number 2
Given: solutions of NaOH, CaCl2, AlCl3, AgNo3, H2C2O4.
Determine in which of the two numbered tubes there are solutions: a) CaCl2, b) AlCl3. Prove their composition
number 5
Given: rusty nail, HCL or H2SO4 solution.
How can I clean an iron nail from rust chemically.
number 7
Given: solutions of FeCl3, NaOH, spirit lamp. Get iron oxide (3) from FeCl3
write the answer as you like, the main thing is to decide

Signs of Chemical Reactions 1. Interaction of iron filings and sulfur powder. - Starting materials:? -Products:? -Signs of reactions:? 2. Interaction

marble with hydrochloric acid. - Starting materials:? -Products:? -Signs of reactions:? 3. Decomposition of hydrogen peroxide. - Starting materials:? -Products:? -Signs of reactions:? 4. Burning wood. - Starting materials:? -Products:? -Signs of reactions:?

Iron filings with yellow powder were calcined, the resulting alloy was treated with a solution of 10% sulfuric acid. escaping gas

passed through chlorine water, precipitated. Determine the formula for the precipitate.

100 points guys! Oh please!!!

1. Are judgments about pure substances and mixtures correct? A. The mixture of sulfur and iron powders is an inhomogeneous mixture. B. Baking soda is a pure substance. 1) only A is true 2) only B is true 3) both judgments are correct 4) both judgments are wrong
2. Are the following judgments about the methods of separating mixtures and the importance of hygiene products correct?
A. A mixture of sulfur and sawdust can be separated by dissolving in water. B. Toothpaste containing fluoride ions helps to strengthen tooth enamel. 1) only A is true 2) only B is true 3) both judgments are correct 4) both judgments are wrong
3. Are the following judgments about pure substances and mixtures correct? A. Table vinegar is a pure substance. B. The iodine solution used to treat wounds is a mixture of substances. 1) only A is true 2) only B is true 3) both judgments are correct 4) both judgments are wrong
4. Are the following judgments about the methods of separation of mixtures and the composition of disinfectants correct? A. An admixture of river sand can be separated from sugar by dissolving and then filtering the mixture. B. Ethyl alcohol is used to prepare an iodine solution. 1) only A is true 2) only B is true 3) both judgments are correct 4) both judgments are incorrect
5. Are the following judgments about pure substances and mixtures correct? A. Sea water is a mixture of substances. B. Ozone is a pure substance. 1) only A is true 2) only B is true 3) both judgments are correct 4) both judgments are wrong
6. Are the following judgments about pure substances and mixtures correct? A. Rainwater is a pure substance. B. Kefir is a mixture of substances. 1) only A is true 2) only B is true 3) both judgments are correct 4) both judgments are wrong
7. Are the following judgments about the types of mixtures and the ability of substances to dissolve in water correct? A. When chalk is dissolved in water, a homogeneous mixture is formed. B. Grease stains on clothing can be removed with tap water. 1) only A is true 2) only B is true 3) both judgments are correct 4) both judgments are wrong
8. Are the following judgments about pure substances and mixtures correct? A. Granite is a pure substance. B. A mixture of vegetable oil and water is a homogeneous mixture. 1) only A is true 2) only B is true 3) both judgments are correct 4) both judgments are wrong
9. Are the following judgments about pure substances and mixtures correct? A. Air is a mixture of substances. B. Oil is a pure substance. 1) only A is true 2) only B is true 3) both judgments are correct 4) both judgments are wrong
10. Are the following judgments about the methods of separation of mixtures and chemical pollution of the environment correct? A. It is possible to purify sugar from the admixture of river sand by performing successive operations: dissolution, filtration, evaporation. B. Plastic bags are easily destroyed by atmospheric agents and do not pose a threat to the environment. 1) only A is true 2) only B is true 3) both judgments are correct 4) both judgments are wrong
11. Are the judgments about the ways of separating mixtures correct? A. A mixture of iron and copper filings can be separated by the action of a magnet. B. A mixture of water and sugar can be separated by filtration. 1) only A is true 2) only B is true 3) both judgments are correct 4) both judgments are wrong

Chapter 3

§ 16. Separation of mixtures

Methods for separating mixtures by particle size,

density, magnetic properties

In laboratory practice and in everyday life, it is very often necessary to isolate individual components from a mixture of substances. If your goal is to obtain a pure form of each substance, this operation is called separation of the mixture. If it is required to separate the desired substance from impurities, the process is more commonly referred to as purification of the substance.

