KALININGRAD COMMERCE AND ECONOMIC COLLEGE

branch of the federal state budgetary

educational institution of higher professional education

RUSSIAN ACADEMY OF PEOPLE'S ECONOMY AND PUBLIC SERVICE

under the PRESIDENT OF THE RUSSIAN FEDERATION

Reference abstract

Topic: "Dispersed systems"

Kaliningrad, 2013

Topic: "Dispersed systems"

Dispersed systems are systems consisting of many small particles distributed in a liquid, solid or gaseous medium.

The dispersed system includes two mandatory components - these aredispersed phase - ground substancedispersion medium - substance in which the dispersed phase is distributed.
All disperse systems are characterized by two main features:

High dispersion.

Heterogeneity.

Disperse systems

Finely dispersed

colloid systems

Roughly dispersed

Suspensions Zoli True

Emulsions Gels

Aerosols

Classification of dispersed systems

According to the state of aggregation of the phases

Both the dispersion 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 state of aggregation of the dispersion medium and the dispersed phase, 9 types of such systems can be distinguished.

Main types of dispersed systems

Dispersion medium

By particle size

According to the degree of dispersion, the systems are divided into types

Coarse particles with a particle radius of more than 100 nm

Colloidal-dispersed (sols) with a particle size of 100 nm to 1 nm.

Molecular or ionic solutions with a particle size of less than 1 nm.

coarse systems.

emulsions (both the medium and the phase are liquids insoluble in each other, in which one of the liquids is suspended in the other in the form of droplets). These are milk, lymph, water-based paints, sour cream, mayonnaise, ice cream, etc.;

Suspensions (the medium is a liquid, and the phase is a solid insoluble in it). These are building solutions (for example, “milk of lime” for whitewashing), river and sea silt suspended in water, mashed soup.

Aerosols - disperse systems, the dispersion medium of which is a gas, and the dispersed phase can be solid particles or liquid droplets. Distinguish between dust, smoke, fog. The first two types of aerosols are suspensions of solid particles in a gas (larger particles in dusts), the last one is a suspension of small liquid droplets in a gas. Bioaerosols - pollen and spores of plants.

Foam - highly concentrated coarse systems in which the dispersion medium is liquid and the dispersed phase is gas.

Powders – the dispersed phase is a solid, and the dispersion medium is a gas.

Coarsely dispersed systems are unstable.

colloid systems

colloid systems - these are dispersed systems in which the particle size of the phase 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 separated by settling with difficulty. They are subdivided intosols (colloidal solutions) andgels(jellies). 1. Colloidal solutions, orsols . This is the majority of fluids of a living cell (cytoplasm, nuclear juice, the contents of organelles and vacuoles) and a living organism as a whole (blood, lymph, tissue fluid, digestive juices). Such systems form adhesives, starch, proteins, and some polymers. Colloidal solutions are outwardly similar to true solutions. They are distinguished from the latter by the resulting "luminous path" - a cone when a beam of light passes through them.This phenomenon is called the Tyndall effect. Larger than in a true solution, the particles of the dispersed phase of the sol reflect light from their surface, and the observer sees a luminous cone in a vessel with a colloidal solution. It does not form in true solution. A similar effect, but only for an aerosol rather than a liquid colloid, can be observed in cinemas when a beam of light from a movie camera passes through the air of the cinema hall. 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 motion. They do not stick together when approaching each other due to the presence of similar electric charges on their surface. But under certain conditions, the process of coagulation can occur.Coagulation - the phenomenon of adhesion of colloidal particles and their precipitation - 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 precipitates formed during the coagulation of sols. These include a large number of polymer gels, confectionery, cosmetic and medical gels so well known to you (gelatin, aspic, jelly, marmalade, Bird's Milk cake) and, of course, an infinite number of natural gels: minerals (opal), jellyfish bodies, cartilage , tendons, hair, muscle and nerve tissue, etc. Over time, the structure of the gels is broken - water is released from them. This phenomenon is calledsyneresis.

Solutions

Solution - a homogeneous (homogeneous) system consisting of particles of a solute, a solvent and the products of their interactionSolutions 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 it is required to emphasize their difference from colloidal solutions.

Table

Examples of dispersed systems

Dispersion medium

Questions for self-examination

What is called a dispersed system, phase, medium? How to relate dispersion to particle size? What disperse systems are colloidal? What is coagulation and what factors cause it? What is the practical significance of coagulation? What is a suspension? What are the main properties of suspensions? What is an emulsion and how can it be broken? Where are aerosols used? What are the methods of destruction of aerosols?

Safety precautions when working with alcohol lamps

When working with alcohol lamps, safety regulations must be observed.

