In our article we will look at what pure substances and mixtures are, and methods for separating mixtures. Each of us uses them in everyday life. 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, for example, a silver ring is immersed in this liquid, 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 a 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, since they do not lead to a change in the chemical composition of the 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. Thus, 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 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 inhomogeneous 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, as a result of oil refining, gasoline, gas oil, kerosene, fuel oil, diesel and engine oil, rocket fuel, acetylene and benzene are obtained. Agree, it is more profitable to use these products than to mindlessly burn oil.
Now let's figure out whether there is such a thing as chemical methods for separating 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 of this process is 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 translated from Latin means “dripping down”. 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 it is necessary to obtain 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 combination 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. Different conditions are required for the forward and reverse processes. In the first case, it is a combination of 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.
Each substance consists of certain particles. For example, water consists of water molecules in which two hydrogen atoms are connected to one oxygen atom. Water molecules differ in composition, shape, size, and properties from molecules of other substances. If the vessel contains only water molecules and no particles of other substances, then such water is a pure substance.
Pure substances. Pure substances are characterized by constant physical properties. For example, only pure water boils at 100 °C and freezes at 0 °C. If salt is dissolved in it, the boiling point will exceed 100 ° C, and the freezing point will decrease. Therefore, during icy conditions, sidewalks are sprinkled with table salt.
The composition of a pure substance is constant, regardless of how it was mined and where the substance is found in nature.
Pure substances are called substances that consist of particles of one substance and are characterized by constant physical properties.
Check out the examples of pure substances in Fig. 22.
When we buy salt, sugar, starch in a store, we think that these are pure substances. However, these food products also contain minor impurities of other substances. Consequently, substances in their pure form are practically never found in nature and everyday life.
Mixtures. In nature, technology, and everyday life, mixtures of two or more substances predominate. Natural mixtures are air, natural gas, oil, milk, sea water, granite, rocks, fruit juices. According to Fig. 23 find out in what states of aggregation mixtures can be found.
The mixtures you know that are created and used by man include: construction mixtures, gasoline, paints, washing powders, toothpastes, ketchups, mayonnaise, various dishes, etc.
Mixture - these are two or more substances mixed together. There are solid, liquid, and gaseous mixtures.
In Fig. Figure 24 shows how a mixture was prepared from citric acid and water. The molecules of these substances are mixed together.
You can also prepare different mixtures, for example tea, soap solution, compote, dough - a mixture of flour, soda and water.
The individual substances in a mixture are usually called components. The components of the natural mixture of granite are easy to see. In another natural mixture - milk - the components are not visible, although it contains many substances, including water, fats, and proteins. These components can be identified using a microscope. But it is not possible to examine the components of such a natural mixture as sea water even under a microscope.
There are mixtures natural And prepared by man. To prepare one mixture you must have two or more substances.Material from the site
A mixture of water and sugar can remain unchanged for a long time. Natural mixture - milk after a few days in a warm place begins to separate into components. Fat accumulates in the upper layer, and underneath it, a condensation of protein molecules and liquid become visible. To get sour cream, butter and cottage cheese separately, the mixture must be divided.
Separate the mixture - means to separate each of its components.
To carry out individual experiments, pure substances are required. Therefore, different methods are used to extract particles of another substance from one substance. You will learn about methods for separating mixtures in the next paragraph.
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Lesson #5
Subject: Pure substances and mixtures.
Target: give the concept of pure substances and mixtures, homogeneous and heterogeneous mixtures; consider natural mixtures: air, natural gas, oil; introduce examples of solid, liquid, gaseous mixtures in nature and everyday life; develop cognitive interest and intellectual abilities; cultivate an 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.
IIMessage of the topic, lesson goals, motivation for learning activities.
We have looked at the concept of “substance”; we know what properties substances have. Today we will get acquainted with the concept of “mixture”. Let's consider how mixtures differ from substances, what types of mixtures there are. Let's get acquainted with natural mixtures and mixtures used in everyday life. (Slide 1)
IIIUpdating basic knowledge.
(Front conversation).
What is the physical body?
What is the material?
What is a substance?
Give examples of substances and materials.
What properties do substances have?
Which properties are called physical and which are called 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.
Mixtures it is a collection of different substances that make up one physical body. Substances that are part of mixtures retain their inherent properties.