In any case, heterogeneous mixtures are easier to separate than homogeneous ones. For this, even in the days of alchemy, many methods were invented. Some of them are based on the difference in particle sizes of the mixture, others on the special properties of their constituent substances.

Imagine that granulated sugar got into the flour. What method of separating this mixture would you suggest? Perhaps the simplest is screening . With the help of a sieve, you can easily separate small particles of flour from relatively large sugar crystals. In agriculture, screening is used to separate plant seeds from foreign debris. In construction, gravel is separated from sand in this way.

With the help of a magnet, iron filings can be easily separated from sulfur powder (Fig. 63). This division is based on a special property of iron - the ability to be attracted to a magnet.

Rice. 63. Separation of iron filings from sulfur powder with a magnet

And if sulfur is mixed not with iron filings, but, for example, with sand, which is completely indifferent to a magnet? And in this case, you can find a way to separate the mixture.

Demo Experiment. A mixture of finely ground sulfur and sand is poured into a glass of water. The sand settles to the bottom, while the sulfur stays on the surface. Sulfur powder can be easily separated with a spoon.

This division is also based on a special property of the substance, this time sulfur. Sulfur powder is poorly wetted by water and is retained on its surface, despite the fact that sulfur is heavier than water and must sink in it. Some ores containing sulfur also have the same property, due to which they are separated from the waste rock, that is, they are enriched. To do this, the ore is crushed, loaded into a huge tank of water and air is supplied from below. Ore particles stick to air bubbles and float to the surface in the form of foam. Heavy particles of sand and other impurities remain at the bottom.

A similar phenomenon can be observed at home (tasks 8 and 9 to this paragraph).

Settling is used to isolate insoluble substances from liquids. If the solid particles are large enough, they quickly settle to the bottom, and the liquid becomes transparent. It can be carefully drained from the sediment, and this simple operation also has its own name - decantation .

The smaller the solids in the liquid, the longer the mixture will settle.

It is possible to separate from each other and two liquids that do not mix with each other.

Demonstration experiment. Equal volumes of water and vegetable oil are poured into a flat-bottomed flask. With vigorous shaking, water and oil are broken into small droplets and mixed, a cloudy mixture is formed. Very quickly this mixture separates again into a heavier water layer and oil floating to the top. It is quite difficult to completely separate the top layer. But with the help of a separating funnel, the separation of such a mixture is not difficult.

Rice. 64. Separation of two immiscible liquids

using a separating funnel

If the particles of an inhomogeneous mixture are very small, it cannot be separated either by settling or filtering. Examples of such mixtures are milk and water-dissolved toothpaste. Such mixtures are separated by centrifugation. Mixtures containing such a liquid are placed in test tubes and rotated at great speed in special apparatuses - centrifuges (Fig. 65). As a result of centrifugation, heavier particles are "pressed" to the bottom of the vessel, and the lungs are on top.

Rice. 65. Centrifuge with tubes

Milk is the smallest particles of fat distributed in an aqueous solution of other substances - sugars, proteins (Fig. 66). To separate such a mixture, a special centrifuge called a separator is used. When separating milk, fats are on the surface, they are easy to separate. What remains is water with dissolved substances in it - this is skimmed milk.

Rice. 66. Milk is the smallest droplets of fat in an aqueous solution

Filtration

You can clear a cloudy liquid or separate an insoluble precipitate using filtering . In the laboratory, special porous paper is used for this. It's called the filter. Solid particles do not pass through the pores of the paper and remain on the filter (Fig. 67). Water with dissolved substances freely seeps through the filter. The resulting solution is completely transparent. He is called filtrate .

Rice. 67. Filtering liquid with sediment through a paper filter

Filtration is a very common process in everyday life, in technology, and in nature. Many people filter the tea leaves through a strainer. Air from dust that has entered the vacuum cleaner is filtered through a paper or fabric filter. Water for drinking and cooking is recommended to be passed through special household filters. In addition to retaining solid particles, coal powder absorbs some of the harmful substances dissolved in it from the water.

At treatment facilities, polluted water is also filtered through a layer of clean sand, on which silt, oil impurities, soil and clay particles are retained. Fuel and oil in a car engine must pass through the filter elements. Cell membranes, walls of the intestines or stomach are also a kind of biological filters, the pores of which let some substances through, while others delay.

Not only liquid mixtures can be filtered. More than once you have seen people in gauze bandages, and you yourself probably had to use it (Fig. 68). Several layers of gauze with cotton wool laid between them purify the inhaled air from dust particles, smog, and pathogenic microbes that “get stuck” in the intricacies of fibers. In industry, special filter devices called respirators are used to protect against dust. The air entering the car engine is also cleaned of dust with fabric or paper filters.

