Laboratory work on the chemistry of the properties of dispersed systems. Dispersed systems. "Properties of alcohols and carboxylic acids"

2.Purpose: Learn to prepare colloidal solutions and know the properties of sols. Learn to determine the electrokinetic potential of sol particles using electrophoresis.

3.Learning objectives:

Colloidal chemistry studies physical and chemical properties heterogeneous high molecular weight compounds in the solid state and in solutions. Many medicines produced in the form of emulsion, suspension, colloidal solutions. The ability to prepare these preparations, to know their expiration dates and storage conditions is impossible without knowledge of the theoretical foundations of colloidal chemistry. Knowledge of electrophoresis, gel filtration and electrodialysis, ultrafiltration will be needed directly in practical work pharmacist

4.Main questions of the topic:

1. The subject of colloid chemistry, its importance in pharmacy.

2. Dispersed systems. Dispersed phase and dispersion medium.

3. Classification of colloidal systems.

4. Methods for obtaining colloidal systems.

5. Methods for purification of colloidal systems.

6. Optical properties of colloidal systems.

7. What is called electrokinetic potential.

8. On what factors does the magnitude of the potential depend?

9. What methods exist for determining potential.

10. What is electrophoresis.

11. How are electrophoretic speed and potential related?

5. Learning and teaching methods: seminar, laboratory work, work in small groups, educational testing on the topic of the lesson.

LABORATORY WORK

Laboratory work: “Preparation of colloidal solutions.”

Reagents and solutions used:

Initial reagents for obtaining colloidal systems:

FeCl 3, AgNO 3, KI – 0.1 N.

K 4 – 0.1 N;

K 4 – saturated solution;

Saturated solution of sulfur in alcohol:

Na 2 S 2 O 3 – 1%

H 2 C 2 O 4 – 1%

Applicable devices and equipment:

1. Conical flasks

2. Rack with test tubes

3. Measuring cylinders of 50 and 100 ml.

Sequence of work:

Experiment No. 1: Preparation of sulfur and rosin hydrosols by solvent replacement.

Rosin and sulfur dissolve in ethyl alcohol with the formation of true solutions. Because Since sulfur and rosin are practically insoluble in water, when their alcohol solutions are added to water, their molecules condense into larger aggregates.

Description of the experience.

A saturated solution of sulfur in absolute alcohol is poured dropwise into distilled water. When shaken, a milky white opalescent sol is obtained.

Preparation of iron oxide hydrate sol by hydrolysis.

A 2% solution of ferric chloride is added dropwise into a test tube with boiling water until a transparent red-brown sol of ferric oxide hydrate is formed.

The essence of the reaction.

Under the influence high temperature The hydrolysis reaction of ferric chloride shifts towards the formation of ferric hydroxide:

FeCl 3 + 3H 2 O Fe(OH) 3 + 3HCl

Molecules of water-insoluble iron oxide hydrate form aggregates of colloidal sizes. The stability of these aggregates is given by ferric chloride present in the solution, and iron ions are adsorbed on the surface of the particles, and chlorine ions are counterions.

The structure of the resulting micelles is schematically expressed by the following formula:

Experiment No. 2. Preparation of manganese dioxide sol.

The preparation of manganese dioxide sol is based on the reduction of potassium permanganate with sodium thiosulfate:

8KMnO 4 + 3Na 2 S 2 O 3 + H 2 O 8MnO 2 + 3Na 2 SO 4 + 3K 2 SO 4 + 2KOH

In the presence of excess permanganate, a manganese sol with negatively charged particles is formed:

Description of the experience:

Pipette 5 ml into a conical flask. 1.5% potassium permanganate solution and diluted with water to 50 ml. Then 1.5 - 2 ml of sodium thiosulfate solution is introduced dropwise into the flask. The result is a cherry-red sol of manganese dioxide.

Experiment No. 3. Preparation of silver iodide sol by double exchange reaction.

By double exchange reaction, a sol can be obtained by mixing dilute solutions of AgNO 3 and KI. In this case, it is necessary to comply with the conditions that one of the starting substances is in excess, since when mixing in equivalent quantities of reagents, an AgI precipitate is formed.

