Homogeneous and inhomogeneous substances definition. Separation of mixtures. Purification of substances. Filtration. Mixtures can be homogeneous or heterogeneous

In the mixture, the starting materials are included unchanged. In this case, the starting substances often become unrecognizable, because the mixture exhibits different physical properties in comparison with each isolated starting substance. When mixed, however, no new substance is produced.

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

If they want to divide the mixture into pure substances, then they use some physical qualities. This results in the selection of the appropriate separation method.

Homogeneous and heterogeneous mixtures

The various 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 pure mixed 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 divided by state of aggregation into the following groups:

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

The difference between pure substances and mixtures

The simplest difference is for gases. A pure complex substance (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 the velocities or masses of the molecules of the 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 for separating substances from a homogeneous (homogeneous) mixture:

  • evaporation
  • crystallization
  • distillation
  • chromatography

see also

Notes (edit)


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See what "Mixture (chemistry)" is in other dictionaries:

    Mixture: A mixture (chemistry) is a product of mixing, a mechanical connection of any substances, characterized by an impurity content above a certain limit. For example: combustible 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 - mechanical mixture of dusty fly ash and slag ... ...

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

    Sfb activated mixture- - a mixture prepared in water with additives passed through a rotary pulsation apparatus and subject to cavitation; allows to obtain an economic effect due to an increase in the specific surface of cement and the formation of cement ... ... Encyclopedia of terms, definitions and explanations of building materials

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

    Concrete mix 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: Concrete properties Encyclopedia headings: Abrasive ... ... Encyclopedia of terms, definitions and explanations of building materials

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

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

    Refractory 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. Study guide, 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 Physics Faculty of Moscow State University. Choosing the level of presentation, we proceeded from the fact that they would read it ...

The composition of the mixture can be different. In life, as a rule, we are faced with mixtures of substances. A mixture is a collection of different substances mixed together, but not chemically bonded. Substances are mixed, but do not react with each other and, in principle, they can be separated. Air, as we know, is a mixture of several substances: oxygen, nitrogen, carbon dioxide, etc. Granite from which obelisks are made is a mixture of quartz, feldspar and mica. Oil is a mixture of over a hundred substances. Milk is also a mixture. When it cools and settles, fat floats on the surface. Gasoline is also a mixture of substances.

A mixture is a collection of various substances that retain their properties.

Distinguish between homogeneous and heterogeneous mixtures.

Homogeneous mixtures are those in which the components cannot be distinguished by observation.

Particles of components are evenly distributed in the mixture. Homogeneous mixtures are, for example, an aqueous solution of sodium chloride, a solution of sugar in water, air, most metal alloys, a mixture of gases.

The physical properties of a homogeneous mixture are partially different from the physical properties of its constituents. For example, the boiling point of pure water is +100 0C, and with salt impurities, the boiling point rises.

Inhomogeneous mixtures are those in which the naked eye or with the help of optical devices can be seen particles of the substance of which the mixture consists.

Inhomogeneous mixtures are, for example, soil, milk, turbid water, most minerals.

The substances that make up the inhomogeneous mixture retain their physical properties. This can be confirmed by such experience. It is known that iron is attracted by a magnet and sinks in water, while sulfur powder, if shaken with water, floats to the surface because it is not wetted with water. By mixing powdered iron with sulfur powder on a piece of paper, we get a grayish-yellow mixture. Dip a piece of this mixture into water and stir. Sulfur and iron will separate: grains of sulfur will float to the surface of the water, and grains of iron will drown. Cover the rest of the mixture with a sheet of paper and bring the magnet closer to it. The grains of iron will be attracted (through the paper) to the magnet, and the sulfur will remain on the paper.

powdered sulfur; c) a mixture of iron and sulfur; d) separation of the mixture when dissolved in water; d) separation of the mixture by the action of a magnet.

Separation methods

Using physical methods, mixtures can be separated into their constituent parts. The separation of mixtures is called purification of substances. The purifying agent is considered to be the substance for the sake of which the separation is carried out. There may be a small amount of it in the mixture. For example, there is incomparably more waste rock in a gold-bearing layer than gold.

