What does the composition of pure substances look like? Pure substances and mixtures

Our whole life is literally built on the work of various chemicals. We breathe air that contains many different gases. The output is carbon dioxide, which is then processed by plants. We drink water or milk, which is a mixture of water with other components (fat, mineral salts, protein, and so on).

A common apple is a whole complex that interacts with each other and our body. As soon as something enters our stomach, the substances included in the product absorbed by us begin to interact with gastric juice. Absolutely every object: a person, a vegetable, an animal is a set of particles and substances. The latter are divided into two different types: pure substances and mixtures. IN this material Let's figure out which substances are pure and which of them belong to the category of mixtures. Let's also look at typical examples of pure substances.

Pure substances

So, in chemistry, pure substances are those substances that always consist of only one single type of particle. And this is the first important property. A pure substance is water, for example, which consists exclusively of water molecules (that is, its own). Also, a pure substance always has a constant composition. Thus, each water molecule consists of two hydrogen atoms and one oxygen atom.

The properties of pure substances, unlike mixtures, are constant and change when impurities appear. Only distilled water has a boiling point, and sea water boils at more high temperature. It should be borne in mind that any pure substance is not absolutely pure, since even pure aluminum has an impurity in its composition, although it has a fraction of 0.001%. The question arises: how to find out the mass of a pure substance? The formula for calculation is as follows - m (mass) of pure substance = W (concentration) of pure substance * mixture / 100%.

There is also such a type of pure substances as special (ultrapure, high-purity). Such substances are used in the production of semiconductors in various measuring and computing devices, nuclear energy and in many other professional fields.

Examples of pure substances

We have already found out that a pure substance is something that contains elements of the same type. A good example pure substance can serve as snow. Essentially it is the same water, but unlike the water we encounter every day, this water is much cleaner and does not contain impurities. Diamond is also a pure substance because it contains only carbon without impurities. The same applies to rock crystal. On a daily basis we come across another example of a pure substance - refined sugar, which contains only sucrose.

Mixtures

We have already looked at pure substances and examples of pure substances, now let's move on to another category of substances - mixtures. A mixture is when several substances are mixed with each other. We come across mixtures on a regular basis, even in everyday life. The same tea or soap solution are mixtures that we use daily. Mixtures can be man-made or natural. They are in solid, liquid and gaseous states. As mentioned above, the same tea is a mixture of water, sugar and tea. This is an example of a mixture created by man. Milk is a natural mixture, since it appears without human intervention during the production process and contains many different components.

Mixtures created by man are almost always durable, while natural mixtures begin to disintegrate into individual particles under the influence of heat (milk, for example, turns sour after a few days). Mixtures are also divided into heterogeneous and homogeneous. Heterogeneous mixtures are inhomogeneous, and their components are visible to the naked eye and under a microscope. Such mixtures are called suspensions, which in turn are divided into suspensions (a substance in a solid state and a substance in a liquid state) and emulsions (two substances in a liquid state). Homogeneous mixtures are homogeneous, and their individual components cannot be seen. They are also called solutions (they can be substances in a gaseous, liquid or solid state).

Characteristics of mixtures and pure substances

For ease of perception, the information is presented in table form.

Methods for obtaining pure substances

In nature, many substances exist in They are used in pharmacology and industrial production.

To obtain pure substances they are used various methods divisions. Heterogeneous mixtures are separated by settling and filtration. Homogeneous mixtures are separated by evaporation and distillation. Let's consider each method separately.

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This method is used to separate suspensions such as a mixture of river sand and water. The main principle on which the settling process is based is the difference in the densities of the substances that will be separated. For example, one heavy substance and water. What pure substances are heavier than water? This is sand, for example, which, due to its mass, will begin to settle to the bottom. Different emulsions are separated in the same way. For example, you can separate from water vegetable oil or oil. During the separation process, these substances form a small film on the surface of the water. IN laboratory conditions the same process is carried out using a separatory funnel. This method of separating mixtures also works in nature (without human intervention). For example, the deposition of soot from smoke and the settling of cream in milk.

