Sand with salt is a homogeneous mixture. Pure substances and mixtures

SECTION I. GENERAL CHEMISTRY

6. Mixtures of substances. Solutions

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

Mixtures are a collection of different substances from which one can be added physical body... 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 physical properties mixtures tend to 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 on 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, table salt, 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 dispersed 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 - polydisperse (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:

* 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.

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.

>> Pure substances and mixtures. Defending. Separation of a mixture of three solids

Pure substances and mixtures

The material in the paragraph will help you:

> realize that absolutely pure substances do not exist;
> distinguish between homogeneous and inhomogeneous mixtures of substances;
> find out in which mixtures the physical properties of the components are preserved, and in which they are not;
> choose a split method mixtures of substances depending on its type.

Pure substances and mixtures.

Each substance always contains a certain amount of impurities. A substance in which there are almost no impurities is called pure. With such substances work in a scientific laboratory, a school chemistry room. Note that absolutely pure substances do not exist.

Each substance contained in the mixture is called a component.

Mixtures in which the components cannot be detected by observation are called homogeneous.

Most metal alloys are homogeneous mixtures as well. For example, in the alloy of gold with copper (it is used to make jewelry), there are no red copper particles and yellow gold particles.

Many items for various purposes are made from materials that are homogeneous mixtures of substances (Fig. 27).

TO homogeneous mixtures all mixes belong gases, including air. There are many homogeneous mixtures of liquids.

Rice. 27. Items made from homogeneous mixtures

This mixture is formed by mixing, for example, alcohol and water.

Give your example of a homogeneous mixture.

Homogeneous mixtures are also called solutions, even if they are solid or gaseous.

For some physical properties homogeneous mixtures differ from their components. Thus, the tin-lead alloy used for soldering melts at a lower temperature than pure metals. Water boils at a temperature of 100 ° C, and water solution salt - at a higher temperature. If the water is cooled to 0 ° C, it will begin to turn into ice. The salt solution remains liquid under these conditions (it freezes at temperatures below 0 ° C). This can be seen in winter, when roads and sidewalks covered with ice are sprinkled with a mixture of salt and sand. The ice melts under the influence of salt; an aqueous solution of salt is formed, which does not freeze in low frost. And sand is needed so that the road is not slippery.

Rice. 28. Inhomogeneous mixture of chalk and water

You know that chalk does not dissolve in water. If its powder is poured into a glass of water, then in the resulting mixture you can always find chalk particles that are visible with the naked eye or through a microscope (Fig. 28).

Mixtures in which the components can be detected by observation are called heterogeneous.

Inhomogeneous mixtures (Fig. 29) include most minerals, soil, Construction Materials, living tissues, turbid water, milk and other food products, some medicines and cosmetics.

Give your example of an inhomogeneous mixture.

In an inhomogeneous mixture, the physical properties of the components are retained. So, iron filings mixed with copper or aluminum do not lose the ability to be attracted to the magnet.

Rice. 29. Inhomogeneous mixtures:
a - a mixture of water and sulfur;
b - a mixture of vegetable oil and water;
c - a mixture of air and water

Water mixed with sand, chalk or clay freezes at 0 ° C and boils at 100 ° C.

Some types of heterogeneous mixtures have special names: foam (for example, foam, soap foam), suspension (mixture of water with a small amount of flour), emulsion (milk, well-shaken vegetable oil with water), aerosol (smoke, fog).

What are the components in each named mixture?

The material outlined above is summarized in Scheme 3.

Scheme 3. Substances and mixtures

It is often necessary to separate the mixture in order to obtain its components or to purify the substance from impurities.

There are many methods for separating mixtures. They are chosen taking into account the type of mixture, the state of aggregation and differences in the physical properties of the components (Scheme 4). You know some of the methods from your natural history course.

Scheme 4. Methods for separation of mixtures

Explain what properties of the components make it possible to separate each inhomogeneous mixture shown in the diagram.

Rice. 30. Worker in the respirator

Let's see how some use methods separation of mixtures.

The filtering process is at the heart of a respirator, a device that protects the lungs of a person working in a dusty environment. The respirator has filters that prevent dust from entering the lungs (Fig. 30). The simplest respirator is a bandage made of several layers of gauze. There is also a filter that extracts dust from the air in the vacuum cleaner.

With the help of a magnet, iron ore is enriched in industry - magnetite.

Due to its ability to be attracted to a magnet, the ore is separated from sand, clay, earth, etc. In this way, iron is extracted from industrial and domestic waste.

Distillation, or distillation, is an important method for separating homogeneous mixtures of liquids1. This method allows you to purify natural water from impurities. The resulting pure (distilled) water is used in research laboratories, in the production of substances for modern technology, in medicine for the preparation of medicines.

1 The term comes from the Latin word distillatio - dripping.

In industry, the distillation of oil (a mixture of many substances, mainly liquids) produces gasoline, kerosene, and diesel fuel.