AgNO 3 + KI AgI + KNO 3

Description of the experience:

2 ml is poured into the flask. 0.1 N KI solution and dilute it with water to 25 ml. 1 ml is poured into another flask. 0.1 N AgNO 3 solution and also diluted with water to 25 ml. The resulting solutions are divided in half and two experiments are carried out:

a) gradually pour the AgNO 3 solution into the KI solution while shaking, obtaining a sol with the following structure:

b) gradually pour the AgNO 3 solution into the KI solution while shaking, obtaining a sol with the following structure:

Experiment No. 4. Preparation of Prussian blue sol by double exchange reaction.

Following the conditions for obtaining solutions using the double exchange reaction described in previous experiments, a Prussian blue sol is obtained, first in an excess of FeCl 3, then in an excess of K 4 .

Description of the experience:

The experiment is carried out as follows: to 20 ml. 0.1% K 4 is added with stirring 5-6 drops of a 2% FeCl 3 solution. A dark blue sol is obtained, the micelle of which has the structure:

Experiment No. 5. Preparation of Prussian blue sol by peptization method.

The preparation of a colloidal solution of Prussian blue by the peptization method comes down to converting the K Fe precipitate obtained by merging into a colloidal state concentrated solutions K 4 and FeCl 3.

Description of the experience:

In a test tube with 5 ml. 2% K4 solution. The resulting precipitate is filtered off, washed with distilled water, and the precipitate is treated on a 3 ml filter. 0.1 N solution of oxalic acid. A blue Prussian blue sol is filtered into a test tube.

Write the structure of the micelle yourself.

6. Literature:

Evstratova K.I. and others. Physical and colloidal chemistry. M., VSh, 1990, p. 365 – 396.

Voyutsky S.S. Colloid chemistry course. 1980, p. 300 – 309.

D.A. Friedrichsberg, Course of colloidal chemistry, St. Petersburg, Chemistry, 1995, p.7-47,196-62

Patsaev A.K., Shitybaev S.A., Narmanov M.M. Guide to laboratory practical exercises in physical colloid chemistry, part 1. Shymkent, 2002, p.24-31

Tests on the topic of the lesson.

7. Control:

1. Colloids, like soaps, are a dipole, are well adsorbed with dirt particles, give them a charge, contribute to their:

A) coagulation; B) peptization; C) coacervation;

2. The ability of a sol to maintain a given degree of dispersion is called:

A) sedimentation resistance;

B) aggressive resistance;

C) dissolution stability.

3. Based on the presence and absence of interaction between particles, the phases of the system are classified into:

A) lyophilic and lyophobic;

B) molecularly dispersed and colloidal dispersed;

C) freely dispersed and coherently dispersed.

4. Peptization of a freshly prepared iron hydroxide precipitate by acting on it with a solution refers to FeCl 3 as:

A) chemical; B) adsorption; C) physical;

5. The ability of phase particles not to settle under the influence of gravity is called:

A) chemical resistance;

B) dissolution stability;

C) sedimentation resistance.

6. The micelle of iron hydrosol obtained from the Fe(OH) 3 precipitate by peptization with a FeCl 3 solution has the form:

A) (mFe(OH) 3 nFeO + (n-x)Cl - ) + x xCl - ;

B) (mFe(OH) 3 nFe +3 3(n-x)Cl - ) +3 x 3xCl - ;

C) (mFe(OH) 3 3nCl - (n-x)Fe +3) - x x Fe +3.

Purpose of the work: familiarization with some methods for obtaining dispersed systems.

Assignment: to obtain a sol of iron (III) oxide by the method of chemical condensation by the exchange reaction of silver iodide sol, by the reduction reaction of manganese dioxide sol, by the hydrolysis reaction, by the method of physical condensation, by the method of pegging, by the method of pegging; emulsion by mechanical dispersion. Determine the sign of the charge of sols particles and create formulas for their micelles. Note the phenomenon of opalescence and the formation of Tyndall's cone.

Equipment and materials: stand with test tubes, 100 ml beakers - 3 pcs., 1 ml pipettes - 2 pcs.; for 5 ml - 2 pcs., for 10 ml - 2 pcs., funnel, filter paper, 100 ml cylinder, magnetic stirrer with a metal rod, cuvette, lamp for illuminating sols, glass slide, spatula. Reagents: AgN0 3 - 0.01 M; Nal (K.I) - 0.01 M; KMP0 4 - 0.01 M; H 2 0 2 - 2%; K 4 - 20%; FeCh - 2 ME; vegetable oil; Ci7 N3sCOOOYa - 0.1 M; MgCl 2 - 0.5 M; alcohol solution of rosin; distilled water.

