes and non-electrolytes.(diskette No. 1: definitions of concepts: electrolytes and non-electrolytes)
It can be seen from the experience that electrolytes include solutions of salts, acids, bases, and non-electrolytes - organic compounds, solids, gases.
What is the difference between electrolytes and non-electrolytes?(connection type.). Those. electrolytes include substances with ionic and covalent-polar bonds.
The ability of electrolytes to conduct electric current is fundamentally different from the ability to conduct electric current of metals. Why? (because the electrical conductivity of metals is due to the movement of electrons, and the electrical conductivity of electrolytes is associated with the movement of ions.)
Let's study the behavior of substances in aqueous solution using sodium chloride as an example.
Experience: we lower the electrodes into a glass with a solution of sodium chloride (the light bulb lights up).
From the result of the experiment, we conclude that under the influence of water, substances undergo changes. Water causes electrolytes to break down into ions. This process is called dissociation.
This process was studied by the Swedish scientist Svante Arrhenius. Let's listen to your classmate's message about his achievements in chemistry (disc #2: portrait of Svante Arrhenius)
Being an adherent of the physical theory of solutions, the Swedish scientist Svante Arrhenius could not answer the question: why does the dissociation of salts and alkalis occur in an aqueous solution? The answer to it was given by Russian chemists Kablukov, Kistyakovsky. The essence of their additions is as follows (for the record): the reason for the dissociation of the electrolyte in the solution is its hydration, i.e. interaction with water molecules. And the ions that are formed during dissociation will be hydrated, i.e. associated with water molecules, and their properties will differ from non-hydrated ones.
What is a water molecule? In general, the water molecule is not charged. But inside the water molecule, the oxygen and hydrogen atoms are arranged so that the positive and negative charges are at opposite ends of the molecule. Therefore, the water molecule is a dipole:
Let us consider the mechanism of dissociation of sodium chloride upon dissolution. What type of connection does this connection have? (ionic).(disk №2: dissociation of substances with ionic structure).
I note that electrolytes that have an ionic structure dissociate most easily.
The dissociation of substances with an ionic bond proceeds in three stages:
at first, randomly moving water molecules near the ions of the crystal are oriented towards them with oppositely charged poles - orientation occurs.
then the water dipoles are attracted, interact with the ions of the surface layer of the crystal, hydration occurs.
When a water molecule moves into a solution, it takes hydrated ions with it. Dissociation takes place.
And how do polar electrolyte molecules react with water molecules?
Similar, but one step more (disc №2: dissociation of substances with a covalent-polar bond):
orientation
hydration
ionization, i.e. the transformation of a covalent-polar bond into an ionic one.
dissociation
Thus, electrolytic dissociation is the process of decomposition of an electrolyte into ions upon dissolution.
It should be taken into account that in electrolyte solutions randomly moving ions can collide and combine into a molecule. This is the process of association.
Pay attention to the sign in the dissociation equation. (disc #1: writing the dissociation equation). Since the number of water molecules that ions attach is unknown, the process of electrolyte dissociation is depicted in a simplified way: NaCl = Na+ +Cl-
For example, write down the abbreviated equation for the dissociation of some substances with an ionic structure: Ca (OH) 2, Na 2 SO 4, Na 3 PO 4, Al 2 (SO 4).
In today's lesson, you learned what electrolytic dissociation is, the dissociation mechanism.
Based on the foregoing, say what processes are encrypted in the poem:
There lived one ionic crystal,
For ions, the house is huge,
He was handsome and even.
But trouble happened to him.
A drop fell on him
And the crystal was gone in an instant:
Spread into ions
His clever water.
The whole family was surprised:
"What happened outside?"
It suddenly appeared next to a series of molecules,
They ran up in a noisy swarm,
Surrounded by a dense formation:
“We want to offer the heroes
our friendship forever...
Hydrogen to anions,
hydroxide to cations,
Do not get away from them ions
Neither here nor there.
(dissolution of a substance with an ionic bond, orientation of water molecules, hydration, dissociation)
Homework: § 35, No. 2,5,6 p.147.
Kazakhstan, North Kazakhstan region, area named after Gabit Musrepov, Sokologorovka village
KSU "Sokologorovskaya secondary school"
Lesson in 9th grade
Topic: "The essence of the dissociation process"
Lesson plan
Topic: The essence of the process of electrolytic dissociation
Lesson Objectives: deepen and generalize knowledge, basic concepts of electrolytic dissociation; to teach how to apply them in compiling 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, crystal hydrates.
Lesson structure
1) Organizational moment
2) Checking homework
3) Learning new material
4) Consolidation of new material
5) Homework, grading
During the classes
1) Organizational moment (3-5 min.)
2) Checking homework (10 min.)
a) Determine the covalent polar and non-polar 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 physical properties CO 2 and SiO 2?
e) List the types chemical bond.
3) Learning new material (15-20 min.)
