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Studying this paragraph will help you:

· distinguish between pure substances and mixtures;

· name methods for separating mixtures;

· give examples of natural mixtures;

· characterize the properties of mixtures.

In chemistry, a distinction is made between pure substances and mixtures of substances. Let's find out how a pure substance differs from a mixture.

PURE SUBSTANCES If a substance is pure, then, apart from its structural particles, there are no other particles. It is worth remembering that even in chemical laboratories, not to mention natural conditions, absolutely PURE substances do not exist. Therefore, the concept of a pure substance is applied to substances in which there are so few impurities that they do not noticeably affect the properties of the substance.

Scientists are trying to isolate substances in as many pure form to study their properties and special uses.

A pure substance is a substance that does not contain impurities of other substances.

MIXTURES. IN Everyday life you are mostly not dealing with pure substances, but with mixtures of substances or materials made from several substances.

Mixtures are obtained by combining several PURE substances.

Give examples of mixtures that you use in everyday life.

In production, we also most often deal with mixtures of substances. Knowledge of the properties of pure substances and their changes under the influence of various impurities is extremely important for correct practical use substances.

In construction, cosmetology and medicine, during cooking, for washing clothes, etc., various mixtures are constantly used. There are mixtures in nature. Are you familiar with gaseous natural mixtures - air and natural gas, liquid natural mixtures - sea and mineral water, oil, milk, solid mixtures - soil, granite and the like.

The substances that make up a mixture are called components of the mixture. Mixtures can be homogeneous or heterogeneous. It all depends on the particle size of the mixture components. In homogeneous mixtures, particles of one substance cannot be seen among the particles of another visually (that is, with the help of vision) or with the help of magnifying devices. For example, pure water and water sweetened with sugar look the same on the outside and under a magnifying glass. Therefore, it is a homogeneous mixture. The material from which window glass is made (Fig. 38) is also a homogeneous mixture of substances formed by the fusion of quartz sand, limestone and soda.

Granite, soil, a mixture of oil and water are examples of heterogeneous mixtures. It is not difficult to detect components in them visually or using magnifying devices.

By mixing two or more substances that are insoluble in each other, you can independently make various heterogeneous mixtures. Moreover, according to your desire, their composition can be different.

PROPERTIES OF MIXTURES. Firstly, the mixtures have an arbitrary composition. So, on the shelves of grocery stores you can see sour cream with different percentages of fat (15%, 20%, 30%). Using sugar, dried tea leaves and water, you prepare a mixture called tea. It is quite obvious that for some of you the drink will be sweeter, for others it will have a dark color, but in each case the sugar will not lose its sweet taste, and the substances of the tea leaves will not lose their color. Preservation of a substance in a mixture its properties is another characteristic feature mixtures.

Rice. 38. Examples of homogeneous mixtures (a - sea water; b - tap water; - milk; d - juice; e - glass; f - gasoline)

The quantitative composition of the mixtures is arbitrary. Substances in the mixture retain their individual properties.

Due to the preservation of the individual properties of substances in the mixture, they can be separated into individual components by physical methods.

The ability to separate mixtures is necessary for every person, regardless of whether it will bind its future profession with chemistry or not.

METHODS FOR SEPARATING MIXTURES. There are many ways to separate mixtures, among which the most common are: settling, filtering, evaporation.

Settling is the simplest way to separate heterogeneous mixtures formed from:

1) a solid substance that is practically insoluble in water;

2) two liquids that do not mix with each other.

Example 1. Let's prepare a mixture of sand and water.

At first it will be cloudy (Fig. 39a), but a little time will pass, and the sand, having a higher density than water, will settle to the bottom, and the layer of water above it will become transparent (Fig. 396). After this, carefully pour the water into another container.

And no matter how careful you are, it will not be possible to completely separate the mixture by settling. Some of the sand will still end up in another vessel, and some water will remain in the glass and soak the sand.

Example 2. From life experience You know that oil does not dissolve in water. Therefore, the mixture of these substances separates quite quickly, and after settling it can be easily separated into components. To do this, chemical laboratories use a separating funnel (Fig. 40).

Consider the substance in which the density - water or oil - is high.

It is clear that the lower layer is formed by water, and the upper layer by oil (Fig. 40a). Therefore, water will be the first to pour out of the separating funnel through the open edge (Fig. 40b). You just need to turn it off in time so that the oil remains in the funnel.

