In our article, we will consider what pure substances and mixtures are, methods for separating mixtures. IN Everyday life each of us uses them. Do pure substances occur in nature at all? And how to distinguish them from mixtures?
Pure substances and mixtures: ways to separate mixtures
Pure substances are substances that contain only particles a certain kind. Scientists believe that they practically do not exist in nature, since all of them, albeit in negligible 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. In the process of their formation, a change in the amount of energy occurs. Moreover, it can both increase and decrease. The only way to separate a pure substance into its individual components is to chemical reaction. For example, only distilled water has a typical boiling and freezing point for this substance, the absence of taste and smell. And its oxygen and hydrogen can be decomposed only by electrolysis.
And how do they differ from pure substances in their totality? Chemistry will help us answer this question. Methods for separating mixtures are physical, since they do not lead to a change in the chemical composition of 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 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. So, pure salt can be obtained from sea water 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 cannot be distinguished with the naked eye. Such mixtures are called homogeneous or homogeneous. Air, gasoline, broth, perfume, sweet and salt water, and an alloy of copper and aluminum are also examples of these. 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 contains liquid and 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 foam, and aerosols include fog, smoke, deodorants, air fresheners, antistatic agents.
Methods for separating mixtures
Of course, many mixtures have more valuable properties than individual individual substances that make up their composition. But even in everyday life there are situations when they need to be separated. And in industry, entire industries are based on this process. For example, from oil as a result of its processing, gasoline, gas oil, kerosene, fuel oil, solar oil and machine oil, rocket fuel, acetylene and benzene are obtained. Agree, it is more profitable to use these products than mindlessly burning oil.
Now let's see if there is such a thing as chemical methods separation of mixtures. Suppose 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 at the same time, there will be no transformation of one substance into another. This means that the basis of this process are physical phenomena.
Methods for separating mixtures depend on state of aggregation, ability to solubility, difference in boiling point, density and composition of its components. Let's consider each of them in more detail with specific examples.
Filtration
This separation method is suitable for mixtures containing 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 freely pass through it, and the sand will remain.
settling
Some methods of separating mixtures are based on the action of gravity. In this way, suspensions and emulsions can be decomposed. If it gets into the water vegetable oil, such a mixture must first be shaken. Then leave it for a while. As a result, the water will be 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 work, a denser liquid is drained into a vessel, and a light one remains.
Settling is characterized by a low speed of the process. It takes a certain amount of time for the precipitate to form. IN industrial environment this method is carried out in special structures called sedimentation tanks.
Magnet action
If the mixture contains metal, then it can be separated using a magnet. For example, separate iron and wood filings. But do all metals have these properties? Not at all. For this method, only mixtures containing ferromagnets are suitable. In addition to iron, these include nickel, cobalt, gadolinium, terbium, dysprosium, holmium, and erbium.
Distillation
This name is translated from Latin means "drip". Distillation is a method of separating mixtures based on the difference in boiling points of substances. Thus, even at home, alcohol and water can be separated. The first substance begins to evaporate already at a temperature of 78 degrees Celsius. Touching the cold surface, the alcohol vapor condenses, turning into a liquid state.
In industry, oil refining products, aromatic substances, pure metals.
Evaporation and crystallization
These separation methods are suitable for liquid solutions. The substances that make up their composition differ in their boiling point. Thus, it is possible to obtain crystals of salt or sugar from the water in which they are dissolved. To do this, the solutions are heated and evaporated to a saturated state. In this case, the crystals are deposited. If it is necessary to obtain pure water, then the solution is brought to a boil, followed by condensation of the vapors on a colder surface.
Methods for separating gas mixtures
Gaseous mixtures are separated by laboratory and industrial ways because this process requires special equipment. Raw materials of natural origin are air, coke, generator, associated and natural gas, which is a collection of hydrocarbons.