Filtration

This method is suitable for obtaining pure substances from heterogeneous mixtures, for example, from a mixture of water and table salt. So how does filtration work to separate the particles of a mixture? The bottom line is that substances have different levels of solubility and particle sizes.

The filter is designed so that only particles of the same solubility or size that it can pass through can pass through it. Larger and other inappropriate particles will not be able to pass through the filter and will be screened out. The role of filters can be played not only by specialized devices and solutions within the laboratory, but also by things familiar to everyone, such as cotton wool, coal, baked clay, pressed glass and other porous objects. Filters are used in real life much more often than you might think.

The familiar vacuum cleaner works on this principle, separating large particles of debris and deftly sucking up small ones that are unable to damage the mechanism. When you're sick, you wear a gauze bandage that can help filter out bacteria. Workers whose profession involves the spread of hazardous gases and dust wear protection against poisoning.

Exposure to magnet and water

In this way, a mixture of iron and sulfur powder can be separated. The separation principle is based on the effect of a magnet on iron. The iron particles will be attracted to the magnet while the sulfur will remain in place. The same method can be used to separate other metal parts from a total mass of different materials.

If sulfur powder mixed with iron powder is poured into water, then non-wettable sulfur particles will float to the surface of the water, while heavy iron will immediately fall to the bottom.

Evaporation and crystallization

This method works with such as a solution of salt in water. It works in natural processes and laboratory conditions. For example, when some lakes heat up, water evaporates, and in its place remains salt. From a chemical point of view, this process is based on the fact that the difference between the boiling points of two substances does not allow them to evaporate at the same time. The destroyed water will turn into steam, and the remaining salt will remain in its normal state.

If the substance that needs to be extracted (sugar, for example) melts when heated, then the water is not completely evaporated. The mixture is first heated, and then the resulting modified mixture is infused so that the sugar particles settle at the bottom. Sometimes it costs more difficult task- separation of a substance with a higher boiling point. For example, separating water from salt. In this case, the evaporated substance must be collected, cooled and condensed. This method of separating homogeneous mixtures is called distillation (or simply distillation). Exist special devices which distill water. Such water (distilled) is actively used in pharmacology or in automotive cooling systems. Naturally, people distill alcohol using the same method.

Chromatography

The last separation method is chromatography. It is based on the fact that some substances tend to absorb other components of substances. It works like this. If you take a piece of paper or fabric on which something is written in ink and immerse part of it in water, you will notice the following: the water will begin to be absorbed by the paper or fabric and will creep up, but coloring matter will lag a little. Using this technique, scientist M.S. Tsvet was able to separate chlorophyll (the substance that gives green color to plants) from the green parts of the plant.

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

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

Contaminants lower the freezing point and raise the boiling point of a pure liquid. For example, if you add salt to water, the freezing point of the solution will decrease.

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

Distinguish homogeneous (homogeneous) and heterogeneous (heterogeneous) mixtures. Feature homogeneous mixture is that there is no interface between the components of such a mixture. In this case, they say that this mixture is single-phase(phase part of the system separated from other parts by a visible interface). Within one phase, the physical properties of the components remain constant. TO homogeneous systems These include true solutions (the particle size of the solute is related to the particle size of the solvent and is ≤10 -9 m).

Feature heterogeneous mixture is that we can observe the interface between its components. When a component passes from one phase to another, its properties change dramatically. Heterogeneous mixtures are also called dispersed systems. Dispersed 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 dissolved substance significantly exceeds the size of the solvent particles and is ≥10 -9 m). Mixtures in which the particle size of the substance is 10 -7 -10 -9 m are classified as colloidal systems.

Dispersed systems include:

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

Emulsions, a mixture of 2 or more immiscible liquids (designation - L/L. Dispersed phase and dispersion medium of liquids differing in density and boiling points).

