A dispersed system is a system in which there is only one substance. Physical chemistry of dispersed systems definition of dispersed systems. Classification of disperse systems
Chemistry lesson in 11th grade: “Dispersed systems and solutions”
The goal is to give the concept of dispersed systems and their classification. Reveal the significance of colloidal systems in the life of nature and society. Show the relativity of dividing solutions into true and colloidal.
Equipment and materials:
Technological maps: diagram-table, laboratory work, instructions.
Equipment for laboratory work:
Reagents: sugar solution, iron (III) chloride solution, a mixture of water and river sand, gelatin, paste, oil, aluminum chloride solution, table salt solution, a mixture of water and vegetable oil.
Chemical beakers
Paper filters.
Black paper.
Flashlights
Progress of a chemistry lesson in 11th grade:
| Lesson stage | Features of the stage | Teacher's actions | Student actions |
| Organizational (2 min.) | Preparing for the lesson | Greets students. |
Getting ready for the lesson. Greet the teacher. |
| Introduction (5 min.) | Introduction to a new topic. |
Leads to the topic of the lesson, tasks and “questions for yourself” Introduces the topic of the lesson. Displays the tasks for today's lesson. |
Take part in the discussion of the topic. Get acquainted with the topic of the lesson and tasks (APPENDIX No. 1) Write down three questions on the topic that you would like answers to. |
|
Theoretical part (15 minutes.) |
Explanation of a new topic. | Gives tasks for working in groups to search for new material (APPENDIX No. 3,4) | Having united in groups, they complete tasks in accordance with the technological map provided by the diagram (APPENDIX No. 4) and the teacher’s requirements. |
| Summing up the theoretical part (8 min.) | Conclusions based on the obtained theoretical knowledge. |
Posts blank diagrams (A3 format) on the board in advance for students to visually fill out. (APPENDIX No. 4) Together with students, formulates the main theoretical conclusions. |
Use a marker to fill out diagrams corresponding to the one you worked on, and report on the work done in groups Record the main conclusions in technological maps. |
| Practical part (10 min.) | Performing laboratory work, consolidating the experience gained. | Offers to perform laboratory work on the topic “Dispersed systems” (APPENDIX No. 2) | Perform laboratory work (APPENDIX No. 2), fill out forms in accordance with the instructions for laboratory work and the requirements of the teacher. |
|
Generalization and conclusions (5 min.) |
Summing up the lesson. Homework. |
Together with the students, he makes a conclusion regarding the topic. Offers to correlate the questions that were written at the beginning of the lesson with what they received at the end of the lesson. |
Summarize, write down homework. |
Forms and methods of control:
Technological diagrams for filling (APPENDIX No. 4).
Laboratory work (APPENDIX No. 2)
Control is carried out frontally in oral and written form. Based on the results of laboratory work, cards with laboratory work are handed over to the teacher for checking.
1. Introduction:
Tell me, what is the difference between marble and granite? What about mineral and distilled water?
(answer: marble is a pure substance, granite is a mixture of substances, distilled water is a pure substance, mineral water- a mixture of substances).
Fine. What about milk? Is it a pure substance or a mixture? What about the air?
The state of any pure substance is described very simply - solid, liquid, gaseous.
But absolutely pure substances do not exist in nature. Even a small amount of impurities can significantly affect the properties of substances: boiling point, electrical and thermal conductivity, reactivity, etc.
Obtaining absolutely pure substances is one of the most important tasks of modern chemistry, because it is the purity of a substance that determines the possibility of it demonstrating its individual means (demonstration of labeled reagents).
Consequently, in nature and the practical life of man one encounters not individual substances, but systems of them.
Mixtures of different substances in different states of aggregation can form heterogeneous and homogeneous systems. Homogeneous systems are solutions, which we learned about in the last lesson.
Today we will get acquainted with heterogeneous systems.
2. The topic of today's lesson is DISPERSE SYSTEMS.
After studying the topic of the lesson, you will learn:
the importance of dispersed systems.
These, as you understand, are our main tasks. They are written in your technological maps. But to make our work more productive and motivated, I suggest that next to the main tasks you write at least three questions that you would like to find an answer to during this lesson.
3. Theoretical part.
Dispersed systems - what are they?
Let's try to derive a definition together based on the construction of words.
1) System (from ancient Greek “system” - a whole made up of parts; connection) - a set of elements that are in relationships and connections with each other, which forms a certain integrity, unity.
2) Dispersion - (from Latin dispersio - scattering) scattering of something, fragmentation.
Dispersed systems are heterogeneous (inhomogeneous) systems in which one substance in the form of very small particles is evenly distributed in the volume of another.
If we look back at the review and previous lesson, we can remember that: Solutions are made up of two components: the solute and the solvent.
Dispersed systems, like mixtures of substances, have a similar structure: they consist of small particles that are evenly distributed in the volume of another substance.
Take a look at your technological maps and try to create two similar schemes from disparate parts: for a solution and for a dispersed system.
Let's check the results by comparing them with the image on the screen.
So, the dispersion medium in the dispersed system acts as a solvent, and is the so-called. the continuous phase, and the dispersed phase is the role of the solute.
Since the dispersion system is a heterogeneous mixture, there is an interface between the dispersed medium and the dispersion phase.
Classification of disperse systems.
You can study each disperse system separately, but it is better to classify them, highlight the general, typical and remember this. To do this, you need to determine on what grounds to do this. You are grouped into groups, each of which is given a task and an accompanying flowchart.
Guided by the literature offered to you, find in the text the classification sign proposed for you to study, study it.