The physical methods for separating mixtures in the gaseous state are as follows:
- Condensation is the process of gradual cooling of a mixture, during which the condensation of its constituents occurs. In this case, first of all, high-boiling substances, which are collected in separators, pass into the liquid state. In this way, hydrogen is obtained from and also ammonia is separated from the unreacted part of the mixture.
- Sorption 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 processes, 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 in which the property of semipermeable partitions is used to selectively pass molecules of various substances.
- Reflux - the process of condensation of high-boiling parts of mixtures as a result of their cooling. In this case, the temperature of the transition to the liquid state of the individual components should differ significantly.
Chromatography
The name of this method can be translated as "I write with color." Imagine that ink is added to the water. If you lower the end of the filter paper into such a mixture, it will begin to be absorbed. In this case, water will be absorbed faster than ink, which is associated with a different degree 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 first are elements or compounds consisting only of particles of a certain type. Their examples are salt, sugar, distilled water. Mixtures are a collection of individual substances. A number of methods are used to separate them. The way they are separated depends on the physical properties of its constituents. The main ones are settling, evaporation, crystallization, filtration, distillation, magnetization and chromatography.
>> Pure substances and mixtures. Settling. Separation of a mixture of three solids
Pure substances and mixtures
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;
> 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 that contains almost no impurities is called pure. With these substances work in the scientific laboratory, school chemistry room. 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) are missing red copper particles and yellow gold particles.
From materials that are homogeneous mixtures of substances, many items for various purposes are made (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
Such a mixture is formed by mixing, for example, alcohol and water.
Give an 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, 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 solution of salt - at a higher temperature. If water is cooled to 0°C, it will begin to turn into ice. A salt solution under these conditions remains a liquid (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, which 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 chalk particles can always be found in the resulting mixture, which 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, cloudy water, milk and other foodstuffs, some medicines and cosmetics.
Give an example of an inhomogeneous 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 0°C and boils at 100°C.
Some types of heterogeneous mixtures have special names: foam (for example, polystyrene, lather), suspension (a mixture of water with a small amount of flour), emulsion (milk, well-shaken vegetable oil with water), aerosol (smoke, mist).
What are the ingredients 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 chosen taking into account the type of mixture, state of aggregation and differences in the physical properties of the components (Scheme 4). Some methods you know from the course of natural history.
Scheme 4. Methods for separating mixtures
Explain what properties of the components make it possible to separate each heterogeneous mixture indicated in the diagram.
Rice. 30. Worker in a respirator
Consider how some methods separation of mixtures.
The filtering process underlies the operation of a respirator, a device that protects the lungs of a person working in a heavily 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. A filter that extracts dust from the air is also in the vacuum cleaner.
With the help of a magnet in industry, iron ore is enriched - magnetite.
Due to the 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.
An important method for separating homogeneous mixtures of liquids is distillation, or distillation. 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 will boil. Non-volatile liquids remain in the vessel.
Rice. 31.Laboratory installation for distillation:
a - ordinary;
1 - a mixture of liquids with different temperatures boiling;
2 - thermometer;
3 - water cooler;
4 - receiver
6 - simplified
Separation various mixtures happens in nature. Dust particles settle from the air, and during rain and snow - water droplets, snowflakes. As a result of settling, cloudy water becomes transparent. Water is also purified from insoluble substances when passing through sand. After the evaporation of water, salts remain on the banks of the estuaries, which were dissolved in it. 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 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.
Inhomogeneous 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).
?
29. What types of mixtures are there 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.
| Pure substances | Mixes | |
| homogeneous | heterogeneous | |
31. Name a few foods that are solutions.
32. What popular drink, depending on the method of preparation, is a homogeneous or heterogeneous mixture?
33. Can an aqueous solution of table salt be turned 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 with pieces of plastic? Name the substances that will remain on the filter.
35. How would you separate the 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 have chosen?
36. Consider an experiment to separate a mixture of table salt, sand, iron and sawdust. Make a plan for it, briefly describe each stage of the experiment and talk about the expected results.
