Here are the names of various chemical systems. Divide them into: mixtures; pure substances and true solutions.

Distilled water

Sea water
Oxygen
Silver

Sodium chloride solution for injection

Hydrogen
Cast iron
Carbon dioxide
Air

Basalt
Glass

Emulsion "oil in water"
Lead

Suggest methods for separating mixtures: a) water and sand; b) wood and iron filings; c) water and ink; d) water and oil.

Pure substances and mixtures.

IN Everyday life each of us is faced with many mixtures of substances, deals not only with pure, but also with polluted substances. It is important to be able to distinguish between these concepts and be able to determine by specific features what you are dealing with: a pure or contaminated substance, an individual substance or a mixture of substances. After all, a person wants to use only the water that does not contain harmful impurities. We want to breathe air that is not polluted by gases that are harmful to health. In medicine and the production of drugs, the problem of obtaining and using pure substances is especially relevant.

Let's get acquainted with the main terms of the lesson.

Mixture- this is what is formed when two or more substances of different properties are mixed.

The substances that make up a mixture are called components. For example, air is a mixture of gases: nitrogen, oxygen, carbon dioxide and others.

If the mass of one component is tens of times less than the mass of another component of the mixture, then it is called impurity. The substance is said to be contaminated. For example, air can be polluted carbon monoxide, a product of incomplete combustion organic compounds especially gasoline. By the way, gasoline is a mixture organic matter- hydrocarbons.

CLASSIFICATION OF MIXTURES

Mixtures differ from each other in appearance. For example, salt water (a mixture of table salt and water) and a mixture of river sand and water. In the first case, the solid-liquid interface cannot be seen. Such a mixture is called homogeneous (or homogeneous). Other examples of homogeneous mixtures are vinegar (a mixture of acetic acid and water), air, sugar syrup.

A mixture of river sand and water is referred to as heterogeneous (or heterogeneous) mixtures, because the composition of such a mixture is not the same at different points in the volume. Mixtures of clay and water, gasoline and water are heterogeneous.

Basically, everything that surrounds us is a mixture of substances. Moreover, there are no substances that are absolutely free of impurities.

But it is customary to talk about the relative purity of a substance, i.e. substances have varying degrees purity.

Degree of purity of a substance

If impurities are not detected when a substance is used for technical purposes, then the substance is called technically clean. For example, the substance from which violet ink is made may contain impurities. But if these impurities do not affect the quality of the ink, then it is technically pure.

If impurities are not detected using chemical reactions, then the substance is assigned to chemically pure. For example, it is distilled water.

Signs of the individuality of a substance

A pure substance is sometimes called an individual substance, because it has well-defined properties. For example, only distilled water has a melting point of 0°C, a boiling point of 100°C, and is tasteless and odorless.

Do the properties of substances change in a mixture? To answer this question, let's do a simple experiment. Mix powders of sulfur and iron. We know that iron is attracted to a magnet, but sulfur is not. Did iron retain its property after mixing with sulfur?

CONCLUSION: The properties of substances in a mixture do not change. Knowledge of the properties of the components of a mixture is used to separate mixtures and purify substances.

Methods for separating mixtures and purifying substances

Let us define the difference between "methods for separating mixtures" and "methods for purifying substances." In the first case, it is important to obtain in pure form all the components that make up the mixture. When purifying a substance, obtaining impurities in a pure form is usually neglected.

SETTLEMENT

How to separate a mixture of sand and clay? This is one of the stages in ceramic production (for example, in the production of bricks). To separate such a mixture, the settling method is used. The mixture is placed in water and stirred. Clay and sand settle in water at different rates. Therefore, sand will settle much faster than clay (Fig. 1).

Rice. 1. Separation of a mixture of clay and sand by settling

The settling method is also used to separate mixtures of water-insoluble solids with different densities. For example, a mixture of iron and sawdust can be separated in this way (the sawdust will float in water, while the iron will settle).

A mixture of vegetable oil and water can also be separated by settling, because the oil does not dissolve in water and has a lower density (Fig. 2). Thus, by settling, it is possible to separate mixtures of liquids insoluble in each other with different densities.

Rice. 2. Separation of a mixture of vegetable oil and water by settling

Filtration

To separate a mixture of table salt and river sand, you can use the settling method (when mixed with water, the salt will dissolve, the sand will settle), but it will be more reliable to separate the sand from the salt solution by another method - the filtration method.

Filtration of this mixture can be carried out using a paper filter and a funnel lowered into a glass. Grains of sand remain on the filter paper, and a clear solution of table salt passes through the filter. In this case, the river sand is the sediment, and the salt solution is the leachate (Fig. 3).

Rice. 3. Using filtration method to separate river sand from salt solution

Filtration can be carried out not only with filter paper, but also with other porous or loose materials. For example, bulk materials include quartz sand, and porous materials include glass wool and baked clay.

Some mixtures can be separated using the "hot filtration" method. For example, a mixture of sulfur and iron powders. Iron melts at over 1500 C and sulfur around 120 C. Molten sulfur can be separated from the iron powder using heated glass wool.

