Examples of some natural and household disperse systems. Dispersed systems. Solid heterogeneous systems

Both the dispersion medium and the dispersed phase can be composed of substances in different states of aggregation. Depending on the combination of states of the dispersion medium and the dispersed phase, eight types of such systems can be distinguished

Classification of dispersed systems by state of aggregation

Also, as a classification feature, we can distinguish such a concept as the size of particles of a dispersed system:

• - Coarsely dispersed (> 10 microns): granulated sugar, soil, fog, raindrops, volcanic ash, magma, etc.
• - Medium-fine (0.1-10 microns): human blood erythrocytes, E. coli, etc.

dispersed emulsion suspension gel

• - Highly dispersed (1-100 nm): influenza virus, smoke, turbidity in natural waters, artificially obtained sols of various substances, aqueous solutions of natural polymers (albumin, gelatin, etc.), etc.
• - Nano-sized (1-10 nm): glycogen molecule, fine pores of coal, metal sols obtained in the presence of molecules of organic substances that limit the growth of particles, carbon nanotubes, magnetic nanothreads made of iron, nickel, etc.

Coarsely dispersed systems: emulsions, suspensions, aerosols

Based on the size of the particles of the substance that make up the dispersed phase, dispersed systems are divided into coarse with particle sizes of more than 100 nm and finely dispersed with particle sizes from 1 to 100 nm. If the substance is fragmented into molecules or ions less than 1 nm in size, a homogeneous system is formed - a solution. The solution is homogeneous, there is no interface between the particles and the medium, and therefore it does not belong to disperse systems. Coarsely dispersed systems are divided into three groups: emulsions, suspensions and aerosols.

Emulsions are dispersed systems with a liquid dispersion medium and a liquid dispersed phase.

They can also be divided into two groups: 1) direct - drops of a non-polar liquid in a polar environment (oil in water); 2) reverse (water in oil). Changes in the composition of emulsions or external influences can lead to the transformation of a direct emulsion into a reverse emulsion and vice versa. Examples of the most well-known natural emulsions are milk (direct emulsion) and oil (reverse emulsion). A typical biological emulsion is fat droplets in the lymph.

Among the emulsions known in human practice are cutting fluids, bituminous materials, pesticides, medicines and cosmetics, and food products. For example, in medical practice, fat emulsions are widely used to provide energy to a starving or weakened body through intravenous infusion. To obtain such emulsions, olive, cottonseed and soybean oils are used. In chemical technology, emulsion polymerization is widely used as the main method for producing rubbers, polystyrene, polyvinyl acetate, etc. Suspensions are coarse systems with a solid dispersed phase and a liquid dispersion medium.

Typically, the particles of the dispersed phase of a suspension are so large that they settle under the influence of gravity - sediment. Systems in which sedimentation occurs very slowly due to the small difference in density of the dispersed phase and the dispersion medium are also called suspensions. Practically significant construction suspensions are whitewash (“lime milk”), enamel paints, and various construction suspensions, for example those called “cement mortar.” Suspensions also include medications, for example liquid ointments - liniments. A special group consists of coarsely dispersed systems, in which the concentration of the dispersed phase is relatively high compared to its low concentration in suspensions. Such dispersed systems are called pastes. For example, dental, cosmetic, hygiene, etc., that are well known to you from everyday life.

Aerosols are coarsely dispersed systems in which the dispersion medium is air, and the dispersed phase can be liquid droplets (clouds, rainbows, hairspray or deodorant released from a can) or particles of a solid substance (dust cloud, tornado)

Colloidal systems - in them the sizes of colloidal particles reach up to 100 nm. Such particles easily penetrate the pores of paper filters, but do not penetrate the pores of biological membranes of plants and animals. Since colloidal particles (micelles) have an electrical charge and solvate ionic shells, due to which they remain suspended, they may not precipitate for quite a long time. A striking example of a colloidal system are solutions of gelatin, albumin, gum arabic, and colloidal solutions of gold and silver.

Colloidal systems occupy an intermediate position between coarse systems and true solutions. They are widespread in nature. Soil, clay, natural waters, many minerals, including some precious stones, are all colloidal systems.

There are two groups of colloidal solutions: liquid (colloidal solutions - sols) and gel-like (jelly - gels).