Rice. 68. A cotton-gauze bandage protects a person from pathogenic microbes,

Adsorption

In technology, the problem often arises of cleaning gases, such as air, from unwanted or harmful components. Many substances have one interesting property - they can "cling" to the surface of porous substances, like iron to a magnet.

Adsorption is the ability of certain solids to absorb gaseous or dissolved substances on their surface.

Substances capable of adsorption are called adsorbents.

Rice. 69. Activated charcoal under magnification

Adsorbents are solids in which there are many internal channels, voids, pores, i.e. they have a very large total absorbing surface. This structure of the adsorbent can be seen with the help of magnifying instruments (Fig. 69). Adsorbents are activated carbon (you probably have it in your home first aid kit), silica gel (you can find a small bag of white peas in the box with new shoes - this is silica gel), filter paper. Different substances "attach" to the surface of adsorbents differently: some are held on the surface firmly, others are weaker. The action of a filtering gas mask is based on the property of activated carbon to absorb harmful gases.

Rice. 70. Appearance filtering gas mask

Activated carbon is able to absorb not only gaseous, but also substances dissolved in liquids. In case of poisoning, it is taken so that toxic substances are adsorbed on it.

student experiment. Use a pipette to drop 3-5 drops of cologne into the flask. Shake the flask, smell its contents. Then add a few corn sticks to it, cork and shake. After 1–2 minutes, open the stopper and smell the contents of the flask. What can be said about the intensity of the smell of cologne in the first and second cases? Explain the result.

Activated charcoal is used in sugar refineries to decolorize syrups so that sugar crystals turn out to be a beautiful, pure white color.

On what properties of substances is the separation of mixtures based? Give examples of separation of mixtures by sieving that you know from everyday life. To separate gold from waste rock, “gold is washed”. What properties of gold and rock particles are used in this case? What is settling and decanting? Give examples. What is filtration and filtrate? What substances and materials can be used to make a filter? Give examples of air filtration methods that are used in everyday life and at work. What is centrifugation? What is this process based on? Where is it applied? Mix a tablespoon of powdered milk and river sand. Pour the mixture into a glass of water. In order for the sand to completely "drown", tap on the outer wall of the glass with a spoon. Which of the components of the mixture remained on the surface of the water? Why? Pour a little dishwashing powder into a glass beaker and pour half a glass of water. A cloudy mixture is formed. The liquid will become transparent only the next day. Why does the mixture stand for so long? Crush five activated charcoal tablets and mix them with a quarter cup of a colored soda, such as Pepsi-Cola. Stir the mixture vigorously with a spoon. What is observed? Compare the color of the settled solution with the color of the original drink.

In laboratory practice, in industry and in everyday life, it is very often necessary to obtain individual components from mixtures of substances. If your goal is to obtain a pure form of each substance, this operation is called separation of the mixture. If it is required to separate the desired substance from impurities, the process is more commonly referred to as purification of the substance.

In any case, heterogeneous mixtures are easier to separate than homogeneous ones. For this, even in the days of alchemy, many methods were invented. Some of them are based on the difference in particle sizes of the mixture, others - on some properties of their constituent substances.

Imagine that granulated sugar got into the flour. What method of separating this mixture would you suggest? Perhaps the simplest is sifting. With the help of a sieve, you can easily separate small particles of flour from relatively large sugar crystals. In agriculture, screening is used to separate plant seeds from foreign debris. In construction, gravel is separated from sand in this way.

With the help of a magnet, iron filings can be easily separated from sulfur powder (Fig. 79). Such a division is based on a special long-known property of iron - the ability to be attracted to a magnet.

Rice. 79.
Separation of iron filings from sulfur powder using a magnet

And if sulfur is mixed not with iron filings, but, for example, with sand, which is completely indifferent to a magnet? And in this case, you can find a way to separate the mixture.

Demo Experience

A mixture of finely ground sulfur and sand is poured into a glass of water. The sand settles to the bottom, while the sulfur stays on the surface. Sulfur powder can be easily collected from the surface with a spoon.

This division is based on a special property of the substance, this time sulfur. Sulfur powder is poorly wetted by water and is retained on its surface, despite the fact that sulfur is heavier than water and must sink in it. Some ores containing sulfur have the same property, due to which they are separated from the waste rock. This process is called rock beneficiation. To do this, the ore is crushed, loaded into a huge tank of water and air is supplied from below. Ore particles stick to air bubbles and float to the surface in the form of foam. Heavy particles of sand and other impurities remain at the bottom.