I. New material

In preparing the lesson, materials of the author were used: N.K.Cheremisina,

chemistry teachers high school № 43

(Kaliningrad),

We live among chemical substances. We inhale air, and this is a mixture of gases ( nitrogen, oxygen and others), exhale carbon dioxide. We wash ourselves water- This is another substance, the most common on Earth. We drink milk- mixture water with tiny drops of milk fat, and not only: there is still milk protein casein, mineral salt, vitamins and even sugar, but not the one with which they drink tea, but a special, milky one - lactose. We eat apples, which consist of a whole range of chemicals - here and sugar, And Apple acid, And vitamins... When the chewed pieces of an apple enter the stomach, human digestive juices begin to act on them, which help to absorb all the tasty and healthy substances not only of the apple, but also of any other food. We not only live among chemicals, but we ourselves are made of them. Every person - his skin, muscles, blood, teeth, bones, hair are built of chemicals, like a house of bricks. Nitrogen, oxygen, sugar, vitamins are substances of natural, natural origin. Glass, rubber, steel is also a substance, more precisely, materials(mixtures of substances). Both glass and rubber are of artificial origin; they did not exist in nature. Completely pure substances are not found in nature or are very rare.

What is the difference between pure substances and mixtures of substances?

An individual pure substance has a certain set of characteristic properties (constant physical properties). Only pure distilled water has tmelt = 0 °С, tboil = 100 °С, and has no taste. Sea water freezes at a lower temperature, and boils at a higher temperature, its taste is bitter-salty. The water of the Black Sea freezes at a lower temperature and boils at a higher temperature than the water of the Baltic Sea. Why? The fact is that sea water contains other substances, for example, dissolved salts, i.e. it is a mixture of various substances, the composition of which varies over a wide range, but the properties of the mixture are not constant. The concept of "mixture" was defined in the 17th century. English scientist Robert Boyle : "A mixture is an integral system consisting of heterogeneous components."

Comparative characteristics of a mixture and a pure substance

Signs of comparison	pure substance	Mixture
Composition	Constant	fickle
Substances	Same	Various
Physical properties	Permanent	Fickle
Energy change during formation	going on	Not happening
Separation	Through chemical reactions	Physical methods

Mixtures differ from each other in appearance.

The classification of mixtures is shown in the table:

Here are examples of suspensions (river sand + water), emulsions (vegetable oil + water) and solutions (air in a flask, salt + water, small change: aluminum + copper or nickel + copper).

In suspensions, solid particles are visible, in emulsions - liquid droplets, such mixtures are called heterogeneous (heterogeneous), and in solutions the components are not distinguishable, they are homogeneous (homogeneous) mixtures.

Methods for separating mixtures

In nature, substances exist in the form of mixtures. For laboratory research, industrial production, for the needs of pharmacology and medicine, pure substances are needed.

Various methods of separation of mixtures are used to purify substances.

These methods are based on differences in physical properties mixture components.

Consider waysseparationheterogeneous And homogeneous mixtures .

Blend example	Separation method
Suspension - a mixture of river sand with water	settling Separation upholding based on different densities of substances. Heavier sand settles to the bottom. You can also separate the emulsion: to separate oil or vegetable oil from water. In the laboratory, this can be done using a separating funnel. Petroleum or vegetable oil forms an upper, lighter layer.As a result of settling, dew falls out of the fog, soot is deposited from smoke, cream is settled in milk. Separation of a mixture of water and vegetable oil by settling
A mixture of sand and table salt in water	Filtration What is the basis for the separation of heterogeneous mixtures using filtering? On various solubility of substances in water and on various sizes of particles. Across the pores of the filter pass only commensurate particles of substances, while larger particles are retained on the filter. This is how you can separate a heterogeneous mixture of table salt and river sand.Various porous substances can be used as filters: cotton wool, coal, fired clay, pressed glass, and others. The filtering method is the basis for the operation of household appliances, such as vacuum cleaners. It is used by surgeons - gauze bandages; drillers and workers of elevators - respiratory masks. With the help of a tea strainer for filtering tea leaves, Ostap Bender, the hero of the work of Ilf and Petrov, managed to take one of the chairs from Ellochka Ogre (“The Twelve Chairs”).
A mixture of iron powder and sulfur	Action by magnet or water Iron powder was attracted by a magnet, but sulfur powder was not.. The non-wettable sulfur powder floated to the surface of the water, while the heavy wettable iron powder settled to the bottom.. Separation of a mixture of sulfur and iron using a magnet and water
A solution of salt in water is a homogeneous mixture	Evaporation or crystallization The water evaporates and salt crystals remain in the porcelain cup. When water is evaporated from lakes Elton and Baskunchak, table salt is obtained. This separation method is based on the difference in the boiling points of the solvent and the solute. If a substance, such as sugar, decomposes when heated, then the water is not completely evaporated - the solution is evaporated, and then from saturated solution sugar crystals are precipitated. Sometimes it is required to remove impurities from solvents with a lower boiling point, for example, water from salt. In this case, the vapors of the substance must be collected and then condensed upon cooling. This method of separating a homogeneous mixture is called distillation or distillation. In special devicesdistillers produce distilled water , whichused for the needs of pharmacology, laboratories, car cooling systems . At home, you can design such a distiller: If, however, a mixture of alcohol and water is separated, then the first to be distilled off (collected in a receiving test tube) is alcohol with t bp = 78 ° C, and water will remain in the test tube. Distillation is used to obtain gasoline, kerosene, gas oil from oil. Separation of homogeneous mixtures

A special method for separating components, based on their different absorption by a certain substance, is chromatography.

