After studying the topic of the lesson, you will learn:
- what are dispersed 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 be 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:
- 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.
- 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.
- 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 appears 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
- Consider carefully the sample given to you (external description). Fill in column No. 1 of the table.
- 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?
- 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).
- 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)
- 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).
Writing rules cinquain:
- The first line contains a single word (usually a noun) for the topic.
- The second line is a description of this topic with two adjectives.
- The third line is three verbs (or verb forms) that name the most characteristic actions of the subject.
- The fourth line is a four-word phrase showing a personal relationship to the topic.
- The last line is a synonym for the topic, emphasizing its essence.
Summer 2008 Vienna. Schönbrunn.
Summer 2008 Nizhny Novgorod region.
Clouds and their role in human life All the nature 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. Krasnova Maria, |
P.S.
Many thanks to Pershina O.G., a chemistry teacher at the Dmitrov gymnasium, in the lesson we worked with the presentation found, and it was supplemented by our examples.
Dispersed systems are systems consisting of many small particles distributed in a liquid, solid or gaseous medium.
The concept of "dispersed" comes from lat. dispersus - fragmented, scattered.
All dispersed systems are characterized by two main features: high fragmentation (dispersion) and heterogeneity.
The heterogeneity of dispersed systems is manifested in the fact that these systems consist of two (or more) phases: a dispersed phase and a dispersion medium. The dispersed phase is a fragmented phase. It consists of particles of an insoluble finely divided substance distributed throughout the volume of the dispersion medium.
High dispersity gives substances new qualitative features: increased reactivity and solubility, color intensity, light scattering, etc. A large interface creates a large supply of surface energy in these systems, which makes them thermodynamically unstable, extremely reactive. Spontaneous processes easily occur in them, leading to a decrease in the surface energy: adsorption, coagulation (adhesion of dispersed particles), the formation of macrostructures, etc. and the behavior of these systems.
Classification of dispersed systems is carried out on the basis of various characteristics, namely: by particle size, by the state of aggregation of the dispersed phase and the dispersion medium, by the nature of the interaction of the particles of the dispersed phase with each other and with the medium.
2.2. Classification of disperse systems
Classification by particle size (dispersity)
dispersion D is the main characteristic of a dispersed system and a measure of the fragmentation of a substance. Mathematically, dispersion is defined as the reciprocal of the particle size:
D = 1/a,
where a- particle size (rib diameter or length), m -1 .
On the other hand, the degree of fragmentation is characterized by the value of the specific surface S oud. The specific surface is found as the ratio of the surface S particles to its volume V or mass t:S oud = S/ V or S oud = S/ m. If the specific surface is determined in relation to the mass of a particle of a crushed substance, then its dimension is m 2 /kg, if in relation to the volume, then the dimension coincides with the dimension of dispersion (m -1).
The physical meaning of the concept of "specific surface" is that it is the total surface of all particles, the total volume of which is 1 m 3 or the total mass of which is 1 kg.
By dispersion, the systems are divided into types:
1) coarsely dispersed (coarse suspensions, suspensions, emulsions, powders) with a particle radius of 10 -4 - 10 -7 m;
2) colloidal-dispersed (sols) with a particle size of 10 -7 - 10 -9 m;
3) molecular and ionic solutions with a particle size of less than 10 -9 m.
In colloidal systems, the highest degree of fragmentation of a substance is achieved, at which the concepts of "phase" and "heterogeneity" are still preserved. Reducing the particle size by another order of magnitude transforms the systems into homogeneous molecular or ionic solutions.
Dispersity affects all the main properties of disperse systems: kinetic, optical, catalytic, etc.
The properties of dispersed systems are compared in Table. 1.2.
T a b l e 1.2. Properties of disperse systems of different types
|
Coarse |
Colloidal-dispersed |
Molecular and ionic (true) solutions |
|
Opaque - reflect light |
Transparent opalescent - scatter light, give a Tyndall cone |
Transparent, non-opalescent, Tyndall's cone is not visible |
|
Particles do not pass through the filter |
Particles pass through the paper filter |
Particles pass through the paper filter |
|
Particles are retained by ultrafilters |
Particles pass through ultrafilters |
|
|
Heterogeneous |
Heterogeneous |
homogeneous |
|
Unstable kinetically and thermodynamically |
Relatively stable kinetically |
Resistant throw. and thermodynamic |
|
grow old in time |
grow old in time |
Don't get old |
|
Particles are visible in an optical microscope |
The particles are visible in the electron. Microscope and ultramicroscope |
Particles are not visible in modern microscopes |
In addition to the particle size, the geometric shape of the particles is of great importance for the properties of dispersed systems. Depending on the crushing conditions of the substance, the shape of the particles of the dispersed phase can be very diverse. One m 3 of the initial substance is fundamentally possible to crush into cubes with an edge length l= 10 -8 m, stretched into a thread with a cross section of 10 -8 x 10 -8 m or flattened into a plate (film) 10 -8 m thick. In each of these cases, the system will be dispersed with all the inherent features.
The specific surface of cubic particles increases from the initial value of 6 m 2 to the value determined by the formula
S oud = S/ V = 6l 2 / l 3 = 6 . 10 8 m -1
For threads S oud= 4-10 8 m -1 ; for film S oud = 2 . 10 8 m -1 .
Particles of cubic, spherical or close to them irregular shape are characteristic of many colloidal solutions - sols and more coarsely dispersed systems - emulsions.
Classification according to the state of aggregation of phases
The most common classification of dispersed systems is based on the state of aggregation of the dispersed phase and dispersion medium. Each of these phases can be in three states of aggregation: gaseous, liquid and solid. Therefore, the existence of eight types of colloidal systems is possible (Table 1.3). The "gas in gas" system is not included in this number, since it is a homogeneous molecular system, there are no interfaces in it. Highly dispersed colloidal solutions belonging to the type of t / l systems are called sols (from Latin solutio - solution). Sols in which water is the dispersion medium are called hydrosols. If the dispersion medium is an organic liquid, the colloidal solution is called an organosol. These latter, in turn, are divided into alkosols, benzols, etherosols, etc., in which the dispersion medium is, respectively, alcohol, benzene, ether, etc. Depending on the state of aggregation of the dispersion medium, lyosols are distinguished - sols with a liquid dispersion medium (from the Greek lios - liquid), aerosols - sols with a gaseous dispersion medium, solid sols - systems of the t / t type. Coarsely dispersed systems of the s/l type are called suspensions, and the s/l type are called emulsions.