Recall

Just like in natural history lessons, you watch the teacher prepare mixtures; you yourself made and separated the mixtures. What methods of separating mixtures do you know?

Rice. 39. Separation of a mixture of insoluble solid and water by settling

Rice. 40. Separation of a heterogeneous mixture of liquid by settling

SEPARATION OF MIXTURES BY FILTERING This method is used to separate heterogeneous mixtures of liquid and insoluble solids, for example water and chalk (Fig. 41). A filter made of special porous paper is placed on the watering can, which is called a filter.

Remember! The edges of the filter should not extend beyond the funnel, but should be 0.2-0.5 cm below its edges. You should ensure that the filter fits tightly to the funnel (for this purpose, the inner wall of the funnel is pre-moistened with water).

The mixture is carefully poured onto the filter using a glass rod. Water penetrates through the pores of the filter into the receiving vessel, and the chalk insoluble in it remains on the filter. Everything that passes through the pores of the filter is called filtrate.

In everyday life, several layers of gauze or other fabric can serve as a filter. The filter can also be a loose bunch of cotton wool. By the way, at home, when the need for filtering arises, a cotton filter is most often used. Sand filters at water treatment plants (Fig. 42), which provide drinking water big cities. Nowadays, at home, many people use household filters to purify water (Fig. 43).

Rice. 41. Separation of a heterogeneous mixture of water and chalk by filtration

Rice. 42. Use of filters in water treatment plants

Rice. 43. Household portable water filter

Rice. 44. Vacuum cleaner (a) and respirator (6) filter the air from dust

Filtration is the separation of a solid from a liquid by passing a mixture of substances through a porous material permeable only to the liquid. It is the most common method for separating heterogeneous mixtures of liquids and solids.

There are also filters that separate air mixtures with dust particles (Fig. 44).

SEPARATION OF MIXTURES BY EVAPORATION. Homogeneous mixtures cannot be separated by settling or filtering. The particles of all components in them are so small that they do not settle and pass through the pores of the filter without delay. To make sure that this is really the case, let's try to filter a homogeneous mixture made from water and copper sulfate (a solid blue color) (Fig. 45). The same blue color of the mixture and the filtrate indicates that it was not possible to separate this mixture by filtration. There was no sediment left on the filter; all components of the mixture passed into the filtrate (Fig. 45a). A homogeneous mixture of table salt and water will behave similarly (Fig. 45(5). To separate such mixtures, another method should be used - evaporation.

Rice. 45. Passing homogeneous liquid mixtures through a filter

Rice. 46. ​​Separation of a mixture of table salt and water by evaporation

For evaporation, you need an alcohol lamp or other heating device, a laboratory stand, and a porcelain cup.

When a mixture of water and salt is heated (Fig. 46a. (7), the liquid component (water) evaporates, and the solid substance (table salt) remains on the walls and bottom of the cup (Fig. 46.).

To separate a mixture means to isolate individual substances from it. Separation can be carried out by filtration, settling, evaporation and some other methods.

1. What is called a pure substance and a mixture?

2. What types of mixtures do you know?

3. How does a homogeneous mixture differ from a heterogeneous one?

4. Give 2-3 examples of natural mixtures, name their component.

5. What methods of separating mixtures do you know?

6. Fill out the table (you will find all the necessary information in the text of the paragraph). Also use stand-alone examples.

7. Match the right and left columns:

8. Which mixture can be separated by filtering and which by evaporation:

a) a mixture of chalk and salt;

b) sea water?

9. From the list above, write down separately the names of pure substances and mixtures: sugar, mineral water, honey, milk, carbon dioxide, vinegar, baking soda.

3 Geography you know that water, after evaporating from the seas and oceans, returns to the earth in the form of rain or snow. So why rainwater and the snow is not salty?

The starting materials are included unchanged in the mixture. In this case, the starting substances often become unrecognizable because the mixture exhibits different physical properties compared to each isolated starting substance. When mixed, however, no new substance arises.

The specific qualities of a mixture, such as density, boiling point or color, depend on the ratio of the mixture components (mass ratio). A mixture of two metals obtained by mixing their melts is called an alloy. In another connection they talk about a conglomerate. Colloidal solutions are in the middle between homogeneous and heterogeneous mixtures. These liquids contain solid particles, each consisting of a small number of molecules. Therefore, such a mixture behaves like a solution.

If they want to separate a mixture into pure substances, then they use some physical properties. This leads to the selection of the appropriate separation method.