At home you can do next experience. Hang a strip of filter paper over the bottle of red ink, dipping only the end of the strip into it. The solution is absorbed by the paper and rises along it. But the border of the rise of the paint lags behind the border of the rise of the water. This is how the separation of two substances occurs: water and the coloring matter in the ink.

With the help of chromatography, the Russian botanist M. S. Tsvet was the first to isolate chlorophyll from the green parts of plants. In industry and laboratories, instead of filter paper for chromatography, starch, coal, limestone, and aluminum oxide are used. Are substances always required with the same degree of purification?

For different purposes, substances with different degrees of purification are needed. Cooking water is sufficiently settled to remove impurities and chlorine used to disinfect it. Drinking water must first be boiled. And in chemical laboratories for the preparation of solutions and experiments, in medicine, distilled water is needed, as purified as possible from the substances dissolved in it. Highly pure substances, the content of impurities in which does not exceed one millionth of a percent, are used in electronics, semiconductor, nuclear technology and other precision industries.

Read L. Martynov's poem "Distilled Water":

Water
Favored
pour!
She
shone
So pure
Whatever to drink
Don't wash.
And it was no accident.
She missed
Willows, tala
And the bitterness of flowering vines,
She missed seaweed
And fish oily from dragonflies.
She missed being wavy
She missed flowing everywhere.
She didn't have enough life.
Clean -
Distilled water!

Application of distilled water

II. Tasks for fixing

1) Work with machines #1-4(necessarydownload the simulator, it will open in the Internet Explorer browser)

Educational experiment
at the beginning of the chemistry course

Separation of mixtures and purification of substances

Continuation. Beginning see No. 19/2007

In nature, pure substances are rare, most often they are part of mixtures. And in everyday life, we are mainly dealing not with individual (separate) substances, but with mixtures or materials of complex composition. The subject of study of the science of chemistry is substance and his transformations. Therefore, students should learn that one of the most important tasks of chemistry is to obtain individual (pure) substances. This problem has two solutions:

synthesis of substances in laboratories, factories, factories and combines from other substances and materials;

separation mixtures(natural or artificial) into separate components - individual substances.

We remind you that tasks for deepening and systematizing students' knowledge are printed in italics.

Mixture separation experiments
and purification of substances by physical methods

Depending on the state of aggregation and the properties of their constituent components, mixtures are homogeneous And heterogeneous. In any case, the substances in the mixture retain their properties.

The separation of a mixture by physical or chemical methods is possible when the substances (components) that make them up have sharply different properties. The choice of method for separating mixtures depends not only on the type of mixture (homogeneous or inhomogeneous) and the individual properties of the components, but also on which substance or substances must be isolated in pure form. At the same time, it should be taken into account that the substances obtained as a result of separation of the mixture will not be absolutely pure substances, but will contain a certain proportion of impurities.

Examine the labels on the packaging of various substances (chemical reagents) in the chemistry room. Pay attention to the color and verbal designations of various purity of substances and the content of impurities in them in accordance with the standard or technical condition each reagent.

AN EXPERIENCE1. Substances in a mixture retain their individual properties

Equipment and materials. Magnet, mortar and pestle, glasses, paper; water, sulfur, iron (powder).

Holding. Pound sulfur in a mortar and pour (2-3 g) onto a sheet of white paper. Another paper add iron powder (2-3 g). Consider external signs these substances. Here and later in this experiment, pay attention to the similarities and differences in the individual properties of iron and sulfur (aggregate state, color, smell, solubility in water, wettability with water, density, magnet action, etc.). Add a pinch each of sulfur and iron to cups of water. Cover portions of the substances on sheets of paper with other sheets and touch them from above with a magnet.

Pound iron powder (2 g) with sulfur (2 g) in a mortar and examine the mixture. Throw a pinch of the resulting mixture into a glass of water. Pour another portion of the mixture onto a sheet of paper, cover with another sheet and bring a magnet. Describe your observations in detail. Answer the questions.

1. Why does finely ground sulfur powder not sink in water? Is this property due to the density of sulfur, or is there another reason?

2. What properties of sulfur and iron did you establish in this experiment?

3. Are these individual properties of the components preserved in the mixture?

4.What properties of sulfur and iron were used in this experiment to separate a mixture of iron and sulfur?

AN EXPERIENCEY 2–3. Heterogeneous mixtures can be separated by settling

Equipment and materials. Support, glasses, cylinders, separating funnels; muddy (clay and sand) water, a mixture of vegetable oil and water.

Holding. Shake cloudy water in a glass and pour suspension into the cylinder. Stir the oil-water mixture thoroughly and pour over emulsion into a separating funnel fixed in a tripod.