Look, I have prepared examples of pure substances. Name these substances and 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 observing?
Answer: 1) sulfur mixed with iron filings. Teacher question: can we distinguish between iron filings and sulfur particles? Answer: yes.
Answer: 2) the water became cloudy and white. Teacher: Let’s leave this mixture for a while. Let's see what happens to her in a few minutes.
Answer 3) sugar dissolved in water. Teacher: Can we see the sugar particles among the water particles with the naked eye? Answer: no. Teacher: let’s leave this mixture for a few minutes.
Teacher: Tell me, what states of aggregation do the substances from which we prepared the mixtures have?
Answer: 1) solid and solid matter, 2) solid and liquid matter, 3) solid and liquid matter.
Teacher: Or it could be a mixture of gaseous substances or a mixture of liquid and gaseous substances.
Students' responses are listened to. 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 the layer of chalk below and the layer of water above it. The sugar solution remained in the same state.
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 particles of its constituent substances cannot be seen even with the help of magnifying instruments is called uniform 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 varied: milky white, gray, pinkish. The whimsical pattern pleases the eye. (Slide 5) Marble is obedient and pliable in the hands of a master; it is easily processed and perfectly polished to a mirror shine. (Slide 6) Marble is a material from which you can make facing tiles, statues or palace columns. A tile, a statue, a column 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: why does marble come in different colors? Why does it have a unique pattern on its surface?
Right. Because in addition to calcium carbonate, it contains impurities that give color. Similarly, glass products come in different colors, which depend on what kind of dye is added to the glass. The rubber material used to make car tires includes 24 components, the most important of which is the 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 of various gases; oil - a natural mixture of organic substances (hydrocarbons); Any minerals or rocks are also solid mixtures of various substances.
Mixtures used in everyday life include, for example, washing powder, culinary mixtures for baking pancakes or cakes, building mixtures, which are classified as heterogeneous mixtures. (Slide 7)
Sometimes the particles of 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 an aqueous mixture that contains small droplets of fat, protein, lactose and other substances. You can see droplets of fat in milk if you examine a drop of milk under a microscope. These mixtures naturally belong to what? Right! These are also heterogeneous mixtures.
The physical state of substances in a mixture may be different. Toothpaste, for example, is a mixture of solid and liquid ingredients.
A mixture of any gases is always homogeneous. For example, clean air is a homogeneous mixture of nitrogen, oxygen, carbon dioxide and noble gases, and water vapor. But dusty air is a heterogeneous mixture of the same gases, only containing dust particles. You've probably seen more than once how early in the morning the sun's rays make their way into the room through loosely drawn curtains. (Slide 9). Their paths are often marked with luminous paths: these dust particles suspended in the air 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 of various liquids, 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.
Handouts with theoretical information.
Gaseous mixtures in nature and everyday life.
Exercise:
What gaseous mixtures are found in nature and used in everyday life?
What is their composition?
Does natural gas smell?
Why does household gas smell?
What safety regulations are you required to follow when using gas at home?
Natural gas and associated petroleum gas are also natural mixtures of gaseous substances, the main component of which is methane CH4. 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. Strong-smelling substances are specially introduced into its composition so that the slightest gas leak can be detected by smell. Why is this necessary? The fact is that both air (necessary for the breathing of all living things) and natural gas (an irreplaceable fuel and raw material for the chemical industry) are a great blessing for humanity, but their mixture turns into a formidable destructive force due to its extreme explosiveness. From media reports, you are certainly aware of the tragedies associated with methane explosions in coal mines, domestic gas explosions as a result of criminal negligence or failure to comply with basic safety standards. If you smell gas in an apartment or in the entrance of your house, you must immediately turn off the taps and valves, ventilate the room, and call a specialized emergency service by calling 104. In this case, it is strictly forbidden to use open fire or turn on or off electrical appliances.
Liquid mixtures in nature and everyday life.
Exercise:
Read the information below and answer the questions.
What liquid mixtures are found in nature and used in everyday life?
What is the most common liquid mixture on earth?
Why can't you drink unboiled tap water?
How can you make tap water suitable for cooking?
Liquid natural mixtures include oil. 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 how significant a role the extraction, refining and export of oil and petroleum products plays in the economy of our state and many other countries.