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

1.5. Methods for separating mixtures

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

filtration,

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

separation using a separating funnel,

centrifugation,

evaporation,

crystallization,

distillation (including fractional distillation),

chromatography,

sublimation and others.

Filtration. Filtration is used to separate liquids from small solid particles suspended in it. (Fig. 37), i.e. filtering liquid through finely porous materials – filters, which allow liquid to pass through and retain solid particles on their surface. A liquid that has passed through a filter and is freed from solid impurities in it is called filtrate.

In laboratory practice it is often used smooth and folded paper filters (Fig. 38), made from unglued filter paper.

To filter hot solutions (for example, for the purpose of recrystallization of salts), use a special hot filter funnel(Fig. 39) with electric or water heating).

Often used vacuum filtration. Filtration under vacuum is used to speed up filtration and more completely release the solid phase from the liquid. For this purpose, a vacuum filtration device is assembled. (Fig.40). It consists of Bunsen flask, porcelain Buchner funnel, safety bottle and vacuum pump(usually water jet).

In the case of filtering a suspension of a slightly soluble salt, the crystals of the latter can be washed with distilled water on a Buchner funnel to remove the original solution from their surface. For this purpose they use washer(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 add it to a glass of water, then when it settles it will settle to the bottom of the glass, because the density of sand is greater than water. Then the water can be separated from the sand simply by draining. This method of settling and then draining the filtrate is called decanting.

Centrifugation. To speed up the process of separating 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 liquid and solid substances 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 done using a separating funnel (Fig.44). This way you can separate, for example, a mixture of benzene and water. A layer of benzene (density  = 0.879 g/cm3) is located above a layer of water, which has a higher density ( = 1.0 g/cm3). By opening the separatory funnel tap, you can carefully drain the bottom layer and separate one liquid from another.

Evaporation(Fig.45)– this method involves removing a solvent, for example, water, from a solution by heating it in an evaporating porcelain dish. In this case, the evaporated liquid is removed, and the dissolved substance remains in the evaporation cup.

Crystallization is the process of releasing crystals of a solid substance when a solution is cooled, for example, after it is evaporated. It should be borne in mind that when the solution is slowly cooled, large crystals form. When cooled rapidly (for example, by cooling with running water), small crystals form.

Distillation- a method of purifying a substance based on the evaporation of a liquid when heated, followed by condensation of the resulting vapors. Purification of water from salts (or other substances, such as coloring agents) dissolved in it is called distillation. distillation, and the purified water itself is distilled.

Fractional distillation (distillation)(Fig.46) used to separate mixtures of liquids with different boiling points. A liquid with a lower boiling point boils faster and passes through the fractional column(or reflux condenser). When this liquid reaches the top of the fractionation column, it enters fridge, cooled with water and through allonge going to receiver(flask or test tube).

Fractional distillation can be used to separate, for example, a mixture of ethanol and water. The boiling point of ethanol is 78 0 C, and that of water is 100 0 C. 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 transform from a solid state to a gaseous state, bypassing the liquid state. Next, the vapors of the substance being purified condense, and impurities that cannot sublimate are separated.

>> Pure substances and mixtures. Advocacy. Separating a mixture of three solids

Pure substances and mixtures

The material in this paragraph will help you:

> realize that absolutely pure substances do not exist;
> distinguish between homogeneous and heterogeneous mixtures of substances;
> find out in which mixtures the physical properties of the components are preserved and in which they are not;
> select separation 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 V scientific laboratory, school chemistry lab. Note that absolutely pure substances do not exist.

Each substance contained in a mixture is called a component.

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

Most metal alloys are also homogeneous mixtures. For example, in an alloy of gold and 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).

All mixtures belong to homogeneous mixtures 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.