Experimenting at home
settling
Pour water into two glasses. Pour 1/2 teaspoon of sand into one glass, and the same amount of starch into another. Stir both mixtures at the same time. Do particles of matter settle in water at the same rate? If not, which particles settle faster and why?
Write down your observations in a notebook.
Separation of a mixture of three solids
Mix small amounts of crushed styrofoam, sand and table salt.
What methods can be used to separate this mixture?
Divide mixture 1 . If heating is necessary, use it very carefully.
Describe each step of the experiment in your notebook.
Popel P. P., Kriklya L. S., Chemistry: Pdruch. for 7 cells. zahalnosvit. navch. zakl. - K .: Exhibition Center "Academy", 2008. - 136 p.: il.
Lesson #5
Topic: Pure substances and mixtures.
Target: give the concept of pure substances and mixtures, homogeneous and heterogeneous mixtures; consider natural mixtures: air, natural gas, oil; to acquaint with examples of solid, liquid, gaseous mixtures in nature and everyday life; develop cognitive interest and intellectual abilities; educate attitude towards chemistry as one of the fundamental sciences.
Equipment: examples of pure substances (sugar, sulfur, iron filings, distilled water, chalk powder), presentation "pure substances and mixtures", multimedia projector and screen.
During the classes.
IClass organization.
IIThe message of the topic, the objectives of the lesson, the motivation of educational activities.
We have considered the concept of "substance", we know what properties substances have. Today we will get acquainted with the concept of "mixture". Consider how mixtures differ from substances, what types of mixtures are. Let's get acquainted with natural mixtures and mixtures used in everyday life. (Slide 1)
IIIUpdating of basic knowledge.
(Front conversation).
What is a physical body?
What is a material?
What is a substance?
Give examples of substances, materials.
What properties do substances have?
Which properties are called physical and which are chemical?
Describe the properties of water, aluminum, oxygen.
IVLearning new material.
Pure substances and mixtures.
Pure substances have constant physical properties, because consist of particles of the same type (identical atoms, identical molecules).
Examples: iron, aluminum, soda, distilled water, sugar, oxygen, etc.
Mixes it is a collection of different substances that make up one physical body. Substances that are part of mixtures retain their inherent properties.
Look at my prepared examples of pure substances. Name these substances, describe their physical properties.
Now I will prepare several mixtures: sulfur and 1) iron filings, 2) water and chalk,
3) water and sugar. What are you watching.
Answer: 1) sulfur mixed with iron filings. Teacher's question: can we distinguish between iron filings and sulfur particles? Answer: yes.
Answer: 2) the water became cloudy white color. Teacher: Let's leave this mixture for a while. Let's see what happens to her in a few minutes.
Answer 3) Sugar is dissolved in water. Teacher: Can we see sugar particles among water particles with the naked eye? Answer: no. Teacher: Let's leave this mixture for a few minutes.
Teacher: Tell me, what aggregate states do the substances from which we prepared the mixtures have?
Answer: 1) solid and solid, 2) solid and liquid, 3) solid and liquid.
Teacher: Or maybe a mixture of gaseous substances or a mixture of liquid and gaseous substances.
Listen to the students' answers. We analyze them and establish that such mixtures are possible, moreover, they exist: air, oxygen dissolved in water.
We return to mixtures of water and chalk, water and sugar. We see that the chalk has settled, and we clearly distinguish between a layer of chalk below and a layer of water above it. The sugar solution remained unchanged.
Homogeneous (homogeneous) and heterogeneous (heterogeneous) mixtures. (Slide 3)
Mixtures in which particles of their constituent substances are visible to the naked eye or under a microscope are called heterogeneous or heterogeneous.
A mixture in which even with the help of magnifying instruments it is impossible to see the particles of its constituent substances is called homogeneous or homogeneous.
Natural mixtures, mixtures used in everyday life. (Teacher's story).