Work order

• 1. Preparation of silver iodide sols by exchange reaction. Prepare a double sol of Agl using solutions of silver nitrate and sodium iodide. In the first case, add a few drops of silver nitrate solution to the sodium iodide solution (about half the test tube) while shaking; in the second case, on the contrary, add a few drops of sodium iodide solution to the silver nitrate solution (about half the test tube) while shaking. In both cases, an opalescent silver iodide sol is formed, but the structure of the double layer of particles is different, which leads to a slight, visually noticeable difference between the sols. Write down the formulas of the micelles, considering the stabilizer in each case to be one of the starting substances - Nal or AgN0 3 .
• 2. Preparation of manganese dioxide sol by reduction reaction.

Add a few drops of hydrogen peroxide solution to the potassium permanganate solution (about half the test tube). The reaction proceeds according to the equation

KMn0 4 + N 2 0 2 = Mn0 2 + KON+ N 2 0 + 0 2.

Consider the dark brown sol of manganese dioxide Mn0 2 formed in the presence of excess potassium permanganate. Check whether the sol gives a Tyndall cone (Fig. 3.1). To do this, pour a small amount of sol into the cuvette and illuminate it with a lamp. Determine the sign of the charge of the particles by the nature of the edge of the sol drop on the filter paper, if it is known that the filter paper moistened with water carries a negative charge. Write down the formula of the micelle.

3. Obtaining rosin sol by solvent replacement method. Rosin is a fragile, glassy, ​​transparent mass from light yellow to dark brown. It's hard component resinous substances of coniferous trees, remaining after distillation of volatile substances (turpentine) from them. Rosin contains 60-92% resin acids, the main of which is abietic acid (Fig. 1.7), 8-20% neutral substances (ssq-, di- and triterpsnoids), 0.5-12% saturated and unsaturated fatty acids. Rosin is practically insoluble in water. When replacing the solvent (alcohol) with water, a “white sol” is formed, which in transmitted light is colored orange, and when illuminated from the side it gives a blue color. The stabilizer of this sol is the oxidation products of rosin and the impurities it contains. The structure of micelles in such ash is not well known.

Rice. 1.7.

Add 1-2 drops of an alcoholic rosin solution to the water (about half the test tube) and shake. Observe the formation of a milky white rosin sol in water in transmitted light and with side lighting. Determine whether the rosin sol produces a Tyndall cone. To do this, pour it into a cuvette with plane-parallel walls and observe whether opalescence appears when a light beam is passed through the cuvette.

• 4. Preparation of Prussian blue sol by peptization method. Add 3-5 drops of ferric chloride solution to a solution of yellow blood salt (about half a test tube). Do not stir and wait until a gel-like sediment forms at the bottom. Carefully drain the liquid over the gel and transfer it with a spatula to a glass with 30-40 ml of distilled water. The gel spontaneously and quickly peptizes with the formation of a dark blue sol of Prussian blue - hexacyano-(H) iron (III) ferrate Fe 4 > Determine the sign of the charge of the particles by the nature of the edge of the sol drop on the filter paper. Write down the formula of the micelle.
• 5. Obtaining an emulsion by mechanical dispersion. To obtain an emulsion, pour 40 ml of sodium oleate solution, which is an emulsifier, into a 100 ml glass and add 10 ml of vegetable oil. Place the glass on a magnetic stirrer, lower a metal rod into the liquid and stir vigorously for 10 minutes. Turn off the stirring mode and divide the resulting emulsion into two parts, measuring 30 ml of emulsion using a cylinder. Transfer this part of the emulsion into a clean glass and leave for comparison. Pour 10 ml of magnesium chloride solution into the remainder of the emulsion while stirring. After 1-2 minutes of stirring, remove the emulsion from the stirrer and place it next to the second glass. Visually note the difference in the state of emulsions and determine their type in two ways. The first method: place a drop of emulsion with a pipette on a clean glass slide and place a drop of water next to it. Tilt the glass so that the drops touch. If they merge, then the dispersion medium is water; if they do not merge, it is oil. Second method: add a drop of emulsion into a test tube with 10 ml of water and shake. If the drop is evenly distributed in the water, then it is a direct O/W emulsion. Drops of W/O emulsion will not disperse in water and will remain on the surface.

When preparing the report, analyze the results obtained and draw conclusions for each item separately.