According to some physical properties homogeneous mixtures differ from their components. Thus, an alloy of tin and lead used for soldering melts at a lower temperature than pure metals. Water boils at a temperature of 100 °C, and an aqueous salt solution boils at a higher temperature. If water is cooled to a temperature of 0 ° C, it will begin to turn into ice. The salt solution remains a 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. Ice melts under the influence of salt; an aqueous solution of salt is formed that does not freeze in mild frost. And sand is needed so that the road is not slippery.

Rice. 28. Heterogeneous 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 to the naked eye or through a microscope (Fig. 28).

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

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

Give your example of a heterogeneous mixture.

In a heterogeneous mixture, the physical properties of the components are preserved. So, iron filings, mixed with copper or aluminum, do not lose their ability to be attracted to a magnet.

Rice. 29. Heterogeneous 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 a temperature of 0C and boils at 100C.

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

What are the components in each named mixture?

The material presented above is summarized in Scheme 3.

Scheme 3. Substances and mixtures

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

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

Scheme 4. Methods for separating mixtures

Explain due to what properties of the components it is possible to separate each heterogeneous mixture indicated in the diagram.

Rice. 30. Worker in a respirator

Let's look at how some use methods separation of mixtures.

The filtration process underlies the operation of a respirator - a device that protects the lungs of a person working in a very dusty room. 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. A vacuum cleaner also has a filter that removes dust from the air.

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

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

An important method for separating homogeneous mixtures of liquids is distillation, or distillation1. This method allows you to clear natural water from impurities. The resulting pure (distilled) water is used in research laboratories, in the production of substances for modern technology, and in medicine for the preparation of medicines.

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

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 using 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 will boil. Non-volatile liquids remain in the vessel.

Rice. 31.Laboratory distillation unit:

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

The separation of various mixtures also occurs in nature. Dust particles settle from the air, and during rain and snow - water droplets and snowflakes. As a result of settling, cloudy water becomes clear. Water is also cleared of insoluble substances when passing through sand. After the water evaporates, the salts that were dissolved in it remain on the banks of the estuaries. Dissolved gases are released from the water flowing from the well.

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

conclusions

Every substance contains impurities. A substance is considered pure if it contains almost no impurities.

Mixtures of substances can be homogeneous or heterogeneous. In a homogeneous mixture, the components cannot be detected by observation, but in a heterogeneous mixture this is possible.

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

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

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

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

31. Name several food products that are solutions.

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

33. Is it possible to turn an aqueous solution of table salt into a heterogeneous mixture? If possible, 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 a mixture of: a) table salt and chalk; b) alcohol and water? What differences in the properties of substances make it possible to use the method you choose?

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 talk about the expected results.

Experimenting at home

Advocacy

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

Write down your observations in your notebook.

Separating 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, use it very carefully.

Describe each stage of the experiment in your notebook.

Popel P. P., Kryklya L. S., Chemistry: Pidruch. for 7th grade zagalnosvit. navch. closing - K.: VC "Academy", 2008. - 136 p.: ill.

Do absolutely pure substances exist? Are substances absolutely pure, containing not a single foreign atom or molecule? Such substances do not exist in nature. Any substance contains a certain amount of impurities. Even well-purified water cannot be considered a pure substance, since oxygen, carbon dioxide, and other gases contained in the air are dissolved in it. All substances in nature are mixtures in one form or another.

If the content of foreign substances in a substance is insignificant, then such substances are conventionally considered pure.

If from tap water significantly remove all substances dissolved in it, then such water can be considered a pure substance. The solubility of air gases in water is extremely low and can be neglected.

Thus, all substances and materials in nature can be divided into individual substances and mixtures of substances.

Even ancient Greek scientists had an idea about mixtures and pure substances. According to these ideas, a pure substance consists of particles of one type, and mixtures consist of different particles. So, a pure substance consists of identical molecules, and mixtures consist of different ones.

In mixtures of substances, the properties of the individual components do not change.

Mixtures, in turn, are divided into homogeneous (homogeneous) and heterogeneous (heterogeneous).