One of the most favorite materials of sculptors and architects is marble (Slide 4). The color of this rock is surprisingly diverse: milky white, gray, pinkish. The whimsical pattern pleases the eye. (Slide 5) Marble is obedient and pliable in the hands of the master, it is easily processed and perfectly polished to a mirror finish. (Slide 6) Marble is a material from which you can make facing tiles, statue or column of the palace. Tiles, statues, columns are physical bodies, products. But the basis of marble is a substance called calcium carbonate. The same substance is part of other minerals: chalk, limestone.
Now let's think about why marble is different color? Why does a unique pattern play on its surface?
Right. Because in addition to calcium carbonate, it contains impurities that give color. Similarly, glass products come in different colors, which depends on what dye is added to the glass. The composition of the rubber material for making car tires includes 24 components, the most important of which is Chemical substance rubber.
So it turns out that there are very few pure substances in nature, in technology, in everyday life. Much more common are mixtures - a combination of two or more substances. Air is a mixture various gases; oil is a natural mixture of organic substances (hydrocarbons); any minerals rocks are also solid mixtures of various substances.
Mixtures used in everyday life include, for example, washing powder, culinary mixes for baking pancakes or cakes, building mixtures, which refer to heterogeneous mixtures. (Slide 7)
Sometimes the particles of the components in mixtures are very small, indistinguishable to the eye. (Slide 8). For example, flour contains grains of starch and protein that cannot be distinguished with the naked eye. Milk is also a water mixture that contains small droplets of fat, protein, lactose and other substances. You can see fat droplets in milk if you look at a drop of milk under a microscope. These mixtures naturally belong to what? Right! These are also heterogeneous mixtures.
The aggregate state of substances in a mixture can be different. Toothpaste, for example, it is a mixture of solid and liquid components.
A mixture of any gases is always homogeneous. For example, fresh air is a homogeneous mixture of nitrogen, oxygen, carbon dioxide and noble gases, water vapor. But dusty air is already a heterogeneous mixture of the same gases, only containing more dust particles. You have probably seen more than once how early in the morning the sun's rays break through the loosely drawn curtains into the room. (Slide 9). Their paths are often marked by luminous paths: these are particles of dust suspended in the air that scatter sunlight. (Slide 10). Smog over a city or over an industrial enterprise is also a heterogeneous mixture: air that contains not only dust particles, but also soot from smoke, droplets various liquids and etc.
VGeneralization and systematization of knowledge.
The class is divided into groups (3-6) depending on the number of students.
Each group is given theoretical material to study a specific issue.
Questions to study in groups:
Gaseous mixtures in nature and everyday life.
Liquid natural mixtures and liquid mixtures used in everyday life.
Solid mixtures in nature and everyday life.
Handout material with theoretical information.
Gaseous mixtures in nature and everyday life.
The task:
What gaseous mixtures are found in nature and are used in everyday life?
What is their composition?
Does natural gas smell?
Why does household gas smell?
What safety regulations do you have to follow when using gas in your home?
Natural gas, associated petroleum gas are also natural mixtures of gaseous substances, the main component of which is methane CH 4 . The same methane enters our apartments through pipelines and burns in the kitchen with a cheerful blue flame. But household gas is also a mixture. Pungently smelling substances are specially introduced into its composition so that you can smell the slightest gas leak by smell. What is it for? The fact is that both air (necessary for the breathing of all living things) and natural gas (an indispensable fuel and raw material for the chemical industry) are a great boon for mankind, but their mixture turns into a formidable destructive force due to extreme explosiveness. From funds messages mass media you certainly know about the tragedies associated with methane explosions in coal mines, explosions domestic gas as a result of criminal negligence or failure to comply with elementary safety standards. If you smell gas in the apartment or in the entrance of your house, you should immediately turn off the taps and valves, ventilate the room, call a specialized emergency service by calling 104. It is strictly forbidden to use open fire, turn on or turn off electrical appliances.
Liquid mixtures in nature and everyday life.