Separation of a mixture is the separation of pure substances from them.

There are many methods for separating mixtures. To separate a mixture, it is necessary to know the properties of the substances that make up its composition, the type of mixture, and the state of aggregation.

Brief description of mixtures

Homogeneous Distillation or Distillation Mixtures of liquids with different boiling points. The mixture of liquids heats up slowly. Under these conditions, the substance, which has the lowest boiling point, evaporates earlier, its vapors are cooled, the condensate is collected in a separate container. Example: extraction of distilled water, separation of alcohol from water, separation of oil into fractions.

Evaporation: Dissolved solid from solution. The mixture is heated. The liquid evaporates and the solid remains in the form of crystals. Example: table salt from a salt solution.

Crystallization: Dissolved solid from concentrated solution. The mixture of solid and liquid is heated. After evaporation of some of the liquid, the mixture is cooled. A solid will precipitate out as crystals. Example: crystallization of sugar into boiled ones.

Chromatography: A mixture of solutes that have different absorption rates. A special chromatographic paper is dipped into the mixture. The components of the mixture are absorbed by this paper at different rates. Each component paints a specific color on the paper. The number of colors indicates the number of components in the mixture.

Inhomogeneous Filtration A mixture of soluble and insoluble substances that have different particle sizes. The mixture is passed through a filter. Insoluble substances do not pass through the pores of the filter and remain on it. Example: sand, sawdust from a solution.

Sedimentation A mixture of two liquids, a solid insoluble substance from a solution with different densities. The mixture is defended. A substance that has a higher density settles to the bottom, while a substance with a lower density remains on the surface. Example: water and oil, water and sawdust, water and sand.

In chemistry, there are concepts of pure substances and mixtures. Pure ones contain molecules of only one substance. In nature, mixtures of different substances predominate.

Concepts

All substances can be divided into two categories - pure and mixed. Pure substances include elements and compounds consisting of the same atoms, molecules or ions. These are substances with a constant composition that retain constant properties.
Examples of pure substances are:

  • metals and inert gases, consisting of atoms;
  • water, made up of water molecules;
  • table salt, consisting of sodium cations and chlorine anions.

Rice. 1. Pure substances.

If sugar is added to the water, it ceases to be a pure substance, a mixture is formed. Mixtures consist of several pure substances of different structure, which are called components. Mixtures can have any state of aggregation. For example, air is a mixture of various gases (oxygen, hydrogen, nitrogen), gasoline is a mixture of organic substances, brass is a mixture of zinc and copper.

Rice. 2. Mixtures.

Each substance retains its properties, so water with salt is salty, and an alloy with iron is attracted by a magnet. However, the properties of the mixture itself can vary in accordance with the quantitative and qualitative composition of the components. For example, distilled water that has undergone maximum purification, depending on the added substances, can acquire a sweet, sour, salty or sour-salty taste. Moreover, the higher the concentration of a certain substance, the more pronounced a certain taste.

By structure, mixtures can be homogeneous or combine substances in different states of aggregation. In accordance with this, there are:

  • homogeneous or homogeneous - particles cannot be detected without chemical analysis, their index is the same anywhere in the sample (metal alloy);
  • heterogeneous or heterogeneous - particles are easy to detect, their frequency is not uniform in different places of the mixture (water with sand).

Heterogeneous mixtures include:

  • suspensions - mixtures of solid and liquid substances (coal and water);
  • emulsions - mixtures of liquids of different density (oil and water).

If one component is ten times inferior in weight to another component, then it is called an impurity.

Cleaning methods

There are no absolutely pure substances. Pure substances are substances containing a small amount of impurities that do not affect the physical and chemical properties of the substance. To maximize the purification of the substance, are used methods for separating mixtures:

  • sedimentation - sedimentation of heavy substances in liquids;
  • filtration - separation of particles from liquid using filters;
  • evaporation - heating the solution until the moisture evaporates;
  • the use of a magnet - selection by magnetization;
  • distillation - separation of substances with different boiling points;
  • adsorption - the accumulation of one substance on the surface of another.

Metals from non-metals can be separated by flotation. It is a process based on the wetting capacity of substances. In this way, iron is separated from sulfur: iron gets wet and settles to the bottom, and sulfur does not get wet and remains on the surface of the water.

