Physics
Laboratory work properties of dispersed systems. Topic: Dispersed systems. Laboratory work “Properties and production of sols. "Penza Multidisciplinary College"

Laboratory work properties of dispersed systems. Topic: Dispersed systems. Laboratory work “Properties and production of sols. "Penza Multidisciplinary College"

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– these 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 of the total surface area of all particles to their total volume or mass (degree of dispersion).

The name of a separate field of chemistry - colloidal - comes from the name colloidal systems. “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.

At certain conditions in a colloidal solution, the coagulation process can begin. Coagulation– the phenomenon of colloidal particles sticking together and precipitating. In this case, the colloidal solution turns into a suspension or gel. 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

In a glass beaker with hot water add 1-2 tablespoons of flour (or gelatin), 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.

OCTOBER COMMUNAL CONSTRUCTION TECHNIQUE

Speciality: ………………………………….

Laboratory works

by subject

COMPLETED Group student

…………….

group number

………………………………

Last name, initials.

CHECKED Chemistry teacher

Shalganova O.L.

Laboratory work No. 1

Subject: " Mixtures and impurities. Preparation of disperse systems and study of their properties.”

Target: Familiarize yourself with the properties of dispersed systems. Learn: prepare suspension and emulsion; solve problems to determine the mass fraction of mixture components and impurities

THEORETICAL REVIEW

Pure substances are very rare in nature; mixtures are most common.

Mixtures of different substances in different states of aggregation can form homogeneous (solutions) and heterogeneous (dispersed) systems. Dispersed-called heterogeneous systems in which one substance is dispersed phase (there may be several of them) in the form of very small particles evenly distributed in the volume of another -

dispersion environment.

The medium and phases are in different states of aggregation - solid, liquid and gaseous. Based on the size of the particles of substances that make up the dispersed phase, dispersed systems are divided into 2 groups:

Coarse(suspensions) with particle sizes greater than 100 nm. These are opaque systems in which the phase and medium are easily separated by settling or filtration. These are emulsions, suspensions, aerosols.

Fine-dispersed with particle sizes from 100 to 1 nm. The phase and medium in such systems are difficult to separate by settling. These are: sols (colloidal solutions - “glue-like”) and gels (jelly). Colloidal systems. transparent and outwardly similar to true solutions, but differ from the latter in the “luminous path” that is formed - a cone when a beam of light is passed through them. This phenomenon is called			Tyndall effect
Under certain conditions, a coagulation process may begin in a colloidal solution. Tyndall effect Coagulation – the phenomenon of colloidal particles sticking together and precipitating. syneresis 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. This phenomenon There are 8 types of disperse systems. (d/s + d/f) G+L→aerosol (fog, clouds, carburetor mixture of gasoline and air in the internal combustion engine G+TV→aerosol (smoke, smog, dust in the air) F+G→foam (carbonated drinks, whipped cream) F+F→emulsion (milk, mayonnaise, blood plasma, lymph, cytoplasm) L+TV→sol, suspension (river and sea silt, mortars, pastes) TV+G→hard foam (ceramics, polystyrene foam, foam rubber, polyurethane, aerated chocolate) What mass of calcium oxide substance can be obtained by thermal decomposition of 600 g of limestone containing 10% impurities? When 10.8 g of anhydrous sodium carbonate reacted with an excess of nitric acid, 2.24 liters (n.s.) of carbon monoxide (IV) were obtained. Calculate the content of impurities in sodium carbonate. PROGRESS

Progress		conclusions
Experience No. 1 Preparation of a suspension of calcium carbonate in water and study of its properties .
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	Observed: ......................................
Experiment No. 2 Preparation of an oil-in-water emulsion and studying its properties
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.	Observed: Add 2-3 drops of glycerin. What happened after it was added? ..................................................................................................................................................................................... Appearance and visibility of particles: Sedimentability and coagulation ability
Appearance after adding glycerin.................................................... ...................
Experiment No. 3 Preparation of a colloidal solution and study of its properties	Add 2-3 drops of glycerin. What happened after it was added? ...................................................................................................................................................... Appearance and visibility of particles: ....................................................................................................................... ................................. Add 1-2 spoons of flour (or gelatin) to a glass beaker with hot water and mix thoroughly. Pass a flashlight beam through the solution against a background of dark paper.