- a mixture in which its components cannot be distinguished visually

– a mixture in which the components of the mixture can be distinguished visually

Homogeneous mixtures can be divided according to their state of aggregation into solid, liquid and gaseous. For example, air is a homogeneous mixture of various gases. Homogeneous mixtures are metal alloys, solutions of salt, sugar in water.

Heterogeneous mixtures can be different. Let's look at two examples of such mixtures. First mixture- a mixture of flour and water. In this mixture, after mixing it, the flour particles are evenly distributed in the water for some time. Such mixtures are called suspensions.

Suspension– a heterogeneous mixture in which solid particles are evenly distributed in a liquid

The second mixture consists of water and sunflower oil. These liquids do not mix with each other. But if the mixture is stirred vigorously, then for some time the oil droplets will be evenly distributed in the water. Such mixtures are called emulsions.

Emulsion– a heterogeneous mixture in which particles of one liquid are evenly distributed in another

Heterogeneous mixtures can also consist of components that are in the same state of aggregation. For example, a mixture of sand and sawdust is heterogeneous, since its components are easy to distinguish visually.

There are many ways in which mixtures of substances can be separated into their individual components.

Methods for separating mixtures

Magnetic action (magnetic separation)

If the mixture contains metal powders with magnetic properties, then these metals can be extracted from the mixture using a magnet. Metals that have magnetic properties include: iron, cobalt, nickel. You just need to sprinkle the mixture on a flat surface and hold it over it with a magnet. The metal particles will be attracted to the magnet.

Settling and decanting

Some mixtures can be separated by settling and then draining the layer of liquid from the settled substance (decantation). This method based on various densities substances. For example, a mixture of sawdust and sand can be separated using this method. The mixture must be poured into a glass of water. Heavy sand particles will settle to the bottom, and light sawdust will float on the surface of the water. By carefully pouring the top layer with sawdust, the mixture will be separated

A mixture of two solids that differ greatly in density can be conveniently separated by passing a stream of water through it. Previously, this was how grains of gold were isolated from crushed gold-bearing rock. Gold-bearing sand was placed on an inclined trench through which a stream of water was released. The flow of water picked up and carried away the waste rock, and heavy grains of gold settled at the bottom of the trench.

The separation of a mixture of liquids that are slightly soluble in each other can be carried out in a separating funnel. For example, a mixture of gasoline and water or sunflower oil and water. Such mixtures quickly separate. Using a separating funnel, the lower layer of liquid can be carefully drained, and upper layer will remain in the funnel.

Filtration

Mixtures containing water-insoluble substances can be separated by filtration. In the laboratory, for filtering, they use a glass funnel into which a filter is inserted - a circle of filter paper folded in four. Filter paper, unlike regular paper, does not contain adhesives, so it easily absorbs and allows liquid to pass through. The pore size in it is such that it allows particles larger in size to be separated from the solution. 0.01 mm.

For example, a mixture of sand and table salt should be poured into a glass of water and stirred well with a glass rod until the salt is completely dissolved, but the sand will not dissolve. Next, the sand must be separated from the salt solution; this can be done by filtration. The filter will be special filter paper.

After filtering the solution, the sand remains on the paper filter, and the salt solution will be collected in a glass or flask.

Filtering makes it easy to purify water or solution from dust particles and other contaminants that have got there, and also separate the sediment from the solution.

In industry, fabrics are often used as filters. For example, in oil mills, crushed sunflower seeds are wrapped in thick cloth and pressed between steel plates.

Vegetable oil passes through the fabric, and a solid mass remains inside - cake

Evaporation

Evaporation method used for isolating a solvent from a solution, concentrating a solution, and crystallizing dissolved substances.

The solution of table salt is poured into a porcelain cup, placed in a tripod ring and heated until the water completely evaporates.

Distillation

A method of separating homogeneous mixtures based on different boiling temperatures of substances is called distillation or distillation.

Suppose you need to separate a mixture of alcohol and water. None of the previously discussed methods is suitable for separating this mixture.