In the laboratory, distillation is carried out on a special installation (Fig. 31). When a mixture of liquids is heated, the substance with the lowest boiling point boils first. Its vapor leaves the vessel, cools, condenses1, and the resulting liquid flows into the receiver. When this substance is no longer in the mixture, the temperature will begin to rise, and over time, another liquid component boils. Non-volatile liquids remain in the vessel.

Rice. 31. Laboratory distillation plant:

a - ordinary;
1 - a mixture of liquids with different boiling points;
2 - thermometer;
3 - water cooler;
4 - receiver
6 - simplified

Separation of various mixtures also occurs in nature. Dust particles settle from the air, and during rain and snow - water droplets, snowflakes. As a result of settling, turbid water becomes transparent. Water is also purified from insoluble substances when passing through the sand. After evaporation of water, salts remain on the banks of estuaries, which were dissolved in it. Dissolved gases are released from the water flowing out of the well.

1 The term comes from the Latin word condensatio - condensation, condensation.

conclusions

Every substance contains impurities. A substance in which there are almost no impurities is considered pure.

Mixtures of substances are homogeneous and heterogeneous. In a homogeneous mixture, the components cannot be detected by observation, but in an inhomogeneous mixture it is possible.

Some of the physical properties of a homogeneous mixture differ from those of the components. In a heterogeneous mixture, the properties of the components are preserved.

Inhomogeneous mixtures of substances are separated by settling, filtration, sometimes by the action of a magnet, and homogeneous mixtures by evaporation and distillation (distillation).

?
29. What types of mixtures are there and how do they differ?

30. Write down the given words and phrases in the corresponding columns of the table below: aluminum, ash, newsprint, mercury, air, iodine tincture, granite, ice from pure water, carbon dioxide, reinforced concrete.

31. Name a few foods that are solutions.

32. What popular drink, depending on the preparation method, is a homogeneous or heterogeneous mixture?

33. Is it possible to turn an aqueous solution of sodium chloride into an inhomogeneous mixture? If so, how to do it?

34. What mixtures can be separated by filtration: a) a mixture of sand and clay; b) a mixture of alcohol and copper filings; c) a mixture of water and gasoline; d) a mixture of water and pieces of plastic? Name the substances that will remain on the filter.

35. How would you divide the mixture: a) table salt and chalk; b) alcohol and water? What are the differences in the properties of substances that make it possible to use the method you have chosen?

36. Consider an experiment to separate a mixture of table salt, sand, iron and sawdust. Make a plan, briefly describe each stage of the experiment, and describe the expected results.

Experimenting at home

Upholding

Pour water into two glasses. Pour 1/2 teaspoon of sand into one glass, and the same amount of starch in the other. Stir both mixtures at the same time. Do particles of substances in water settle at the same speed? If not, which particles are settling faster and why?

Write down your observations in a notebook.

Separation of a mixture of three solids

Mix small amounts of crushed foam, sand and table salt.

What methods can be used to separate this mixture?

Divide the mixture 1. If heating is necessary, do it very carefully.

Describe each stage of the experiment in a notebook.

Popel P.P., Kriklya L.S., Khimia: Pidruch. for 7 cl. zagalnoosvit. navch. prl. - К .: EC "Academy", 2008. - 136 p .: il.

Pure substance contains only one kind of particles. Examples are silver (contains only silver atoms), sulfuric acid, and carbon monoxide (IV) (contain only the molecules of the corresponding substances). All pure substances have constant physical properties, for example, melting point (T m) and boiling point (T bale).

A substance is not pure if it contains any amount of one or more other substances - impurities.

Contamination lowers the freezing point and increases the boiling point of a clean liquid. For example, if you add salt to the water, the freezing point of the solution will drop.

Mixes consist of two or more substances. Soil, sea water, air are all examples of different mixtures. Many mixtures can be divided into constituent parts - Components- based on the difference in their physical properties.

Distinguish homogeneous (homogeneous) and heterogeneous (inhomogeneous) mixtures. Feature homogeneous mixture is that no interface is observed between the components of such a mixture. In this case, the mixture is said to be single phase(phase part of the system separated from other parts by a visible interface). Within one phase, the physical properties of the components are kept constant. TO homogeneous systems include true solutions (the particle size of the solute correlates with the size of the solvent particles and is ≤10 -9 m).

Feature heterogeneous mixture is that we can observe the interface between its components. During the transition from one phase of a component to another, its properties change dramatically. Heterogeneous mixtures are otherwise called dispersed systems. Disperse systems consist of a dispersion medium (solvent, continuous phase) and a dispersed phase (solute or discontinuous phase)

TO heterogeneous mixtures include dispersed systems (the particle size of the solute is significantly greater than the size of the solvent particles and is ≥10 -9 m). Mixtures in which the particle size of a substance is 10 -7 -10 -9 m are referred to colloidal systems.

Dispersed systems include:

Suspensions, a mixture consisting of a solid and a liquid phase (designation S / L; T - dispersed phase, L - dispersion medium)

Emulsions, a mixture of 2 or more immiscible liquids (designation - Zh / Zh. Disperse phase and dispersion medium of a liquid differing in density and boiling point).

These systems will be discussed in more detail in the topic solutions and dispersed systems.