Homogeneous and heterogeneous mixtures

Different types of mixtures can be classified into 2 groups:

• Heterogeneous mixtures are not completely mixed, since pure substances exist in clearly demarcated phases, that is, they are multiphase materials
• Homogeneous mixtures are mixed pure substances at the molecular level, that is, they are single-phase materials.

Homogeneous mixtures are divided according to their state of aggregation into three groups:

• gas mixtures;
• solutions;
• solid solutions.

Heterogeneous mixtures of two substances can be separated according to states of aggregation into the following groups:

A measure indicating the proportion of substances in a mixture is concentration.

Difference between pure substances and mixtures

This distinction is most simple for gases. Clean compound(for example, water) consists of one type of molecules, and a mixture of gases consists of several types (for example, oxygen and hydrogen molecules). A mixture of gases can be separated by physical methods (for example, diffusion), but a complex substance cannot.

With regard to liquid and solid mixtures, everything is not always obvious.

Separation of mixtures

There are various methods for separating mixtures. For gases, these methods are based on the difference in speed or mass of molecules of substances included in the mixture.

1. The main methods for isolating substances from a heterogeneous (heterogeneous) mixture:

• upholding

• filtration

• magnet action

2. The main methods of isolating substances from a homogeneous (homogeneous) mixture:

• evaporation

• crystallization

• distillation

• chromatography

see also

Notes

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See what “Mixture (chemistry)” is in other dictionaries:

Mixture: A mixture (chemistry) is a product of mixing, a mechanical combination of any substances, characterized by an impurity content above a certain limit. For example: flammable mixture, helium-oxygen mixture. Random, disorderly, devoid of... ... Wikipedia

Ash and slag mixture- Ash and slag mixture – a mixture consisting of ash and slag formed at thermal power plants when coal is burned in the furnaces of boiler units. [GOST 25137 82] Ash and slag mixture - a mechanical mixture of dusty fly ash and slag... ...

- (Eschka mixture) a mixture of two parts MgO and one part Na2CO3, a reagent that absorbs sulfur and chlorine oxides well. For example, to determine the sulfur content in coal, a sample of coal is burned with an Eshka mixture. In this case, soluble sulfates are formed... ... Wikipedia

Activated mixture SFB- – a mixture prepared with water with additives, passed through a rotary pulsation apparatus and subject to cavitation; allows you to obtain an economic effect by increasing the specific surface of cement and the formation of cement... ... Encyclopedia of terms, definitions and explanations of building materials

Asphalt concrete mixture- - a rationally selected mixture of mineral materials [crushed stone (gravel) and sand with or without mineral powder] with bitumen, taken in certain proportions and mixed in a heated state. [GOST 9128 97] Term heading: Asphalt... ... Encyclopedia of terms, definitions and explanations of building materials

Concrete mixture of specified quality- is a concrete mixture, the required properties and additional characteristics of which are specified to the manufacturer, who is responsible for providing these required properties and additional characteristics. [GOST 7473 2010] Term heading:... ... Encyclopedia of terms, definitions and explanations of building materials

Concrete mixture of a given standardized composition- is a concrete mixture of a given composition, the composition of which is determined by a standard or other technical document, for example, production standards. [GOST 7473 2010] Term heading: Properties of concrete Encyclopedia headings: Abrasive... ... Encyclopedia of terms, definitions and explanations of building materials

Concrete mixture of a given composition- is a concrete mixture, the composition of which and the components used in preparation are specified by the manufacturer, who is responsible for ensuring this composition. [GOST 7473 2010] Term heading: Properties of concrete Encyclopedia headings: ... ... Encyclopedia of terms, definitions and explanations of building materials

Fireproof concrete mixture- – a refractory mixture consisting of refractory powders and refractory cement, ready for use after the introduction of liquid. [GOST R 52918 2008] Term heading: Concreting technologies Encyclopedia headings: Abrasive equipment,… … Encyclopedia of terms, definitions and explanations of building materials

Fireproof mixture- – unshaped refractory consisting of refractory powders, ready for use after the introduction of the binder. [GOST R 52918 2008] Refractory mixture - unshaped refractories consisting of refractory powders, requiring the introduction of a binder. [GOST... Encyclopedia of terms, definitions and explanations of building materials

Books

• Fundamentals of general and physical chemistry. Textbook, Eremin Vadim Vladimirovich, Borshchevsky Andrey Yakovlevich. The book is created on the basis of a one-year course “General and physical chemistry” for 2nd year students of the Faculty of Physics of Moscow State University. When choosing the level of presentation, we assumed that it would be read...