Alcohol and water have different boiling points. So, water boils at +100°C and alcohol at +78°C. When heating such a mixture, the alcohol will boil earlier and begin to evaporate. Alcohol vapor enters the refrigerator - a tube cooled running water. In the refrigerator, alcohol vapor condenses into liquid and is collected in a receiver flask. Water remains in the reaction flask. This way you can separate the alcohol from the water. The distillation installation diagram is shown in the figure.

• There are no absolutely pure substances in nature
• Homogeneous (homogeneous) mixture- a mixture in which all its components are in the same state of aggregation
• Heterogeneous mixture– a mixture in which the components of the mixture are in different states of aggregation
• Suspension– a heterogeneous mixture in which solid particles are evenly distributed in a liquid
• Emulsion– a heterogeneous mixture in which particles of one liquid are evenly distributed in another
• The main methods of separating mixtures: magnetic action, decantation, filtration, evaporation, distillation, extraction

In our article we will look at what pure substances and mixtures are, and methods for separating mixtures. IN Everyday life Each of us uses them. Are pure substances even found in nature? And how to distinguish them from mixtures?

Pure substances and mixtures: methods for separating mixtures

Substances that contain only certain types of particles are called pure. Scientists believe that they practically do not exist in nature, since they all, albeit in insignificant proportions, contain impurities. Absolutely all substances are also soluble in water. Even if immersed in this liquid, for example, silver ring, the ions of this metal will go into solution.

A sign of pure substances is the constancy of composition and physical properties. During their formation, the amount of energy changes. Moreover, it can both increase and decrease. A pure substance can only be separated into its individual components using chemical reaction. For example, only distilled water has the boiling and freezing point typical for this substance, and lacks taste and smell. And its oxygen and hydrogen can only be decomposed by electrolysis.

How do their aggregates differ from pure substances? Chemistry will help us answer this question. Methods for separating mixtures are physical because they do not lead to a change chemical composition substances. Unlike pure substances, mixtures have variable composition and properties, and they can be separated by physical methods.

What is a mixture

A mixture is a collection of individual substances. An example of this is sea water. Unlike distilled, it has a bitter or salty taste, boils at a higher temperature, and freezes at a lower temperature. Methods for separating mixtures of substances are physical. Yes, from sea ​​water Pure salt can be obtained by evaporation and subsequent crystallization.

Types of mixtures

If you add sugar to water, after a while its particles will dissolve and become invisible. As a result, they will be impossible to distinguish with the naked eye. Such mixtures are called homogeneous or homogeneous. Examples of them are also air, gasoline, broth, perfume, sweet and salt water, an alloy of copper and aluminum. As you can see, they can be in different states of aggregation, but liquids are most common. They are also called solutions.

In heterogeneous, or heterogeneous mixtures particles of individual substances can be distinguished. Iron and wood filings, sand and table salt are typical examples. Heterogeneous mixtures are also called suspensions. Among them, suspensions and emulsions are distinguished. The former consists of a liquid and a solid. So, an emulsion is a mixture of water and sand. An emulsion is a combination of two liquids with different densities.

There are heterogeneous mixtures with special names. So, an example of foam is polystyrene foam, and aerosols include fog, smoke, deodorants, air fresheners, and antistatic agents.

Methods for separating mixtures

Of course, many mixtures have more valuable properties than the individual substances included in their composition. But even in everyday life, situations arise when they need to be separated. And in industry, entire productions are based on this process. For example, from oil as a result of its processing, gasoline, gas oil, kerosene, fuel oil, diesel fuel and machine oil, rocket fuel, acetylene and benzene. Agree, it is more profitable to use these products than to mindlessly burn oil.

Now let's see if there is such a thing as chemical methods separation of mixtures. Let's say we need to obtain pure substances from an aqueous solution of salt. To do this, the mixture must be heated. As a result, the water will turn into steam and the salt will crystallize. But in this case there will be no transformation of some substances into others. This means that the basis this process are physical phenomena.