Is the Tyndall effect observed?................................................... ............................

...................................................................... ............................................................................................................................................................................. ............................................................................................................................................................................. .............................................................................................................................................................................

General conclusion:

Laboratory work No. 2 Subject:

Target: “Solutions.

THEORETICAL REVIEW

Preparation of solutions" Get acquainted with the concepts of solution, concentration, solvent, solutes.

Learn to calculate mass fraction, percentage, molar concentration, as well as prepare solutions based on these calculations. Solution- This is a homogeneous system consisting of a solvent, solutes and products of their interaction. A solvent is most often a substance that, in its pure form, has the same state of aggregation as the solution, or is present in excess. By state of aggregation

solutions are distinguished: liquid, solid, gaseous.

According to the ratio of solvent and solute: dilute, concentrated, saturated, unsaturated, supersaturated. The composition of a solution is usually expressed by the content of the soluble substance in it in the form of mass fraction, percentage concentration and molarity. Mass fraction ( = dimensionless quantity) is the ratio of the mass of the dissolved substances to the mass of the entire solution:

dimensionless quantity) is the ratio of the mass of the dissolved W

m.d.(%) is a value indicating how many grams of dissolved substance are contained in 100 g. solution :

The composition of a solution is usually expressed by the content of the soluble substance in it in the form of mass fraction, percentage concentration and molarity. % = dimensionless quantity) is the ratio of the mass of the dissolved substances to the mass of the entire solution: 100%

dimensionless quantity) is the ratio of the mass of the dissolved solution

Molar concentration, or molarity(mol/liter) is a value indicating how many moles of a soluble substance are contained in 1 liter of solution:

cm =dimensionless quantity) is the ratio of the mass of the dissolved rast.

thingM( substances to the mass of the entire solution: ) r V .

PROGRESS

solution	Work progress, task
Solution, calculations Experiment No. 1 Preparation of a salt solution
NaCL : Exercise	.................................................... ....................................................	.................................................... .................................................... .................................................... ....................................................
	Determine the mass of sodium chloride and the mass of water that will be required to prepare a 20% saline solution weighing 10 g. .................................................... .................................................... .................................................... ....................................................

Find: ................................................ .... ........................................................ ...... Experience No. 2 The composition of a solution is usually expressed by the content of the soluble substance in it in the form of mass fraction, percentage concentration and molarity. % Preparation of sugar solution and determination of it

NaCL : and See

Determine W% and cm of a sugar solution consisting of 20 g. water and 5g. sugar (C 12 H 22 O 11), if the density of this solution is 1.25 g/ml. How will the W% of this solution change if 50 g of water is added to it?

.................................................... ....................................................

…………………………...............

.................................................... .................................................... ....................................................

Make calculations and prepare a solution Experience No. 3

NaCL :

Preparation of vinegar solution from vinegar essence

How many grams of 70% vinegar essence and water do you need to take to prepare 200g. solution of 9% table vinegar (density 1.008 g/ml)

.................................................... .................................................... ....................................................

....................................................

…………………………................... Make calculations and prepare a solution.

Is the Tyndall effect observed?................................................... .................................................................................................................................................................................

Conclusion:

Laboratory work No. 3Subject: "Classes Not"

Target: organic matter Get acquainted with the concepts of acid, base, oxide, amphoteric hydroxide, salts, obtain and explore the most common simple substances .

THEORETICAL REVIEW

and connections

INORGANIC COMPOUNDS

- Acids

strong

Monobase

Polybasic

For example:N 2 CL,H 4

Hydroxides

Soluble

Insoluble

Mono-acid

Polyacid

- Salts

sour

Polybasic

Basic

KHSO 4, ALOHCL,

Oxides

salt-forming

sour

Acidic

Polybasic Amphoteric 2, COM 2 CaO, C 3

O non-salt-forming Amphoteric

For example:

Polybasic

grounds, NaOH(Ca) 2

-amphoteric

Polybasic

hydroxides 2

Zn(OH)

Progress

PROGRESS

conclusions

Drawings, reactions, observations.Experience No. 1 Getting to know the properties

inorganic acids

Carefully! Acid contact with skin causes chemical burns! Let's study physical properties

Observed:

............................................................................

acids: sulfuric, hydrochloric, nitric and acetic. Add 1-2 drops of water to sulfuric and acetic acid, add 1 drop of methyl orange (or other indicator).