Mark your observations after 1, 2, 5 minutes. Decant liquid from the cylinder into a clean glass. Consider the residue in the cylinder and the water in the glass.

Turn the faucet of the separating funnel and drain the lower layer of liquid from it into a beaker.

1.What properties of the components made it possible to separate these mixtures?

2. Is it possible to assert that the substances isolated from the mixture (which ones?) are pure?

3. Give examples of the separation of mixtures by settling used in practice. On the difference of what properties of substances is this method based?

AN EXPERIENCE4. Separation of inhomogeneous mixtures
can be accelerated by centrifugation

Equipment and materials. Centrifuge; cloudy (clay) water.

Holding. Pour the suspension into centrifuge tubes, place them in the centrifuge sockets and turn on the device according to the instructions (or use a manual centrifuge) for 3–5 minutes. Drain the water into a clean glass.

AN EXPERIENCES 5–6. Suspensions can be divided
on components by filtration

Equipment and materials. Stand with ring, filter funnel, glasses, glass rods, filter paper, cotton wool, gauze; cloudy water, 3% copper(II) sulfate solution.

Holding. Assemble the filtration unit and filter cloudy water first through a layer of gauze, then through cotton wool, and finally using filter paper with sufficiently fine pores. Carry out a similar experiment with a solution of copper(II) sulfate.

Record your observations, compare filtrate purity when using different filter media and using different methods to separate mixtures. Draw the appropriate conclusions.

1. Can a mixture of water and vegetable oil or other emulsions be separated by filtration?

2. Give examples of practical separation of mixtures by filtration. What is this method of separation of mixtures based on?

3.Which mixtures can be separated by filtration, and which mixtures cannot be separated by this method?

AN EXPERIENCE7. Some mixtures can be separated with a magnet

Equipment and materials. Magnet, pieces of paper 10x10 cm; a mixture of iron powder and sand, a set (mixture) of coins of various denominations, a mixture magnetite with waste rock.

Holding. The mixture is placed on a sheet of paper, covered with another sheet, a magnet is brought up and, without removing it, the top sheet is turned over with a substance attracted to the magnet.

Describe your observations. Check what other substances and materials are attracted by the magnet.

1.What substances or materials were isolated from mixtures using a magnet?

2.What is the method of magnetic separation of mixtures based on? Give examples of using this method in practice.

AN EXPERIENCE8. Flotation applied
for mineral processing

Equipment and materials. Tall beaker, spatula; a mixture of finely ground sulfur with sand, water.

Holding. Using a spatula, pour a mixture of sulfur and sand into a glass of water in small portions, mixing the contents of the glass well each time.

Describe your observations. Specify the density of sand, sulfur and water from the reference book and write down their values ​​in a notebook.

1. Have you noticed any contradictions between the properties of sulfur and the density of this substance?

2. Give examples of the practical application of flotation as a method of separation of substances in mineral processing. What is this method based on?

AN EXPERIENCES 9–10. Is it possible by evaporating solutions
get salt and granulated sugar?

Equipment and materials. Tripod with ring, grid, porcelain cups for evaporation, spirit lamp (burner); 30% salt solution, 40% sugar solution.

Holding. Assemble the evaporator. Pour 3-4 ml of common salt solution into a cup and boil the liquid almost to dryness. Use crucible tongs to remove the cup from the heat and make sure that the water has completely evaporated. Otherwise, carefully bring the experiment to the end, avoiding excessive overheating of the salt. (Caution! Hot concentrated solution may splatter.) After the cup of salt has cooled, collect the dry residue on a clean sheet of paper. Similarly (be careful!) Evaporate 3-4 ml of sugar solution. Try to collect the dry residue in this case as well.

Describe your observations and compare the results of evaporating salt and sugar solutions. pay attention to appearance received substances. Remember that tasting substances in the laboratory is strictly prohibited!

1. Can all solids dissolved in water be obtained in pure form by evaporating the solution under normal conditions?

2. Give examples of obtaining substances in pure form by evaporation in practice. What is this method based on?

AN EXPERIENCE11. Can sea water be turned into fresh water?

Equipment and materials. Installation for distillation of water, broken faience, glass slides, pipettes, crucible tongs; 3% common salt solution (imitation sea ​​water).

Holding. Evaporate a drop of "sea water" on a glass slide and prove that this liquid sample is a solution. (In place of the evaporated drop, a “stain” of salt will remain.) Assemble the installation for distillation of water or its simplified version, having previously placed pieces of broken earthenware in the distillation flask (for uniform boiling of the liquid) and distilled
2–3 ml distillate. Check the purity of the sample of the received portion of distilled water by evaporation on a glass slide.

Describe your observations, compare the results of evaporating drops of "sea" and distilled water, evaluate the effectiveness of this method of purification of substances.

1. Which mixtures (homogeneous or heterogeneous) can be separated by distillation?

2. Which components of mixtures can and which cannot be isolated by distillation?

3. Give examples of the practical application of distillation (distillation). What is this purification method based on?

AN EXPERIENCE12. Beautiful crystals can be "grown" at home

Equipment and materials. Glasses, heating device, nylon thread, glass rod; copper sulfate, table salt and other salts, water.