It is necessary to use the spirit lamp only for the purpose indicated in its technical passport.

It is forbidden to refuel the spirit lamp near devices with an open flame.

Do not fill the spirit lamp with fuel more than half the volume of the tank.

Do not move or carry a spirit lamp with a burning wick.

Fill the spirit lamp only with ethyl alcohol.

Extinguish the flame of the spirit lamp only with a cap.

Do not keep on the desktop where the spirit lamp is used, flammable substances and materials that can ignite from short-term exposure to an ignition source with low thermal energy (flame of a match, alcohol lamp).

When working, do not tilt the spirit lamp, and if such a need arises, use spirit lamps operating in an inclined position (faceted spirit lamps).

If the spirit lamp overturns and spills burning alcohol on the table, immediately cover the spirit lamp with a thick cloth, and if necessary, use a fire extinguisher to extinguish the flame.

The room in which the work with the alcohol lamp (alcohol lamps) is performed must be equipped with primary fire extinguishing equipment, for example, a powder fire extinguisher of the OP-1 or OP-2 brand.

Literature

HELL. Zimon "Entertaining colloidal chemistry", Moscow, "Agar", 2008 ON THE. Zharkikh "Chemistry for Economic Colleges", Rostov-on-Don, "Phoenix", 2008 Physical and colloidal chemistry in public catering, Moscow, Alfa - M 2010. E.A. Arustamov "Nature Management", Moscow, "Dashkov and K", 2008. http://en.wikipedia.org http://festival.1september.ru/articles/575855/

Most of the substances around us are mixtures of various substances, so the study of their properties plays an important role in the development of chemistry, medicine, the food industry and other sectors of the national economy. The article deals with the questions of what is the degree of dispersion, and how it affects the characteristics of the system.

What are disperse systems?

Before proceeding to a discussion of the degree of dispersion, it is necessary to clarify to which systems this concept can be applied.

Imagine that we have two different substances that may differ from each other in chemical composition, for example, table salt and pure water, or in the state of aggregation, for example, the same water in liquid and solid (ice) states. Now you need to take and mix these two substances and mix them intensively. What will be the result? It depends on whether the chemical reaction took place during mixing or not. When talking about dispersed systems, it is believed that no reaction occurs during their formation, that is, the initial substances retain their structure at the microlevel and their inherent physical properties, for example, density, color, electrical conductivity, and others.

Thus, a dispersed system is a mechanical mixture, as a result of which two or more substances are mixed with each other. When it is formed, the concepts of "dispersion medium" and "phase" are used. The first has the property of continuity within the system and, as a rule, is found in it in a large relative amount. The second (dispersed phase) is characterized by the property of discontinuity, that is, in the system it is in the form of small particles, which are limited by the surface separating them from the medium.

Homogeneous and heterogeneous systems

It is clear that these two components of the dispersed system will differ in their physical properties. For example, if you throw sand into the water and stir it, then it is clear that the grains of sand existing in the water, the chemical formula of which is SiO 2, will not differ in any way from the state when they were not in the water. In such cases, one speaks of heterogeneity. In other words, a heterogeneous system is a mixture of several (two or more) phases. The latter is understood as some finite volume of the system, which is characterized by certain properties. In the example above, we have two phases: sand and water.

However, the size of the particles of the dispersed phase, when they are dissolved in any medium, can become so small that they cease to exhibit their individual properties. In this case, one speaks of homogeneous or homogeneous substances. Although they contain several components, they all form one phase throughout the entire volume of the system. An example of a homogeneous system is a solution of NaCl in water. When it dissolves, due to interaction with polar H 2 O molecules, the NaCl crystal decomposes into separate cations (Na +) and anions (Cl -). They are homogeneously mixed with water, and it is no longer possible to find the interface between the solute and the solvent in such a system.

Particle size

What is the degree of dispersion? This value needs to be considered in more detail. What does she represent? It is inversely proportional to the particle size of the dispersed phase. It is this characteristic that underlies the classification of all substances under consideration.

When studying disperse systems, students often get confused in their names, because they believe that their classification is also based on the state of aggregation. This is not true. Mixtures of different states of aggregation really have different names, for example, emulsions are water substances, and aerosols already suggest the existence of a gas phase. However, the properties of disperse systems depend mainly on the particle size of the phase dissolved in them.

Common classification

The classification of dispersed systems according to the degree of dispersion is given below:

• If the conditional particle size is less than 1 nm, then such systems are called real, or true solutions.
• If the conditional particle size lies between 1 nm and 100 nm, then the substance in question will be called a colloidal solution.
• If the particles are larger than 100 nm, then we are talking about suspensions or suspensions.