Table 2..2. Main types of disperse systems
|
Disp phase |
Display environment | ||
|
Not creatures. |
|||
|
Liquid |
Fog, clouds, liquid drug aerosols |
||
|
solid body |
Smoke, dust, powders, aerosols of solid drugs |
||
|
Liquid |
Foams, gas emulsions |
||
|
Liquid |
Emulsions (milk, medicinal emulsions) |
||
|
solid body |
Suspensions, colloidal solutions |
||
|
solid body |
Hard foams, bread, pumice, silica gel, activated carbons |
||
|
Liquid |
Pearls, capillary systems, cement stone, gels |
||
|
solid body |
Colored glasses, minerals, alloys |
Classification according to the absence or presence of interaction between the particles of the dispersed phase
According to the kinetic properties of the dispersed phase, all disperse systems can be divided into two classes: free-dispersed, in which the particles of the dispersed phase are not bound to each other and can move freely (lyosols, aerosols, suspensions, emulsions), and bound-dispersed, in which one of phases are structurally fixed and cannot move freely. This class includes gels and jellies, foams, capillary-porous bodies (diaphragms), solid solutions, etc.
Classification according to the degree of interaction of the dispersed phase with the dispersion medium
To characterize the interaction between the substance of the dispersed phase and the liquid dispersion medium, the concepts of "lyophilicity" and "lyophobicity" are used. Under the interaction of the phases of dispersed systems, solvation (hydration) processes are meant, i.e., the formation of solvate (hydrate) shells from the molecules of the dispersion medium around the particles of the dispersed phase. Systems in which the interaction of particles of the dispersed phase with the solvent is strongly expressed are called freeze-dried(in relation to water - hydrophilic). If the particles of the dispersed phase consist of a substance that weakly interacts with the medium, the systems are lyophobic(in relation to water - hydrophobic). The term "lyophilic" comes from the Greek. 1uo - I dissolve and philia - love; "lyophobic" from luo - I dissolve and phobia - hatred, which means "not loving dissolution." Well-solvating lyophilic disperse systems are formed by spontaneous dispersion. Such systems are thermodynamically stable. Examples of such systems are dispersions of some clays and surface-active substances (surfactants), solutions of macromolecular substances (HMW).
In hydrophobic sols, the particles consist of sparingly soluble compounds; the affinity of the dispersed phase to the solvent is absent or weakly expressed. Such particles are poorly solvated. Hydrophobic sols are the main class of colloidal solutions with pronounced heterogeneity and high specific surface area.
General chemistry: textbook / A. V. Zholnin; ed. V. A. Popkova, A. V. Zholnina. - 2012. - 400 p.: ill.
Chapter 13. PHYSICAL CHEMISTRY OF DISPERSIVE SYSTEMS
Chapter 13. PHYSICAL CHEMISTRY OF DISPERSIVE SYSTEMS
Life is a special colloidal system... it is a special realm of natural waters.
IN AND. Vernadsky
13.1 DISPERSIVE SYSTEMS, THEIR CLASSIFICATIONS, PROPERTIES
Colloidal solutions
The material basis of modern civilization and the very existence of man and the entire biological world is associated with disperse systems. A person lives and works in an environment of dispersed systems. Air, especially the air of working rooms, is a dispersed system. Many food products, semi-finished products and products of their processing are dispersed systems (milk, meat, bread, butter, margarine). Many medicinal substances are produced in the form of thin suspensions or emulsions, ointments, pastes or creams (protargol, collargol, gelatinol, etc.). All living systems are dispersed. Muscle and nerve cells, fibers, genes, viruses, protoplasm, blood, lymph, cerebrospinal fluid - all these are highly dispersed formations. The processes occurring in them are controlled by physical and chemical laws, which are studied by the physicochemistry of disperse systems.
Dispersed systems are systems in which the substance is in a state of more or less high fragmentation and is evenly distributed in the environment. The science of highly dispersed systems is called colloid chemistry. Living matter is based on compounds that are in a colloidal state.
The dispersed system consists of a dispersion medium and a dispersed phase. There are several classifications of dispersed systems based on various features of dispersed systems.
1. According to the state of aggregation dispersion medium All disperse systems can be reduced to 3 types. Dispersed systems with gaseous
dispersion medium - aerosols(smoke, indoor air, clouds, etc.). Disperse systems with a liquid dispersion medium - lyosols(foams, emulsions - milk, suspensions, dust that has entered the respiratory tract; blood, lymph, urine are hydrosols). Dispersed systems with a solid dispersion medium - solidozoli(pumice, silica gel, alloys).
2. The second classification groups dispersed systems depending on the particle size of the dispersed phase. The measure of fragmentation of particles is either the transverse particle size - the radius (r), or
(radius) of particles (r) is expressed in centimeters, then the dispersion D is the number of particles that can be packed closely along the length of one centimeter. Finally, it is possible to characterize the specific surface (∑), the units of ∑ are m 2 /g or m 2 /l. Under specific surface understand the relationship of the surface (S) of the dispersed phase to its
coefficient of dependence of the specific surface on the shape of the particles. The specific surface area is directly proportional to dispersion (D) and inversely proportional to the transverse particle size (r). With increasing dispersion, i.e. with decreasing particle size, its specific surface area increases.
The second classification groups disperse systems depending on the particle size of the dispersed phase into the following groups (Table 13.1): coarse systems; colloidal solutions; true solutions.
Colloidal systems can be gaseous, liquid and solid. The most common and studied liquid (lyosols). Colloidal solutions are commonly referred to as sols for short. Depending on the nature of the solvent - dispersion medium, i.e. water, alcohol or ether, lyosols are called respectively hydrosols, alkosols or etherosols. According to the intensity of interaction between the particles of the dispersed phase and the dispersion medium, the sols are divided into 2 groups: lyophilic- intensive interaction, as a result of which developed solvate layers are formed, for example, a sol of protoplasm, blood, lymph, starch, protein, etc.; lyophobic sols- weak interaction of the particles of the dispersed phase with the particles of the dispersion medium. Sols of metals, hydroxides, practically all classical colloidal systems. IUDs and surfactant solutions are separated into separate groups.
Table 13.1. Classification of disperse systems by particle size and their properties
A great contribution to the theory of colloidal solutions was made by our domestic scientists I.G. Borshchov, P.P. Weimarn, N.P. Peskov, D.I. Mendeleev, B.V. Deryagin, P.A. Rebinder, etc.
Any colloidal solution is a microheterogeneous, multiphase, highly and polydisperse system with a high degree of dispersion. The condition for the formation of a colloidal solution is the insolubility of the substance of one phase in the substance of another, because only between such substances can physical interfaces exist. According to the strength of the interaction between the particles of the dispersed phase, free-dispersed and bound-dispersed systems are distinguished. An example of the latter are biological membranes.