Create a cluster (block diagram), indicating the characteristics and properties of dispersed systems, give examples of it. To help you with this, a blank flowchart has already been provided for you to fill out.
4. Conclusion on the theoretical task.
Let's summarize.
I ask one person from each team to come out and fill out the diagrams posted on the board.
(students come up and fill out each of the diagrams with a marker, and then report on the work done)
Well done, now let's fix it:
What is the basis for the classification of disperse systems?
What types of disperse systems are divided into?
What features of colloidal solutions do you know?
What is another name for gels? What is their significance? What makes them special?
5. Practical part.
Now that you are familiar with the features of dispersed systems and their classification, and have also determined by what principle dispersed systems are classified, I suggest you consolidate this knowledge in practice by completing the appropriate laboratory work offered to you on a separate form.
You are grouped into groups of 2 people. For each group you have attached a corresponding form with laboratory work, as well as a specific set of reagents that you need to study.
You have been given a sample of the dispersed system.
Your task: using the instructions, determine which dispersion system was given to you, fill out the table and draw a conclusion about the features of the dispersion system.
6. Generalization and conclusions.
So, in this lesson, we studied in more depth the classification of dispersed systems, their importance in nature and human life.
However, it should be noted that there is no sharp boundary between the types of disperse systems. The classification should be considered relative.
Now let’s get back to the tasks assigned for today’s lesson:
What are disperse systems?
what are disperse systems?
What properties do disperse systems have?
the importance of dispersed systems.
Pay attention to the questions you have written down for yourself. In the reflection frame, note the usefulness of this lesson.
7. Homework.
We constantly encounter dispersed systems in nature and everyday life; even in our body there are dispersed systems. In order to consolidate knowledge about the importance of dispersed systems, you are asked to complete homework in the form of an essay/
Choose a disperse system that you constantly encounter in your life. Write a 1-2 page essay: “What is the significance of this dispersed system in human life? What similar disperse systems with similar functions are still known?”
Thank you for the lesson.
Dispersed systems. Definition. Classification.
Solutions
In the previous paragraph we talked about solutions. Let us briefly recall this concept here.
Solutions are called homogeneous (homogeneous) systems consisting of two or more components.
Homogeneous system is a homogeneous system, chemical composition And physical properties in which all parts are the same or change continuously, without jumps (there are no interfaces between parts of the system).
This definition of a solution is not entirely correct. It rather refers to true solutions.
At the same time, there are also colloidal solutions, which are not homogeneous, but heterogeneous, i.e. consist of different phases separated by an interface.
In order to achieve greater clarity in definitions, another term is used - dispersed systems.
Before considering dispersed systems, let’s talk a little about the history of their study and the appearance of such a term as colloidal solutions.
Background
Back in 1845, the chemist Francesco Selmi, while studying the properties of various solutions, noticed that biological fluids - serum and blood plasma, lymph and others - differ sharply in their properties from ordinary true solutions, and therefore such liquids were called pseudo-solutions.
Colloids and crystalloids
Further research in this direction, carried out since 1861 by the English scientist Thomas Graham, showed that some substances that quickly diffuse and pass through plant and animal membranes easily crystallize, while others have a low ability to diffusion, do not pass through membranes and do not crystallize , but form amorphous precipitates.
Graham named the first crystalloids, and the second – colloids(from the Greek word kolla - glue and eidos - kind) or glue-like substances.
In particular, it was found that substances capable of forming amorphous sediments, such as albumin, gelatin, gum arabic, iron and aluminum hydroxides and some other substances, diffuse in water slowly compared to the diffusion rate of crystalline substances such as table salt , magnesium sulfate, cane sugar, etc.
The table below shows the diffusion coefficients D for some crystalloids and colloids at 18°C.
The table shows that there is an inverse relationship between molecular weight and diffusion coefficient.
In addition, crystalloids were found to have the ability not only to diffuse quickly, but also dialyze, i.e. pass through membranes, as opposed to colloids, which have larger molecular sizes and therefore diffuse slowly and do not penetrate membranes.
The walls of a bull's bladder, cellophane, films of ferrous-cyanide copper, etc. are used as membranes.
Based on his observations, Graham established that all substances can be divided into crystalloids and colloids.
Russians disagree
Against such strict division chemical substances a professor at Kyiv University objected I.G. Borschev(1869). Borshchev's opinion was later confirmed by the research of another Russian scientist Weimarn, who proved that the same substance, depending on conditions, can exhibit the properties of colloids or crystalloids.
For example, a solution of soap in water has the properties colloid, and soap dissolved in alcohol exhibits properties true solutions.
In the same way, crystalline salts, for example, table salt, dissolved in water, give true solution, and in benzene – colloidal solution and so on.
Hemoglobin or egg albumin, which has the properties of colloids, can be obtained in a crystalline state.
DI. Mendeleev believed that any substance, depending on the conditions and nature of the environment, can exhibit properties colloid. Currently, any substance can be obtained in a colloidal state.
Thus, there is no reason to divide substances into two separate classes - crystalloids and colloids, but we can talk about the colloidal and crystalloid states of the substance.
The colloidal state of a substance means a certain degree of its fragmentation or dispersion and the presence of colloidal particles in suspension in a solvent.
Science studying physicochemical characteristics heterogeneous highly dispersed and high-molecular systems is called colloid chemistry.
Dispersed systems
If one substance, which is in a crushed (dispersed) state, is evenly distributed in the mass of another substance, then such a system is called dispersed.