Guidelines for conducting

Discipline: Chemistry

Subject:

Duration: 2 hours

For specialties: technical profile

Subject: Preparation of a suspension of calcium carbonate in water. Preparation of emulsion

motor oil. Familiarization with the properties of dispersed systems.

Goals of work: 1. We consolidate and deepen knowledge about the preparation of calcium carbonate suspension in

water, obtaining an emulsion of motor oil. Let's get acquainted with the properties of dispersed

2. We develop the ability to logically present the material.

3. We develop the skill of designing laboratory work according to the standard.

Theoretical foundations :

Among the variety of mixtures, a special place is occupied by heterogeneous ones, that is, those whose component particles are visible to the naked eye or with the help of optical instruments(magnifying glass, magnifying glass, microscope).

Heterogeneous mixtures can consist of both uniformly and unevenly distributed components. In the first case, heterogeneous mixtures are called dispersed systems.

Dispersed systems are called heterogeneous mixtures in which one substance in the form of very small particles is evenly distributed in another.

The substance that is distributed in another is called dispersed phase . The substance in which the dispersed phase is distributed is called dispersion medium .

Depending on state of aggregation dispersed phase and dispersion medium, eight types of dispersed systems are distinguished.

Classification of disperse systems

Based on the particle size of the dispersed phase, they are distinguished:

Coarse dispersed systems (apply) - particle size more than 100 pm;

Fine-dispersed (colloidal) systems (or colloids) - particle size from 1 to 100 pm.

The interaction of calcium hydroxide solution with carbon dioxide you can get a coarse dispersed system:

Ca(OH) 2 + CO 2 = CaCO 3 ↓+ H 2 0

Slightly soluble calcium carbonate in the form of tiny grains is suspended in water. The resulting cloudy liquid is a dispersed system called suspension .

However, a little time will pass, and the calcium carbonate particles will settle to the bottom of the glass under the influence of gravity, and the liquid will become transparent. This is proof that our system turned out to be coarsely dispersed.

Coarsely dispersed systems with a solid dispersed phase and a liquid dispersion medium are called suspensions .

Suspensions include many paints, whitewash, mortars (cement mortar, concrete), pastes (including toothpastes), creams, ointments.

A coarse dispersed system can be obtained from two liquids that do not mix with each other, for example, by shaking vegetable oil with water. This mixture is called emulsion. Over time, it stratifies, since it also represents a coarsely dispersed system. Examples of emulsions include milk (droplets of fat in a water base), mayonnaise, milky sap of rubber trees (latex), and pesticide preparations for treating crops.

Aerosols- these are coarse systems in which the dispersion medium is air, and the dispersed phase can be liquid droplets (clouds, rainbows, hairspray or deodorant released from a can) or particles solid (dust cloud, smog).

If the particles of the dispersed phase are small enough, the colloidal system is called finely dispersed and resembles a true solution, hence the name colloidal solution. Such a system is formed, for example, when a small amount of egg white is dissolved in water.

In appearance, it is difficult to distinguish a colloidal solution from the real one; for this, you can use the specific optical property of colloidal solutions. It consists in the appearance of a luminous path in a colloidal solution when a beam of light is passed through it. This phenomenon is called Tyndall effect. This effect can be observed by passing a laser pointer beam through a protein solution.

Tyndall effect. Transmission of light through solutions:

1 - true solution; 2 - colloidal solution

The Tyndall effect is explained by the fact that the particle size of the dispersed phase (from 1 to 100 nm) in a colloidal system is approximately 1/10 of the wavelength of visible radiation. Particles of this size cause light scattering, resulting in a characteristic visual effect.

There are several main ways to obtain colloidal systems. One of them is the crushing of a substance into small particles, which can be carried out mechanically using special machines - colloid mills. This is how, for example, ink, liquid watercolors, water-emulsion and water-dispersion paints are obtained.

The classification of disperse systems can be presented as follows:

The most important types of colloidal systems are sols and gels (jelly).

Zoli are colloidal systems in which the dispersion medium is a liquid and the dispersed phase is a solid.

Over time, when heated or under the influence of electrolytes, sol particles can become larger and settle. This process is called coagulation.

Gels- a special gelatinous colloidal state. In this case, individual sol particles are associated with each other, forming a continuous spatial network. Solvent particles get inside the mesh cells. The dispersed system loses its fluidity, turning into a jelly-like state. When heated, the gel can turn into a sol.