Place a granule of zinc (or aluminum). 3 Complete the equations:CH→ ....................................

COOH + 2 CL,H 4 + CH→ ....................................

…………………………

ZnH

Experience No. 2

Introduction to the properties of bases

Carefully! Contact of alkali on the skin causes chemical burns!

Observed:

Let's study the physical properties of sodium and calcium hydroxides. Let's place them in a test tube with water.

groundsAdd 1 drop of phenolphthalein to each. 2 CL,H 4 → ....................................

Neutralize sulfuric acid solutions.(Complete the equation:) 2 Add 1 drop of phenolphthalein to each. 2 CL,H 4 → ................................

…………………………

Experience No. 3Experience No. 1 salts

A ) Salts react with acids to form a new salt and an acid.

Put a piece of chalk in a test tube and add 1-2 drops of HCL solution. Pass the resulting gas through an indicator solution (methyl orange)

Let's make a reaction:

CaCO 3 +NSL→ ..............................................

…………………………

……………………………………………………

…………………………

……………………………………………………

…………………………

Observed

: .............................................................................................................................................. .................

Observed:

..................................................................................................................................................

b ) Salts react with alkalis, forming water-insoluble bases and a new salt.

Place 1 ml of salt solutions in two test tubes

FeSO 4 and CuSO 4, add 1-2 drops of NaOH.

Add to the resulting iron precipitate

1-2 drops H 2 SO 4

We will heat the copper deposit for a long time until it decomposes (copper (II) oxide + water) :

Let's make up reactions 4 + grounds ………………………

FeSOFe 2 + COOH + 2 CL,H 4  ........................................

Observed:................................................................................................................................................

(HE)WITH 4 + grounds …… ……………………

(HE)uSOFe 2 u  ………………............

Observed:

. ...........................................................................................................................................................

let's heat it up.

c) The interaction of salts with each other

Let's add it to the test tube

We will heat the copper deposit for a long time until it decomposes (copper (II) oxide + water) :

Experiment No. 1 Preparation of a salt solution + 1 ml of sodium chloride solution and add the same amount of silver nitrate solution. 3  ……………….........

Observed:

………………………………………………………………………....

AgNOd) Interaction of salts with m

metals

We will heat the copper deposit for a long time until it decomposes (copper (II) oxide + water) :

In a test tube with 1 ml. CuSO 4 place an iron paper clip. To speed up the process, add 1-2 drops of sulfuric acid. 4 + FeSO ……………….........

Observed:

………………………………………………………………………....

Is the Tyndall effect observed?................................................... ............................

............................................................................................................................................................................ .

CuSO

Goal of the work

Acquaintance with methods for obtaining dispersed systems, the structure of micelles, and the stability of colloidal solutions.

Brief theoretical information Dispersed systems - these are heterogeneous systems consisting of at least two phases, one of which (dispersed phase) is fragmented, discontinuous, and the other ( dispersion medium

) is an unfragmented, continuous part.

Based on particle size, disperse systems are classified as follows:	System name	Character and size
	Heterogeneity and	particles, m
	Heterogeneity and	particles, m
sustainability	Coarse systems	Large particles
Heterogeneous, unstable	10–5 –10–7	Large particles
(suspensions, emulsions, aerosols)	Colloidal dispersed	Colloidal particles,
Microheterogeneous,	10–7 –10–9	systems (sols)
quite stable	True solutions	Molecules, ions,
quite stable	10 –10	Molecules, ions,

Homogeneous, stable Colloidal solutions

are called highly dispersed heterogeneous systems in which at least one substance is in a colloidal state. The substance is crushed into particles 10–7–10–9 m in size (dispersed phase), invisible in an optical microscope, distributed in a dispersion medium.