Rice. 3. Flotation.

What have we learned?

From the 8th grade chemistry lesson, they learned about the concepts of mixtures and pure substances. Elements and compounds consisting of homogeneous molecules, atoms or ions, as well as having constant properties, are called pure. Mixtures include several pure substances of different concentration and structure. The compounds can be mixed completely, forming homogeneous substances, or combined inhomogeneously. Various methods are used to separate mixtures.

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SECTION I. GENERAL CHEMISTRY

6. Mixtures of substances. Solutions

6.2. Mixtures, their types, names, composition, separation methods

Mixtures are a collection of various substances from which one physical body can be composed. Each substance that is contained in the mixture is called a component. When mixed, a new substance does not arise. All substances that are part of the mixture retain their inherent properties. But the physical properties of the mixture, as a rule, differ from the physical properties of the individual components. Mixtures are homogeneous and heterogeneous.

Homogeneous (homogeneous) mixtures are mixtures in which the components are mixed at the molecular level (single-phase material); they cannot be detected when viewed with the naked eye and even when using powerful optical instruments. For example, aqueous solutions of sugar, sodium chloride, alcohol, acetic acid, metal alloys, air.

Inhomogeneous (heterogeneous) mixtures form the so-called dispersed systems. They are formed by mixing two or more substances that do not dissolve in each other (do not form homogeneous systems) and do not react chemically. The components of dispersed systems are called the dispersion medium and the dispersed phase; there is a separation surface between them.

According to the particle size of the dispersed phase, the systems are divided into:

Coarsely dispersed (> 10 -5 m);

Microheterogeneous (10 -7 -10 -5 m);

Ultra-microheterogeneous (10 -9 -10 -7 m), or sols (colloidal systems) 1.

If the particles of the dispersed phase have the same size, the systems are called monodisperse; if different - polydispersed (such are almost all natural systems). Depending on the state of aggregation of the dispersion medium and the dispersed phase, such simple dispersed systems are distinguished:

Dispersed phase

Dispersion medium

Designations

Name

Example

gaseous

gaseous

y / y

not formed *

liquid

y / y

gas emulsion, foam

sea, soap foam

solid

g / t

porous body (hard foam) **

pumice stone, activated carbon

liquid

gaseous

y / y

spray can

clouds, fog

liquid

y / y

emulsion

milk, oil

solid

p / t

capillary systems

foam sponge soaked in water

solid

gaseous

t / y

spray can

smoke, sandstorm

liquid

t / y

suspension, sol, suspension

paste, suspension of clay in water

solid

t / t

solid heterogeneous system

rocks, concrete, alloys

* Gases form homogeneous mixtures (gaseous solutions).

** Porous bodies, according to the size of the cavities, are divided into:

Microporous (2 nm);

Lesoporous (2-50 nm);

Macroporous (> 50 nm).

The mixtures are separated using physical methods. To separate heterogeneous mixtures, sedimentation, filtration, flotation and sometimes the action of a magnet are used.

Upholding

For separating a mixture containing solid water-insoluble particles or liquids that are insoluble in each other. Solid insoluble Particles or liquid droplets settle to the bottom of the vessel or float to the surface of the mixture. Separation funnel separates liquids that do not mix

clay and water; copper filings, sawdust and water; oil and water

Filtration

For separating a mixture of soluble and insoluble substances in a solvent. Solid insoluble particles remain on the filter

water + sand; water + sawdust

Flotation

For separation of mixtures of substances with different wettability values

Mineral processing

Magnet action

For the separation of mixtures containing iron or other metals ( Ni, Co ) that are attracted by a magnet (ferromagnets)

iron + sulfur; iron + sand

To separate homogeneous mixtures, evaporation and distillation (distillation) are used.

_____________________________________________________________

1 If the particle size of the dispersed phase does not exceed the size of molecules or ions (up to 1 nm), such systems are called true solutions.