Of course, the most common liquid mixture, or rather 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, the main part of which is sodium chloride. Unlike pure sea water, it has a bitter-salty taste and 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 household chemicals are all mixtures of substances. Even tap water cannot be considered a pure substance: it contains dissolved salts and tiny insoluble impurities; it is disinfected by chlorination. This water should not 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 cannot be prepared using tap water. For this purpose, water 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 used in everyday life?
Why is coal called “black gold”?
How is coal used?
Solid mixtures are also widespread. As we have already said, rocks are mixtures of several substances. Soil, clay, sand are also mixtures. Solid mixtures include glass, ceramics, and alloys. Everyone is familiar with culinary mixtures or mixtures that form washing powders.
Coal - solid fuel mineral of plant origin, a solid mixture with a high carbon content (75-97 percent, the rest is impurities). Coal is the main wealth of the Donetsk basin, represented by various grades from long-flame and coking to gas, fat and anthracite. 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 industries. Fertilizers, plastics, paints, liquid and gaseous fuels, aromatic substances, and medicines are made from coal. Coal is therefore called “black gold”.
Natural solid mixtures also include ores (mineral resources 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.)
VILesson summary.
Today we looked at the concepts of “pure substances” and “mixtures”. We found out which groups the mixtures are divided into. We learned which mixtures are found in nature and which ones are used in everyday life. The ratings today are: ……
VIIHomework message.
You need to learn the supporting notes for this lesson.
SECTION I. GENERAL CHEMISTRY
6. Mixtures of substances. Solutions
6.2. Mixtures, their types, names, composition, separation methods
Mixtures are a collection of different substances from which one physical body can be formed. Each substance contained in a mixture is called a component. When mixed, a new substance does not appear. All substances that are part of the mixture retain their inherent properties. But the physical properties of the mixture, as a rule, differ from the physical properties of the individual components. Mixtures can be homogeneous or heterogeneous.
Homogeneous (homogeneous) mixtures are mixtures in which the components are mixed at the molecular level (single-phase material); they cannot be detected when viewed with the naked eye or even when using powerful optical instruments. For example, aqueous solutions of sugar, table salt, alcohol, acetic acid, metal alloys, air.
Inhomogeneous (heterogeneous) mixtures form 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 disperse systems are called dispersion medium and dispersed phase; there is an interface between them.
Based on the particle size of the dispersed phase, 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 dispersed phase particles have the same size, the systems are called monodisperse; if different, they are polydisperse (almost all natural systems are such). Depending on the state of aggregation of the dispersion medium and the dispersed phase, the following simple disperse systems are distinguished:
|
Dispersed phase |
Dispersive medium |
Designations |
Name |
Example |
|
gaseous |
gaseous |
y/y |
not formed* |
|
|
liquid |
y/y |
gas emulsion, foam |
sea, soap foam |
|
|
hard |
g/t |
porous body (solid foam)** |
pumice, activated carbon |
|
|
liquid |
gaseous |
y/y |
aerosol |
clouds, fog |
|
liquid |
y/y |
emulsion |
milk, oil |
|
|
hard |
r/t |
capillary systems |
foam sponge soaked in water |
|
|
hard |
gaseous |
t/y |
aerosol |
smoke, sandstorm |
|
liquid |
t/y |
suspension, sol, suspension |
paste, a suspension of clay in water |
|
|
hard |
t/t |
solid heterogeneous system |
rocks, concrete, alloys |
* Gases form homogeneous mixtures (gaseous solutions).
** Porous bodies are divided into:
Microporous (2 nm);
Lesoporous (2-50 nm);
Macroporous (> 50 nm).
Mixtures are separated using physical methods. To separate heterogeneous mixtures, sedimentation, filtration, flotation, and sometimes the action of a magnet are used.
|
Advocacy |
To separate a mixture containing solid particles insoluble in water 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 separatory funnel to separate liquids that do not mix. |
clay and water; copper filings, sawdust and water; oil and water |
|
Filtration |
To separate 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 indices |
Mineral beneficiation |
|
Action of a magnet |
For separating mixtures containing iron or other metals ( Ni, Co ), which are attracted by a magnet (ferromagnets) |
iron + sulfur; iron + sand |
To separate homogeneous mixtures, evaporation and distillation (distillation) are used.