1) In terms of particle size, colloidal solutions occupy an intermediate position between true solutions (10–10 m) and coarse systems (more than 10–7 m), therefore methods for producing colloidal systems can be divided into two main groups: dispersion

– crushing of large particles to colloidal dispersion;

Dispersive methods include primarily mechanical grinding methods. This is abrasion, crushing, impact, splitting. In laboratories and industry, crushers and millstones are used for these purposes.

And mills various types(spherical, colloidal).

Chemistry. Lab. workshop

To reduce energy costs, surfactants are used, the presence of which facilitates dispersion and the effect of adsorption reduction in strength, or the P. A. Rebinder effect, is observed.

IN currently widely used an ultrasonic method in which tensile forces arise due to alternating local compression and expansion of the liquid during the passage of a wave.

The method of a voltaic arc that occurs between electrodes in a liquid is also used ( electrical dispersion). In this way, alkali metal hydrosols are obtained.

IN Condensation methods for producing dispersed systems are based on the processes of formation of a new phase from molecules, ions, and atoms in a homogeneous environment. In this case, the system must be in a supersaturated state. If chemical potential substances in the new phase are less than in the original phase, then the process is possible

Based on the nature of the forces causing condensation, a distinction is made between physical and chemical condensation.

Physical condensation requires the creation of conditions under which molecules or ions will condense, forming a dispersed phase, and condensation should stop when the particles reach colloidal sizes. Physical condensation can be accomplished from vapors or by solvent exchange.

Vapor condensation is achieved by changing the system parameters. For example, when the temperature decreases, the steam becomes supersaturated and partially condenses, which leads to the formation of a new phase.

IN solvent replacement method change the composition and properties of the environment. For example, a large volume of water is poured into a saturated solution of molecular sulfur in ethyl alcohol. The new mixed solution turns out to be supersaturated, and sulfur molecules form particles of a new phase. This method produces sols of sulfur, phosphorus, arsenic, rosin, cellulose acetate, and organic substances. In this case, initial solutions of substances in ethyl alcohol or acetone are poured into water.

Methods chemical condensation are also based on the separation of a new phase from a supersaturated solution, but it is formed as a result chemical reaction, for example, oxidation reactions, hydrolysis, dissociation, double exchange. The size of the resulting particles depends on the ratio of the rates of embryo formation and its growth. In order for small particles to be obtained, the first factor must be predominant. A reaction is necessary

conduct in a dilute solution to reduce the growth rate of crystalline particles. This makes it possible to obtain particles with a size of 10–7–10–9 m, which ensures sedimentation stability of the system.

Another condition: one of the reactants must be taken in excess in order to form an electrical double layer (DEL) on the surface, which will ensure aggregative stability. For example, reaction

AgNO3 + KCl = AgCl + KNO3 under certain conditions leads to the formation of a new phase. If there is an excess of potassium chloride on the surface of the crystals

Chemistry. Lab. workshop

LABORATORY WORK 14. OBTAINING DISPERSE SYSTEMS. STABILITY OF COLLOIDAL SOLUTIONS

Brief theoretical information

silver chloride forms an electrical double layer. The crystal together with the electrical double layer is called a micelle. It is depicted in the form of a micelle formula, in our case it has the form

(m nCl– (n – x)K+ )x– xK+ .

At the center of the micelle is crystalline body, called an aggregate, ions are adsorbed on it, capable of completing it crystal lattice. These ions tell the unit electric charge and are called potential-determining, together they form the core of the micelle. The core creates an electrostatic field, under the influence of which counterions are attracted to it from the solution, forming adsorption and diffuse layers. The expression in curly brackets represents a colloidal particle. It consists of a crystal m, potential-determining ions nCl–, counterions of the adsorption layer (n – x)K+ and ions of the diffuse layer of the micelle xK+.

The micelle is electrically neutral, but the colloidal particle has a charge. If the charges of the ions of the inner and outer plates are not the same, coefficients are added to the formula. For example, a colloidal solution of Prussian blue can be obtained by the reaction

4FeCl3 + 3K4 = Fe4 3 + 12 KCl

For the case of excess iron (III) chloride, the micelle formula has the form

(m3 ] nFe3+ 3(n – x)Cl– ) 3xCl–

To obtain dispersed systems, physicochemical crushing of sediments, or peptization, is used. Formally, peptization can be classified as a dispersion method, but the peptized sediment is already dispersed material, brought to a colloidal degree of grinding, in which the particles have formed large aggregates as a result of sticking together. There are three ways to convert such a precipitate into a colloidal solution.