In such systems, the fragmented substance is usually called dispersed phase, and the environment in which it is distributed is dispersion medium.
So, for example, a system representing agitated clay in water consists of suspended small particles of clay - the dispersed phase and water - the dispersion medium.
Dispersed(fragmented) systems are heterogeneous.
Dispersed systems, in contrast to heterogeneous ones with relatively large, continuous phases, are called microheterogeneous, and colloidal dispersed systems are called ultramicroheterogeneous.
Classification of disperse systems
Classification of dispersed systems is most often made based on degree of dispersion or state of aggregation dispersed phase and dispersion medium.
Classification by degree of dispersion
All dispersed systems Based on the size of dispersed phase particles, they can be divided into the following groups:
For reference, here are the units of size in the SI system:
1 m (meter) = 102 cm (centimeter) = 103 mm (millimeter) = 106 microns (micrometer) = 109 nm (nanometer).
Sometimes other units are used - mk (micron) or mmk (millimicron), and:
1 nm = 10 -9 m = 10 -7 cm = 1 mmk;
1 µm = 10 -6 m = 10 -4 cm = 1 µm.
Coarse dispersed systems.
These systems contain as a dispersed phase the largest particles with a diameter of 0.1 microns and above. These systems include suspensions And emulsions.
Suspensions are systems in which a solid substance is in a liquid dispersion medium, for example, a suspension of starch, clay, etc. in water.
Emulsions are called dispersion systems of two immiscible liquids, where droplets of one liquid are suspended in the volume of another liquid. For example, oil, benzene, toluene in water or droplets of fat (diameter from 0.1 to 22 microns) in milk, etc.
Colloidal systems.
They have the particle size of the dispersed phase from 0.1 µm to 1 µm(or from 10 -5 to 10 -7 cm). Such particles can pass through the pores of filter paper, but do not penetrate the pores of animal and plant membranes.
Colloidal particles if they have an electric charge and solvation-ion shells, they remain in a suspended state and, without changing conditions, may not precipitate for a very long time.
Examples of colloidal systems include solutions of albumin, gelatin, gum arabic, colloidal solutions of gold, silver, arsenic sulfide, etc.
Molecular dispersed systems.
Such systems have particle sizes not exceeding 1 mm. Molecular dispersed systems include true solutions of non-electrolytes.
Ion-dispersed systems.
These are solutions of various electrolytes, such as salts, bases, etc., which disintegrate into corresponding ions, the sizes of which are very small and go far beyond
10 -8 cm.
Clarification on the representation of true solutions as dispersed systems.
From the classification given here it is clear that any solution (both true and colloidal) can be represented as a dispersed medium. True and colloidal solutions will differ in the particle sizes of the dispersed phases. But above we wrote about the homogeneity of true solutions, and dispersion systems are heterogeneous. How to resolve this contradiction?
If speak about structure true solutions, then their homogeneity will be relative. The structural units of true solutions (molecules or ions) are much smaller than the particles of colloidal solutions. Therefore, we can say that compared to colloidal solutions and suspensions, true solutions are homogeneous.
If we talk about properties true solutions, then they cannot be fully called dispersed systems, since the mandatory existence of dispersed systems is the mutual insolubility of the dispersed substance and the dispersion medium.
In colloidal solutions and coarse suspensions, the dispersed phase and the dispersion medium practically do not mix and do not react chemically with each other. This cannot be said at all about true solutions. In them, when dissolved, substances mix and even interact with each other. For this reason, colloidal solutions differ sharply in properties from true solutions.
The sizes of some molecules, particles, cells.
As the particle sizes change from the largest to the smallest and back, the properties of dispersed systems will change accordingly. Wherein colloidal systems occupy as it were intermediate position between coarse suspensions and molecular disperse systems.
Classification according to the state of aggregation of the dispersed phase and dispersion medium.
Foam is a dispersion of gas in a liquid, and in foams the liquid degenerates into thin films separating individual gas bubbles.
Emulsions are dispersed systems in which one liquid is crushed by another liquid that does not dissolve it (for example, water in fat).
Suspensions are called low-disperse systems of solid particles in liquids.
Combinations of three types of aggregative states make it possible to distinguish nine types of dispersed systems:
Dispersed phase | Dispersive medium | Title and example |
|---|---|---|
Gaseous | Gaseous | No disperse system is formed |
Gaseous | Gas emulsions and foams |
|
Gaseous | Porous bodies: foam pumice |
|
Gaseous | Aerosols: fogs, clouds |
|
Emulsions: oil, cream, milk, margarine, butter |
||
Capillary systems: Liquid in porous bodies, soil, soil |
||
Gaseous | Aerosols (dusts, fumes), powders |
|
Suspensions: pulp, sludge, suspension, paste |
||
Solid systems: alloys, concrete |
Sols are another name for colloidal solutions.
Colloidal solutions are also called sols(from Latin solutus - dissolved).
Dispersed systems with a gaseous dispersion medium are called aerosols. Fogs are aerosols with a liquid dispersed phase, and dust and smoke are aerosols with a solid dispersed phase. Smoke is a more highly dispersed system than dust.
Dispersed systems with a liquid dispersion medium are called lysols(from the Greek “lios” - liquid).
Depending on the solvent (dispersion medium), i.e. water, benzene alcohol or ether, etc., there are hydrosols, alcosols, benzols, etherosols, etc.
Cohesively dispersed systems. Gels.
Dispersed systems can be freely dispersed And cohesively dispersed depending on the absence or presence of interaction between particles of the dispersed phase.