Most biological fluids of the cell (the already mentioned cytoplasm, nuclear juice - karyoplasm, contents of vacuoles) and the living organism as a whole are colloidal solutions (sols). All vital processes that occur in living organisms are associated with the colloidal state of matter. In every living cell, biopolymers (nucleic acids, proteins, glycosaminoglycans, glycogen) are found in the form of dispersed systems.

Gels are colloidal systems in which particles of the dispersed phase form a spatial structure.

Gels can be: food - marmalade, marshmallows, jellied meat, jelly; biological - cartilage, tendons, hair, muscle and nerve tissue, jellyfish bodies; cosmetics - shower gels, creams; medical - medicines, ointments; mineral - pearls, opal, carnelian, chalcedony.

Colloidal systems are of great importance for biology and medicine. The composition of any living organism includes solid, liquid and gaseous substances that are in a complex relationship with the environment. From a chemical point of view, the body as a whole is a complex collection of many colloidal systems.

Biological fluids (blood, plasma, lymph, cerebrospinal fluid, etc.) are colloidal systems in which organic compounds such as proteins, cholesterol, glycogen and many others are in a colloidal state. Why does nature give such preference to him? This feature is primarily due to the fact that a substance in a colloidal state has a large interface between phases, which contributes to better metabolic reactions.

Examples of natural and artificial disperse systems. Minerals and rocks as natural mixtures

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. The clouds of our planet are the same living entities as all the nature that surrounds us. They are of great importance for the Earth, as they are information channels. After all, clouds consist of the capillary substance of water, and water, as you know, is a very good storage device for information. The water cycle in nature leads to the fact that information about the state of the planet and the mood of people accumulates in the atmosphere, and, together with clouds, moves throughout the entire space of the Earth. An amazing creation of nature - clouds, which give people joy, aesthetic pleasure and simply the desire to sometimes look at the sky.

Fog can also be an example of a natural disperse system, the accumulation of water in the air, when tiny condensation products of water vapor are formed (at an air temperature above? 10° - tiny droplets of water, at? 10..? 15° - a mixture of water droplets and crystals ice, at a temperature below? 15° - ice crystals sparkling in the sun's rays or in the light of the moon and lanterns). Relative air humidity during fogs is usually close to 100% (at least exceeds 85-90%). However, in severe frosts (? 30° and below) in populated areas, at railway stations and airfields, fogs can be observed at any relative air humidity (even less than 50%) - due to the condensation of water vapor formed during fuel combustion (in engines, furnaces, etc.) and released into the atmosphere through exhaust pipes and chimneys.

The continuous duration of fogs usually ranges from several hours (and sometimes half an hour to an hour) to several days, especially in the cold season.

Fogs prevent the normal operation of all types of transport (especially aviation), so fog forecasts are of great economic importance.

An example of a complex disperse system is milk, the main components of which (not counting water) are fat, casein and milk sugar. The fat is in the form of an emulsion and when the milk stands, it gradually rises to the top (cream). Casein is contained in the form of a colloidal solution and is not released spontaneously, but can easily be precipitated (in the form of cottage cheese) when milk is acidified, for example, with vinegar. Under natural conditions, casein is released when milk sours. Finally, milk sugar is in the form of a molecular solution and is released only when water evaporates.

Many gases, liquids and solids dissolve in water. Sugar and table salt dissolve easily in water; carbon dioxide, ammonia and many other substances, when colliding with water, go into solution and lose their previous state of aggregation. A solute can be isolated from a solution in a certain way. If you evaporate a solution of table salt, the salt remains in the form of solid crystals.

When substances are dissolved in water (or another solvent), a uniform (homogeneous) system is formed. Thus, a solution is a homogeneous system consisting of two or more components. Solutions can be liquid, solid and gaseous. Liquid solutions include, for example, a solution of sugar or table salt in water, alcohol in water, and the like. Solid solutions of one metal in another include alloys: brass is an alloy of copper and zinc, bronze is an alloy of copper and tin, and the like. A gaseous substance is air or any mixture of gases.