The task:
Read the information below and answer the questions.
What liquid mixtures are found in nature and are used in everyday life?
What is the most common liquid mixture on earth?
Why can't you drink unboiled tap water?
How can you do tap water suitable for cooking?
Oil is a liquid natural mixture. It contains hundreds of different components, mainly carbon compounds. Oil is called the "blood of the Earth", "black gold", and you are well aware of the significant role in the economy of our state and many other countries played by the extraction, processing and export of oil and oil products.
Of course, the most common liquid mixture, or rather a solution, is the water of the seas and oceans. You already know that one liter of sea water contains on average 35 g of salts, most of which are sodium chloride. Unlike pure water, sea water has a bitter-salty taste, it freezes not at 0 ° C, but at -1.9 ° C.
You come across liquid mixtures in everyday life all the time. Shampoos and drinks, potions and preparations household chemicals are all mixtures of substances. Even tap water cannot be considered a pure substance: it contains dissolved salts, the smallest insoluble impurities, it is disinfected by chlorination. Such water cannot be drunk unboiled, it is not recommended to use it for cooking. Special household filters will help purify tap water not only from solid particles, but also from some dissolved impurities. Even reagent solutions tap water you can't cook. Water for this is purified by distillation, which you will learn about a little later.
Solid mixtures in nature and everyday life.
What solid mixtures are found in nature and are used in everyday life?
Why is coal called "black gold"?
How is coal used?
Solid mixtures are also widespread. As we have said, rocks are mixtures of several substances. Soil, clay, sand are also mixtures. Solid mixtures include glass, ceramics, alloys. Everyone is familiar with cooking mixtures or mixtures that form washing powders.
Coal - solid combustible mineral of plant origin solid mixture with a high carbon content (75-97 percent, the rest is impurities). Coal - the main wealth of the Donetsk basin, is represented by various grades from long-flame and coking to gas, fat and anthracites. It gives life to many industrial enterprises and transport, thermal power plants, is the most important energy source, the most valuable raw material for the chemical and coke industry. Fertilizers, plastics, paints, liquid and gaseous fuels, aromatic substances, medicines are made from coal. Coal is therefore called "black gold".
Natural solid mixtures also include ores (minerals from which metals are obtained): iron, mercury, nepheline, polymetallic, copper ores, etc.
(Representatives of the groups tell the class about the results of their work.)
VISummary of the lesson.
Today we have considered the concepts of "pure substances" and "mixtures". We found out into which groups the mixtures are divided. We learned which mixtures are found in nature, and which are used in everyday life. Ratings today are: ......
VIIHomework message.
You need to learn the reference notes for this lesson.
A pure substance has a definite constant composition or structure(salt, sugar).
A pure substance can be element or connection.
An atom is the smallest particle of an element that retains all of its properties.. Chemical element is made up of atoms of the same type. In an element, all atoms are the same and have the same number protons. The elements are, in a way, " building blocks"of any substance. You can give a construction analogy:
Building materials (brick, concrete, sand ...) are elements
Building structures (houses, bridges, roads…) is a substance
2. Connections of elements
The connection consists of at least two elements. All the same water consists of a combination of two elements of hydrogen and one element of oxygen - H 2 O. In other words, by combining these two elements in this way, we will get water and only water!
Although water is made up of the elements hydrogen and oxygen, its chemical and physical properties differ from those of pure hydrogen and oxygen.
To "separate" water into hydrogen and oxygen, a chemical reaction is necessary.
3. Blends
Mixtures are physical combinations of pure substances that do not have a definite or pure composition.
An example of a mixture is ordinary tea (drink), which many people prepare and drink on their own in the morning. Someone loves strong tea(a large amount of tea leaves), someone likes sweet tea (a large amount of sugar) ... As you can see, a mixture called "tea" always turns out a little different, although it consists of the same components (ingredients). However, it should be noted that each component of the mixture retains a set of its characteristics, therefore, different substances can be isolated from the mixture. For example, you can easily separate a mixture of salt and sand. To do this, just place the mixture in water, wait until the salt dissolves and filter the resulting solution. The result is pure sand.