TO freely dispersed systems include aerosols, lysols, diluted suspensions and emulsions. They are fluid. In these systems, particles of the dispersed phase have no contacts, participate in random thermal motion, and move freely under the influence of gravity.
The pictures above show free-dispersed systems:
In the pictures a B C depicted corpuscular-dispersed systems:
a, b- monodisperse systems,
V- polydisperse system,
On the image G depicted fiber-dispersed system
On the image d depicted film-dispersed system
- solid. They arise when particles of the dispersed phase come into contact, leading to the formation of a structure in the form of a framework or network.
This structure limits the fluidity of the dispersed system and gives it the ability to retain its shape. Such structured colloidal systems are called gels.
The transition of a sol to a gel, which occurs as a result of a decrease in the stability of the sol, is called gelation(or gelatinization).
In the pictures a B C depicted cohesive dispersed systems:
A- gel,
b- coagulum with a dense structure,
V- coagulum with a loose “arched” structure
In the pictures g, d depicted capillary-dispersed systems
Powders (pastes), foams– examples of cohesively dispersed systems.
The soil, formed as a result of contact and compaction of dispersed particles of soil minerals and humus (organic) substances, is also a coherently dispersed system.
A continuous mass of substance can be penetrated by pores and capillaries, forming capillary-dispersed systems. These include, for example, wood, leather, paper, cardboard, fabrics.
Lyophilicity and lyophobicity
A general characteristic of colloidal solutions is the property of their dispersed phase to interact with the dispersion medium. In this regard, two types of sols are distinguished:
1. Lyophobic(from Greek phobia - hatred) And
2.Lyophilic(from Greek philia – love).
U lyophobic In sols, the particles have no affinity for the solvent, interact weakly with it, and form around themselves a thin shell of solvent molecules.
In particular, if the dispersion medium is water, then such systems are called hydrophobic, for example, sols of metals iron, gold, arsenic sulfide, silver chloride, etc.
IN lyophilic systems there is an affinity between the dispersed substance and the solvent. The particles of the dispersed phase, in this case, acquire a more voluminous shell of solvent molecules.
In the case of an aqueous dispersion medium, such systems are called hydrophilic, such as solutions of protein, starch, agar-agar, gum arabic, etc.
Coagulation of colloids. Stabilizers.
Substance at the interface.
All liquids and solids are limited by an outer surface at which they come into contact with phases of a different composition and structure, for example, vapor, another liquid or a solid.
Properties of matter in this interfacial surface, with a thickness of several diameters of atoms or molecules, differ from the properties inside the volume of the phase.
Inside the volume of a pure substance in a solid, liquid or gaseous state, any molecule is surrounded by similar molecules.
In the boundary layer, molecules are in interaction with another number of molecules (different in comparison with the interaction inside the volume of the substance).
This occurs, for example, at the interface of a liquid or solid with its vapor. Either in the boundary layer molecules of a substance interact with molecules of another chemical nature, for example, at the boundary of two mutually poorly soluble liquids.
As a result, differences in the nature of the interaction inside the bulk of the phases and at the phase boundary arise force fields associated with this unevenness. (More on this in the section Surface tension of a liquid.)
The greater the difference in the intensity of intermolecular forces acting in each of the phases, the greater the potential energy of the interphase surface, briefly called surface energy.
Surface tension
To estimate surface energy, a quantity such as specific free surface energy is used. It is equal to the work spent on the formation of a unit area of a new phase interface (assuming a constant temperature).
In the case of a boundary between two condensed phases, this quantity is called boundary tension.
When talking about the boundary of a liquid with its vapors, this quantity is called surface tension.
Coagulation of colloids
All spontaneous processes occur in the direction of decreasing the energy of the system (isobaric potential).
Similarly, processes spontaneously occur at the phase interface in the direction of decreasing free surface energy.
Free energy the less, the smaller the phase interface.
And the phase interface, in turn, is related to the degree of dispersion of the dissolved substance. The higher the dispersion (smaller particles of the dispersed phase), the larger the interface between the phases.
Thus, in dispersed systems there are always forces leading to a decrease in the total interphase surface, i.e. to particle enlargement. Therefore, the merging of small droplets in fogs, rain clouds and emulsions occurs - the aggregation of highly dispersed particles into larger formations.
All this leads to the destruction of dispersed systems: fogs and rain clouds rain, emulsions separate, colloidal solutions coagulate, i.e. are separated into a sediment of the dispersed phase (coagulate) and a dispersion medium or, in the case of elongated particles of the dispersed phase, turn into a gel.
The ability of fragmented systems to maintain their inherent degree of dispersion is called aggregative stability.
Stabilizers for dispersed systems
As stated earlier, dispersed systems are fundamentally thermodynamically unstable. The higher the dispersion, the greater the free surface energy, the greater the tendency to spontaneously reduce dispersion.
Therefore, to obtain stable, i.e. long-lasting suspensions, emulsions, colloidal solutions, it is necessary not only to achieve the desired dispersion, but also to create conditions for its stabilization.
In view of this, stable disperse systems consist of at least three components: a dispersed phase, a dispersion medium and a third component - disperse system stabilizer.
The stabilizer can be either ionic or molecular, often high-molecular, in nature.
Ionic stabilization of sols of lyophobic colloids is associated with the presence of low concentrations of electrolytes, creating ionic boundary layers between the dispersed phase and the dispersion medium.
High-molecular compounds (proteins, polypeptides, polyvinyl alcohol and others) added to stabilize dispersed systems are called protective colloids.