Regarding the above classification, let's clarify two points: firstly, the given figures are approximate, that is, a system in which the particle size is 3 nm is not necessarily a colloid, it can also be a true solution. This can be established by studying its physical properties. Secondly, you may notice that the list uses the phrase "conditional size". This is due to the fact that the shape of the particles in the system can be completely arbitrary, and in the general case has a complex geometry. Therefore, they speak of a certain average (conditional) size.

True Solutions

As mentioned above, the degree of dispersion of particles in real solutions is so high (their size is very small,< 1 нм), что не существует поверхности раздела между ними и растворителем (средой), то есть имеет место однофазная гомогенная система. Для полноты информации напомним, что размер атома составляет порядка одного ангстрема (0,1 нм). Последняя цифра говорит о том, что частицы в настоящих растворах имеют атомные размеры.

The main properties of true solutions that distinguish them from colloids and suspensions are the following:

• The state of the solution exists for an arbitrarily long time unchanged, that is, no precipitate of the dispersed phase is formed.
• The dissolved substance cannot be separated from the solvent by filtration through plain paper.
• The substance is also not separated as a result of the process of passage through the porous membrane, which is called dialysis in chemistry.
• It can be separated from the solvent only by changing the state of aggregation of the latter, for example, by evaporation.
• For it is possible to carry out electrolysis, that is, to pass an electric current if a potential difference (two electrodes) is applied to the system.
• They don't scatter light.

An example of true solutions is the mixing of various salts with water, for example, NaCl (table salt), NaHCO 3 (baking soda), KNO 3 (potassium nitrate) and others.

Colloidal solutions

These are intermediate systems between true solutions and suspensions. However, they have a number of unique characteristics. Let's list them:

• They are mechanically stable for an arbitrarily long time if the environmental conditions do not change. It is enough to heat the system or change its acidity (pH value), as the colloid coagulates (precipitates).
• They are not separated using filter paper, however, the dialysis process leads to separation of the dispersed phase and the medium.
• As with true solutions, electrolysis can be carried out for them.
• For transparent colloidal systems, the so-called Tyndall effect is characteristic: passing a beam of light through this system, you can see it. This is due to the scattering of electromagnetic waves in the visible part of the spectrum in all directions.
• The ability to adsorb other substances.

Colloidal systems, due to the listed properties, are widely used by humans in various fields of activity (food industry, chemistry), and are also often found in nature. An example of a colloid is butter, mayonnaise. In nature, these are fogs, clouds.

Before proceeding to the description of the last (third) class of disperse systems, let us explain in more detail some of the named properties for colloids.

What are colloidal solutions?

For this type of dispersed systems, the classification can be given, taking into account the different aggregate states of the medium and the phase dissolved in it. Below is the relevant table/

The table shows that colloidal substances are present everywhere, both in everyday life and in nature. Note that a similar table can also be given for suspensions, remembering that the difference with colloids in them is only in the size of the dispersed phase. However, suspensions are mechanically unstable and therefore are of less practical interest than colloidal systems.

The reason for the mechanical stability of colloids

Why mayonnaise can lie in the refrigerator for a long time, and suspended particles in it do not precipitate? Why don't paint particles dissolved in water eventually "fall" to the bottom of the vessel? The answer to these questions is Brownian motion.

This type of movement was discovered in the first half of the 19th century by the English botanist Robert Brown, who observed under a microscope how small pollen particles move in water. From a physical point of view, Brownian motion is a manifestation of the chaotic movement of liquid molecules. Its intensity increases if the temperature of the liquid is raised. It is this type of movement that causes small particles of colloidal solutions to be in suspension.

adsorption property

Dispersion is the reciprocal of the average particle size. Since this size in colloids lies in the range from 1 nm to 100 nm, they have a very developed surface, that is, the ratio S / m is a large value, here S is the total interface area between the two phases (dispersion medium and particles), m - total mass of particles in solution.

The atoms that are on the surface of the particles of the dispersed phase have unsaturated chemical bonds. This means that they can form compounds with other molecules. As a rule, these compounds arise due to van der Waals forces or hydrogen bonds. They are able to hold several layers of molecules on the surface of colloidal particles.

A classic example of an adsorbent is activated carbon. It is a colloid, where the dispersion medium is a solid, and the phase is a gas. The specific surface area for it can reach 2500 m 2 /g.

Degree of dispersion and specific surface area

Calculating the S/m value is not an easy task. The fact is that the particles in a colloidal solution have different sizes, shapes, and the surface of each particle has a unique relief. Therefore, theoretical methods for solving this problem lead to qualitative results, and not to quantitative ones. Nevertheless, it is useful to give the specific surface formula from the degree of dispersion.