A similar phenomenon can be observed at home (see tasks 8 and 9 to this paragraph).

Settling is used to isolate insoluble substances from liquids. If the solid particles are large enough, they quickly settle to the bottom, and the liquid becomes transparent. It can be carefully drained from the sediment, and this simple operation is called decantation.

The smaller the solids in the liquid, the longer the mixture will settle.

It is possible to separate from each other and two liquids that do not mix with each other.

Demo Experience

Equal volumes of water and vegetable oil are poured into a flat-bottomed flask. With vigorous shaking, water and oil are broken into small droplets and mixed, a cloudy mixture is formed. Very quickly this mixture separates again into a heavier water layer and oil floating to the top. It is quite difficult to completely separate the top layer. But with the help of a separating funnel, the separation of such a mixture is not difficult (Fig. 80).

Rice. 80.
Separation of two immiscible liquids using a separating funnel

If the particles of an inhomogeneous mixture are very small, it cannot be separated either by settling or filtering. Examples of such mixtures are milk or water-dissolved toothpaste. Such mixtures are separated by centrifugation. They are placed in special vessels (for example, test tubes), which are rotated at great speed in special apparatuses - centrifuges (Fig. 81). As a result, the heavier particles are "pressed" to the bottom of the vessel, and the lighter particles are on top.

Rice. 81.
Centrifuge with test tubes

Milk is the smallest particles of fat, as well as other substances - sugars, proteins, distributed in an aqueous solution (Fig. 82). To separate such a mixture, a special centrifuge called a separator is used. When separating milk, fats are on the surface, they are easy to separate. What remains is water with dissolved substances in it - this is skimmed milk.

Rice. 82.
Milk is tiny droplets of fat in an aqueous solution.

2. Filtering

Turbid liquid can be cleared or an insoluble precipitate can be separated by filtration. In the laboratory, special porous paper is used for this. It's called the filter. Solid particles do not pass through the pores of the paper and settle on it (Fig. 83). Water with the substances dissolved in it freely seeps through the filter paper. The resulting solution is completely transparent. It is called the filtrate.

Rice. 83.
Filtration of liquid with sediment through a paper filter

Filtration is a common process in everyday life, in technology, and in nature. Many people filter the tea leaves through a strainer. Air from dust that has entered the vacuum cleaner is filtered through a paper or fabric filter. Water for drinking and cooking is recommended to be passed through special household filters. In addition to the fact that they retain solid particles, the carbon powder of a household filter “absorbs” some harmful substances dissolved in it from the water.

At treatment facilities, polluted water is also filtered through a layer of clean sand, on which silt, oil product impurities, soil and clay particles linger.

Fuel and oil in a car engine must pass through the filter elements.

Not only liquid mixtures can be filtered. More than once you have seen people in gauze bandages, and you yourself probably had to use them (Fig. 84).

Rice. 84.
Cotton-gauze bandage protects a person from pathogenic microbes

Several layers of gauze with cotton wool laid between them purify the inhaled air from dust particles, smog, and pathogenic microbes. In industry, special filter devices called respirators are used to protect against dust. The air entering the car engine is also cleaned of dust with fabric or paper filters.

3. Adsorption

In technology, the problem often arises of cleaning gases, such as air, from unwanted or harmful components.

Adsorbents are basically substances that have a very large total absorbent surface. Such a structure of the adsorbent can be examined with the help of magnifying instruments (Fig. 85).

Rice. 85.
Adsorbent - activated carbon under a microscope

A similar substance is activated charcoal (you probably have it in your home first aid kit), silica gel (you can find a small bag of white peas in the box with new shoes, this is silica gel), filter paper. Different substances "attach" to the surface of adsorbents differently: some are held firmly on the surface, others are weaker. The action of a filtering gas mask is based on the property of activated carbon to absorb harmful gases (Fig. 86).

Rice. 86.
The action of a filtering gas mask is based on the property of activated carbon to absorb harmful gases.

Activated carbon is able to absorb not only gaseous, but also substances dissolved in liquids. In medical practice, it is used for poisoning to adsorb harmful substances.

Activated charcoal is used in sugar factories to decolorize syrups so that the sugar crystals turn out to be a beautiful white color.