Adsorbed at the phase interface, they form mesh and gel-like structures in the surface layer, creating a structural-mechanical barrier that prevents the integration of particles of the dispersed phase.
Structural-mechanical stabilization is crucial for the stabilization of suspensions, pastes, foams, and concentrated emulsions.
Dispersed systems
Pure substances are very rare in nature. Mixtures of different substances in different states of aggregation can form heterogeneous and homogeneous systems - dispersed systems and solutions.
Dispersed
are called heterogeneous systems in which one substance in the form of very small particles is evenly distributed in the volume of another.
The substance that is present in smaller quantities and distributed in the volume of another is called dispersed phase
. It may consist of several substances.
The substance present in larger quantities, in the volume of which the dispersed phase is distributed, is called dispersion medium
. There is an interface between it and the particles of the dispersed phase; therefore, dispersed systems are called heterogeneous (inhomogeneous).
Both the dispersion medium and the dispersed phase can be represented by substances in different states of aggregation - solid, liquid and gaseous.
Depending on the combination of the aggregate state of the dispersion medium and the dispersed phase, 9 types of such systems can be distinguished.
Based on the particle size of the substances that make up the dispersed phase, dispersed systems are divided into coarsely dispersed (suspensions) with particle sizes of more than 100 nm and finely dispersed (colloidal solutions or colloidal systems) with particle sizes from 100 to 1 nm. If the substance is fragmented into molecules or ions less than 1 nm in size, a homogeneous system is formed - a solution. It is uniform (homogeneous), there is no interface between the particles and the medium.
Already a quick acquaintance with disperse systems and solutions shows how important they are in Everyday life and in nature.
Judge for yourself: without Nile silt a great civilization would not have taken place Ancient Egypt; without water, air, rocks and minerals, the living planet would not exist at all - our common home - the Earth; without cells there would be no living organisms, etc.
Classification of disperse systems and solutions
Suspend
Suspend
- these are dispersed systems in which the phase particle size is more than 100 nm. These are opaque systems, individual particles of which can be seen with the naked eye. The dispersed phase and the dispersion medium are easily separated by settling. Such systems are divided into:
1) emulsions
(both the medium and the phase are liquids insoluble in each other). These are well-known milk, lymph, water-based paints, etc.;
2) suspensions
(the medium is a liquid, and the phase is a solid insoluble in it). This mortars(for example, “lime milk” for whitewashing), river and sea silt suspended in water, a living suspension of microscopic living organisms in sea water - plankton, which giant whales feed on, etc.;
3) aerosols
- suspensions in gas (for example, in air) of small particles of liquids or solids. Distinguish between dust, smoke, and fog. The first two types of aerosols are suspensions of solid particles in gas (larger particles in dust), the latter is a suspension of small droplets of liquid in gas. For example, natural aerosols: fog, thunderclouds - a suspension of water droplets in the air, smoke - small solid particles. And the smog hanging over largest cities world, also an aerosol with a solid and liquid dispersed phase. Residents of settlements near cement factories suffer from the finest cement dust always hanging in the air, which is formed during the grinding of cement raw materials and the product of its firing - clinker. Similar harmful aerosols - dust - are also present in cities with metallurgical production. Smoke from factory chimneys, smog, tiny droplets of saliva flying out of the mouth of a flu patient, and also harmful aerosols.
Aerosols play an important role in nature, everyday life and production activities person. Accumulations of clouds, processing of fields with chemicals, application of paint and varnish coatings using a spray gun, spraying of fuels, production of dry milk products, treatment respiratory tract(inhalation) - examples of those phenomena and processes where aerosols are beneficial. Aerosols are fogs over the sea surf, near waterfalls and fountains; the rainbow that appears in them gives a person joy and aesthetic pleasure.
For chemistry highest value have dispersed systems in which the medium is water and liquid solutions.
Natural water always contains dissolved substances. Natural aqueous solutions participate in soil formation processes and supply plants with nutrients. Complex life processes occurring in human and animal bodies also occur in solutions. Many technological processes in the chemical and other industries, for example, the production of acids, metals, paper, soda, fertilizers, take place in solutions.
Colloidal systems
Colloidal systems
- these are dispersed systems in which the phase particle size is from 100 to 1 nm. These particles are not visible to the naked eye, and the dispersed phase and the dispersion medium in such systems are difficult to separate by settling.
They are divided into sols (colloidal solutions) and gels (jelly).
1.
Colloidal solutions, or sols.
This is the majority of the fluids of a living cell (cytoplasm, nuclear juice - karyoplasm, contents of organelles and vacuoles) and the living organism as a whole (blood, lymph, tissue fluid, digestive juices, humoral fluids, etc.). Such systems form adhesives, starch, proteins, and some polymers.
Colloidal solutions can be obtained as a result chemical reactions; for example, when solutions of potassium or sodium silicates (“soluble glass”) react with acid solutions, a colloidal solution of silicic acid is formed. A sol is also formed during the hydrolysis of iron chloride (III) in hot water. Colloidal solutions are similar in appearance to true solutions. They are distinguished from the latter by the “luminous path” that is formed - a cone when a beam of light is passed through them.
Particles of the dispersed phase of colloidal solutions often do not settle even during long-term storage due to continuous collisions with solvent molecules due to thermal movement. They do not stick together when approaching each other due to the presence of electric charges of the same name on their surface. But under certain conditions, a coagulation process can occur.
Coagulation - the phenomenon of colloidal particles sticking together and precipitating - is observed when the charges of these particles are neutralized when an electrolyte is added to the colloidal solution. In this case, the solution turns into a suspension or gel. Some organic colloids coagulate when heated (glue, egg white) or when the acid-base environment of the solution changes.