Holding. Prepare 250-300 ml of brine solution saturated at 30°C (from available). If the solution contains visible impurities, filter it into a large beaker.

Tie a thin nylon thread to the middle of the glass rod. Put the stick on top of the glass, and lower the free end of the thread into the solution almost to the bottom of the vessel. After 1-2 days, inspect the thread and remove all the crystals from it, except for one - the largest and most regular shape. The solution can be heated again until the precipitated crystals dissolve and, after cooling, the thread with the crystal is lowered into it again. The operation is carried out until a large crystal is obtained. Grown crystals are best stored in transparent closed vessels, providing them with labels.

Sketch the resulting crystals, compare the shapes of large and small crystals of the same substance and the shapes of crystals of different substances. Draw the appropriate conclusions.

Give examples of the practical application of crystallization and recrystallization as a method of purification of substances. What is this method based on?

AN EXPERIENCE13. Solubility of iodine in hexane is higher than in water

Equipment and materials. Separating funnel, glass; iodine water, hexane (you can take uncolored gasoline or straight-distilled kerosene).

Holding. Pour 5–10 ml of iodine water into a separating funnel and carefully add 2–3 ml of solvent along the vessel wall. Note that solvent is lighter than water. Close the funnel with a stopper and carefully, holding the stopper, stir the mixture. Note that the iodine has moved from the aqueous layer to the solvent layer.

Describe your observations, compare the colors of the initial and obtained solutions. Explain these changes. Look up the definition of "extraction" in the dictionary.

Give examples of the practical application of extraction as a method of purification and isolation of substances. What is this method based on?

AN EXPERIENCE14. Black charcoal discolors ink

Equipment and materials. Conical flask, accessories for filtering; water, ink, activated carbon tablets.

Holding. Pour 40–50 ml of water into the flask and add 1–3 drops of ink to make a slightly colored solution. Add 3-5 tablets of activated charcoal to the flask and stir the mixture vigorously in a circular motion of the flask. Let the mixture stand. If no discoloration occurs, add a few more charcoal tablets and repeat mixing. Making sure that adsorption completely, filter the mixture.

What is the basis of the phenomenon of adsorption and where does it find practical use?

AN EXPERIENCE15. We "write" with paints

Equipment and materials. Filter paper, pipettes, water, felt-tip pens in various colors.

Holding. With several touches of a colored felt-tip pen at the same point, you will get a small but intensely colored spot on the filter paper. Put a drop of alcohol or water in the center of the stain and as it spreads, add more drops of solvent. If the dye is homogeneous, then the colored ring will turn out to be homogeneous. If the felt-tip pen dye consists of a mixture of several colors, then you will get chromatogram of several colors corresponding to the composition of the dye. The method of separating complex dyed mixtures into its constituent parts in this case is called paper chromatography. A colored spot can also be obtained on paper using two or more felt-tip pens and the experiment can be repeated.

Describe your observations in an experiment on the separation of a mixture by chromatography. The method is based on different degrees of adsorption of substances by special adsorbents.

Give examples of the separation of substances by chromatography using various adsorbents. What is this method based on?

Questions and tasks for systematization
and generalizations of the concepts of the topic

1. Make a separation plan for the following mixtures:

a) sand, salt;

b) sand, clay, sawdust;

c) sand, iodine, table salt;

d) small iron nails, household waste;

e) iron filings, table salt, sulfur.

2. If the cook oversalted the soup, it is recommended to put a small linen bag of rice (20–30 g) into the pan for 10–15 minutes. What is the basis of the action of this "grandmother's secret"? Can you suggest another way to fix the issue?

3. The flour is sifted through a sieve before making the dough. Can screening be attributed to one of the purification methods of substances? If so, what is this method based on?

4. In well-known fairy tales, the stepmother or other evil spirits forced the heroine to separate certain mixtures into separate components. Remember what these mixtures were and on the basis of what method they were separated?

G.I.Shtrempler,
Professor of the Department of Chemistry
and teaching methods
Saratov State
university

Printed with a continuation

Abstract by discipline: Chemistry

On the topic: Methods for separating mixtures

Riga - 2009

Introduction…………………………………………………………………………..page 3

Types of mixtures………………………………………………………………………p.4

Methods for separating mixtures……………………………………………………..page 6

Conclusion……………………………………………………………………….page 11

List of references………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………..p.12

Introduction

In nature, substances in their pure form are very rare. Most of the objects around us are made up of a mixture of substances. In a chemical laboratory, chemists work with pure substances. If the substance contains impurities, then any chemist can separate the substance needed for the experiment from impurities. To study the properties of substances, it is necessary to purify this substance, i.e. split into component parts. The separation of a mixture is a physical process. Physical Methods separation of substances are widely used in chemical laboratories, in the production of food products, in the production of metals and other substances.

Types of mixtures

There are no pure substances in nature. When considering boulders, granite, we are convinced that they consist of grains, veins of various colors; milk contains fats, proteins, water; oil and natural gas contain organic substances called hydrocarbons; air contains various gases; natural water is not a chemically pure substance. A mixture is a mixture of two or more dissimilar substances.