Classification by state of aggregation. The most general classification of dispersed systems is based on the difference in the state of aggregation between the dispersed phase and the dispersed phase. Combinations of three types of state of aggregation make it possible to distinguish nine types of dispersed systems. For brevity, they are usually denoted by a fraction, the numerator of which indicates the dispersed phase, and the denominator indicates the dispersion medium, for example, for the “gas in liquid” system the designation G/L is accepted.

Classification of dispersed systems according to the state of aggregation of the dispersed phase and dispersion medium

All of the above combinations are possible and actually exist.

The first case stands somewhat apart - G 1 / G 2. As a rule, mixtures of gases form a homogeneous molecular disperse system. And only some gases at high pressure are capable of producing a mixture with limited solubility - heterogeneous mixtures. It should also be noted the originality of such systems as foams, polystyrene foams, concentrated emulsions, and pastes. The peculiarity lies in the fact that in this case not only the dispersed phase is dispersed, but also the dispersion medium, since the particles of the dispersed material are separated by a thin film of the medium; the thickness of the film can reach colloidal dimensions, i.e. the medium is also colloidally dispersed, but only in one dimension - thickness.

In the colloidal dispersed state, the dispersed phase consists of a relatively small number of molecules. Individual colloidal particles are essentially nuclei of a phase, the state of aggregation of which is sometimes difficult to establish with complete confidence.

In addition, experience shows that the difference in the state of aggregation of a dispersed substance (with a constant state of aggregation of the dispersion medium) does not entail significant changes in the properties of the colloidal system. In this regard, the classification is simplified, and the possible nine types of dispersed systems can be reduced to three - according to the aggregate state of the medium: systems with a gaseous, liquid and solid medium. For brevity, they are called aerosols, lyosols and solidosols, respectively. Depending on the nature of the dispersion medium, lyosols are called hydrosols, alcosols, etherosols, etc. The dispersion medium of these sols is water, alcohol, and ether, respectively. Microheterogeneous systems with a liquid dispersion medium and a solid dispersed phase are called suspensions, and with a liquid dispersed phase - emulsions.

These three groups of sols differ significantly from each other in properties, in particular stability. The question of the stability of colloidal systems is a very important question that directly concerns their very existence. Therefore, it deserves a closer look. It was previously noted that colloidal disperse systems are thermodynamically unstable. But this position should be clarified, especially since for different sols (aerosols, lyosols, solidosols) the final situation is different.

Suspensions- dispersed systems in which the dispersed phase is a solid and the dispersion medium is a liquid, and the solid is practically insoluble in the liquid. To prepare a suspension, you need to grind the substance to a fine powder, pour it into a liquid in which the substance does not dissolve, and shake well (for example, shaking clay in water). Over time, the particles will fall to the bottom of the vessel. This process is called sedimentation. Obviously, the smaller the particles, the longer the suspension will last. Therefore, the larger the particles, the higher the sedimentation instability.

Emulsions- dispersed systems in which both the dispersed phase and the dispersion medium are mutually immiscible liquids. An emulsion can be prepared from water and oil by shaking the mixture for a long time. An example of an emulsion is milk, in which small globules of fat float in the liquid. Suspensions and emulsions are two-phase systems.

Foam. Like emulsions, foams are coarsely dispersed systems. Therefore, in many technological processes, foams are obtained by the same dispersion methods that are used to obtain gas bubbles.

Aerosol– a dispersed system consisting of small, solid or liquid particles suspended in a gaseous environment. Aerosols, the dispersed phase of which consists of liquid droplets, are called mists, and in the case of a solid dispersed phase, fumes. Dust is classified as coarse aerosols.

By particle size freely dispersed systems are divided

Ultramicroheterogeneous systems are also called colloidal solutions or sols. Depending on the nature of the dispersion medium, sols are divided into solid sols, aerosols (sols with a gaseous dispersion medium) and lyosols (sols with a liquid dispersion medium). TO microheterogeneous systems include suspensions, emulsions, foams and powders. Most common coarse systems are solid-gas systems, such as sand. Connectedly dispersed systems (porous bodies) according to the classification of M.M. Dubinin is divided into groups

Dispersed systems and colloidal chemical processes take place both in the food industry and in public catering. Colloidal chemical processes, such as swelling, dissolution, gelation, aggregation, coagulation, precipitation, peptization, adsorption, underlie the production of many food products: broths, ice cream, various confectionery products, dairy products, as well as bakery, winemaking, brewing Butter, margarine, mayonnaise, sour cream, cream, milk are complex colloidal systems. To control technological processes of food production, economic engineers need knowledge of the characteristics of dispersed systems and their basic properties.