2.
Gels
, or jellies, which are gelatinous sediments formed during the coagulation of sols. These include a large number of polymer gels, so well known to you confectionery, cosmetic and medical gels (gelatin, jellied meat, jelly, marmalade, Bird's Milk cake) and of course an endless variety of natural gels: minerals (opal), jellyfish bodies, cartilage , tendons, hair, muscle and nervous tissue, etc. The history of the development of life on Earth can simultaneously be considered the history of the evolution of the colloidal state of matter. Over time, the structure of the gels is disrupted and water is released from them. This phenomenon is called syneresis
.
Solutions
A solution is called
homogeneous system consisting of two or more substances.
Solutions are always single-phase, that is, they are a homogeneous gas, liquid or solid. This is due to the fact that one of the substances is distributed in the mass of the other in the form of molecules, atoms or ions (particle size less than 1 nm).
Solutions are called true
, if you want to emphasize their difference from colloidal solutions.
A solvent is considered to be a substance whose state of aggregation does not change during the formation of a solution. For example, water in aqueous solutions of table salt, sugar, carbon dioxide. If a solution was formed by mixing gas with gas, liquid with liquid, and solid with solid, the solvent is considered to be the component that is more abundant in the solution. So, air is a solution of oxygen, noble gases, carbon dioxide in nitrogen (solvent). Table vinegar, which contains from 5 to 9% acetic acid, is a solution of this acid in water (the solvent is water). But in acetic essence, acetic acid plays the role of solvent, since its mass fraction is 70-80%, therefore, it is a solution of water in acetic acid.
When crystallizing a liquid alloy of silver and gold, solid solutions of different compositions can be obtained.
Solutions are divided into:
molecular - these are aqueous solutions of non-electrolytes - organic substances (alcohol, glucose, sucrose, etc.);
molecular ion- these are solutions of weak electrolytes (nitrous, hydrosulfide acids, etc.);
ionic - these are solutions strong electrolytes(alkalis, salts, acids - NaOH, K 2 S0 4, HN0 3, HC1O 4).
Previously, there were two points of view on the nature of dissolution and solutions: physical and chemical. According to the first, solutions were considered as mechanical mixtures, according to the second - as unstable chemical compounds of particles of a dissolved substance with water or another solvent. The last theory was expressed in 1887 by D.I. Mendeleev, who devoted more than 40 years to the study of solutions. Modern chemistry considers dissolution as a physicochemical process, and solutions as physicochemical systems.
A more precise definition of a solution is:
Solution
- a homogeneous (homogeneous) system consisting of particles of a dissolved substance, a solvent and the products of their interaction.
The behavior and properties of electrolyte solutions, as you well know, are explained by another important theory of chemistry - the theory of electrolytic dissociation, developed by S. Arrhenius, developed and supplemented by the students of D. I. Mendeleev, and primarily by I. A. Kablukov.
Questions to consolidate:
1. What are disperse systems?
2. When the skin is damaged (wound), blood clotting is observed - coagulation of the sol. What is the essence of this process? Why does this phenomenon perform a protective function for the body? What is the name of a disease in which blood clotting is difficult or not observed?
3. Tell us about the importance of various disperse systems in everyday life.
4. Trace the evolution of colloidal systems during the development of life on Earth.
Dispersion systems can be divided according to the particle size of the dispersion phase. If the particle size is less than one nm, these are molecular ionic systems, from one to one hundred nm are colloidal, and more than one hundred nm are coarse. The group of molecularly dispersed systems is represented by solutions. This homogeneous systems, which consist of two or more substances and are single-phase. These include gas, solid or solutions. In turn, these systems can be divided into subgroups:
- Molecular. When organic substances such as glucose combine with non-electrolytes. Such solutions were called true so that they could be distinguished from colloidal ones. These include solutions of glucose, sucrose, alcohol and others.
- Molecular-ionic. In case of interaction between weak electrolytes. This group includes acidic solutions, nitrogenous, hydrogen sulfide and others.
- Ionic. Compound of strong electrolytes. Prominent representatives are solutions of alkalis, salts and some acids.
Colloidal systems
Colloidal systems are microheterogeneous systems in which the sizes of colloidal particles vary from 100 to 1 nm. They may not precipitate for a long time due to the solvation ionic shell and electric charge. When distributed in a medium, colloidal solutions uniformly fill the entire volume and are divided into sols and gels, which in turn are precipitates in the form of jelly. These include albumin solution, gelatin, colloidal silver solutions. Jellied meat, soufflé, puddings are bright colloidal systems found in everyday life.
Coarse systems
Opaque systems or suspensions in which fine particle ingredients are visible to the naked eye. During the settling process, the dispersed phase is easily separated from the dispersed medium. They are divided into suspensions, emulsions, and aerosols. Systems in which a solid with larger particles are placed in a liquid dispersion medium are called suspensions. These include aqueous solutions of starch and clay. Unlike suspensions, emulsions are obtained by mixing two liquids, in which one is distributed in droplets into the other. An example of an emulsion is a mixture of oil and water, droplets of fat in milk. If small solid or liquid particles are distributed in a gas, these are aerosols. Essentially, an aerosol is a suspension in gas. One of the representatives of a liquid-based aerosol is fog - this is a large number of small water droplets suspended in the air. Solid aerosol - smoke or dust - a multiple accumulation of small solid particles also suspended in the air.