If we assume that all particles of the system have a spherical shape and the same size, then as a result of simple calculations, the following expression is obtained: S ud = 6 / (d * ρ), where S ud is the surface area (specific), d is the diameter of the particle, ρ - the density of the substance of which it consists. It can be seen from the formula that the smallest and heaviest particles will make the largest contribution to the quantity under consideration.

An experimental method for determining S ud is to calculate the volume of gas that is adsorbed by the substance under study, as well as to measure the pore size (dispersed phase) in it.

Lyophilic and lyophobic systems

Lyophilicity and lyophobicity are those characteristics that, in fact, determine the existence of the classification of disperse systems in the form in which it is given above. Both concepts characterize the force bond between the molecules of the solvent and the solute. If this relationship is large, then they speak of lyophilicity. So, all salts in water are lyophilic, since their particles (ions) are electrically connected with polar H 2 O molecules. If we consider systems such as butter or mayonnaise, then these are representatives of typical hydrophobic colloids, since they contain fat molecules (lipids ) are repelled from polar H2O molecules.

It is important to note that lyophobic (hydrophobic if the solvent is water) systems are thermodynamically unstable, which distinguishes them from lyophilic ones.

Suspension properties

Now consider the last class of disperse systems - suspensions. Recall that they are characterized by the fact that the smallest particle in them is larger than or of the order of 100 nm. What properties do they have? Below is the relevant list:

• They are mechanically unstable, so a precipitate forms in them in a short period of time.
• They are cloudy and opaque to sunlight.
• The phase can be separated from the medium using filter paper.

Examples of suspensions in nature include cloudy water in rivers or volcanic ash. Human use of suspensions is associated, as a rule, with medicine (drug solutions).

Coagulation

What can be said about mixtures of substances with different degrees of dispersion? Partially, this issue has already been covered in the article, since in any disperse system the particles have a size that lies within certain limits. Here we only consider one curious case. What happens if you mix a colloid and a true electrolyte solution? The weighted system will be broken, and its coagulation will occur. Its reason lies in the influence of the electric fields of the ions of a true solution on the surface charge of colloidal particles.

Sections: Chemistry

Class: 11

After studying the topic of the lesson, you will learn:

• what are disperse systems?
• what are dispersed systems?
• What are the properties of dispersed systems?
• 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 which, in the form of very small particles, is evenly distributed in the volume of the other.

The substance breaks up into ions, molecules, atoms, which means it “splits up” into the smallest particles. “Crushing” > dispersion, i.e. substances are dispersed to different particle sizes, visible and invisible.

A substance that is present in a smaller amount, disperses and is distributed in the volume of another, is called dispersed phase. It may consist of several substances.

A substance that is present in a larger amount, in the volume of which the dispersed phase is distributed, is called dispersed medium. Between it and the particles of the dispersed phase there is an interface, therefore, disperse systems are called heterogeneous (non-uniform).

Both the dispersed medium and the dispersed phase can represent substances that are in various states of aggregation - solid, liquid and gaseous.

Depending on the combination of the state of aggregation of the dispersed medium and the dispersed phase, 9 types of such systems can be distinguished.

Table
Examples of dispersed systems

Dispersion medium	Dispersed phase	Examples of some natural and domestic 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, simums (dust and sand storms), aerosols
Liquid	Gas	Effervescent drinks, foam
	Liquid	emulsions. Body fluids (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, bricks and ceramics, foam rubber, aerated chocolate, powders
	Liquid	Wet soil, medical and cosmetic products (ointments, mascara, lipstick, etc.)
	Solid	Rocks, colored glasses, some alloys

According to the particle size of the substances that make up the dispersed phase, dispersed systems are divided into coarse (suspensions) with particle sizes over 100 nm and finely dispersed (colloidal solutions or colloidal systems) with particle sizes from 100 to 1 nm. If the substance is fragmented to molecules or ions smaller 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, there would be no living planet at all - our common home - the Earth; without cells, there would be no living organisms, and so on.

SUSPENSIONS

Suspensions are dispersed systems in which the particle size of the phase 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, filtering. Such systems are divided into:

1. Emulsions ( both the medium and the phase are liquids insoluble in each other). From water and oil, you can prepare an emulsion by shaking the mixture for a long time. These are milk, lymph, water-based paints, etc., well known to you.
2. Suspensions(the medium is a liquid, the phase is a solid insoluble in it). To prepare a suspension, the substance must be ground to a fine powder, poured into a liquid and shaken well. Over time, the particle will fall to the bottom of the vessel. Obviously, the smaller the particles, the longer the suspension will last. These are building solutions, river and sea silt suspended in water, a living suspension of microscopic living organisms in sea water - plankton, which feed on giants - whales, etc.
3. Aerosols suspensions in a gas (for example, in air) of small particles of liquids or solids. Dusts, smokes, fogs differ. The first two types of aerosols are suspensions of solid particles in a gas (larger particles in dusts), the last one is a suspension of liquid droplets in a gas. For example: fog, thunderclouds - a suspension of water droplets in the air, smoke - small solid particles. And the smog hanging over the largest cities of the world is also an aerosol with a solid and liquid dispersed phase. Residents of settlements near cement plants 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. The smoke of factory pipes, smog, the smallest 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. Cloud accumulation, field treatment with chemicals, paint spraying, respiratory treatment (inhalation) are examples of phenomena and processes where aerosols are beneficial. Aerosols - fogs over the sea surf, near waterfalls and fountains, the rainbow that arises in them gives a person joy, aesthetic pleasure.

For chemistry, the most important are dispersed systems in which the medium is water and liquid solutions.

Natural water always contains dissolved substances. Natural aqueous solutions are involved in the processes of soil formation and supply plants with nutrients. The complex life processes that occur in human and animal organisms also occur in solutions. Many technological processes in the chemical and other industries, such as the production of acids, metals, paper, soda, fertilizers, proceed in solutions.

COLLOID SYSTEMS

Colloid systems – these are dispersed systems in which the particle size of the phase is from 100 to 1 nm. These particles are not visible to the naked eye, and the dispersed phase and the dispersed medium in such systems are separated by settling with difficulty.

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. Due to this, the colloidal particle in it appears as a bright dot on a dark background.

They are divided into sols (colloidal solutions) and gels (jelly).

1. Colloidal solutions, or sols. This is the majority of fluids of a living cell (cytoplasm, nuclear juice - karyoplasm, the 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”) interact with acid solutions, a colloidal solution of silicic acid is formed. The 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 outwardly similar to true solutions. They are distinguished from the latter by the resulting “luminous path” - a cone when a beam of light passes through them. This phenomenon is called the Tyndall effect. Larger than in a true solution, the particles of the dispersed phase of the sol reflect light from their surface, and the observer sees a luminous cone in a vessel with a colloidal solution. It does not form in true solution. A similar effect, but only for an aerosol rather than a liquid colloid, can be observed 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 - a true solution of sodium chloride;
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 motion. They do not stick together when approaching each other due to the presence of similar electric charges on their surface. This is explained by the fact that substances in a colloidal, i.e., in a finely divided state, have a large surface. Either positively or negatively charged ions are adsorbed on this surface. For example, silicic acid adsorbs negative ions SiO 3 2-, which are abundant 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, the process of coagulation can occur. When boiling some colloidal solutions, desorption of charged ions occurs, i.e. colloidal particles lose their charge. They start to thicken and settle down. The same 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 sticking together of colloidal particles and their precipitation - 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, confectionery, cosmetic and medical gels so well known to you (gelatin, jelly, marmalade, Bird's Milk cake) and, of course, an infinite number of natural gels: minerals (opal), jellyfish bodies, cartilage, tendons , hair, muscle and nerve tissue, etc. The history of development on Earth can be simultaneously considered the history of the evolution of the colloidal state of matter. Over time, the structure of the gels is broken (peeled 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 disperse system. Your task is to determine which disperse system you have been given.

Issued to students: sugar solution, iron (III) chloride solution, a mixture of water and river sand, gelatin, aluminum chloride solution, common salt solution, a mixture of water and vegetable oil.

Instructions for performing a laboratory experiment

1. Consider carefully the sample given to you (external description). Fill in column No. 1 of the table.
2. Stir the dispersion system. Watch for the ability to settle.

Sediments or exfoliates within a few minutes, or with difficulty over a long period of time, or does not settle. Fill in column No. 2 of the table.

If you do not observe particle settling, examine it for coagulation. 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 watching? Fill in column No. 3 of the table. (Filter some into a test tube).
2. Pass a beam of light from a flashlight through the solution against a background of dark paper. What are you watching? (you can see the Tyndall effect)
3. Make a conclusion: what is this dispersed system? What is a dispersed medium? What is the dispersed phase? What are the particle sizes in it? (column No. 5).

cinquain("cinquain" - from fr. word meaning "five") is a poem of 5 lines on a specific topic. For composition cinquain 5 minutes are given, after which the written poems can be voiced and discussed in pairs, groups or for the whole audience.