Try to answer next question: “Would it be correct to study the properties of water using sea water?” Naturally, no, because sea water is not pure H2O, but a mixture of different substances in it. First of all, these are salts (their main mass constitutes sodium chloride), they give sea water a peculiar bitter-salty taste. Absolutely every substance that can be isolated from water has certain properties. However, the water itself, which is not contaminated with foreign impurities or contains extremely little of them - distilled water - has specific properties. It freezes at a temperature of 0°C, while ocean water freezes at a temperature of -1.9°C.

Natural water cannot be completely pure. Rainwater is the cleanest, but it also contains a certain amount of impurities that are captured from the air.

In everyday life, we, as a rule, encounter not pure substances, but mixtures of substances. Such mixtures can be heterogeneous (for example, muddy water from a river contains insoluble particles of sand and clay, they can be seen with the naked eye) and homogeneous (solutions of sugar, alcohol) in which the interface between substances cannot be seen.

Homogeneous mixtures can be divided into liquid, solid and gaseous. The most important gaseous mixture is air; it is a mixture of oxygen, nitrogen, carbon dioxide, argon, and other substances. Solid mixtures include glass and various alloys - bronze, brass, steel.

The composition of various mixtures can be quite diverse; they, unlike pure substances, have different properties. Pure water turns into ice at a temperature of 0°C; if we dissolve table salt in it, its freezing point will drop significantly. Such methods, for example, are used by lazy city utility workers when, during periods of severe frost and ice, they sprinkle the sidewalks with technical table salt.

Mixture composition can be determined using chemical analysis. This method is widespread; it is necessary in solving the most important economic problems, as well as scientific and technical problems.

Condition monitoring environment is impossible without determining the concentration of impurities that pollute air, water and soil. When exploring various minerals, analysis of rocks and ores is used. Let us remember Sherlock Holmes, the famous detective, the protagonist of numerous works by A. Conan Doyle: he always managed to determine the guilt or innocence of a suspect using chemical analysis, which took up a significant part of the detective’s free time. Both an archaeologist and a criminologist, a physician and an art critic cannot do without chemical analysis. In addition, it is worth mentioning space research, the study of the atmospheric gases of planets, their rocks, and the study of the composition of lunar soil is impossible without carrying out this labor-intensive process.

Using special technologies and methods using chemical analysis, it is possible to create especially pure substances, the content of impurities in them, which affects their properties, does not exceed one hundred thousandth or even one millionth of a percent. Such substances play vital role in nuclear energy, fiber optics, semiconductor industry. Particularly pure substances, or rather their properties, are necessary to create fundamentally new devices or technological processes.

One of the most important problems chemistry is the purification of substances. To purify natural water from suspended particles, it is passed through a layer of porous substance, for example coal, or baked clay. If we're talking about O large quantities water, then in such situations filters made of sand and gravel are used.

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All existing objects, liquids and gases are pure substances and mixtures. Without knowing what they are, it is very easy to confuse them. How to distinguish one from the other? Let's figure it out.

From elements to substance

IN currently known in the world 118 chemical elements. They have their own names and chemical symbols, which are designated with Latin letters. Each of them represents one type of atom, which has a certain number of electrons arranged in a strict order.

The elements are unique Construction Materials. They can be compared to bricks: when they touch, they form walls, or even an entire building. Thus, by combining with each other, atoms of one element can “build” a simple substance (oxygen O 2, hydrogen H 2, nitrogen N 2, etc.). Complex, in turn, is formed from the fusion of different elements (water H 2 O, ammonia NH 3, etc.).

In both cases they are pure substances. Why? Because the connection occurs through chemical reactions. In this case, energy can be released or absorbed.

What is a mixture?

A mixture also consists of two or more different components. But its constituent parts are not individual elements, but substances (they can be both complex and simple). Mixtures can be heterogeneous or homogeneous.

The first ones are much easier to understand. In them, the components are mixed purely mechanically and are easily separated from each other by filtration, magnet, settling and other methods. Heterogeneous mixtures are heterogeneous, and their components entirely retain their individual properties.

An example of such formation is the addition of river sand to water. They will not be able to mix and form a new substance, and are easily separated if you use a sieve.