§ 13. MIXTURES AND THEIR COMPOSITION

In everyday life, we rarely encounterpure substances. As fewexamples of pure substances include sugar, lanepotassium manganate (potassium permanganate), table salt (andthen, if various additives are not added to it, for examplemeasures containing iodine for disease preventionthyroid gland)(fig. 7).Much more often than ussurround mixtures of substances that contain two or more individual compounds, called components of the mixture.


Fig. 7. Sugar (a), potassium permanganate (b), salt (c) - examples
pure substances used in everyday life

Mixtures differ in the size of their constituent particles of substances. Sometimes these particles are quite large: if you mix river sand with sugar, you can easily distinguish individual crystals from each other.

Mixes , in which particles of their constituent substances are visible with the naked eye or under a microscope, are called heterogeneous , orheterogeneous ... Such mixtures include, for example, washing powder, culinary mixtures for baking pancakes or cakes, building mixtures.
There are mixtures, during the formation of which substances are crushed into tiny particles (molecules, ions), which are indistinguishable even under a microscope. No matter how you peer into the air, you will not be able to visually distinguish the molecules of its constituent gases. It is useless to look for "heterogeneity" in solutions of acetic acid or sodium chloride in water. Such mixes are called homogeneous , or homogeneous .
Homogeneous mixtures, like chemicals, can be divided into gaseous, liquid and solid according to their state of aggregation. The most familiar natural gas mixtures you are familiar with are air, and natural and associated petroleum gases are already familiar to you.
Undoubtedly, the most common liquid mixture on Earth, or rather a solution, is the water of the seas and oceans. One liter of seawater contains on average 35 g of salts, the main part of which is sodium chloride. Unlike pure water, sea water has a bitter-salty taste, freezes not at 0 ° C, but at –1.9 ° C.
You constantly come across liquid mixtures in your daily life. Shampoos and drinks, potions and household chemicals are all mixtures of substances. Even
tap water cannot be considered a pure substance: it contains dissolved salts, the smallest insoluble impurities and microorganisms, which are partially eliminated by chlorination or ozonation. However, in this case, it is recommended to boil the water. Special household filters will help make the water drinkable and clean it not only of solid particles, but also of some dissolved impurities. Solid mixtures are also widespread. As we said, rocks are a mixture of several substances. Soil, clay, sand are also mixtures. Solid artificial mixtures include glass, ceramics, alloys. Everyone is familiar with cooking mixes or mixes that form laundry detergents.
As you know from biology, the composition of the air we breathe in and then out is not the same. In the exhaled air, there is less oxygen, but more carbon dioxide and water vapor. But "more" and "less" are relative concepts.
The composition of the mixtures can be expressed quantitatively, i.e. in numbers. The composition of the gas mixture is expressed by the volume fraction of each of its components.
Volume fraction of gas in the mixture called the ratio of the volume of a given gas to the total volume of the mixture, expressed in fractions of a unit or percent.
ϕ (gas) = V ( gas ) NS 100 (%). V ( mixes )
The volume fraction of gas in the mixture is denoted by the letter ϕ (phi). This value shows how much of the total volume of the mixture is occupied by a particular gas. For example, you know that the volume fraction of oxygen in the air is 21%, nitrogen - 78%. The remaining 1% is accounted for by noble gases, carbon dioxide and other air components.
It is obvious that the sum of the volume fractions of all gases in the mixture is equal to 100%.
The composition of liquid and solid mixtures is usually expressed by a quantity called the mass fraction of the component.
Mass fraction of a substance in a mixture called the ratio of the mass of a given substance to the total mass of the mixture, expressed in fractions of a unit or percent.
ω (substances) = m (in-va) NS 100 (%). m ( mixes )

Almost any tablet in a home medicine cabinet is a compressed mixture of one or more medicinal substances and a filler, which can be gypsum, starch, glucose. Building and culinary mixtures, perfume compositions and paints, fertilizers and plastics have a composition that can be expressed in mass fractions of their constituent components.
Substances with impurities are also mixtures. Only in such mixtures it is customary to isolate the main (main) substance, and the extraneous components are called in one word - impurities. The fewer there are, the purer the substance.