Writing rules cinquain:

1. The first line contains a single word (usually a noun) for 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) that name the most characteristic actions of the subject.
4. The fourth line is a four-word phrase showing a personal relationship to 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 around us - the organisms of animals and plants, the hydrosphere and atmosphere, the earth's crust and bowels are a complex set of many diverse and diverse coarse and colloidal systems. The development of colloid chemistry is associated with topical problems in various areas of natural science and technology. The presented picture shows clouds - one of the types of aerosols of colloidal disperse systems. In the study of atmospheric precipitation, meteorology relies on the theory 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 store of 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 space of the Earth. Clouds are an amazing creation of nature, which gives a person joy, aesthetic pleasure. Krasnova Maria, 11th "B" class

P.S.
Many thanks to Pershina O.G., a chemistry teacher at the Dmitrov gymnasium, in the lesson we worked with the found presentation, and it was supplemented by our examples.

Disperse 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 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 a smaller amount and distributed in the volume of another is called dispersed phase . It may consist of several substances.
A substance that is present in a larger amount, 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, disperse systems are called heterogeneous (non-uniform).
Both the dispersion 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 state of aggregation of the dispersion medium and the dispersed phase, 9 types of such systems can be distinguished.

According to the particle size of the substances that make up the dispersed phase, dispersed systems are divided into coarse (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 to molecules or ions smaller than 1 nm in size, a homogeneous system is formed - a solution. It is homogeneous (homogeneous), there is no interface between the particles and the medium.

Even a cursory acquaintance with disperse systems and solutions shows how important they are 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, there would be no living planet at all - our common home - the Earth; without cells there would be no living organisms, etc.

Classification of dispersed systems and solutions

suspension

suspension - these are dispersed systems in which the particle size of the phase 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 milk, lymph, water-based paints, etc., well known to you;
2) suspensions (the medium is a liquid, and the phase is a solid insoluble in it). These are building solutions (for example, “milk of lime” 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 a gas (for example, in air) of small particles of liquids or solids. Distinguish between dust, smoke, fog. The first two types of aerosols are suspensions of solid particles in a gas (larger particles in dusts), the last one is a suspension of small liquid droplets in a gas. For example, natural aerosols: fog, thunderclouds - a suspension of water droplets in the air, smoke - small solid particles. And the smog hanging over the largest cities of the world is also an aerosol with a solid and liquid dispersed phase. Residents of settlements near cement plants suffer from the finest cement dust always hanging in the air, which is formed during the grinding of cement raw materials and its firing product - clinker. Similar harmful aerosols - dust - are also found in cities with metallurgical industries. The smoke of factory pipes, smog, the smallest 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. Cloud accumulations, chemical treatment of fields, paint spraying, spraying of fuels, dry dairy products, respiratory treatment (inhalation) are examples of phenomena and processes where aerosols are beneficial. Aerosols - fogs over the sea surf, near waterfalls and fountains, the rainbow that arises in them gives a person joy, aesthetic pleasure.
For chemistry, the most important are dispersed systems in which the medium is water and liquid solutions.
Natural water always contains dissolved substances. Natural aqueous solutions are involved in the processes of soil formation and supply plants with nutrients. The complex life processes that occur in human and animal organisms also occur in solutions. Many technological processes in the chemical and other industries, such as the production of acids, metals, paper, soda, fertilizers, proceed in solutions.

colloid systems

colloid systems - these are dispersed systems in which the particle size of the phase 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 separated by settling with difficulty.
They are divided into sols (colloidal solutions) and gels (jelly).
1. Colloidal solutions or sols. This is the majority of fluids of a living cell (cytoplasm, nuclear juice - karyoplasm, the contents of organelles and vacuoles) and a 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 of chemical reactions; for example, when solutions of potassium or sodium silicates (“soluble glass”) interact with acid solutions, a colloidal solution of silicic acid is formed. The sol is also formed during the hydrolysis of iron (III) chloride in hot water. Colloidal solutions are outwardly similar to true solutions. They are distinguished from the latter by the resulting "luminous path" - a cone when a beam of light passes through them.

This phenomenon is called Tyndall effect . Larger than in a true solution, the particles of the dispersed phase of the sol reflect light from their surface, and the observer sees a luminous cone in a vessel with a colloidal solution. It does not form in true solution. A similar effect, but only for an aerosol rather than a liquid colloid, can be observed in cinemas when a beam of light from a movie camera passes through the air of the cinema hall.

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 motion. They do not stick together when approaching each other due to the presence of similar electric charges on their surface. But under certain conditions, the process of coagulation can occur.

Coagulation - the phenomenon of adhesion of colloidal particles and their precipitation - 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 precipitates formed during the coagulation of sols. These include a large number of polymer gels, confectionery, cosmetic and medical gels so well known to you (gelatin, aspic, jelly, marmalade, Bird's Milk cake) and, of course, an infinite number of natural gels: minerals (opal), jellyfish bodies, cartilage , tendons, hair, muscle and nervous tissues, etc. The history of the development of life on Earth can be simultaneously considered the history of the evolution of the colloidal state of matter. Over time, the structure of the gels is broken - water is released from them. This phenomenon is called syneresis .