Mixtures can be divided into two large groups (ri

If the components of the mixture are visible to the naked eye, then such mixtures are called heterogeneous. For example, a mixture of wood and iron filings, a mixture of water and vegetable oil, a mixture of river sand and water, etc.

If the components of the mixture cannot be distinguished with the naked eye, then such mixtures are called homogeneous. Such mixtures as milk, oil, a solution of sugar in water, etc. are classified as homogeneous mixtures.

There are solid, liquid and gaseous substances. Substances can be mixed in any state of aggregation. State of aggregation mixture defines a substance that is quantitatively superior to the rest.

Heterogeneous mixtures are formed from substances of different aggregate states, when the substances do not mutually dissolve and mix poorly (Table 1)

Types of heterogeneous mixtures
before mixing	Examples
hard/solid	Minerals; iron/sulfur
solid/liquid	Lime mortar; wastewater
solid/gaseous	Smoke; dusty air
liquid/solid	Pearl; minerals; water/ice
liquid / liquid	Milk; vegetable oil/water
liquid/gaseous	Fog; clouds
gaseous/solid	Styrofoam
gaseous/liquid	soap foam

Homogeneous mixtures are formed when substances dissolve well in each other and mix well (Table 2).

Types of homogeneous mixtures
Aggregate state of the constituent parts before mixing	Examples
hard/solid	Alloy of gold and silver
solid/liquid	sugar/water
solid/gaseous	Vapors of iodine in the air
liquid/solid	swollen gelatin
liquid / liquid	alcohol/water
liquid/gaseous	Water/air
gaseous/solid	Hydrogen in palladium
gaseous/liquid

When mixtures are formed, chemical transformations usually do not occur, and the substances in the mixture retain their properties. Differences in the properties of substances are used to separate mixtures.

Methods for separating mixtures

Mixtures, both inhomogeneous and homogeneous, can be divided into constituent parts, i.e. for pure substances. Pure substances are substances that cannot be separated into two or more other substances using physical methods and do not change their physical properties. There are various methods for separating mixtures; certain methods for separating mixtures are used depending on the composition of the mixture.

1. Screening;
2. Filtration;
3. settling;
4. Decantation
5. centrifugation;
6. Evaporation;
7. Evaporation;
8. Recrystallization;
9. Distillation (distillation);
10. Freezing;
11. The action of the magnet;
12. Chromatography;
13. Extraction;
14. Adsorption.

Let's get acquainted with a few of them. Here it should be noted that it is easier to separate heterogeneous mixtures than homogeneous ones. Below we give examples of the separation of substances from homogeneous and heterogeneous mixtures.

Screening.

Let's imagine that granulated sugar got into the flour. Perhaps the easiest way to separate is screening. With the help of a sieve, you can easily separate small particles of flour from relatively large sugar crystals. In agriculture, screening is used to separate plant seeds from foreign debris. In construction, gravel is separated from sand in this way.

Filtration

The solid component of the suspension is separated from the liquid filtering, using paper or fabric filters, cotton wool, a thin layer of fine sand. Let's imagine that we are given a mixture of table salt, sand and clay. It is required to separate table salt from the mixture. To do this, place the mixture in a beaker with water and shake. Table salt dissolves and sand settles. Clay does not dissolve and does not settle to the bottom of the glass, so the water remains cloudy. To remove insoluble clay particles from the solution, the mixture is filtered. To do this, you need to assemble a small filter device from a glass funnel, filter paper and a tripod. The salt solution is filtered out. To do this, the filtered solution is carefully poured into a funnel with a tightly inserted filter. Sand and clay particles remain on the filter, and a clear salt solution passes through the filter. Recrystallization is used to isolate salt dissolved in water.

recrystallization, evaporation

Recrystallization a method of purification is called, in which the substance is first dissolved in water, then the solution of the substance in water is evaporated. As a result, water evaporates, and the substance is released in the form of crystals.
Let's give an example: It is required to isolate table salt from a solution.
Above, we considered an example when it was necessary to isolate table salt from a heterogeneous mixture. Now let's separate the table salt from a homogeneous mixture. The solution obtained by filtration is called the filtrate. The filtrate must be poured into a porcelain cup. Place the cup with the solution on the tripod ring and heat the solution over the flame of the spirit lamp. The water will begin to evaporate and the volume of the solution will decrease. Such a process is called evaporation. As the water evaporates, the solution becomes more concentrated. When the solution reaches a state of saturation with table salt, crystals will appear on the walls of the cup. At this point, stop heating and cool the solution. Chilled table salt will stand out in the form of crystals. If necessary, salt crystals can be separated from the solution by filtration. The solution must not be evaporated until the water has completely evaporated, since other soluble impurities can also precipitate in the form of crystals and contaminate the table salt.