Laboratory experience

Use a pipette to drop 3-5 drops of cologne into the flask. Shake the vessel, smell its contents. Then add a few corn sticks to the flask. Close it with a cork, shake it. After 1-2 minutes, open the cork and smell the contents of the flask. What can be said about the intensity of the smell of cologne in the first and second cases? Explain the result.

Questions and tasks

1. On what properties of substances is the separation of mixtures based?
2. Give examples of separation of mixtures by sieving that you know from everyday life.
3. To separate gold from waste rock, gold is “washed”. What properties of gold and rock particles are used in this case?
4. What is settling and decanting? Give examples.
5. What is filtration and filtrate? What substances and materials can be used to make a filter?
6. Give examples of air filtration methods that are used in everyday life and at work.
7. What is centrifugation? What is this process based on? Where is it applied?
8. Mix a tablespoon of powdered milk and river sand. Pour the mixture into a glass of water, but do not stir. In order for the sand to completely settle to the bottom, gently tap the outer wall of the glass with a spoon. Which of the components of the mixture remained on the surface of the water? Why?
9. Pour a little dishwashing powder into a glass beaker and pour half a glass of water. A cloudy mixture is formed. The liquid will become transparent only the next day. Why does the mixture stand for so long?
10. Crush five activated charcoal tablets and mix them with a quarter cup of colored sparkling water, such as Pepsi Cola. Stir the mixture vigorously with a spoon. What is observed? Compare the color of the settled solution with the color of the original drink.

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

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

Some physical properties of a homogeneous mixture differ from those of the components.

In a heterogeneous mixture, the properties of the components are preserved.

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

Pure substances and mixtures

We live among chemicals. We inhale air, and this is a mixture of gases (nitrogen, oxygen and others), we exhale carbon dioxide. We wash ourselves with water - this is another substance, the most common on Earth. We drink milk - a mixture of water with the smallest droplets of milk fat, and not only: there is also casein milk protein, mineral salts, vitamins and even sugar, but not the one with which they drink tea, but a special milk - lactose. We eat apples, which consist of a whole range of chemicals - sugar, malic acid, vitamins... apple, but also any other food. We not only live among chemicals, but we ourselves are made of them. Every person - his skin, muscles, blood, teeth, bones, hair are built of chemicals, like a house of bricks. Nitrogen, oxygen, sugar, vitamins are substances of natural, natural origin. Glass, rubber, steel are also substances, more precisely, materials (mixtures of substances). Both glass and rubber are of artificial origin; they did not exist in nature. Completely pure substances are not found in nature or are very rare.

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

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

Almost all natural substances, food products (except salt, sugar, and some others), many medicinal and cosmetic products, household chemicals, and building materials are mixtures.

Comparative characteristics of a mixture and a pure substance

Each substance contained in a mixture is called a component.

Classification of mixtures

There are homogeneous and heterogeneous mixtures.

Homogeneous mixtures (homogeneous)

Add a small portion of sugar to a glass of water and stir until all the sugar is dissolved. The liquid will taste sweet. Thus, the sugar did not disappear, but remained in the mixture. Ho, we will not see its crystals, even when examining a drop of liquid in a powerful microscope. The prepared mixture of sugar and water is homogeneous; the smallest particles of these substances are evenly mixed in it.

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

Most metal alloys are also homogeneous mixtures. For example, an alloy of gold and copper (used to make jewelry) lacks red copper particles and yellow gold particles.

From materials that are homogeneous mixtures of substances, many items for various purposes are made.

All mixtures of gases, including air, belong to homogeneous mixtures. There are many homogeneous mixtures of liquids.

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

Let us give examples of solutions (air in a flask, table salt + water, small change: aluminum + copper or nickel + copper).

Heterogeneous mixtures (heterogeneous)

You know that chalk does not dissolve in water. If its powder is poured into a glass of water, then chalk particles can always be found in the resulting mixture, which are visible to the naked eye or through a microscope.

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

Heterogeneous mixtures include most minerals, soil, building materials, living tissues, turbid water, milk and other foods, some medicines and cosmetics.

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.

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

Methods for separating mixtures

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

There are many methods for separating mixtures. They are chosen taking into account the type of mixture, state of aggregation and differences in the physical properties of the components.

Methods for separating mixtures

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

Consider methods for separating heterogeneous and homogeneous mixtures.

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

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

If you hang a strip of filter paper over a vessel with red ink, immersing only the end of the strip in them. The solution is absorbed by the paper and rises along it. But the border of the rise of the paint lags behind the border of the rise of the water. This is how the separation of two substances occurs: water and the coloring matter in the ink.

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

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