The preparation of colloidal solutions is carried out by two methods: dispersion of large particles to a colloidal degree of dispersion and condensation - the creation of conditions under which atoms, molecules or ions are combined into aggregates of a colloidal degree of dispersion.
Metals, sparingly soluble salts in water, oxides and hydroxides, and many non-polar organic substances can form hydrosols. Substances that dissolve well in water, but are poorly soluble in non-polar compounds, are not able to form hydrosols, but can form organosols.
As stabilizers substances are used that prevent the aggregation of colloidal particles into larger ones and their precipitation. This effect is possessed by: a small excess of one of the reagents from which the substance of the dispersed phase is obtained, surfactants, including proteins and polysaccharides.
To achieve the dispersion required for colloidal systems (10 -7 -10 -9 m) apply:
Mechanical crushing using ball and colloid mills in the presence of a liquid dispersion medium and a stabilizer;
The action of ultrasound (for example, sulfur hydrosol, graphite, metal hydroxides, etc.);
Peptization method, adding a small amount of electrolyte - peptizer;
One of the varieties of the condensation method is the solvent replacement method, which results in a decrease in the solubility of the substance of the dispersed phase. Molecules of a substance condense into particles of colloidal size as a result of the destruction of the solvate layers of molecules in a true solution and the formation of larger particles. At the heart of the chemi-
Thermal condensation methods are chemical reactions (oxidation, reduction, hydrolysis, exchange) leading to the formation of poorly soluble substances in the presence of certain stabilizers.
13.2. MOLECULAR-KINETIC PROPERTIES OF COLLOID SOLUTIONS. OSMOSIS.
OSMOTIC PRESSURE
Brownian motion - this is the thermal motion of particles in colloidal systems, which has a molecular-kinetic nature. It has been established that the movement of colloidal particles is a consequence of random impacts inflicted on them by molecules of a dispersion medium that are in thermal motion. As a result, the colloidal particle often changes its direction and speed. For 1 s, a colloidal particle can change its direction more than 10 20 times.
by diffusion called a spontaneously proceeding process of leveling the concentration of colloidal particles in a solution under the influence of their thermal chaotic movement. The phenomenon of diffusion is irreversible. The diffusion coefficient is numerically equal to the amount of a substance diffused through a unit area per unit time at a concentration gradient of 1 (i.e., a concentration change of 1 mol/cm 3 at a distance of 1 cm). A. Einstein (1906) derived an equation relating the diffusion coefficient to the absolute temperature, viscosity and particle size of the dispersed phase:
where T- temperature, K; r- particle radius, m; η - viscosity, N s / m 2; to B- Boltzmann's constant, 1.38 10 -23; D- diffusion coefficient, m 2 / s.
The diffusion coefficient is directly proportional to the temperature and inversely proportional to the viscosity of the medium (η) and particle radius (r). The cause of diffusion, as well as Brownian motion, is the molecular-kinetic motion of the particles of the solvent and the substance. It is known that the kinetic energy of a moving molecule is the smaller, the larger its volume (Table 13.2).
Using the Einstein equation, you can easily determine the mass of 1 mole of a substance if you know D, Tη and r. From equation (13.1) one can determine r:
where R- universal gas constant, 8.3 (J / mol-K); N a Avogadro constant.
Table 13.2. Diffusion coefficient of some substances
In the case when the system is separated from other parts of the system by a partition that is permeable to one component (for example, water) and impermeable to another (for example, a solute), diffusion becomes one-way (osmosis). The force that causes osmosis per unit of membrane surface is called osmotic pressure. The role of semi-permeable partitions (membranes) can be performed by tissues of humans, animals and plants (urinary bladder, intestinal walls, cell membranes, etc.). For colloidal solutions, the osmotic pressure is less than in true solutions. The diffusion process is accompanied by the appearance of a potential difference as a result of different ion mobility and the formation of a concentration gradient (membrane potential).
Sedimentation. The distribution of particles is influenced not only by diffusion, but also by the gravitational field. The kinetic stability of a colloidal system depends on the action of two oppositely directed factors: the force of gravity, under which the particles settle, and the force at which the particles tend to disperse throughout the volume and counteract the settling.
Optical properties of colloidal solutions. Light scattering. D. Rayleigh equation. It is impossible to distinguish between colloidal and true solutions at first glance. A well-prepared sol is an almost pure transparent liquid. Its microheterogeneity can be detected by special methods. If a sol located in an unlit place is illuminated with a narrow beam, then when viewed from the side, one can see a bright cone, the top of which is located at the point where the beam enters the inhomogeneous space. This is the so-called Tyndall's cone - a kind of turbid glow of colloids, observed under side illumination, is called the Faraday-Tyndall effect.
The reason for this phenomenon characteristic of colloids is that the size of colloidal particles is less than half the wavelength of light, while diffraction of light is observed, as a result of scattering, the particles glow, turning into an independent light source, and the beam becomes visible.
The theory of light scattering was developed by Rayleigh in 1871, who derived an equation for spherical particles relating the intensity of incident light (I 0) to the intensity of light scattered by a unit volume of the system (I p).
where I, I0- intensity of scattered and incident light, W/m 2 ; k p is the Rayleigh constant, a constant depending on the refractive indices of the substances of the dispersed phase and the dispersion medium, m -3 ; with v- concentration of sol particles, mol/l; λ is the wavelength of the incident light, m; r- particle radius, m.
13.3. MICELLAR THEORY OF THE STRUCTURE OF COLLOID PARTICLES
Micelles form the dispersed phase of the sol, and the intermicellar liquid forms a dispersion medium, which includes a solvent, electrolyte ions, and nonelectrolyte molecules. A micelle consists of an electrically neutral aggregate and an ionic particle. The mass of a colloidal particle is concentrated mainly in the aggregate. The aggregate can have both amorphous and crystalline structure. According to the Panet-Fajans rule, ions are irreversibly adsorbed on the aggregate with the formation of strong bonds with the atoms of the aggregate, which are part of the crystal lattice of the aggregate (or isomorphic with it). An indicator of this is the insolubility of these compounds. They're called potential determining ions. As a result of selective adsorption of ions or ionization of surface molecules, the aggregate acquires a charge. Thus, the aggregate and potential-determining ions form the core of a micelle and group around the core ions of the opposite sign - counterions. The aggregate together with the ionogenic part of the micelles form a double electric layer (adsorption layer). The aggregate together with the adsorption layer is called a granule. The charge of the granule is equal to the sum of the charges of counterions and potential-determining ions. ionogenic
part of the micelle consists of two layers: adsorption and diffuse. This completes the formation of an electrically neutral micelle, which is the basis of a colloidal solution. A micelle is shown as colloid-chemical formula.