Dispersed systems are systems consisting of a substance, crushed into particles of larger or smaller size, and distributed in another substance. The same substance can be in varying degrees of fragmentation: macroscopically visible particles (>0.2-0.1 mm, eye resolution), microscopically visible particles (from 0.2-0.1 mm to 400-300 nm* , the resolving power of the microscope when illuminated with white light) and in the molecular (or ionic) state. Between the world of molecules and microscopically visible particles there is a region of fragmentation of matter with a complex of new properties inherent in this form of organization of matter. Such particles, invisible under an optical microscope, are called colloidal, and the crushed (dispersed) state of substances with particle sizes from 400-300 nm to 1 nm - colloidal state of the substance.

Dispersed systems consist of a continuous continuous phase - dispersion medium, in which crushed particles are distributed, and the crushed particles themselves of one size or another shape located in this environment - dispersed phase. Dispersed systems are heterogeneous, i.e. they are characterized by the existence of real physical phase interfaces between the dispersion phase and the dispersed medium.

A prerequisite for obtaining dispersed systems is the mutual insolubility of the dispersible substance and the dispersion medium. For example, it is impossible to obtain colloidal solutions of sugar or table salt in water, but they can be obtained in kerosene or benzene, in which these substances are practically insoluble.

A quantitative characteristic of the dispersion (fragmentation) of a substance is the degree of dispersity (degree of fragmentation, D) - the reciprocal of the size (a) of dispersed particles:

Here a is equal to either the diameter of spherical or fibrous particles, or the length of the edge of cubic particles, or the thickness of the films (Fig. 1). The smaller the particle sizes, the greater the dispersion, and vice versa.

*1 nm (nanometer) = 10 –6 mm.

Disperse system- formations of two or more phases (bodies) that practically do not mix and do not react chemically with each other. In a typical case of a two-phase system, the first of the substances ( dispersed phase) finely distributed in the second ( dispersion medium). If there are several phases, they can be separated from each other physically (centrifuge, separate, etc.).

Typically dispersed systems are colloidal solutions and sols. Dispersed systems also include the case of a solid dispersed medium in which the dispersed phase is located.

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  The most general classification of disperse systems is based on the difference in the state of aggregation of the dispersion medium and the dispersed phase (phases). Combinations of three types of state of aggregation make it possible to distinguish nine types of two-phase disperse systems. For brevity, they are usually denoted by a fraction, the numerator of which indicates the dispersed phase, and the denominator indicates the dispersion medium; for example, for the gas-in-liquid system the designation G/L is accepted.

  Designation	Dispersed phase	Dispersive medium	Title and example
  Y/Y	Gaseous	Gaseous	Do not form dispersed systems
  F/G	Liquid	Gaseous	Aerosols: fogs, clouds
  T/G	Hard	Gaseous	Aerosols (dusts, fumes), powdery substances
  G/F	Gaseous	Liquid	Gas emulsions and foams
  F/F	Liquid	Liquid	Emulsions: oil, cream, milk
  T/F	Hard	Liquid	Suspensions and sols: pulp, sludge, suspension, paste
  H/T	Gaseous	Hard	Porous bodies: foam polymers, pumice
  W/T	Liquid	Hard	Capillary systems (fluid-filled porous bodies): soil, soil
  T/T	Hard	Hard	Solid heterogeneous systems: alloys, concrete, glass-ceramics, composite materials

  Based on the kinetic properties of the dispersed phase, two-phase disperse systems can be divided into two classes:

  • Freely dispersed systems, in which the dispersed phase is mobile;
  • Cohesively dispersed systems, in which the dispersion medium is solid, and the particles of their dispersed phase are interconnected and cannot move freely.

  In turn, these systems are classified according to the degree of dispersion.

  Systems with dispersed phase particles of equal size are called monodisperse, and systems with particles of unequal size are called polydisperse. As a rule, the real systems around us are polydisperse.

  There are also dispersed systems with a larger number of phases - complex dispersed systems. For example, when a liquid dispersion medium boils with a solid dispersed phase, a three-phase system “vapor - drops - solid particles” is obtained.