Solutions

The 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 salt, sugar, carbon dioxide. If the solution was formed by mixing a gas with a gas, a liquid with a liquid, and a solid with a solid, the solvent is considered to be the component that is more 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 a solvent, since its mass fraction is 70-80%, therefore, it is a solution of water in acetic acid.

During the crystallization of a liquid alloy of silver and gold, solid solutions of various 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 (nitrogen, hydrosulfide acids, etc.);
ionic - these are solutions of 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 put forward 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 - homogeneous (homogeneous) system consisting of particles of the dissolved substance, solvent and products of their interaction.

The behavior and properties of electrolyte solutions, as you well know, is 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 first of all by I. A. Kablukov.

Questions for consolidation:
1. What are dispersed 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. Follow the evolution of colloidal systems during the development of life on Earth.

There are no elements in nature that are pure. Basically, they are all mixtures. They, in turn, can be heterogeneous or homogeneous. They are formed from substances in the state of aggregation, thus creating a certain dispersion system in which there are various phases. In addition, mixtures usually contain a dispersion medium. Its essence lies in the fact that it is considered an element with a large volume in which some substance is distributed. In a dispersed system, the phase and the medium are located in such a way that there are particles of the interface between them. Therefore, it is called heterogeneous or heterogeneous. In view of this, the action of the surface, and not of the particles as a whole, is of great importance.

Classification of the dispersed system

The phase, as is known, is represented by substances having a different state. And these elements are divided into several types. The state of aggregation of the dispersed phase depends on the combination of the medium in it, resulting in 9 types of systems:

1. Gas. Liquid, solid and the element in question. Homogeneous mixture, fog, dust, aerosols.
2. Liquid dispersed phase. Gas, solid, water. Foams, emulsions, sols.
3. Solid dispersed phase. Liquid, gas and the substance considered in this case. Soil, means in medicine or cosmetics, rocks.

As a rule, the dimensions of a dispersed system are determined by the size of the phase particles. There is the following classification:

• rough (suspensions);
• subtle and true).

Particles of the dispersion system

When analyzing coarse mixtures, one can observe that the particles of these compounds in the structure can be seen with the naked eye, due to the fact that their size is more than 100 nm. Suspensions, as a rule, refer to a system in which the dispersed phase is separable from the medium. This is because they are considered opaque. Suspensions are divided into emulsions (insoluble liquids), aerosols (fine particles and solids), suspensions (solid in water).

A colloidal substance is anything that has the quality of having another element evenly dispersed over it. That is, it is present, or rather, it is part of the dispersed phase. This is a state when one material is completely distributed in another, or rather in its volume. In the milk example, liquid fat is dispersed in an aqueous solution. In this case, the smaller molecule is within 1 nanometer and 1 micrometer, making it invisible to the optical microscope when the mixture becomes homogeneous.

That is, no part of the solution has a greater or lesser concentration of the dispersed phase than any other. We can say that it is colloidal in nature. The larger one is called the continuous phase or dispersion medium. Since its size and distribution do not change, and the element in question is distributed over it. Types of colloids include aerosols, emulsions, foams, dispersions, and mixtures called hydrosols. Each such system has two phases: a dispersed and a continuous phase.

Colloids by history

Intense interest in such substances was present in all sciences at the beginning of the 20th century. Einstein and other scientists carefully studied their characteristics and applications. At the time, this new field of science was the leading research area for theorists, researchers and manufacturers. After the peak of interest until 1950, research on colloids declined significantly. It is interesting to note that since the recent emergence of higher power microscopes and "nanotechnologies" (the study of objects of a certain tiny scale), there has been a renewed scientific interest in the study of new materials.

More about these substances

There are elements observed both in nature and in artificial solutions that have colloidal properties. For example, mayonnaise, cosmetic lotion, and lubricants are types of artificial emulsions, and milk is a similar mixture that occurs naturally. Colloidal foams include whipped cream and shaving foam, while edible items include butter, marshmallows, and jelly. In addition to food, these substances exist in the form of certain alloys, paints, inks, detergents, insecticides, aerosols, styrofoam, and rubber. Even beautiful natural objects like clouds, pearls and opals have colloidal properties because they have another substance evenly distributed through them.

Obtaining colloidal mixtures

By enlarging small molecules to the 1 to 1 micrometer range, or by reducing large particles to the same size. Colloidal substances can be obtained. Further production depends on the type of elements used in the dispersed and continuous phases. Colloids behave differently than regular liquids. And this is observed in transport and physico-chemical properties. For example, a membrane may allow a true solution with solid molecules attached to liquid molecules to pass through it. Whereas a colloidal substance which has a solid dispersed through a liquid will be stretched by the membrane. The parity of the distribution is uniform up to the point of microscopic equality in the gap over the entire second element.