Let us consider the structure of a hydrosol micelle using the example of the formation of a colloidal solution of barium sulfate under the condition of an excess of BaCl 2:
Sparingly soluble barium sulfate forms a crystalline aggregate consisting of m BaSO 4 molecules. Adsorbed on the surface of the aggregate n Ba 2+ ions. There are 2(n - x) chloride ion C1 - . The remaining counterions (2x) are located in the diffuse layer:
The structure of a micelle of a barium sulfate sol obtained with an excess of sodium sulfate is written as:
From the above data, that the sign of the charge of a colloidal particle depends on the conditions for obtaining a colloidal solution.
13.4. ELECTROKINETIC POTENTIAL
COLLOID PARTICLES
Zeta-(ζ )-potential. The value of the charge of the ζ-potential is determined by the charge of the granule. It is determined by the difference between the sum of the charges of the potential-determining ions and the charges of the counterions located in the adsorption layer. It decreases as the number of counterions in the adsorption layer increases and can become equal to zero if the charge of the counterions is equal to the charge of the nucleus. The particle will be in an isoelectric state. The magnitude of the ζ-potential can be used to judge the stability of a disperse system, its structure, and electrokinetic properties.
The ζ-potential of different cells of the body varies. Living protoplasm is negatively charged. At pH 7.4, the value of the ζ-potential of erythrocytes is from -7 to -22 mV, in humans it is -16.3 mV. Monocytes are about 2 times lower. The electrokinetic potential is calculated by determining the speed of particles of the dispersed phase during electrophoresis.
The electrophoretic mobility of particles depends on a number of quantities and is calculated using the Helmholtz-Smoluchowski equation:
where and ef- electrophoretic mobility (electrophoresis speed), m/s; ε is the relative permittivity of the solution; ε 0 - electrical constant, 8.9 10 -12 A s / W m; Δφ - potential difference from an external current source, V; ζ - electrokinetic potential, V; η is the viscosity of the dispersion medium, N s/m 2 ; l- distance between electrodes, m; to f- coefficient, the value of which depends on the shape of the colloidal particle.
13.5. ELECTROKINETIC PHENOMENA.
ELECTROPHORESIS. ELECTROPHORESIS
IN MEDICAL AND BIOLOGICAL RESEARCH
Electrokinetic phenomena reflect the relationship that exists between the motion of the phases of a dispersed system relative to each other and the electrical properties of the interface between these phases. There are four types of electrokinetic phenomena - electrophoresis, electroosmosis, flow potential (flow) and subsidence potential (sedimentation). Electrokinetic phenomena were discovered by F.F. Reiss. In a piece of wet clay, he immersed two glass tubes at some distance, into which he poured a little quartz sand, poured water to the same level and lowered the electrodes (Fig. 13.1).
By passing a direct current, Reiss found that in the anode space the water above the sand layer becomes cloudy due to the appearance of a suspension of clay particles, at the same time the water level in the knee decreases; in the cathode tube, the water remains clear, but its level rises. Based on the results of the experiment, we can conclude that clay particles moving towards the positive electrode are negatively charged, and the adjacent layer of water is positively charged, as it moves towards the negative pole.
Rice. 13.1. Electrokinetic phenomena of motion of particles of the dispersed phase
in a dispersed system
The phenomenon of the movement of charged particles of the dispersed phase relative to the particles of the dispersion medium under the action of an electric field is called electrophoresis. The phenomenon of movement of a liquid relative to the solid phase through a porous solid (membrane) is called electroosmosis. Under the conditions of the described experiment, two electrokinetic phenomena were observed simultaneously - electrophoresis and electroosmosis. The movement of colloidal particles in an electric field is clear evidence that colloidal particles carry a charge on their surface.
A colloidal particle - a micelle can be considered as a complex ion of huge size. A colloidal solution undergoes electrolysis under the influence of direct current, colloidal particles are transferred to the anode or cathode (depending on the charge of the colloidal particle). Thus, electrophoresis is the electrolysis of a highly dispersed system.
Later, 2 phenomena opposite to electrophoresis and electroosmosis were discovered. Dorn discovered that when any particles settle in a liquid, such as sand in water, an EMF occurs between 2 electrodes inserted at different points in the liquid column, called sedimentation potential (Dorn effect).
When a liquid is forced through a porous partition, on both sides of which there are electrodes, an EMF also appears - flow (flow) potential.
The colloidal particle moves at a speed proportional to the valueζ -potential. If the system has a complex mixture, then it is possible to study and separate it using the electrophoresis method based on the electrophoretic mobility of particles. This is widely used in biomedical research in the form of macro and micro electrophoresis.
The generated electric field causes the particles of the dispersed phase to move at a speed proportional to the value of the ζ-potential, which can be observed by moving the interface between the test solution and the buffer using optical devices. As a result, the mixture is divided into a number of fractions. When registering, a curve with several peaks is obtained, the height of the peak is a quantitative indicator of the content of each fraction. This method makes it possible to isolate and study individual fractions of blood plasma proteins. The electrophoregrams of the blood plasma of all people are normally the same. In pathology, they have a characteristic appearance for each disease. They are used to diagnose and treat diseases. Electrophoresis is used to separate amino acids, antibiotics, enzymes, antibodies, etc. Microelectrophoresis consists in determining the speed of movement of particles under a microscope, electrophoresis - on paper. The phenomenon of electrophoresis occurs during the migration of leukocytes into inflammatory foci. Immunoelectrophoresis, disk electrophoresis, isotachophoresis, etc. are being developed and implemented as methods of treatment. They solve many medical and biological problems, both preparative and analytical.
13.6. STABILITY OF COLLOID SOLUTIONS. SEDIMENTATION, AGGREGATION AND CONDENSATION STABILITY OF LYOSOLS. FACTORS AFFECTING SUSTAINABILITY
The question of the stability of colloidal systems is a very important question relating directly to their very existence. Sedimentation stability- resistance of the particles of the dispersed system to settling under the action of gravity.
Peskov introduced the concept of aggregative and kinetic stability. Kinetic stability- the ability of the dispersed phase of the colloidal system to be in a suspended state, not to sediment and counteract the forces of gravity. Highly dispersed systems are kinetically stable.
Under aggregative stability it is necessary to understand the ability of a disperse system to maintain the initial degree of dispersion. This is only possible with a stabilizer. The consequence of violation of aggregative stability is kinetic instability,
for the aggregates formed from the initial particles under the action of gravity stand out (settle or float up).