Settling, decanting

Used to isolate insoluble substances from liquids. upholding. If the solid particles are large enough, they quickly settle to the bottom, and the liquid becomes transparent. It can be carefully drained from the sediment, and this simple operation also has its own name - decantation. The smaller the solids in the liquid, the longer the mixture will settle. It is possible to separate from each other and two liquids that do not mix with each other.

centrifugation

If the particles of an inhomogeneous mixture are very small, it cannot be separated either by settling or filtering. Examples of such mixtures are milk and water-dissolved toothpaste. Such mixtures are divided centrifugation. Mixtures containing such a liquid are placed in test tubes and rotated at high speed in special apparatuses - centrifuges. As a result of centrifugation, heavier particles are "pressed" to the bottom of the vessel, and the lungs are on top. Milk is the smallest particles of fat distributed in an aqueous solution of other substances - sugars, proteins. To separate such a mixture, a special centrifuge called a separator is used. When separating milk, fats are on the surface, they are easy to separate. What remains is water with dissolved substances in it - this is skimmed milk.

Adsorption

In technology, the problem often arises of cleaning gases, such as air, from unwanted or harmful components. Many substances have one interesting property - they can "cling" to the surface of porous substances, like iron to a magnet. Adsorption called the ability of some solids to absorb gaseous or dissolved substances on their surface. Substances capable of adsorption are called adsorbents. Adsorbents are solid substances in which there are many internal channels, voids, pores, i.e. they have a very large total absorbing surface. Adsorbents are activated carbon, silica gel (in the box with new shoes you can find a small bag of white peas - this is silica gel), filter paper. Various substances“cling” to the surface of adsorbents is not the same: some are held on the surface firmly, others are weaker. Activated carbon is able to absorb not only gaseous, but also substances dissolved in liquids. In case of poisoning, it is taken so that toxic substances are adsorbed on it.

Distillation (distillation)

Two liquids that form a homogeneous mixture, such as ethanol with water, separated by distillation or distillation. This method is based on the fact that the liquid is heated to the boiling point and its vapor is removed through a gas outlet tube into another vessel. Cooling, the vapor condenses, and impurities remain in the distillation flask. The distillation apparatus is shown in Fig. 2

The liquid is placed in a Wurtz flask (1), the neck of the Wurtz flask is tightly closed with a stopper with a thermometer (2) inserted into it, while the mercury reservoir should be at the level of the outlet tube opening. The end of the outlet tube is inserted through a tightly fitted stopper into the Liebig refrigerator (3), at the other end of which the allonge (4) is fixed. The narrowed end of the allonge is lowered into the receiver (5). The lower end of the refrigerator jacket is connected with a rubber hose to a water tap, and from the upper end a drain is made into the sink. The refrigerator jacket should always be filled with water. The Wurtz flask and condenser are fixed in separate racks. The liquid is poured into the flask through a funnel with a long tube, filling the distillation flask to 2/3 of its volume. For uniform boiling, several boiling points are placed on the bottom of the flask - glass capillaries sealed at one end. After closing the flask, water is supplied to the refrigerator and the liquid in the flask is heated. Heating can be carried out on a gas burner, electric stove, water, sand or oil bath - depending on the boiling point of the liquid. In no case should flammable and combustible liquids (alcohol, ether, acetone, etc.) be heated over an open fire in order to avoid accidents: only a water or other bath should be used. The liquid should not be evaporated completely: 10-15% of the initially taken volume should remain in the flask. A new portion of the liquid can be poured only when the flask has cooled slightly.

Freezing

Substances with different melting points are separated by the method freezing, cooling the solution. By freezing, you can get very clean water at home. To do this, pour tap water into a jar or mug and put it in the freezer of the refrigerator (or take it out in the cold in winter). As soon as about half of the water turns into ice, the unfrozen part of it, where impurities accumulate, must be poured out, and the ice allowed to melt.

In industry and laboratory conditions use methods for separating mixtures based on other different properties of the constituent parts of the mixture. For example, iron filings can be isolated from a mixture magnet. The ability of substances to dissolve in various solvents is used in extraction- a method for separating solid or liquid mixtures by treating them with various solvents. For example, iodine aqueous solution can be isolated by any organic solvent in which iodine dissolves better.

Conclusion

In laboratory practice and in everyday life, it is very often necessary to isolate individual components from a mixture of substances. Note that mixtures include two or more substances, divided into two large groups: homogeneous and heterogeneous. There are various ways of separating mixtures, such as filtration, evaporation, distillation (distillation) and others. Methods for separating mixtures mainly depend on the type and composition of the mixture.

List of used literature

1. S.Ozols, E.Lepiņš chemistry for elementary school., 1996. P. 289

2. Information from the Internet

Lesson material contains information about various ways separation of mixtures and purification of substances. You will learn how to use knowledge of the differences in the properties of the components of a mixture to select the optimal method for separating a given mixture.

Topic: Initial chemical ideas

Lesson: Methods for separating mixtures and purifying substances

Let us define the difference between "methods for separating mixtures" and "methods for purifying substances." In the first case, it is important to obtain in pure form all the components that make up the mixture. When purifying a substance, obtaining impurities in a pure form is usually neglected.

SETTLEMENT

How to separate a mixture of sand and clay? This is one of the stages in ceramic production (for example, in the production of bricks). To separate such a mixture, the settling method is used. The mixture is placed in water and stirred. Clay and sand settle in water at different rates. Therefore, sand will settle much faster than clay (Fig. 1).