After studying the topic of the lesson, you will learn:
- What are disperse systems?
- what are disperse systems?
- What properties do disperse systems have?
- the importance of dispersed systems.
Pure substances are very rare in nature. Crystals of pure substances - sugar or table salt, for example, can be obtained in different sizes - large and small. Whatever the size of the crystals, they all have the same internal structure for a given substance - a molecular or ionic crystal lattice.
In nature, mixtures of various substances are most often found. Mixtures of different substances in different states of aggregation can form heterogeneous and homogeneous systems. We will call such systems dispersed.
A dispersed system is a system consisting of two or more substances, one of them in the form of very small particles evenly distributed in the volume of the other.
A substance breaks down into ions, molecules, atoms, which means it “splits” into tiny particles. “Crushing” > dispersing, i.e. substances are dispersed until different sizes particles visible and invisible.
A substance that is present in a smaller quantity, dispersed and distributed in the volume of another is called dispersed phase. It may consist of several substances.
The substance present in larger quantities, in the volume of which the dispersed phase is distributed, is called dispersed medium. There is an interface between it and the particles of the dispersed phase; therefore, dispersed systems are called heterogeneous (inhomogeneous).
Both the dispersed medium and the dispersed phase can be represented by substances in various states of aggregation - solid, liquid and gaseous.
Depending on the combination of the aggregate state of the dispersed medium and the dispersed phase, 9 types of such systems can be distinguished.
Table
Examples of dispersed systems
| Dispersive medium | Dispersed phase | Examples of some natural and household disperse systems |
| Gas | Gas | Always homogeneous mixture (air, natural gas) |
| Liquid | Fog, associated gas with oil droplets, carburetor mixture in car engines (gasoline droplets in the air), aerosols | |
| Solid | Dust in the air, smoke, smog, simooms (dust and sand storms), aerosols | |
| Liquid | Gas | Effervescent drinks, foams |
| Liquid | Emulsions. Liquid media of the body (blood plasma, lymph, digestive juices), liquid contents of cells (cytoplasm, karyoplasm) | |
| Solid | Sols, gels, pastes (jelly, jellies, glues). River and sea silt suspended in water; mortars | |
| Solid | Gas | Snow crust with air bubbles in it, soil, textile fabrics, brick and ceramics, foam rubber, aerated chocolate, powders |
| Liquid | Wet soil, medical and cosmetical tools(ointments, mascara, lipstick, etc.) | |
| Solid | Rocks, colored glasses, some alloys |
Based on the size of the particles of substances that make up the dispersed phase, dispersed systems are divided into coarse (suspensions) with particle sizes greater than 100 nm and finely dispersed (colloidal solutions or colloidal systems) with particle sizes from 100 to 1 nm. If the substance is fragmented into molecules or ions less than 1 nm in size, a homogeneous system is formed - solution. It is homogeneous, there is no interface between the particles and the medium.
Dispersed systems and solutions are very important in everyday life and in nature. Judge for yourself: without the Nile silt the great civilization of Ancient Egypt would not have taken place; without water, air, rocks and minerals, the living planet would not exist at all - our common home - the Earth; without cells there would be no living organisms, etc.
SUSPENSION
Suspensions are dispersed systems in which the phase particle size is more than 100 nm. These are opaque systems, individual particles of which can be seen with the naked eye. The dispersed phase and the dispersed medium are easily separated by settling and filtration. Such systems are divided into:
- Emulsions ( both the medium and the phase are liquids insoluble in each other). An emulsion can be prepared from water and oil by shaking the mixture for a long time. These are well-known milk, lymph, water-based paints, etc.
- Suspensions(medium is a liquid, phase is a solid insoluble in it). To prepare a suspension, you need to grind the substance to a fine powder, pour it into the liquid and shake well. Over time, the particle will fall to the bottom of the vessel. Obviously than smaller particle, the longer the suspension will remain. These are construction solutions, river and sea silt suspended in water, a living suspension of microscopic living organisms in sea water - plankton, which feeds giants - whales, etc.
- Aerosols suspensions in a gas (for example, in air) of small particles of liquids or solids. There are dusts, smokes, and fogs. The first two types of aerosols are suspensions of solid particles in gas (larger particles in dust), the latter is a suspension of liquid droplets in gas. For example: fog, thunderclouds - a suspension of water droplets in the air, smoke - small solid particles. And the smog hanging over the world's largest cities is also an aerosol with a solid and liquid dispersed phase. Residents of settlements near cement factories suffer from the finest cement dust always hanging in the air, which is formed during the grinding of cement raw materials and the product of its firing - clinker. Smoke from factory chimneys, smog, tiny droplets of saliva flying out of the mouth of a flu patient are also harmful aerosols. Aerosols play an important role in nature, everyday life and human production activities. The accumulation of clouds, the treatment of fields with chemicals, the application of paint and varnish coatings using a spray gun, the treatment of the respiratory tract (inhalation) are examples of those phenomena and processes where aerosols are beneficial. Aerosols are fogs over the sea surf, near waterfalls and fountains; the rainbow that appears in them gives a person joy and aesthetic pleasure.
For chemistry, dispersed systems in which the medium is water and liquid solutions are of greatest importance.
Natural water always contains dissolved substances. Natural aqueous solutions participate in soil formation processes and supply plants with nutrients. Complex life processes occurring in human and animal bodies also occur in solutions. Many technological processes in chemical and other industries, for example, the production of acids, metals, paper, soda, fertilizers, occur in solutions.