True Solutions

Colloidal dispersion is represented as a homogeneous mixture. The element consists of two systems: continuous and dispersed phase. This indicates that this case is related to because they are directly related to the above mixture of several substances. In a colloid, the second has the structure of tiny particles or drops, which are evenly distributed in the first. From 1 nm to 100 nm is the size constituting the dispersed phase, or rather the particles, in at least one dimension. In this range, the dispersed phase - with the indicated dimensions, can be called approximate elements that fit the description: colloidal aerosols, emulsions, foams, hydrosols. Affected by the chemical composition of the surface to a large extent particles or droplets present in the considered compositions.

Colloidal solutions and systems

It should be taken into account that the size of the dispersed phase is a hard-to-measure variable in the system. Solutions are sometimes characterized by their own properties. To make it easier to perceive the indicators of the compositions, colloids resemble them and look almost the same. For example, if it has a liquid-dispersed, solid form. As a result, particles will not pass through the membrane. While other components like dissolved ions or molecules are able to pass through it. If it is simpler to analyze, it turns out that the dissolved components pass through the membrane, and colloidal particles cannot pass through the phase under consideration.

The appearance and disappearance of color characteristics

Due to the Tyndall effect, some of these substances are translucent. In the structure of the element, it is the scattering of light. Other systems and compositions come with some shade or even be opaque, with a certain color, even if some are even dim. Many familiar substances, including butter, milk, cream, aerosols (fog, smog, smoke), asphalt, paints, paints, glue, and sea foam, are colloids. This field of study was introduced in 1861 by the Scottish scientist Thomas Graham. In some cases, a colloid can be considered as a homogeneous (not heterogeneous) mixture. This is because the distinction between "dissolved" and "granular" matter can sometimes be the subject of an approach.

Hydrocolloid types of substances

This component is defined as a colloidal system in which particles are dispersed in water. Hydrocolloid elements, depending on the amount of liquid, can take on various states, for example, a gel or a sol. They are irreversible (single-component) or reversible. For example, agar, the second type of hydrocolloid. May exist in gel and sol states, and alternate between states with addition or removal of heat.

Many hydrocolloids are derived from natural sources. For example, carrageenan is extracted from algae, gelatin is from bovine fat, and pectin is from citrus peel and apple pomace. Hydrocolloids are used in food mainly to affect texture or viscosity (sauce). Also used for skin care or as a healing agent after injury.

Essential characteristics of colloidal systems

It can be seen from this information that colloidal systems are a subsection of the dispersed sphere. They, in turn, can be solutions (sols) or gels (jelly). The former are in most cases created on the basis of living chemistry. The latter are formed under the sediments that occur during the coagulation of the sols. Solutions can be aqueous with organic substances, with weak or strong electrolytes. The particle sizes of the dispersed phase of colloids are from 100 to 1 nm. They cannot be seen with the naked eye. As a result of settling, the phase and medium are difficult to separate.

Classification according to the types of particles of the dispersed phase

multimolecular colloids. When, in dissolution, atoms or smaller molecules of substances (having a diameter of less than 1 nm) combine together to form particles of similar sizes. In these sols, the dispersed phase is a structure that consists of aggregates of atoms or molecules with a molecular size of less than 1 nm. For example, gold and sulfur. These are held together by van der Waals forces. They usually have a lyophilic character. This means a significant interaction of particles.

high molecular weight colloids. These are substances that have large molecules (so-called macromolecules), which, when dissolved, form a certain diameter. Such substances are called macromolecular colloids. These dispersed phase forming elements are typically polymers having very high molecular weights. Natural macromolecules are starch, cellulose, proteins, enzymes, gelatin, etc. Artificial macromolecules include synthetic polymers such as nylon, polyethylene, plastics, polystyrene, etc. They are usually lyophobic, which means in this case a weak interaction particles.

related colloids. These are substances that, when dissolved in a medium, behave like normal electrolytes at low concentration. But they are colloidal particles with a larger enzymatic component of the components due to the formation of aggregated elements. The aggregate particles thus formed are called micelles. Their molecules contain both lyophilic and lyophobic groups.

Micelles. They are clustered or aggregated particles formed by the association of a colloid in solution. Common examples are soaps and detergents. The formation occurs above a certain Kraft temperature, and above a certain critical micellization concentration. They are able to form ions. Micelles can contain up to 100 molecules or more, for example sodium stearate is a typical example. When it dissolves in water, it gives off ions.