Rice. 1. Separation of a mixture of clay and sand by settling

The settling method is also used to separate mixtures of water-insoluble solids with different densities. For example, a mixture of iron and sawdust can be separated in this way (the sawdust will float in water, while the iron will settle).

A mixture of vegetable oil and water can also be separated by settling, because the oil does not dissolve in water and has a lower density (Fig. 2). Thus, by settling, it is possible to separate mixtures of liquids insoluble in each other with different densities.

Rice. 2. Separation of a mixture of vegetable oil and water by settling

To separate a mixture of table salt and river sand, you can use the settling method (when mixed with water, the salt will dissolve, the sand will settle), but it will be more reliable to separate the sand from the salt solution by another method - the filtration method.

Filtration of this mixture can be carried out using a paper filter and a funnel lowered into a glass. Grains of sand remain on the filter paper, and a clear solution of table salt passes through the filter. In this case, the river sand is the sediment, and the salt solution is the leachate (Fig. 3).

Rice. 3. Using filtration method to separate river sand from salt solution

Filtration can be carried out not only with filter paper, but also with other porous or loose materials. For example, bulk materials include quartz sand, and porous materials include glass wool and baked clay.

Some mixtures can be separated using the "hot filtration" method. For example, a mixture of sulfur and iron powders. Iron melts at over 1500 C and sulfur around 120 C. Molten sulfur can be separated from the iron powder using heated glass wool.

Salt can be isolated from the filtrate by evaporation, i.e. heat the mixture and the water will evaporate and the salt will remain on the porcelain cup. Evaporation, the partial evaporation of water, is sometimes used. As a result, a more concentrated solution is formed, upon cooling of which the solute is released in the form of crystals.

If a substance capable of magnetization is present in the mixture, then it is easy to isolate it in its pure form using a magnet. For example, a mixture of sulfur and iron powders can be separated in this way.

The same mixture can be separated by another method, using knowledge of the wettability of the components of the mixture with water. Iron is wetted by water, i.e. water spreads over the surface of the iron. Sulfur is not wetted by water. If you put a piece of sulfur in water, it will sink, because. The density of sulfur is greater than the density of water. But the sulfur powder will emerge, because. air bubbles stick to the grains of sulfur that are not wetted by water and push them to the surface. To separate the mixture, you need to place it in water. The sulfur powder will float and the iron will sink (Fig. 4).

Rice. 4. Separation of a mixture of sulfur and iron powders by flotation

The method of separating mixtures based on the difference in the wettability of the components is called flotation (French flotter - to float). Consider a few more methods for the separation and purification of substances.

One of the oldest methods of separating mixtures is distillation (or distillation). Using this method, it is possible to separate components that are soluble in each other and have different boiling points. This is how distilled water is obtained. Water with impurities is boiled in one vessel. The resulting water vapor condenses upon cooling in another vessel in the form of already distilled (pure) water.

Rice. 5. Obtaining distilled water

Components with similar properties can be separated using the chromatography method. This method is based on the different absorption of the substances to be separated by the surface of another substance.

For example, red ink can be separated into its components (water and dye) by chromatography.

Rice. 6. Separation of red ink by paper chromatography

In chemical laboratories, chromatography is carried out using special instruments - chromatographs, the main parts of which are a chromatographic column and a detector.

Adsorption is widely used in chemistry to purify certain substances. It is the accumulation of one substance on the surface of another substance. Adsorbents include, for example, activated carbon.

Try dropping an activated charcoal tablet into a container of colored water, stir, filter, and you will see that the filtrate has become colorless. Carbon atoms attract molecules, in this case, the dye.

Currently, adsorption is widely used for water and air purification. For example, water filters contain activated carbon as an adsorbent.

1. Collection of tasks and exercises in chemistry: 8th grade: to the textbook by P.A. Orzhekovsky and others. "Chemistry, Grade 8" / P.A. Orzhekovsky, N.A. Titov, F.F. Hegel. – M.: AST: Astrel, 2006.

2. Ushakova O.V. Chemistry workbook: 8th grade: to the textbook by P.A. Orzhekovsky and others. “Chemistry. Grade 8” / O.V. Ushakova, P.I. Bespalov, P.A. Orzhekovsky; under. ed. prof. P.A. Orzhekovsky - M .: AST: Astrel: Profizdat, 2006. (p. 10-11)

3. Chemistry: 8th grade: textbook. for general institutions / P.A. Orzhekovsky, L.M. Meshcheryakova, L.S. Pontak. M.: AST: Astrel, 2005.(§4)

4. Chemistry: inorg. chemistry: textbook. for 8 cells. general institutions / G.E. Rudzitis, FuGyu Feldman. - M .: Education, JSC "Moscow textbooks", 2009. (§ 2)

5. Encyclopedia for children. Volume 17. Chemistry / Chapter. edited by V.A. Volodin, leading. scientific ed. I. Leenson. – M.: Avanta+, 2003.

Additional web resources

1. A single collection of digital educational resources ().

2. Electronic version of the journal "Chemistry and Life" ().

Homework

From the textbook P.A. Orzhekovsky and others. "Chemistry, Grade 8" from. 33 Nos. 2,4,6,T.