Aggregative and kinetic stability are interrelated. The greater the aggregative stability of the system, the greater its kinetic stability. Stability is determined by the result of the struggle between gravity and Brownian motion. This is an example of the manifestation of the law of unity and the struggle of opposites. Factors that determine the stability of systems: Brownian motion, dispersion of particles of the dispersed phase, viscosity and ionic composition of the dispersion medium, etc.
Stability factors of colloidal solutions: the presence of an electric charge of colloidal particles. Particles carry the same charge, so when they meet, the particles repel each other; the ability to solvate (hydrate) the ions of the diffuse layer. The more hydrated the ions in the diffuse layer, the thicker the overall hydration shell, the more stable the system. The elastic forces of the solvate layers have a wedging effect on dispersed particles and prevent them from approaching; adsorption-structuring properties of systems. The third factor is related to the adsorption properties of disperse systems. On the developed surface of the dispersed phase, molecules of surface-active substances (surfactants) and macromolecular compounds (HMCs) are easily absorbed. Large sizes of molecules carrying their own solvation layers create adsorption-solvation layers of considerable length and density on the particle surface. Such systems are close in stability to lyophilic systems. All these layers have a certain structure, they are created according to P.A. Rebinder structural-mechanical barrier on the way of convergence of dispersed particles.
13.7. SOLE COAGULATION. COAGULATION RULES. KINETICS OF COAGULATION
Sols are thermodynamically unstable systems. The particles of the dispersed phase of the sols tend to reduce the free surface energy by reducing the specific surface of the colloidal particles, which occurs when they are combined. The process of combining colloidal particles into larger aggregates, and eventually precipitating them, is called coagulation.
Coagulation is caused by various factors: mechanical impact, temperature change (boiling and freezing), radiation
ion, foreign matter, especially electrolytes, time (aging), concentration of the dispersed phase.
The most studied process is the coagulation of sols by electrolytes. There are the following rules for the coagulation of sols with electrolytes.
1. All electrolytes are capable of causing coagulation of lyophobic sols. The coagulating effect (P) is possessed by ions having a charge opposite to the charge of the granule (potential-determining ions) and the same sign as counterions (Hurdy's rule). Coagulation of positively charged sols is caused by anions.
2. The coagulating ability of ions (P) depends on the magnitude of their charge. The higher the charge of the ion, the higher its coagulating effect. (Schulze's rule): PA1 3+ > PCa 2+ > PK + .
Accordingly, for the coagulation threshold, we can write:
those. the lower the ion charge, the higher the concentration will coagulate.
3. For ions of the same charge, the coagulating ability depends on the radius (r) of the solvated ion: the larger the radius, the greater its coagulating effect:
4. Each electrolyte is characterized by a threshold concentration of the colloidal solution coagulation process (coagulation threshold), i.e. the smallest concentration, expressed in millimoles, that must be added to one liter of a colloidal solution in order to cause it to coagulate. The coagulation threshold or threshold concentration is denoted C k. The coagulation threshold is a relative characteristic of the stability of the sol with respect to a given electrolyte and is the reciprocal of the coagulating ability:
5. The coagulating effect of organic ions is greater than that of inorganic ones; coagulation of many lyophobic sols occurs earlier,
than their isoelectric state is reached, at which explicit coagulation begins. This action is called critical. Its value is +30 mV.
The coagulation process for each dispersed system proceeds at a certain speed. The dependence of the coagulation rate on the concentration of the coagulating electrolyte is shown in fig. 13.2.
Rice. 13.2. Dependence of the coagulation rate on the concentration of electrolytes.
Explanations in the text
Three regions and two characteristic points of A and B are identified. The area bounded by the OA line (along the concentration axis) is called the area of latent coagulation. Here, the coagulation rate is almost zero. This is the sol stability zone. Between points A and B there is an area of slow coagulation, in which the coagulation rate depends on the electrolyte concentration. Point A corresponds to the lowest electrolyte concentration, at which explicit coagulation begins (coagulation threshold), and has a critical value. This stage can be judged by external signs: a change in color, the appearance of turbidity. There is a complete destruction of the colloidal system: the release of the substance of the dispersed phase into a precipitate, which is called coagulate. At point B, rapid coagulation begins, i.e., all collisions of particles are effective and do not depend on the electrolyte concentration. At point B, the ζ-potential is equal to 0. The amount of substance necessary for coagulation of a colloidal solution depends on whether the electrolyte is added immediately or gradually, in small portions. It has been observed that in the latter case more substance has to be added to bring about the same coagulation phenomenon. This phenomenon is used in drug dosing.
If you merge two colloidal solutions with opposite charges, they quickly coagulate. The process is electrostatic in nature. It is used for industrial and waste water treatment. At waterworks, aluminum sulfate or iron (III) chloride is added to the water before sand filters. During their hydrolysis, positively charged sols of metal hydroxides are formed, which cause coagulation of negatively charged particles of microflora, soil, and organic impurities.
Coagulation phenomena play a very important role in biological systems. Whole blood is an emulsion. Formed elements of blood - a dispersed phase, plasma - a dispersion medium. Plasma is a more highly dispersed system. Dispersed phase: proteins, enzymes, hormones. The blood coagulation system and the anti-coagulation system work. The first is provided by thrombin, which acts on fibrinogen and causes the formation of fibrin filaments (blood clot). Erythrocytes sediment at a certain rate (ESR). The clotting process ensures minimal blood loss and the formation of blood clots in the circulatory system. In pathology, erythrocytes adsorb large molecules of gamma globulins and fibrinogens and the ESR increases. The main anticoagulant ability of blood is heparin anticoagulant of blood. In clinics, coagulograms are used - a set of tests for blood coagulation and anticoagulation (prothrombin content, plasma recalcification time, heparin tolerance, total fibrinogen, etc.), this is important for severe bleeding, with the formation of blood clots. Blood clotting must be taken into account when it is preserved. Ca 2+ ions are removed with sodium nitrate to precipitate, which increases clotting. Apply anticoagulant, heparin, dicoumarin. Polymers used for endoprosthesis replacement of elements of the cardiovascular system must have antithrombogenic or thromboresistant properties.
13.8. STABILIZATION OF COLLOID SYSTEMS (PROTECTION OF COLLOID SOLUTIONS)
Stabilization of colloidal solutions with respect to electrolytes by creating additional adsorption layers on the surface of colloidal particles with enhanced structural and mechanical properties, adding a small amount of a solution of high
comolecular compounds (gelatin, sodium caseinate, egg albumin, etc.) was called colloid protection. Protected sols are highly resistant to electrolytes. The protected sol acquires all the properties of the adsorbed polymer. The dispersed system becomes lyophilic and therefore stable. The protective effect of the IUD or surfactant is characterized by a protective number. The protective number should be understood as the minimum mass of IUD (in milligrams) that must be added to 10 ml of the investigated Sol in order to protect it from coagulation when 1 ml of a 10% sodium chloride solution is introduced into the systems. The degree of protective action of HMS solutions depends on: the nature of the HMS, the nature of the protected sol, the degree of dispersion, the pH of the medium, and impurities.