The first way is adsorption peptization. A peptizing agent is added to the precipitate, the ions of which form a double electrical layer on the surface of the particles, which helps them repel each other. For example, a solution of iron (III) chloride is added to a fresh loose precipitate of iron (III) hydroxide, which creates an electric double layer and the particles go into solution.

The second method is peptization by surface dissociation . When adding acid or alkali to amphoteric hydroxide aluminum, soluble compounds are formed that form an electrical double layer.

The third method is peptization by washing the precipitate. He uses

occurs when, due to a high electrolyte concentration, the electrical double layer on the surface of the particles is compressed. Washing helps to reduce the electrolyte concentration and, as a consequence, increase the thickness of the double

Chemistry. Lab. workshop

LABORATORY WORK 14. OBTAINING DISPERSE SYSTEMS. STABILITY OF COLLOIDAL SOLUTIONS

Brief theoretical information

a strong electrical layer, which leads to an increase in the distance of action of repulsive forces, and this causes colloidal dissolution of the precipitate.

The most important and complex problem of colloidal chemistry is the stability of disperse systems. In colloidal systems, two types of stability are distinguished: sedimentation and aggregation.

The dispersed system is considered sedimentation-resistant, if the particles do not settle and are in stable equilibrium. This is possible if the particle sizes are constant. But particles of the dispersed phase tend to enlarge by sticking together or recrystallizing, which leads to a violation of sedimentation stability and sedimentation.

Aggregate stability– the ability of a disperse system to keep particle sizes constant. Stability can be lost through coagulation, which is the process of particles sticking together to form larger aggregates. In this case, sedimentation stability is lost and the dispersed system is destroyed with the formation of sediments of various structures, which are called coagulates. Coagulation can occur under the influence of temperature (heating, freezing), chemical agents, mechanical factors and other reasons that can destroy the energy barrier.

All electrolytes cause coagulation after reaching a critical concentration value Sk, which is called the coagulation threshold - this is the minimum concentration of an electrolyte in a colloidal solution that causes its coagulation. The coagulating effect is possessed by the electrolyte ion that has a charge identical to the charge of the counterions of the micelle. The coagulating ability of ions increases with increasing their charge and size.

There are concentration and neutralization coagulation with electrolytes.

Concentration coagulation observed with increasing electrolyte concentration, while the diffuse layer of counterions of the micelle contracts, turning into an adsorption layer. As a result, the electrokinetic potential decreases, which leads to coagulation.

At neutralization coagulation The ions of the added electrolyte neutralize the potential-determining ions, they lose their charge and stick together.

The modern theory of stability of dispersed systems or the DLFO theory (Deryagin, Landau, Verwey, Overbeck) states that forces of intermolecular attraction and repulsion act between particles of the dispersed phase. Their balance determines the behavior of the system. According to this theory, the coagulation threshold is determined by the formula

Сk = const/z6 ,

where z is the valence of the coagulator ion.

If we take Ck for a monovalent ion as unity, then according to the equation

Chemistry. Lab. workshop

LABORATORY WORK 14. OBTAINING DISPERSE SYSTEMS. STABILITY OF COLLOIDAL SOLUTIONS

Brief theoretical information

C1 k : C2 k : C3 k = 729: 114: 1

As a rule, experimental and theoretical data agree well.

Experimental part

Experiment 1 Preparation of dispersed systems

physical condensation method (solvent replacement)

Rosin sol. To 10 ml of distilled water, add 15 drops of a 5% solution of rosin in ethyl alcohol while shaking. A milky white sol of rosin is formed in water with negative charge particles. Why does rosin form a true solution in alcohol, but a colloidal one in water?

Sulfur sol. To 50 ml of water, add 1 ml of a saturated solution of sulfur in acetone while shaking. A bluish-white opalescent sulfur sol with a negative charge of colloidal particles is formed.