COLLOIDAL SYSTEMS
Colloidal systems (translated from the Greek “colla” - glue, “eidos” - glue-like type) – These are dispersed systems in which the phase particle size is from 100 to 1 nm. These particles are not visible to the naked eye, and the dispersed phase and dispersed medium in such systems are difficult to separate by settling.
From the course general biology You know that particles of this size can be detected using an ultramicroscope, which uses the principle of light scattering. Thanks to this, the colloidal particle in it appears as a bright dot against a dark background.
They are divided into sols (colloidal solutions) and gels (jelly).
1. Colloidal solutions, or sols. This is the majority of the fluids of a living cell (cytoplasm, nuclear juice - karyoplasm, contents of organelles and vacuoles). And the living organism as a whole (blood, lymph, tissue fluid, digestive juices, etc.) Such systems form adhesives, starch, proteins, and some polymers.
Colloidal solutions can be obtained as a result of chemical reactions; for example, when solutions of potassium or sodium silicates (“soluble glass”) react with acid solutions, a colloidal solution of silicic acid is formed. A sol is also formed during the hydrolysis of iron (III) chloride in hot water.
A characteristic property of colloidal solutions is their transparency. Colloidal solutions are similar in appearance to true solutions. They are distinguished from the latter by the “luminous path” that is formed - a cone when a beam of light is passed through them. This phenomenon is called the Tyndall effect. The particles of the dispersed phase of the sol, larger than in the true solution, reflect light from their surface, and the observer sees a luminous cone in the vessel with the colloidal solution. It is not formed in a true solution. You can observe a similar effect, but only for an aerosol and not a liquid colloid, in the forest and in cinemas when a beam of light from a movie camera passes through the air of the cinema hall.
Passing a beam of light through solutions;
a – true sodium chloride solution;
b – colloidal solution of iron (III) hydroxide.
Particles of the dispersed phase of colloidal solutions often do not settle even during long-term storage due to continuous collisions with solvent molecules due to thermal movement. They do not stick together when approaching each other due to the presence of electric charges of the same name on their surface. This is explained by the fact that substances in a colloidal, i.e., finely divided, state have a large surface area. Either positively or negatively charged ions are adsorbed on this surface. For example, silicic acid adsorbs negative ions SiO 3 2-, of which there are many in solution due to the dissociation of sodium silicate:
Particles with like charges repel each other and therefore do not stick together.
But under certain conditions, a coagulation process can occur. When some colloidal solutions are boiled, desorption of charged ions occurs, i.e. colloidal particles lose their charge. They begin to enlarge and settle. The same thing is observed when adding any electrolyte. In this case, the colloidal particle attracts an oppositely charged ion and its charge is neutralized.
Coagulation - the phenomenon of colloidal particles sticking together and precipitating - is observed when the charges of these particles are neutralized when an electrolyte is added to the colloidal solution. In this case, the solution turns into a suspension or gel. Some organic colloids coagulate when heated (glue, egg white) or when the acid-base environment of the solution changes.
2. Gels or jellies are gelatinous precipitates formed during the coagulation of sols. These include a large number of polymer gels, so well known to you confectionery, cosmetic and medical gels (gelatin, jellied meat, marmalade, Bird's Milk cake) and of course an endless variety of natural gels: minerals (opal), jellyfish bodies, cartilage, tendons , hair, muscle and nerve tissue, etc. The history of development on Earth can simultaneously be considered the history of the evolution of the colloidal state of matter. Over time, the structure of the gels is disrupted (flakes off) - water is released from them. This phenomenon is called syneresis.
Perform laboratory experiments on the topic (group work, in a group of 4 people).
You have been given a sample of the dispersed system. Your task: to determine which disperse system was given to you.
Given to students: sugar solution, iron (III) chloride solution, a mixture of water and river sand, gelatin, aluminum chloride solution, table salt solution, a mixture of water and vegetable oil.
Instructions for performing laboratory experiments
- Carefully examine the sample given to you (external description). Fill out column No. 1 of the table.
- Stir the disperse system. Observe the ability to settle.
It settles or stratifies within a few minutes, or with difficulty over a long period of time, or does not settle. Fill out column No. 2 of the table.
If you do not observe particle settling, examine it for the coagulation process. Pour a little solution into two test tubes and add 2-3 drops of yellow blood salt to one and 3-5 drops of alkali to the other, what do you observe?
- Pass the dispersed system through the filter. What are you observing? Fill out column No. 3 of the table. (Filter some into a test tube).
- Shine a flashlight beam through the solution against a background of dark paper. What are you observing? (Tyndall effect can be observed)
- Draw a conclusion: what kind of dispersed system is this? What is a dispersed medium? What is the dispersed phase? What are the particle sizes in it? (column No. 5).
Writing rules syncwine:
- The first line uses one word (usually a noun) to name the topic.
- The second line is a description of this topic with two adjectives.
- The third line is three verbs (or verb forms), naming the most characteristic actions of the subject.
- The fourth line is a four-word phrase that shows a personal attitude towards the topic.
- The last line is a synonym for the topic, emphasizing its essence.
Summer 2008 Vienna. Schönbrunn.
Summer 2008, Nizhny Novgorod region.
Clouds and their role in human life All the nature that surrounds us - animal and plant organisms, the hydrosphere and atmosphere, the earth's crust and subsoil are a complex collection of many different and different types of coarse and colloidal systems. Krasnova Maria, |
P.S.
Many thanks to O.G. Pershina, chemistry teacher at the Dmitrov Gymnasium, during the lesson we worked with the presentation we found, and it was supplemented with our examples.