The phenomenon of colloidal protection in the body plays a very important role in a number of physiological processes. Various proteins, polysaccharides, peptides have a protective effect in the body. They adsorb Ca on colloidal particles of such hydrophobic body systems as carbonates, calcium phosphates, translating them into a stable state. Examples of protected sols are blood and urine. If you evaporate 1 liter of urine, collect the resulting precipitate and then try to dissolve it in water, then this requires 14 liters of solvent. Therefore, urine is a colloidal solution in which dispersed particles are protected by albumins, mucins and other proteins. Serum proteins increase the solubility of calcium carbonate by almost 5 times. The increased content of calcium phosphate in milk is due to protein protection, which is violated during aging.
In the development of atherosclerosis, the leucetine-cholesterol balance plays an important role, in violation of which the ratio between cholesterol, phospholipids and proteins changes, leading to the deposition of cholesterol on the walls of blood vessels, resulting in atherocalcinosis. A large role in protection is given to large-molecular fat-protein components. On the other hand, the ability of blood to hold in a dissolved state in high concentrations of carbon and oxygen gases is also due to the protective effect of proteins. In this case, proteins envelop gas microbubbles and protect them from sticking together.
Protection of colloidal particles used in the manufacture of drugs. In the body, it is often necessary to introduce medicinal substances in a colloidal state so that they are evenly distributed in the body and absorbed. So, colloidal solutions of silver, mercury, sulfur protected by protein substances, used
as drugs (protargol, collargol, lysorginone), become not only insensitive to electrolytes, but can also be evaporated to dryness. The dry residue after treatment with water again turns into a sol.
13.9. PEPTIZATION
Peptization - process, the reverse of coagulation, the process of transition of the coagulate to the sol. Peptization occurs when substances are added to the precipitate (coagulate) that facilitate the transition of the precipitate into a sol. They are called pepti congestion. Typically, peptizers are potential-determining ions. For example, a precipitate of iron (III) hydroxide is peptized with iron (III) salts. But the solvent (H 2 O) can also play the role of a peptizer. The peptization process is due to adsorption phenomena. The peptizer facilitates the formation of an electric double layer structure and the formation of a zeta potential.
Consequently, the peptization process is mainly due to the adsorption of potential-determining ions and the desorption of counterions, which result in an increase in the ζ-potential of dispersed particles and an increase in the degree of solvation (hydration), the formation of solvate shells around the particles that produce a wedging effect (adsorption peptization).
In addition to adsorption, there are also dissolution peptization. This type covers everything when the peptization process is associated with a chemical reaction of surface molecules of the dispersed phase. It consists of two phases: the formation of a peptizer by chemical reaction of the introduced electrolyte of the peptizer with a dispersed particle; adsorption of the resulting peptizer on the surface of the dispersed phase, leading to the formation of micelles and peptization of the precipitate. A typical example of dissolution peptization is the peptization of metal hydroxides with acids.
The maximum fineness of the sols obtained by adsorption peptization is determined by the degree of fineness of the primary particles that form the precipitate flakes. During dissolution peptization, the fragmentation boundary of particles can leave the region of colloids and reach the molecular degree of dispersion. The process of peptization is of great importance in living organisms, since the colloids of cells and biological fluids are constantly exposed to the action of electrolytes in the body.
The action of many detergents, including detergents, is based on the phenomenon of peptization. The colloidal ion of soap is a dipole, it is adsorbed by dirt particles, gives them a charge and promotes their peptization. Dirt in the form of a sol is easily removed from the surface.
13.10. GELS AND JELLS. THIXOTROPY. SYNERESIS
Solutions of HMS and sols of some hydrophobic colloids are capable of undergoing changes under certain conditions: loss of fluidity, gelation, gelation of solutions occur, and jellies and gels (from Latin “frozen”) are formed.
Jellies (gels)- these are solid non-fluid, structured systems resulting from the action of molecular cohesive forces between colloidal particles or macromolecules of polymers. The forces of intermolecular interaction lead to the formation of a spatial mesh frame, the cells of spatial meshes are filled with a liquid solution, like a sponge soaked in liquid. The formation of jelly can be represented as salting out of the IUD or the initial stage of coagulation, the occurrence of coagulation structuring.
An aqueous solution of gelatin, when the mixture is heated to 45 ° C, becomes a homogeneous liquid medium. When cooled to room temperature, the viscosity of the solution increases, the system loses fluidity, gels, the consistency of the semi-solid mass retains its shape (it can be cut with a knife).
Depending on the nature of the substances that form the jelly or gel, there are: built from hard particles - fragile (irreversible); formed by flexible macromolecules - elastic (reversible). Brittle ones are formed by colloidal particles (TiO 2, SiO 2). Dried is a hard foam with a large specific surface area. Dried jelly does not swell, drying causes irreversible changes.
Elastic gels are formed by polymers. When dried, they are easily deformed, compressed, a dry polymer (pyrogel) is obtained, which retains elasticity. It is able to swell in a suitable solvent, the process is reversible and can be repeated many times.
Weak molecular bonds in jellies can be mechanically destroyed (by shaking, pouring, temperature). Breaking the bond causes the destruction of the structure, the particles acquire the ability
to thermal motion, the system liquefies and becomes fluid. After some time, the structure spontaneously recovers. This can be repeated dozens of times. This reversible transformation is called thixotropy. This isothermal transformation can be represented by the scheme:
Thixotropy is observed in weak solutions of gelatin, cell protoplasm. The reversibility of thixotropy indicates that the structuring in the corresponding systems is due to intermolecular (van der Waals) forces - a coagulation-thixotropic structure.
Gels in the body are the brain, skin, eyeball. The condensation-crystallization type of structure is characterized by a stronger chemical bond. In this case, the reversibility of thixotropic changes is violated (silicic acid gel).