Mixtures can be homogeneous or heterogeneous.
In a homogeneous mixture, particles of the substances that make up the mixture cannot be detected. Samples taken in different places such a mixture will be the same (for example, sweet tea, in which the poured sugar has completely dissolved).
However, if sugar is not completely dissolved in a glass of tea, then we will get a heterogeneous mixture. Indeed, if you try such tea, then from the surface it will not be as sweet as from the bottom, because. the concentration of sugar will be different.
SECTION I. GENERAL CHEMISTRY
6. Mixtures of substances. Solutions
6.2. Mixtures, their types, names, composition, separation methods
Mixtures are a combination of different substances that can form one physical body. Each substance that is contained in a mixture is called a component. Mixing does not create a new substance. All substances that are part of the mixture retain their inherent properties. But the physical properties of the mixture are generally different from the physical properties of the individual components. Mixtures are homogeneous and heterogeneous.
Homogeneous (homogeneous) mixtures are mixtures in which the components are mixed at the molecular level (single-phase material); they are impossible to detect when viewed with the naked eye and even when using powerful optical instruments. For example, aqueous solutions of sugar, sodium chloride, alcohol, acetic acid, metal alloys, air.
Heterogeneous (heterogeneous) mixtures form the so-called dispersed systems. They are formed by mixing two or more substances that do not dissolve in each other (do not form homogeneous systems) and do not react chemically. The components of dispersed systems are called the dispersion medium and the dispersed phase; there is an interface between them.
According to the particle size of the dispersed phase, the systems are divided into:
Coarse (> 10 -5 m);
Microheterogeneous (10 -7 -10 -5 m);
Ultramicroheterogeneous (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, the following simple disperse systems are distinguished:
|
Dispersed phase |
dispersion medium |
Notation |
Name |
Example |
|
gaseous |
gaseous |
y/y |
not formed* |
|
|
liquid |
y/y |
gas emulsion, foam |
sea, soap foam |
|
|
solid |
g/t |
porous body ( hard foam)** |
pumice, Activated carbon |
|
|
liquid |
gaseous |
y/y |
spray can |
clouds, fog |
|
liquid |
y/y |
emulsion |
milk, oil |
|
|
solid |
r/t |
capillary systems |
foam sponge soaked in water |
|
|
hard |
gaseous |
t/y |
spray can |
smoke, sandstorm |
|
liquid |
t/y |
suspension, sol, slurry |
paste, suspension of clay in water |
|
|
solid |
t/t |
solid heterogeneous system |
rocks, concrete, alloys |
* Gases form homogeneous mixtures (gaseous solutions).
** Porous bodies according to the size of the cavities are divided into:
Microporous (2 nm);
Lesoporous (2-50 nm);
Macroporous (> 50 nm).
Mixtures are separated using physical methods. To separate heterogeneous mixtures, settling, filtration, flotation, and sometimes the action of a magnet are used.
|
settling |
To separate a mixture containing solid water-insoluble particles or liquids insoluble in each other. Solid insoluble Particles or drops of liquid settle to the bottom of the vessel or float to the surface of the mixture. Use a separating funnel to separate liquids that do not mix |
clay and water; copper filings, sawdust and water; oil and water |
|
Filtration |
For separating a mixture of soluble and insoluble substances in a solvent. Solid insoluble particles remain on the filter |
water + sand; water + sawdust |
|
Flotation |
For separating mixtures of substances with different wettability values |
Mineral enrichment |
|
Magnet action |
For separating mixtures containing iron or other metals ( Ni, Co ) that are attracted by a magnet (ferromagnets) |
iron + sulfur; iron + sand |
Evaporation and distillation (distillation) are used to separate homogeneous mixtures.
_____________________________________________________________
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.