In some areas of technology, the use of insufficiently pure substances is unacceptable. In the nuclear power industry, increased requirements are imposed not only on the purity of nuclear fuel, but also on the substances from which the installations themselves are made. A computer microcircuit cannot be made without a particularly pure silicon crystal. The light signal in the fiberglass cable, "stumbling" on foreign impurities, "goes out".
To separate the components of a mixture or to purify the base substance from impurities, various techniques and methods are used. As a rule, substances in a mixture retain their physical properties: boiling point, melting point, solubility in various solvents. Since the properties of one substance are different
from the properties of another, it is possible to separate the mixture into separate components. The transition of substances from one state of aggregation to another is often used.
The separation of mixtures of liquid substances is based on the difference in their boiling points. Such a process, as you know from the example of oil refining, is called rectification, or distillation. You already know that any gases mix in any ratio. Is it possible to separate individual components from a mixture of gases? This is not an easy task. But scientists have come up with a very effective solution. The mixture of gases can be converted to liquid and distilled. For example, air under strong cooling and compression is liquefied and then allowed to boil off one after the other of the individual components, since they have different boiling points. The first of
liquid air evaporates nitrogen, it has the lowest boiling point (-196 ° C). Then argon (–186 ° С) can be removed from the liquid mixture of oxygen and argon.
There remains practically pure oxygen (its boiling point is –183 ° С, Fig. 8), which is quite suitable for gas welding, chemical production, and also for medical purposes.
Distillation is used not only to separate mixtures into individual components, but also to purify substances.
Tap water is clean, transparent, odorless ... But is this substance pure from the point of view of a chemist? Look into the kettle: scale and brownish deposits remain in
as a result of repeated boiling of water in it. What about limescale on the taps? Both natural and tap water is a mixture, a solution of solid and gaseous substances.


Rice. 8. In liquid form
oxygen is colored light
blue

Of course, their content in water is very small, but these impurities can lead not only to the formation of scale, but also to more serious consequences. It is no coincidence that drugs for injections, reagent solutions, and electrolyte for a car battery are prepared only using purified water, called distilled water.
Where did this name come from? The point is that distillation is also called distillation. The essence of distillation is that the mixture is heated to a boil, the resulting vapors of the pure substance are removed, cooled and again converted into a liquid. But it no longer contains contaminants.
In laboratory conditions, distillation is carried out on a special installation (Fig. 9). In a distillation flask equipped with a thermometer, pour the mixture to be separated, for example, water with substances dissolved in it, and heat to boiling. The flask is connected to a descending condenser - a device for condensing vapors of a boiling substance. For this purpose, cold water is supplied to the refrigerator jacket through rubber hoses. Drops of pure substance condensed in the refrigerator fall into the receiving flask.



Rice. 9. Laboratory installation for distillation of liquids:
1 - distillation flask; 2 - thermometer; 3 - refrigerator;
4 - receiver

What to do if you want to isolate from the solution not a liquid, but a solid dissolved in it? For this, the crystallization method is used. It is possible to isolate the solid from the solution by crystallization by evaporation of the solvent. For this purpose special porcelain cups are intended (fig. 10).


Rice. 10. Evaporation
solution in porcelain
a cup

This method is widely used for the extraction of salt from concentrated solutions of salt lakes.
Around wormwood and a smack of cinchona,
And, with strong sodium salt,
Plain colored by rays
An even wave licks a little.
N. Ushakov
In nature, salt lakes are a kind of giant bowls. Due to the evaporation of water on the shores of such lakes, a huge amount of salt crystallizes, which, after purification, falls on our table (Fig. 11).



Rice. 11. Extraction of salt in salt lakes
It is not necessary to evaporate the solvent during crystallization. It is known that when heated, the solubility of most solids in water increases; when cooling a solution saturated with heating, a certain amount of crystals will precipitate.
Laboratory experiment. To 5 g of orange crystals of potassium dichromate add several crystals of potassium permanganate (potassium permanganate) as an impurity. The mixture is dissolved in 8-10 ml of boiling water. When the solution is cooled, the solubility of potassium dichromate decreases sharply, the substance precipitates. Crystals of dichromate purified from potassium permanganate are separated, washed with several milliliters of ice water. If you dissolve the purified substance in water, then by the color of the solution you can determine that it does not contain potassium permanganate, it remained in the original solution.
To isolate insoluble substances from liquids, use the method upholding ... It is based on a different density of substances. If the solid particles are large enough, they quickly settle to the bottom, and the liquid becomes transparent (Fig. 12). It can be carefully drained from the sediment. The smaller the size of the solid particles in the liquid, the longer the mixture will settle.