Methods for separating mixtures depend on the state of aggregation, solubility, difference in boiling point, density and composition of its components. Let's look at each of them in more detail using specific examples.

Filtration

This separation method is suitable for mixtures that contain a liquid and an insoluble solid. For example, water and river sand. This mixture must be passed through a filter. As a result, clean water will pass through it freely, but the sand will remain.

Advocacy

Some methods for separating mixtures rely on gravity. In this way, suspensions and emulsions can be separated. If vegetable oil gets into the water, the mixture must first be shaken. Then leave it for a while. As a result, the water will end up at the bottom of the vessel, and the oil will cover it in the form of a film.

In laboratory conditions, they are used for settling. As a result of its operation, the denser liquid is drained into the vessel, and the lighter liquid remains.

Settlement is characterized by a low speed of the process. It takes a certain amount of time for a precipitate to form. In industrial conditions, this method is carried out in special structures called settling tanks.

Action by magnet

If the mixture contains metal, it can be separated using a magnet. For example, separate iron and wood filings. But do all metals have these properties? Not at all. Only mixtures containing ferromagnets are suitable for this method. In addition to iron, these include nickel, cobalt, gadolinium, terbium, dysprosium, holmium, and erbium.

Distillation

This name is translated from Latin language means "dropping". Distillation is a method of separating mixtures based on differences in boiling points of substances. Thus, even at home you can separate alcohol and water. The first substance begins to evaporate already at a temperature of 78 degrees Celsius. Touching a cold surface, alcohol vapor condenses, turning into a liquid state.

In industry, petroleum products, aromatic substances, and pure metals are obtained in this way.

Evaporation and crystallization

These methods of separating mixtures are suitable for liquid solutions. The substances that make up them differ in their boiling point. In this way, salt or sugar crystals can be obtained from the water in which they are dissolved. To do this, the solutions are heated and evaporated to a saturated state. In this case, crystals are deposited. If you need to get clean water, then the solution is brought to a boil, followed by condensation of vapors on a colder surface.

Methods for separating gas mixtures

Gaseous mixtures are separated by laboratory and industrial methods, since this process requires special equipment. Raw materials of natural origin are air, coke oven, generator, associated and natural gas, which is a collection of hydrocarbons.

Physical methods for separating mixtures in a gaseous state are as follows:

• Condensation is the process of gradual cooling of a mixture, during which condensation of its components occurs. In this case, first of all, high-boiling substances, which are collected in separators, pass into a liquid state. In this way, hydrogen is obtained from and ammonia is also separated from the unreacted part of the mixture.
• Sorbing is the absorption of some substances by others. This process has opposite components, between which equilibrium is established during the reaction. For the forward and reverse process you need various conditions. In the first case, this combination high pressure and low temperature. This process is called sorption. Otherwise, the opposite conditions are used: low pressure at high temperature.
• Membrane separation is a method that uses the property of semi-permeable partitions to selectively allow molecules of various substances to pass through.
• Refluxation is the process of condensation of high-boiling parts of mixtures as a result of their cooling. In this case, the temperature of transition to the liquid state of individual components should differ significantly.

Chromatography

The name of this method can be translated as “I write with color.” Imagine adding ink to water. If you dip the end of a filter paper into this mixture, it will begin to be absorbed. In this case, water will be absorbed faster than ink, which is due to the different degrees of sorption of these substances. Chromatography is not only a method for separating mixtures, but also a method for studying such properties of substances as diffusion and solubility.

So, we got acquainted with such concepts as “pure substances” and “mixtures”. The former are elements or compounds consisting only of particles of a certain type. Examples of these are salt, sugar, distilled water. Mixtures are a collection of individual substances. A number of methods are used to separate them. The method of their separation depends on the physical properties of its components. The main ones include settling, evaporation, crystallization, filtration, distillation, magnetic action and chromatography.