You can get the gel chemically, if, for example, a few drops of sodium hydroxide solution are added to a solution of copper(II) sulfate, a gel of copper(II) hydroxide precipitate is formed:

CuSO 4 + 2NaOH = Cu(OH) 2 ↓ + Na 2 SO 4

Precipitates of metal hydroxides and silicic acid are usually called gelatinous.

Gels are widely used in our everyday life. Everyone knows food gels (marshmallows, marmalade, jellied meat), cosmetic (shower gel), and medical ones.

Gels with a liquid dispersion medium are characterized by the phenomenon syneresis (or separation) - spontaneous release of liquid. In this case, the particles of the dispersed phase become denser, stick together and form a solid colloid, and fluidity returns to the dispersion medium.

Most often, we have to fight the phenomenon of syneresis, since it is this phenomenon that limits the shelf life of food cosmetic and medical gels.

For example, when marmalade and Bird's Milk cake are stored for a long time, liquid is released and they become unfit for consumption.

From a solid colloid of gelatin (a product of protein origin) when swollen in warm water A gelatinous gel - jelly - is formed. But in culinary recipes They always warn: you cannot bring the jelly to a boil, otherwise the gel will turn into a sol and will not take on a gelatinous form.

The world around us is a colorful variety of different dispersed systems. Let's look around.

For example, cosmetics and hygiene products: toothpaste, soap, shampoo, nail polish, lipstick, mascara, cream, a cloud of deodorant released from a can - everything

These are dispersed systems. Now let's look into the kitchen. Milk, meat broth, cake, marshmallows, mayonnaise, ketchup are also dispersed systems. Let's go outside and see dispersed systems again: clouds, smoke, smog, fog. Let's look at the pharmacy - and again dispersed systems: ointments, gels, pastes, sprays, suspensions. Our own body is a combination of countless colloidal systems: cell contents, blood, lymph, digestive juice, tissue fluids. It is not for nothing that biologists agree that the emergence of life on our planet is the evolution of colloidal systems.

Incoming control:

We answer the questions:

1. Describe the concept of “dispersed system”.

How does a dispersed system differ from other mixtures?

2. What types of disperse systems, depending on the state of aggregation of the medium and phase, do you know? Give examples. Describe their significance in nature and human life.

Work progress:

Experiment No. 1 Preparation of a suspension of calcium carbonate in water

Equipment and reagents: laboratory stand with foot, stand with test tubes, calcium hydroxide Ca(OH) 2 (limewater).

Pour 4-5 ml of freshly prepared calcium hydroxide solution (limewater) into a test tube and carefully blow exhaled air through the tube.

Lime water becomes cloudy as a result of the following reaction:

Ca(OH) 2 + CO 2 = ...

Experiment No. 2 Obtaining a motor oil emulsion

Equipment and reagents: laboratory stand with foot, stand with test tubes, motor oil.

Add some motor oil to a conical flask filled with water and shake.

We answer the question: What are we seeing?

Experience No. 3 Familiarization with dispersed systems

Prepare a small collection of samples of disperse systems from suspensions, emulsions, pastes and gels available at home. Provide each sample with a factory label. Exchange collections with a neighbor and then distribute the collection samples in accordance with the classification of disperse systems.

Check the expiration dates of food, medical and cosmetic gels.

We answer the question: What property of gels determines the shelf life?

Output control:

We answer the questions:

1. What processes occurring in dispersed systems limit the shelf life of products, medicines and cosmetics?

We complete the task:

Give examples of emulsions, suspensions, sols, aerosols, gels and add them to the table.

Draw a general conclusion in accordance with the goals set for you in this work.

References:

1. O.S. Gabrielyan , I.G. Ostroumova “Chemistry” [text]: - textbook for professions and specialties Technical profile. Moscow, Publishing house "Academy", 2012

2. Gabrielyan O.S. Chemistry in tests, tasks, exercises: textbook. aid for students avg. prof. educational institutions/ O.S. Gabrielyan, G.G. Lysova - M., 2006.

3. Gabrielyan O.S. Workshop on general, inorganic and organic chemistry: textbook. aid for students avg. prof. textbook institutions / Gabrielyan O.S., Ostroumov I.G., Dorofeeva N.M. – M., 2007.

4. Erokhin Yu.M. Chemistry: textbook for secondary vocational schools, 4th ed. M.: Publishing Center Academy, 2004-384 p.