Sulfur sol. To 50 ml of water, add 4-5 ml of a saturated solution of sulfur in ethyl alcohol while shaking. A bluish opalescent sulfur sol is formed in the form of negatively charged colloidal particles.

Anthracene sol. To 50 ml of water, add 0.5 ml of a saturated solution of anthracene in ethyl alcohol from a dropper while shaking. A blue-white opalescent sol of anthracene in water with negatively charged colloidal particles is formed.

Paraffin sol. Add 1 ml of a saturated solution of paraffin in ethyl alcohol to 50 ml of water from a dropper while shaking. An opalescent paraffin sol is formed in the form of negatively charged colloidal particles.

Experiment 2 Preparation of dispersed systems by chemical condensation

Metallic silver sol. Reduce the silver salt with tannin in an alkaline medium to metal. To do this, dilute 2 ml of a 1.7% solution of silver nitrate with water to 100 ml and add 1 ml of a 0.1% solution of tannin, then 3-4 drops of a 1% solution of potassium carbonate. A red-brown negative sol of metallic silver is formed. The reaction in an alkaline environment will be

6AgNO3 + C76 H52 O46 + 3K2 CO3 =

6Ag + C76 H52 O49 + 6KNO3 + 3CO2

Chemistry. Lab. workshop

LABORATORY WORK 14. OBTAINING DISPERSE SYSTEMS. STABILITY OF COLLOIDAL SOLUTIONS

experimental part

The inner lining of the DES is apparently formed by OH– ions, which are adsorbed on silver.

Manganese dioxide sol. Dilute 5 ml of a 1% solution of potassium permanganate with water to 50 ml and add dropwise 2 ml of a 1% solution of sodium thiosulfate. A cherry-red manganese dioxide sol is formed.

Manganese dioxide sol. Dilute 5 ml of a 1.5% solution of potassium permanganate with water to 100 ml, heat to a boil. Over 15 minutes, inject 5 ml of concentrated ammonia in small portions (0.5 ml each). A red-brown manganese dioxide sol is formed.

Silver iodide sol. Dilute 10 drops of a 1.7% solution of silver nitrate with water to 100 ml and add dropwise while shaking 1 ml of a 1.7% solution of potassium iodide. A bluish opalescent sol of silver iodide is formed.

Prussian blue sol. Dilute 0.1 ml of a saturated FeCl3 solution in 100 ml of water. Add 1 drop of 20% K4 solution into the diluted solution while shaking. Prussian blue sol is formed of blue color Fe4 3.

Iron hydroxide sol. To 50 ml of boiling distilled water, add in small portions 5–10 ml of 2% FeCl3 solution. As a result of hydrolysis, a cherry-red iron hydroxide sol is formed.

Experiment 3 Obtaining dispersed systems using the dispersion method

Fluorescein sol. To 5 ml of distilled water, add 2-3 drops of soda solution and add a small grain of fluorescein. Shake the solution, pay attention to its color in transmitted and reflected light.

Starch sol. Thoroughly grind 0.5 g of starch in a porcelain mortar, transfer it to a porcelain cup and mix with 10 ml of distilled water, then add another 90 ml of water. Bring the mixture to a boil while constantly stirring. You will get a 0.5% starch sol.

Gelatin sol. Pour 0.5 g of gelatin into 50 ml of distilled water and heat in a water bath at 40–50 o C until the swollen gelatin is completely dissolved.

Egg albumin sol. Add 10 g of albumin powder or chicken egg white to a 100 ml volumetric flask and shake with 50 ml of cold distilled water until completely dissolved. Fill the flask with water to the mark. The result is a protein sol.

Chalk suspension. Fill 2 test tubes with distilled water to half the volume, add 1 ml of 0.5% gelatin solution to one of them. Then add 2 g of chalk to the test tubes and shake vigorously. A stable suspension of chalk was formed in a test tube with gelatin (suspension stabilizer).