  Another example of a complex disperse system is milk, the main components of which (not counting water) are fat, casein and milk sugar. The fat is in the form of an emulsion and when the milk stands, it gradually rises to the top (cream). Casein is contained in the form of a colloidal solution and is not spontaneously released, but can easily be precipitated (in the form of cottage cheese) when milk is acidified, for example, with vinegar. Under natural conditions, casein is released when milk sours. Finally, milk sugar is in the form of a molecular solution and is released only when water evaporates.

  Freely dispersed systems

  Based on particle size, freely dispersed systems are divided into:

  Ultramicroheterogeneous systems are also called colloidal or sols. Depending on the nature of the dispersion medium, sols are divided into solid sols, aerosols (sols with a gaseous dispersion medium) and lyosols (sols with a liquid dispersion medium). Microheterogeneous systems include suspensions, emulsions, foams and powders. The most common coarse systems are solid-gas systems (for example, sand).

  Colloidal systems play a huge role in biology and human life. In biological fluids of the body, a number of substances are in a colloidal state. Biological objects (muscle and nerve cells, blood and other biological fluids) can be considered as colloidal solutions. The dispersion medium of blood is plasma - an aqueous solution of inorganic salts and proteins.

  Cohesively dispersed systems

  Porous materials

  Porous materials are divided according to pore size, according to the classification of M. M. Dubinin, into:

  Based on geometric characteristics, porous structures are divided into regular(in which in the body volume there is a correct alternation of individual pores or cavities and channels connecting them) and stochastic(in which the orientation, shape, size, relative position and relationships of the pores are random). Most porous materials are characterized by a stochastic structure. The nature of the pores also matters: open the pores communicate with the surface of the body so that liquid or gas can be filtered through them; dead-end pores also communicate with the surface of the body, but their presence does not affect the permeability of the material; closed pores .

  Solid heterogeneous systems

  A typical example of solid heterogeneous systems are the recently widely used composite materials - artificially created solid, but heterogeneous, materials that consist of two or more components with clear interfaces between them. In most of these materials (with the exception of layered ones), the components can be divided into matrix and included in it reinforcing elements; in this case, the reinforcing elements are usually responsible for the mechanical characteristics of the material, and the matrix ensures the joint operation of the reinforcing elements. Some of the oldest composite materials include

  Sections: Chemistry

  Class: 11

  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 to different particle sizes, 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	Moist soil, medical and cosmetic products (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:

  1. 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.
  2. 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, the smaller the particles, the longer the suspension will persist. 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.
  3. 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 the chemical and other industries, for example, the production of acids, metals, paper, soda, fertilizers, take place 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.

  You know from your general biology course 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

  1. Carefully examine the sample given to you (external description). Fill out column No. 1 of the table.
  2. 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?

  1. 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).
  2. Shine a flashlight beam through the solution against a background of dark paper. What are you observing? (Tyndall effect can be observed)
  3. 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).
  Sinkwine("syncwine" – from fr. word meaning "five") is a 5-line poem on a specific topic. For essay syncwine 5 minutes are given, after which the written poems can be voiced and discussed in pairs, groups or to the whole audience.

  Writing rules syncwine:

  1. The first line uses one word (usually a noun) to name the topic.
  2. The second line is a description of this topic with two adjectives.
  3. The third line is three verbs (or verb forms) naming the most characteristic actions of the subject.
  4. The fourth line is a four-word phrase that shows a personal attitude towards the topic.
  5. 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. The development of colloidal chemistry is associated with current problems in various fields of natural science and technology. The picture presented shows clouds - one of the types of aerosols of colloidal disperse systems. In the study of atmospheric precipitation, meteorology relies on the study of aerodisperse systems. The clouds of our planet are the same living entities as all the nature that surrounds us. They are of great importance for the Earth, as they are information channels. After all, clouds consist of the capillary substance of water, and water, as you know, is a very good storage device for information. The water cycle in nature leads to the fact that information about the state of the planet and the mood of people accumulates in the atmosphere, and, together with clouds, moves throughout the entire space of the Earth. Clouds are an amazing creation of nature that gives people joy and aesthetic pleasure. Krasnova Maria, 11th "B" grade

  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.