5. Rudzitis G.E., Feldman F.G. Chemistry: organic chemistry: textbook for 10th grade. OU, 8th ed. M. Education, 2001, 160 p.

6. www.twirpx.com - Educational materials.

7. www.amgpgu.ru - Lecture course.

8. www.uchportal.ru – Teacher’s portal.

9. http://o5-5.ru – 5 and 5 Educational material.

Laboratory work No. 2

Topic: Preparation of a suspension of calcium carbonate in water. Preparation of motor oil emulsion. Familiarization with the properties of disperse systems.

Goals: study methods of preparing emulsions and suspensions; learn to distinguish a colloidal solution from a true one; practice experimental work skills, observing safety rules when working in the chemistry classroom.

Guidelines:

Dispersed systems are systems in which small particles of a substance, or dispersed phase, are distributed in a homogeneous medium (liquid, gas, crystal), or dispersed phase

The chemistry of dispersed systems studies the behavior of a substance in a highly fragmented, highly dispersed state, characterized by a very high ratio total area the surface of all particles to their total volume or mass (degree of dispersion).

From the name of colloidal systems comes the name of a separate field of chemistry - colloidal. “Colloidal chemistry” is the traditional name for the chemistry of dispersed systems and surface phenomena. The most important feature of the dispersed state of a substance is that the energy of the system is mainly concentrated at the phase interface. When dispersing, or grinding, a substance, a significant increase in the surface area of ​​the particles occurs (with a constant total volume). In this case, the energy spent on grinding and overcoming the forces of attraction between the resulting particles goes into the energy of the surface layer - surface energy. The higher the degree of grinding, the greater the surface energy. Therefore, the field of chemistry of disperse systems (and colloidal solutions) is considered the chemistry of surface phenomena.

Colloidal particles are so small (contain 103–109 atoms) that they are not retained by conventional filters, are not visible in a regular microscope, and do not settle under the influence of gravity. Their stability decreases over time, i.e. they are subject to "aging". Dispersed systems are thermodynamically unstable and tend to a state with the lowest energy, when the surface energy of the particles becomes minimal. This is achieved by reducing the total surface area as the particles become larger (which can also occur when other substances are adsorbed on the particle surface).

Classification of disperse systems

Dispersed phase	Dispersive	System name
		(No disperse system is formed)
	Liquid		Foam of carbonated water, gas bubbles in liquid, soap suds
	Solid	Solid foam	Foam plastic, microcellular rubber, pumice, bread, cheese
Liquid		Aerosol	Fog, clouds, spray from an aerosol can
	Liquid	Emulsion	Milk, butter, mayonnaise, cream, ointment
	Solid	Solid emulsion	Pearl, opal
Solid		Aerosol, powder	Dust, smoke, flour, cement
	Liquid	Suspension, sol (colloidal solution)	Clay, paste, silt, liquid lubricating oils containing graphite or MoS
	Solid	Solid sol	Alloys, colored glasses, minerals

Methods for studying dispersed systems (determination of the size, shape and charge of particles) are based on the study of their special properties due to heterogeneity and dispersity, in particular optical ones. Colloidal solutions have optical properties that distinguish them from real solutions - they absorb and scatter light passing through them. When viewing a dispersed system from the side through which a narrow beam of light passes, a luminous bluish so-called Tyndall cone is visible inside the solution against a dark background. The Tyndall cone is brighter, the higher the concentration and the larger the particle size. The intensity of light scattering increases with short-wave radiation and with a significant difference in the refractive indices of the dispersed and dispersed phases. As the particle diameter decreases, the absorption maximum shifts to the short-wavelength part of the spectrum, and highly dispersed systems scatter shorter wavelengths. light waves and therefore have a bluish color. Methods for determining the size and shape of particles are based on light scattering spectra.

Under certain conditions, a coagulation process may begin in a colloidal solution. Coagulation– the phenomenon of colloidal particles sticking together and precipitating. In this case, the colloidal solution turns into a suspension or gel. Gels or jellies are gelatinous sediments formed during the coagulation of sols. Over time, the structure of the gels is disrupted (flakes off) - water is released from them (the phenomenon syneresis

Instruments and reagents; mortar and pestle, spoon-spatula, glass, glass rod, flashlight, test tube; water, calcium carbonate (a piece of chalk), oil, surfactant, flour, milk, toothpaste, starch solution, sugar solution. Work progress: 1 Safety briefing Safety measures: Use glassware with care . First aid rules: If injured by glass, remove the fragments from the wound, lubricate the edges of the wound with iodine solution and bandage it. If necessary, consult a doctor .