Chemistry. Lab. workshop

LABORATORY WORK 14. OBTAINING DISPERSE SYSTEMS. STABILITY OF COLLOIDAL SOLUTIONS

experimental part

Preparation of iron(III) hydroxide sol by peptization

Add 20 ml of water to 5 ml of a 2% FeCl3 solution, then add a concentrated ammonia solution until a Fe(OH)3 precipitate forms. Rinse the resulting sediment with distilled water and separate by decantation (decantation is draining the liquid from the settled sediment). To do this, shake the sediment with plenty of water, and after settling, carefully drain the clear liquid above the sediment. The end of laundering is judged by the absence of ammonia odor. Pour the washed sediment into two flasks. Add a solution of iron (III) chloride as a peptizer to one (2 ml of a saturated solution is diluted with water to 100 ml), and leave the other for comparison. Shake the precipitate with the peptizer and carefully heat to a boil. When peptization occurs, a red-brown sol of iron(III) hydroxide is obtained.

Experiment 5 Coagulation of sols with electrolytes and determination of the coagulation threshold

Pour 5 ml of iron (III) hydroxide sol into a test tube, and 0.002 M sodium sulfate solution into a burette. From the burette, slowly pour the sodium sulfate solution into the test tube containing the iron (III) hydroxide sol, stirring thoroughly. A sign of the onset of coagulation is the turbidity of the sol throughout the entire volume of the solution. Calculate the coagulation threshold using the formula

C k = 5 1000 ,

where c is the electrolyte concentration, mol/l; ν – volume of consumed electrolyte, ml; Ck – coagulation threshold, mol/l.

Repeat the experiment using 0.002 M Na3PO4 solution as the coagulating electrolyte. Determine the coagulation threshold. Enter the experimental data into the table:

Electrolyte	Coagulating ion	Coagulation threshold	Relative
Electrolyte	Coagulating ion	Coagulation threshold	coagulating ability
Na2SO4	2−
Na2SO4	SO 4
Na3PO4	3−
Na3PO4	PO 4

Relative coagulation capacity is calculated by dividing the higher coagulation threshold by the lower coagulation threshold. Explain why the coagulating ability of one ion is higher than the other?

Chemistry. Lab. workshop

LABORATORY WORK 14. OBTAINING DISPERSE SYSTEMS. STABILITY OF COLLOIDAL SOLUTIONS

Examples of solving typical problems

Example 1. Write the micelle formula for the reaction

Na2 SO4 + BaCl2 = BaSO4 ↓ + 2NaCl – stabilizer (excess) Na2 SO4.

Solution: Barium sulfate precipitates, its molecules combine and form the core of the colloidal particle m. On the surface of the core, stabilizer ions SO4 2–, similar in nature to the composition of the core, are adsorbed from the solution, and the particle acquires a negative charge. These adsorbed ions are called potential-determining ions. A negatively charged particle attracts ions of the opposite sign from the solution - Ba2+ counterions. Counterions are in motion and some of them are adsorbed on the particle. Adsorbed potential-determining ions and counterions form an adsorption layer. The other part of the counterions is in the liquid phase and forms a mobile diffusion layer. The core together with the adsorption layer is called a colloidal particle and has a charge identical to the charge of the potential-determining ion. The colloidal particle and counterions of the diffuse layer form a micelle. The charge of the micelle is zero.

The structure of the BaSO4 sol micelle can be represented by the following diagram:

(m nSO 2 4 − (n – x)Na+ )x– xNa+ .

Example 2. In what order should Na2SO4 and BaCl2 solutions be combined to obtain a colloidal particle carrying a positive electric charge?

Solution. In example 1, a colloidal particle with a negative charge was obtained. To recharge it, you need to take a BaCl2 solution (in excess) as a stabilizer and add a Na2 SO4 solution to it. IN in this case Ba2+ ions will be adsorbed as potential-determining ions, and the particle will acquire positive charge, counterions

– Cl– . The formula of the resulting micelle will be

(m nBa2+ (n – x)Cl– )x+ xCl– .

Example 3. Silver iodide sol obtained by the reaction

KJ + AgNO3 = AgJ + KNO3

Chemistry. Lab. workshop

LABORATORY WORK 14. OBTAINING DISPERSE SYSTEMS. STABILITY OF COLLOIDAL SOLUTIONS

Examples of solving typical problems

with some excess KJ, coagulate with solutions of potassium sulfate and calcium acetate. Which electrolyte has the stronger coagulating effect?