Electrolytes and non-electrolytes. The features of the dissolution of substances with various types of chemical bonds in water can be studied experimentally by studying the electrical conductivity of solutions of these substances using a device for testing the electrical conductivity of solutions.
If the electrodes of the device are immersed, for example, in a dry table salt, the lamp will not light up. The same result will be obtained if the electrodes are lowered into distilled water. However, when the electrodes are immersed in an aqueous solution of sodium chloride, the bulb starts to glow. This means that sodium chloride solution conducts electricity. 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, such as sugar, glucose, alcohol, oxygen, nitrogen, do not conduct electricity. Based on these properties, all substances are divided into e electrolytes And non-electrolytes.
The mechanism of dissolution in water of substances with different nature of the chemical bond. Why do salts, alkalis and acids in an aqueous solution conduct an electric current from the examples considered? 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.
For a correct understanding of the mechanism of dissolution of substances with an ionic bond in water, it should also be taken into account that in water molecules there are covalent highly polar bonds between 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 their positive poles - to 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 dielectric constant of water, which at 20ºС is equal to 81. The chemical bond between ions in water is weakened by 81 times compared to vacuum.
When substances with a highly polar covalent bond are dissolved in water, for example, hydrogen chloride HCl, the nature of the chemical bond changes, i.e. under the influence of polar water molecules, the covalent polar bond turns into an ionic one, and then the process of splitting off particles.
When electrolytes are melted, the oscillatory movements particles, which leads to a weakening of the bond between them. As a result, the crystal lattice is also destroyed. Consequently, when salts and alkalis are dissolved, these substances decompose into ions.
The process of decomposition of the electrolyte into ions when it is dissolved in water or melted is called electrolytic dissociation.
Basic theoretical provisions 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 free ions were present in an 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's get acquainted with the phenomena that occur when substances are dissolved 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, because due to an increase in temperature, part of the water can turn into steam and, under its pressure, can throw 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 a strong cooling is observed that the glass even freezes to it. Why, when dissolving substances, heating is observed in some cases, and cooling in others?
When dissolved solids their destruction occurs crystal lattices and the distribution of the resulting particles between solvent molecules. Wherein the necessary energy is absorbed from the outside and cooling occurs. On this basis, the dissolution process should be attributed to physical phenomena.
Why does heating occur when some substances are dissolved?
As we know, the release of heat is a sign of a chemical reaction. Consequently, when dissolved, and chemical reactions . 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 molecule of sulfuric acid attaches one or two molecules of water.
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 can be seen that when solids are dissolved in water, both physical and chemical processes occur. If as a result of hydration more energy is released than it is spent on the destruction of the crystals of the substance, then the dissolution is accompanied by heating, if vice versa - by cooling.
Consequently, dissolution is a physicochemical process.
Such an 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. they developed hydrate theory of solutions.
When studying the processes of hydration, scientists had a question: with what particles does water react?
I.A.Kablukov and V.A.Kistyakovsky, independently of one another, suggested that electrolyte ions react with water molecules, i.e. going on ion hydration. This
4) Consolidation of new material (5-7 min.)
a) When did research on the composition of air begin?
b) What substances are present in the air?
c) Which scientist first established the composition of French air in 1774?
5) Homework, grading (3 min.)
§26 retelling pp.70-72; exercises No. 3, 4,5 p.72
2
7
Anions Cations Anode Cathode - +
Solution Crystal NaCl Na + + Cl H2OH2O H2OH2O Fig.4.
10 HCl solution H + + Cl - H2OH2O H2OH2O Rice HCl Cl - H+H+ + - H+H Cl-Cl-
14 Verification test. Option 1. Option 2. 1. Non-electrolytes include: 1) sodium carbonate 2) ethanol 3) hydrochloric acid 4) zinc nitrate 1. Non-electrolytes include: 1) barium chloride 2) sugar 3) sulphuric acid 4) potassium carbonate 2. With the formation of metal cations and anions of the acid residue, it dissociates: 1). copper (II) hydroxide 2). sodium hydroxide 3). aluminum chloride 4). carbonic acid 2. With the formation of metal cations and anions of the acid residue, it dissociates: 1) sucrose 2) sodium hydroxide 3) aluminum bromide 4) nitric acid 3. Both substances in the group are electrolytes: 1). CH4, CO2 2). C2H5OH, HNO3 3). CaO, BaSO4 4). NaCl, KOH 3. Electrolytes are both substances in the group: 1). glycerin, SO2 2). CuCl2, KOH 3). BaO, K2SO4 4). Fe(OH)3, H2SiO3 4. Most hydrogen ions are formed during dissociation equal to: 1). HI 2). H2CO3 3). H2S 4). H2SiO3 4. Most hydrogen ions are formed during dissociation equal to: 1). H3PO4 2). H2SO4 3). HNO3 4). HF 5. The sum of the coefficients in the aluminum sulfate dissociation equation is: 1). 4 2). 6 3). 2 4) The sum of the coefficients in the sodium carbonate dissociation equation is: 1). 4 2). 3 3). 2 4). one