The jelly is a non-equilibrium state of the system, a certain stage of the slowly proceeding process of phase separation and the approach of the system to the state of equilibrium. The process is reduced to the gradual compression of the jelly frame into a denser compact mass with compression of the second mobile liquid phase, which is mechanically held in the spatial grid of the frame. On the surface of the jelly during storage, at first, separate drops of liquid appear, over time they increase and merge into a continuous mass of the liquid phase. This spontaneous process of jelly exfoliation is called syneresis. For fragile jellies, syneresis is an irreversible aggregation of particles, compaction of the entire structure. For IUD jelly, increasing the temperature can stop syneresis and return the jelly to its original position. The separation of coagulated blood clots, the hardening of bread, the soaking of confectionery are examples of syneresis. The tissues of young people are elastic, contain more water, elasticity is lost with age, less water is syneresis.
13.11. QUESTIONS AND TASKS FOR SELF-CHECK
PREPARED FOR CLASSES AND EXAMS
1. Give the concept of dispersed systems, dispersed phase and dispersion medium.
2. How are disperse systems classified according to the state of aggregation of the dispersed phase and dispersion medium? Give examples of biomedical profile.
3. How are dispersed systems classified according to the strength of intermolecular interaction in them? Give examples of biomedical profile.
4. The main part of the "artificial kidney" apparatus is the dialyzer. What is the principle of the device of the simplest dialyzer? What impurities can be removed from the blood by dialysis? What factors influence the rate of dialysis?
5. In what ways can a solution of a low molecular weight substance and a colloidal solution be distinguished? What properties are these methods based on?
6. In what ways can a sol be distinguished from a coarse system? What properties are these methods based on?
7. What are the methods for obtaining colloidal-dispersed systems? How do they differ from each other?
8. What are the features of the molecular-kinetic and optical properties of colloidal-dispersed systems? What distinguishes them from true solutions and coarse systems?
9. Give the concept of aggregative, kinetic and condensation stability of disperse systems. Factors that determine the stability of systems.
10. Show the relationship between the electrokinetic properties of colloidal dispersed systems.
11. What electrokinetic phenomena are observed during mechanical mixing of the particles of the dispersed phase: a) relative to the dispersion medium; b) relative to the particles of the dispersed phase?
12. Explain which of the following preparations refers to colloidal solutions: a) a preparation of barium sulfate in water, used as a contrast agent in X-ray studies with a particle size of 10 -7 m; b) a preparation of silver in water - collargol, used to treat purulent wounds with a particle size of 10 -9 m.
13. The concept of coagulation of sols. Coagulation of lyophilic sols. What are the external signs of coagulation? Specify the possible coagulation products of sols.
14. Factors causing coagulation of sols. Rules for the coagulation of sols by electrolytes. Kinetics of coagulation. coagulation threshold.
15. As a result of violation of micro (Ca 2+) - and macro (C 2 O 4 2-) -element and acid-base homeostasis in the gastrointestinal tract, the following reaction occurs in the kidneys:
What is the charge of the sol? Which of the indicated ions will have a coagulating effect for the particles of this sol: K + , Mg 2+ , SO 4 2- , NO 3 - , PO 4 3- , Al 3+ ?
A calcium oxalate sol is formed. Let us write down the formula of the micelle of the sol
(13.3.).
The charge of the granule of the sol is positive, which means that the ions will have a coagulating effect (k) for the particles of this sol: SO 4 2-, PO 4 3-, NO 3 -, according to Hardy's rule. The higher the charge of the coagulating ion, the stronger its coagulating effect (Schulze's rule). According to the Schulze rule, these anions can be arranged in the following row: C to P0 4 3-> C to SO 4 2-> C to NO 3 -. The lower the ion charge, the higher concentrations will cause coagulation. The coagulation threshold (p) is a relative characteristic of the stability of the sol with respect to a given electrolyte and is the reciprocal of
13.12. TESTS
1. Choose the wrong statement:
a) condensation methods for obtaining colloidal solutions include OVR, hydrolysis, solvent replacement;
b) dispersion methods for obtaining colloidal solutions include mechanical, ultrasonic, peptization;
c) optical properties of colloidal systems include opalescence, diffraction, the Tyndall effect;
d) the molecular-kinetic properties of colloidal systems include Brownian motion, light scattering, and a change in the color of the solution.
2. Choose the wrong statement:
a) electrophoresis is the movement of a dispersed phase in an electric field relative to a stationary dispersion medium;
b) electroosmosis is the movement in the electric field of the dispersion medium relative to the stationary dispersed phase;
c) the penetration of liquids containing therapeutic ions and molecules through the capillary system under the influence of an electric field is called electrodialysis;
d) electrophoresis is used to separate proteins, nucleic acids and blood cells.
3. A colloidal solution that has lost fluidity is:
a) emulsion;
b) gel;
c) sol;
d) suspension.
4. Blood plasma is:
a) sol;
b) gel;
c) true solution;
d) emulsion.
5. A heterogeneous system consisting of a microcrystal of a dispersed phase surrounded by solvated stabilizer ions is called:
a) a granule;
b) the core;
c) the unit;
d) micelle.
6. When a micelle is formed, potential-determining ions are adsorbed according to the rule:
a) Schulze-Hardy;
b) Rebinder;
c) Panet Faience;
d) Shilova.
7. A micelle granule is an aggregate:
a) together with the adsorption layer;
b) diffusion layer;
c) adsorption and diffusion layers;
d) potential-determining ions.
8. The interfacial potential is the potential between:
a) solid and liquid phases;
b) adsorption and diffuse layers at the slip boundary;
c) nucleus and counterions;
d) potential-determining ions and counterions.
9. The ability of finely porous membranes to retain particles of the dispersed phase and freely pass ions and molecules is called:
No. 6. For the classification of dispersed systems, see Table. 3.
|
CLASSIFICATION OF DISPERSIVE SYSTEMS Table BY AGGREGATE STATE |
||
|
Dispersion medium |
dispersed |
Examples of some natural and domestic disperse systems |
|
Liquid |
Fog, associated gas with oil droplets, carburetor mixture in car engines (gasoline droplets in the air), aerosols |
|
|
Solid |
Dust in the air, fumes, smog, simums (dust and sandstorms), solid aerosols |
|
|
Liquid |
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, |
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 | |
Chemistry lesson in grade 11: "Dispersed systems and solutions"
The goal is to give the concept of dispersed systems, their classification. To reveal the importance of colloidal systems in the life of nature and society. Show the relativity of dividing solutions into true and colloidal.
Equipment and materials:
Technological maps: diagram-table, laboratory work, instructions.
Equipment for laboratory work:
Reagents: sugar solution, iron (III) chloride solution, a mixture of water and river sand, gelatin, paste, oil, aluminum chloride solution, common salt solution, a mixture of water and vegetable oil.
Chemical beakers
Paper filters.
Black paper.