1.5. Separation methods for mixtures

Traditional methods that are used in laboratory practice to separate mixtures into individual components are:

filtration,

decantation ( in chemical laboratory practice and chemical technology mechanical separation of the solid phase of the dispersed system (suspension) from the liquid by draining the solution from the sediment),

separation with a separating funnel,

centrifugation,

evaporation,

crystallization,

distillation (including fractional distillation),

chromatography,

sublimation and others.

Filtration. Filtration is used to separate liquids from fine solid particles suspended in it. (fig. 37), i.e. filtering liquid through finely porous materials - filters that allow liquid to pass through and retain solid particles on their surface. The liquid that has passed through the filter and is freed from the solid impurities contained in it is called filtrate.

In laboratory practice, they are often used smooth and folded paper filters (fig. 38) made of non-glued filter paper.

For filtering hot solutions (for example, for the purpose of recrystallizing salts), use a special hot filter funnel(fig. 39) with electric or water heating).

Often used vacuum filtration... Vacuum filtration is used to accelerate filtration and more complete removal of the solid phase from the liquid. For this purpose, a vacuum filtration device is assembled. (fig. 40)... It consists of Bunsen flasks, porcelain Buchner funnel, safety flask and vacuum pump(usually water jet).

In the case of filtration of a suspension of a poorly soluble salt, the crystals of the latter can be washed with distilled water on a Buchner funnel to remove the initial solution from their surface. For this purpose use wash bottle(fig. 41).

Decantation... Liquids can be separated from insoluble solids by decantation (fig. 42)... This method can be used if the solid has a higher density than the liquid. For example, if river sand is added to a glass of water, then during settling it will settle to the bottom of the glass, because the density of the sand is greater than that of water. Then the water can be separated from the sand by simply draining. This method of settling and then draining the filtrate is called decantation.

Centrifugation. To accelerate the separation of very small particles that form stable suspensions or emulsions in a liquid, the centrifugation method is used. This method can be used to separate mixtures of liquids and solids that differ in density. The division is carried out in manual or electric centrifuges (fig. 43).

Separation of two immiscible liquids, having different densities and not forming stable emulsions, can be carried out using a separating funnel (fig. 44)... In this way, for example, a mixture of benzene and water can be separated. A layer of benzene (density  = 0.879 g / cm 3) is located above a layer of water, which has a high density ( = 1.0 g / cm 3). By opening the tap of the separating funnel, you can carefully drain the bottom layer and separate one liquid from the other.

Evaporation(fig. 45)- this method involves removing a solvent, for example water, from a solution while heating it in an evaporating porcelain cup. In this case, the evaporated liquid is removed, and the solute remains in the evaporation dish.

Crystallization Is the process of separating crystals of a solid when cooling a solution, for example, after evaporating it. It should be borne in mind that when the solution is slowly cooled, large crystals are formed. On rapid cooling (for example, when cooling with running water), small crystals are formed.

Distillation- a method of cleaning a substance based on the evaporation of a liquid upon heating, followed by condensation of the resulting vapors. Purification of water from salts dissolved in it (or other substances, for example, coloring) by distillation is called distillation, and the purified water itself is distilled.

Fractional distillation (distillation)(fig. 46) used to separate mixtures of liquids with different boiling points. Liquid with a lower boiling point boils faster and passes through earlier fractional column(or dephlegmator). When this liquid reaches the top of the fractional column, it enters refrigerator, is cooled by water and through allonge going to receiver(flask or test tube).

Fractional distillation can separate, for example, a mixture of ethanol and water. The boiling point of ethanol is 78 0 С, and the boiling point of water is 100 0 С. Ethanol evaporates more easily and is the first to enter the receiver through the refrigerator.

Sublimation - the method is used to purify substances that, when heated, can pass from solid state into gaseous, bypassing liquid state... Further, the vapors of the purified substance are condensed, and the impurities that are not capable of sublimation are separated.

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 organic matter, 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 substances. 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 - isolation 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.

Test by topic

Assessment of the report

Average rating: 4.5. Total ratings received: 327.

§ 13. MIXTURES AND THEIR COMPOSITION

IN Everyday life we rarely come acrosspure 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 chemical substances, on aggregate state can be divided into gaseous, liquid and solid. 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. In one liter sea ​​water on average, it contains 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 from solid particles, but also from some dissolved impurities. Solid mixtures are also widespread. As we have already 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.
Obviously, 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 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, "bumping" into 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 into a liquid and distilled. For example, air under strong cooling and compression is liquefied and then allowed to boil off one by one the individual components, since they have different temperatures boiling. 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 ° C, 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, clear, 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.
Under 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 the 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, rubber hoses are fed into the refrigerator jacket cold water... 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
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 being purified, 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 a solution saturated with heating is cooled, 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 stratify. 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 that 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 solid particles 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 laid 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 by the state of aggregation of the substances forming them, by the sign of homogeneity?
2. Is the phrase "air molecules" correct? Why? Name the constant, variable and random constituents of 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 forest park 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 mixture separation 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) solution 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 the artist" and "Famous perfumers" using the resources of the Internet.