Homogeneous mixtures form a seemingly homogeneous substance. They are gases, solid or liquid solutions. Their components also retain their primary properties, but cannot be separated mechanically. To separate them, more sophisticated methods are used: distillation, crystallization, sorption (absorption), extraction (dissolution of one component), etc.

A typical homogeneous mixture is air. It consists of various gases, grains of dust, drops of water. Sea water is also not a pure substance. In addition to water itself, it contains metal salts (sodium, chlorine, potassium and others).

Differences between mixtures and substances

Sometimes mixtures and pure substances are very easy to confuse. For example, brass has metallic properties and looks like some kind of metal. However, it is an alloy that consists of copper, zinc and other components (often tin, nickel, lead, iron).

What's the difference? The main difference is that the substance is a completely homogeneous formation. Its components can only be separated using chemical reactions. The properties of a pure substance differ from the properties of its components separately; it is a new structure and acquires different qualities.

In addition, the substance has permanent staff. There is even a special register with a list of all known structures. The mixture, on the contrary, does not have a clear composition. The same brass may have less nickel and more of another metal, but it is still brass. For example, you can add more or less sugar to tea, but this will not stop it being tea. If from a molecule clean water H 2 O remove oxygen (O), then it will not be water, but a molecule of hydrogen - a colorless gas.

Extra pure substance

In nature, mixtures are more common than substances. Thus, the earth’s crust contains many minerals, metal ores and gases, but it is difficult to call them pure. Most of them contain impurities.

They are generally not suitable for industrial production. Therefore, they are cleaned and separated from each other in every possible way. Substances that contain such a small percentage of impurities that they cannot affect its properties are called ultrapure or especially pure. They are obtained through very careful purification. Thus, to create semiconductors you need the most homogeneous substance possible, so not only the material for it is removed from impurities, but also the air in the room where it is produced.

I. New material

When preparing the lesson, the following materials were used by the author: N.K. Cheremisina,

chemistry teacher 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. Let's 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 also milk protein here casein, mineral salt, vitamins and even sugar, but not the kind with which they drink tea, but a special one, milk - lactose. We eat apples, which consist of a whole range of chemicals - here and sugar, And Apple acid, And vitamins... When chewed apple pieces enter the stomach, human digestive juices begin to act on them, which help to absorb all the tasty and useful material not only apples, but 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 is 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. Absolutely pure substances are not found in nature or are found very rarely.

How do pure substances differ from mixtures of substances?

An individual pure substance has a certain set of characteristic properties (constant physical properties). Only pure distilled water has melting point = 0 °C, boiling point = 100 °C, and has no taste. Sea water freezes at a lower temperature and boils at a higher temperature; its taste is bitter and 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 widely, but the properties of the mixture are not constant. The definition of the concept “mixture” was given in the 17th century. English scientist Robert Boyle : "Mixture - complete system, consisting of heterogeneous components."

Comparative characteristics of the mixture and pure substance

The mixtures differ from each other in appearance.

The classification of mixtures is shown in the table:

Let us give examples of suspensions (river sand + water), emulsions (vegetable oil + water) and solutions (air in a flask, table salt + water, small coin: aluminum + copper or nickel + copper).

In suspensions, particles of a solid substance are visible, in emulsions - droplets of liquid, 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, and for the needs of pharmacology and medicine, pure substances are needed.

Used for purification of substances various ways separation of mixtures

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

Let's consider waysseparationheterogeneous And homogeneous mixtures .

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

You can try the following experiment at home. Hang a strip of filter paper over a container 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 paint rise boundary lags behind the water rise boundary. This is how two substances are separated: water and the coloring matter in the ink.

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

For different purposes, substances with varying degrees of purification are required. Cooking water should be left to stand sufficiently to remove impurities and chlorine used to disinfect it. Water for drinking must first be boiled. And in chemical laboratories for preparing solutions and conducting experiments, in medicine, distilled water is needed, purified as much as possible from substances dissolved in it. Particularly 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
To pour!
She
Shined
So pure
No matter what to get drunk,
No washing.
And this was not without reason.
She missed
Willows, tala
And the bitterness of flowering vines,
She didn't have enough seaweed
And fish, fatty from dragonflies.
She missed being wavy
She missed flowing everywhere.
She didn't have enough life
Clean –
Distilled water!

Using distilled water

II. Tasks for consolidation

1) Work with simulators No. 1-4(necessarydownload the simulator, it will open in the Internet Explorer browser)