Flashlights
The course of the lesson in chemistry in grade 11:
| Lesson stage | Stage features | Teacher actions | Student actions |
| Organizational (2 min.) | Preparing for the lesson | Greets students. |
Getting ready for the lesson. Greet the teacher. |
| Introduction (5 min.) | Introduction to a new topic. |
Leads to the topic of the lesson, tasks and “questions for yourself” Introduces the topic of the lesson. Displays the tasks of today's lesson. |
Take part in the discussion of the topic. Get acquainted with the topic of the lesson and tasks (APPENDIX No. 1) Write down three questions on the topic that you would like to have answered. |
|
Theoretical part (15 minutes.) |
Explanation of the new topic. | Gives tasks for working in groups to search for new material (APPENDIX No. 3,4) | Having united in groups, they perform tasks in accordance with the technological map provided by the scheme (APPENDIX No. 4) and the requirements of the teacher. |
| Summing up the theoretical part (8 min.) | Conclusions based on the obtained theoretical knowledge. |
In advance, he hangs out empty diagrams (A3 format) on the board for visual filling by students. (APPENDIX №4) Together with students formulates the main theoretical conclusions. |
The markers fill in the schemes corresponding to the one they worked on, report on the work done in groups Write down the main conclusions in technological maps. |
| Practical part (10 min.) | Performing laboratory work, consolidating the experience gained. | Offers to perform laboratory work on the topic "Dispersed systems" (APPENDIX No. 2) | Perform laboratory work (APPENDIX No. 2), fill out the forms, in accordance with the instructions for laboratory work and the requirements of the teacher. |
|
Summary and conclusions (5 min.) |
Summing up the lesson. Homework. |
Together with the students makes a conclusion about the topic. Suggests to correlate the questions that were written at the beginning of the lesson with those received at the end of the lesson. |
Summing up, writing down homework. |
Forms and methods of control:
Technological schemes for filling (APPENDIX No. 4).
Laboratory work (APPENDIX No. 2)
Control is carried out frontally in oral and written form. Based on the results of the laboratory work, the cards with laboratory work are handed over to the teacher for verification.
1. Introduction:
What is the difference between marble and granite? What about mineral and distilled water?
(answer: marble is a pure substance, granite is a mixture of substances, distilled water is a pure substance, mineral water is a mixture of substances).
Good. What about milk? Is it a pure substance or a mixture? And the air?
The state of any pure substance is described very simply - solid, liquid, gaseous.
But absolutely pure substances do not exist in nature. Even a small amount of impurities can significantly affect the properties of substances: boiling point, electrical and thermal conductivity, reactivity, etc.
Obtaining absolutely pure substances is one of the most important tasks of modern chemistry, because it is the purity of a substance that determines the possibility of manifestation of its individual means (demonstration of labeled reagents).
Consequently, in nature and the practical life of man, there are not individual substances, but their systems.
Mixtures of different substances in different states of aggregation can form heterogeneous and homogeneous systems. Homogeneous systems are the solutions that we got acquainted with in the last lesson.
Today we will get acquainted with heterogeneous systems.
2. The topic of today's lesson is DISPERSIVE SYSTEMS.
After studying the topic of the lesson, you will learn:
the importance of dispersed systems.
This, as you understand, is our main task. They are written in your technological maps. But to make our work more productive and motivated, I suggest that you write at least three questions next to the main tasks that you would like to find an answer to in the course of this lesson.
3. Theoretical part.
Dispersed systems - what is it?
Let's try together to derive a definition based on the construction of words.
1) System (from other Greek “system” - a whole made up of parts; connection) - a set of elements that are in relationships and connections with each other, which forms a certain integrity, unity.
2) Dispersion - (from lat. dispersio - dispersion) scatter of something, crushing.
Disperse systems are heterogeneous (heterogeneous) systems in which one substance in the form of very small particles is evenly distributed in the volume of another.
If we go back to the review and the previous lesson, we can remember that: Solutions are made up of two components: a solute and a solvent.
Dispersed systems, as mixtures of substances, have a similar structure: they consist of small particles that are evenly distributed in the volume of another substance.
Take a look at your technological maps and try to make two similar schemes from disparate parts: for a solution and for a dispersed system.
Let's check the results by comparing them with the image on the screen.
So, the dispersion medium in the disperse system plays the role of a solvent, and is the so-called. continuous phase, and the dispersed phase - the role of the solute.
Since the dispersion system is a heterogeneous mixture, there is an interface between the dispersion medium and the dispersion phase.
Classification of dispersed systems.
You can study each disperse system separately, but it is better to classify them, highlight the common, typical, and remember it. To do this, you need to determine on what grounds to do this. You are united in groups, each of which is given a task and a flowchart attached to it.
Guided by the literature offered to you, find in the text the attribute of classification proposed for you to study, study it.
Create a cluster (block diagram), indicating the signs and properties of disperse systems, give examples to it. To help you with this, you have already been provided with a blank flowchart for you to complete.
4. Conclusion on the theoretical task.
Let's summarize.
From each team, I ask one person to come out and fill in the diagrams posted on the board.
(students come up and fill in each of the schemes with a marker, after which they report on the work done)
Well done, now let's fix:
What is the basis for the classification of disperse systems?
What are the types of dispersed systems?
What features of colloidal solutions do you know?
What is another name for gels? What value do they have? What is their feature?
5. Practical part.
Now that you are familiar with the features of disperse systems and their classification, and also determined by what principle disperse systems are classified, I suggest that you consolidate this knowledge in practice by completing the appropriate laboratory work offered to you on a separate form.
You are in groups of 2 people. For each group, you have an appropriate form with laboratory work, as well as a specific set of reagents that you need to study.
You have been given a sample of the disperse system.
Your task: using the instructions, determine which dispersion system you were given, fill in the table and draw a conclusion about the features of the dispersion system.
6. Generalization and conclusions.
So, in this lesson, we have studied in more depth the classification of dispersed systems, their importance in nature and human life.
However, it should be noted that there is no sharp boundary between the types of disperse systems. The classification should be considered relative.
And now back to the tasks set for today's lesson:
what are dispersed systems?
what are dispersed systems?
What are the properties of dispersed systems?
the importance of dispersed systems.
Pay attention to the questions you wrote down for yourself. In the reflection box, mark the usefulness of this lesson.
7. Homework.
We are constantly faced with dispersed systems in nature and everyday life, even in our body there are dispersed systems. In order to consolidate knowledge about the significance of disperse systems, you are invited to do your homework in the form of an essay /
Choose a disperse system that you constantly encounter in your life. Write an essay on 1-2 pages: “What is the significance of this dispersed system in human life? What similar disperse systems with similar functions are still known?
Thank you for the lesson.