Experience No. 1. Preparation of a suspension of calcium carbonate in water

Suspensions have a number of general properties with powders, they are similar in dispersion. If the powder is placed in a liquid and mixed, it forms a suspension, and when dried, the suspension turns back into a powder.

Pour 4-5 ml of water into a glass test tube and add 1-2 spoons of calcium carbonate. Close the test tube with a rubber stopper and shake the test tube several times. Describe the appearance and visibility of the particles. Assess sedimentability and coagulation ability Record observations.

What does the resulting mixture look like?

Experience No. 2. Preparation of motor oil emulsion

Pour 4-5 ml of water and 1-2 ml of oil into a glass test tube, close with a rubber stopper and shake the test tube several times. Study the properties of the emulsion. Describe the appearance and visibility of the particles Assess the ability to settle and the ability to coagulate Add a drop of surfactant (emulsifier) ​​and mix again. Compare the results. Record your observations.

Experience No. 3. Preparation of a colloidal solution and study of its properties

Add 1-2 spoons of flour (or gelatin) to a glass beaker with hot water and mix thoroughly. Assess the ability to settle and the ability to coagulate. Pass a flashlight beam of light through the solution against a background of dark paper. Is there a Tyndall effect?

Questions for conclusions

How to distinguish a colloidal solution from a true one?

The importance of dispersed systems in everyday life.

Experiment 3. Preparation of motor oil emulsion

Experiment 2. Preparation of calcium carbonate suspension

Description laboratory equipment

Materials Equipment

chalk microtubes 2 pcs.

motor oil : porcelain mortar

toothpaste, test tube holder

cream (for body, face, hands),

jelly candies, marshmallows,

candies "bird's milk" and others

Methodology for completing the task

Pour 4-5 drops of freshly prepared solution into a test tube

calcium hydroxide (lime water) and carefully through a straw

blow exhaled air through it.

Lime water becomes cloudy as a result of the following reaction:

Ca(OH) 2 + CO 2 = CaCO 3 + H 2 O

Place 4 drops of motor oil and 10 drops of water in a test tube. Shake the contents of the test tube vigorously until a cloudy yellow colloidal solution forms. Leave the resulting solution for 2 minutes. Observe the changes that occur.

Prepare a small collection of samples of disperse systems from suspensions, emulsions, pastes and gels available at home. Provide each sample with a factory label.

Exchange collections with a neighbor and then distribute the collection samples in accordance with the classification of disperse systems.

Check the expiration dates of food, medical and cosmetic gels. What property of gels determines their shelf life?

Security questions for self-test

Option 1

1. In the case of sea foam, the dispersed phase is: a) solid b) liquid c) gaseous

2. Smog is: a) sol b) gel c) foam d) aerosol 3. Emulsions include: a) soap solution b) sea silt c) milk d) lymph 4. The division of solutions into true and colloidal is due to: a) color b) temperature c) particle size d) transparency 5. The dispersed phase is: a) a substance, which is more in the dispersed system b) a substance, which is less in the dispersed system c) a mixture of all substances that the dispersed system contains d) a substance, with particle size less than 1 nm

Option 2 1. In the case of aerated chocolate, the dispersed medium is: a) solid b) liquid c) gaseous 2. Smoke is: a) sol b) gel c) aerosol d) foam 3. The phenomenon of coagulation is characteristic of: a) sols b) gels c) emulsions d) aerosols 4. In the case of cast iron, the dispersed phase is: a) solid b) liquid c) gaseous 5. Kissel is: a) true solution b) colloidal solution c) aerosol d) suspension

Option 3

1. Define what sols and gels are? 2. What subgroups can gels be divided into? 3. What determines the shelf life of cosmetic, medical and food gels? 4. Describe the concept of “sols”. What groups are sols divided into? Give examples and tell us about their meaning 5. Describe the phenomena of coagulation and syneresis

24 6. Which practical significance has syneresis in industrial production? 7. Describe the concept of “gels”. What groups are gels divided into? Give examples of each group of gels and tell us about their meaning

Requirements for the content and format of a laboratory report

Write down in the journal of laboratory and practical exercises:

1. Name of experience

2. Brief description experience

3. Observations

4. Conclusion to work

List of references and Internet sources

Textbook O.S. Gabrielyan for SPO, 2008, p. 58 - 64