Solution. The structure of a sol micelle is as follows:

(m (n – x)J– xK+ )x– nK+ .

The ions that form the diffuse layer, i.e. counterions, are K+ cations. Therefore, when determining the coagulating effect, it is necessary to compare the charges of the cations of the introduced electrolyte. Since the charge of the Ca2+ ion is higher than the charge of the K+ ion, then, in accordance with the Schulze-Hardy rule, the coagulating effect of Ca(CH3 COO)2 is stronger.

Example 4. How will the coagulation threshold of the As2 S3 sol change if 1.2 10–6 m3 of NaCl solution with a concentration of 0.5 kmol/m3 is required to coagulate 10 10–6 m3 of sol? Determine the coagulation threshold under the influence of a MgCl2 solution with a concentration of 0.036 kmol/m3 (it will require 0.4 10–6 m3 per

10 10–6 m3 of sol) and an AlCl3 solution with a concentration of 0.01 kmol/m3 (it will require 0.1 10–6 m3 per 10 10–6 m3 of sol). Check the fulfillment of the condition C1 k : C2 k : C3 k = = 729: 114: 1 = 1: (1/26) : (1/36) = 1: 0.016: 0.0014.

Solution. Let's use the formula

Ck = cV w ,

where c is the electrolyte concentration (kmol.m-3); V – volume of electrolyte solution; w is the volume of the sol.

The formula is valid for (V<< w):

Ck (NaCl) =	0,5 1, 2 10− 6
Ck (NaCl) =		10− 6
		10− 6
	0,036 0, 4 10− 6
Ck(MgCl2) =			1.44 10 kmol/m,
Ck(MgCl2) =	10 10− 6		1.44 10 kmol/m,
	10 10− 6
Ck(AlCl3) =		0,01 0,1 10− 6

		10 10− 6
		10 10− 6

Ck (NaCl): Ck (MgCl2): Ck (AlCl3) = 6 10–2: 1.44 10–3: 1 10–4 = 1: 0.024: 0.0017.

From the calculations obtained it follows that the condition of coagulation by oppositely charged ions is satisfactorily fulfilled.

Chemistry. Lab. workshop

LABORATORY WORK 14. OBTAINING DISPERSE SYSTEMS. STABILITY OF COLLOIDAL SOLUTIONS

Test questions and tasks

1. What systems are called dispersed?

2. What is the difference between true solutions, colloidal and coarsely dispersed systems?

3. Name the methods for obtaining disperse systems.

4. What explains the stability of sols?

5. What is peptization? What are the types of peptization?

6. What is chemical and physical condensation?

7. What conditions must be observed when obtaining a sol by chemical condensation?

8. Write the micelle formula for the reactions:

a) AgNO3 + NaCl = AgCl + NaNO3 – NaCl stabilizer.

b) K4 + 2CuSO4 = Cu2 + 12KCl – stabilizer CuSO4.

9. Which process is called coagulation and which sedimentation?

10. What is the coagulation threshold?

11. How does the coagulating effect of the electrolyte change with increasing charge of the ioncoagulator and its size?

12. What ideas is the DLFO theory based on?

13. Why do electrolytes cause coagulation of dispersed systems?

14. What is neutralization coagulation and how does it differ from concentration coagulation?

Chemistry. Lab. workshop

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. This is a solid component of the 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 is orange in transmitted light, and blue when illuminated from the side. 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 gives 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.

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

3.Learning objectives:

Colloidal chemistry studies physicochemical characteristics heterogeneous high-molecular compounds in the solid state and in solutions. Many medications are produced in the form of emulsions, suspensions, and colloidal solutions. The ability to prepare these drugs, to know their expiration dates and storage conditions is impossible without knowledge theoretical foundations colloid 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 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 to form 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 of high temperature, the hydrolysis reaction of ferric chloride shifts towards the formation of iron 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 KFe precipitate obtained by merging concentrated solutions of K4 and FeCl3 into a colloidal state.

Description of the experience:

In a test tube with 5 ml. 2% K4 solution. The resulting precipitate is filtered, 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, pp. 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 the sol to retain this degree 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.