Rice. 12. Deposition of soil in water

LABORATORNY EXPERIMENT Pour some dish cleaning powder into a glass beaker and pour half a glass of water. A cloudy mixture forms.
The liquid will become transparent only the next day. Why does this mixture sit for so long? By settling, mixtures of two liquids, insoluble in each other, are also separated. If water gets into the lubrication system of the car, the oil will have to be drained. However, after a while, the mixture will separate. The higher density water forms the bottom layer, with the oil layer on top.A mixture of water and oil, water and vegetable oil is similarly defended.


To separate such mixtures, it is convenient to use
special laboratory glassware, called a separating funnel (Fig. 13).



Rice. 13. Separation of two immiscible liquids using a separating funnel
Laboratory experiment. Equal volumes of water and vegetable oil are poured into a conical flask. With vigorous shaking, water and oil break into small droplets, forming a cloudy mixture. It is poured into a separating funnel. After a while, the mixture stratifies into a heavier aqueous layer and oil, which floats up. By opening the tap of the separating funnel, the aqueous layer is separated from the oil.
It is possible to separate particles of a solid insoluble matter from a liquid using filtration. In the laboratory, a special porous paper called filter paper is used for this. The solids do not pass through the pores of the paper and remain on the filter. A liquid with substances dissolved in it (it is called a filtrate) freely seeps through it and becomes completely transparent.
Filtration - a very common process in everyday life, in technology, and in nature. At water treatment plants, water is filtered through a layer of clean sand, which retains silt, impurities of oil products, soil and clay particles. Fuel and oil in a car engine must pass through the filter elements. Cell membranes, the walls of the intestine or stomach are also a kind of biological filters, the pores of which allow some substances to pass through and retain others.
You can filter not only liquid mixtures. More than once you have seen people in gauze bandages, and you yourself, probably, had to use them. Several layers of gauze with cotton padding between them clean the inhaled air from dust particles, smog, pathogenic microbes (Fig. 14). In industry, special devices called respirators are used to protect the respiratory system from dust. The air entering the car engine is also cleaned of dust with fabric or paper filters.


Rice. 14. Physicians and microbiologists protect the respiratory organs with special dressings.


? 1. What is a mixture? What types of mixtures are distinguished according to the state of aggregation of the substances forming them, according to the sign of homogeneity?
2. Is the phrase "air molecules" correct? Why? What are the constant, variable and random constituents of the air? Make an assumption about the relative content of individual components in the air after a thunderstorm, in deep gorges and on mountain peaks, in a forested area and near a large industrial enterprise.

3. How much oxygen is contained in 500 Nm3 of air?
4. In the natural gas of a certain field, the volume fractions of saturated hydrocarbons are equal: methane - 85%, ethane - 10%, propane - 4% and butane - 1%. How much of each gas can be obtained from 125 liters of natural gas (n.o.)?
5. The composition of dry cement mixture for plastering includes 25% cement and 75% sand. How many kilograms of each component do you need to take to prepare 150 kg of such a mixture?
6. Name the methods of separation of mixtures known to you. What is at the heart of each of them? Suggest a way to separate the following mixtures:
a) iron and copper shavings;
b) sand and sawdust;
c) gasoline and water;
d) chalk whitewashing (divided into chalk and water);
e) a solution of ethyl alcohol in water.
7. During a flu epidemic, doctors recommend wearing gauze bandages. For what? How to make such a bandage? How long can you wear it? How to restore the protective properties of the dressing?
8. Prospectors separated golden sand from ordinary sand by stirring up the soil in water and draining the cloudy liquid from the sediment. This is where the expression "wash the gold" came from. What do you think, on what property of golden sand is its separation from the grains of waste rock based?
9. Prepare messages on the topics: "Paints in the hands of an artist" and "Famous perfumers" using Internet resources.


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