_____________________________________________________________
1 If the particle sizes of the dispersed phase do not exceed the sizes of molecules or ions (up to 1 nm), such systems are called true solutions.
Studying this paragraph will help you:
· distinguish between pure substances and mixtures;
· name methods for separating mixtures;
· give examples of natural mixtures;
· characterize the properties of mixtures.
In chemistry, a distinction is made between pure substances and mixtures of substances. Let's find out how a pure substance differs from a mixture.
PURE SUBSTANCES If a substance is pure, then, apart from its structural particles, there are no other particles. It is worth remembering that even in chemical laboratories, not to mention natural conditions, absolutely PURE substances do not exist. Therefore, the concept of a pure substance is applied to substances in which there are so few impurities that they do not noticeably affect the properties of the substance.
Scientists are trying to isolate substances in as pure a form as possible to study their properties and special uses.
A pure substance is a substance that does not contain impurities of other substances.
MIXTURES. In everyday life, you mostly deal not with pure substances, but with mixtures of substances or materials made from several substances.
Mixtures are obtained by combining several PURE substances.
Give examples of mixtures that you use in everyday life.
In production, we also most often deal with mixtures of substances. Knowledge of the properties of pure substances and their changes under the influence of various impurities is extremely important for the correct practical use of substances.
In construction, cosmetology and medicine, during cooking, for washing clothes, etc., various mixtures are constantly used. There are mixtures in nature. You are familiar with gaseous natural mixtures - air and natural gas, liquid natural mixtures - sea and mineral water, oil, milk, solid mixtures - soil, granite and the like.
The substances that make up a mixture are called components of the mixture. Mixtures can be homogeneous or heterogeneous. It all depends on the particle size of the mixture components. In homogeneous mixtures, particles of one substance cannot be seen among the particles of another visually (that is, with the help of vision) or with the help of magnifying devices. For example, pure water and water sweetened with sugar look the same on the outside and under a magnifying glass. Therefore, it is a homogeneous mixture. The material from which window glass is made (Fig. 38) is also a homogeneous mixture of substances formed by the fusion of quartz sand, limestone and soda.
Granite, soil, a mixture of oil and water are examples of heterogeneous mixtures. It is not difficult to detect components in them visually or using magnifying devices.
By mixing two or more substances that are insoluble in each other, you can independently make various heterogeneous mixtures. Moreover, according to your desire, their composition can be different.
PROPERTIES OF MIXTURES. Firstly, the mixtures have an arbitrary composition. So, on the shelves of grocery stores you can see sour cream with different percentages of fat (15%, 20%, 30%). Using sugar, dried tea leaves and water, you prepare a mixture called tea. It is quite obvious that for some of you the drink will be sweeter, for others it will have a dark color, but in each case the sugar will not lose its sweet taste, and the substances of the tea leaves will not lose their color. Preservation of a substance’s properties within a mixture is another characteristic feature of mixtures.
Rice. 38. Examples of homogeneous mixtures (a - sea water; b - tap water; - milk; d - juice; e - glass; f - gasoline)
The quantitative composition of the mixtures is arbitrary. Substances in the mixture retain their individual properties.
Due to the preservation of the individual properties of substances in a mixture, they can be separated into individual components by physical methods.
The ability to separate mixtures is necessary for every person, regardless of whether she will connect her future profession with chemistry or not.
METHODS FOR SEPARATING MIXTURES. There are many ways to separate mixtures, among which the most common are: settling, filtering, evaporation.
Settling is the simplest way to separate heterogeneous mixtures formed from:
1) a solid substance that is practically insoluble in water;
2) two liquids that do not mix with each other.
Example 1. Let's prepare a mixture of sand and water.
At first it will be cloudy (Fig. 39a), but a little time will pass, and the sand, having a higher density than water, will settle to the bottom, and the layer of water above it will become transparent (Fig. 396). After this, carefully pour the water into another container.
And no matter how careful you are, it will not be possible to completely separate the mixture by settling. Some of the sand will still end up in another vessel, and some water will remain in the glass and soak the sand.
Example 2. From life experience you know that oil does not dissolve in water. Therefore, the mixture of these substances separates quite quickly, and after settling it can be easily separated into components. To do this, chemical laboratories use a separating funnel (Fig. 40).
Consider the substance in which the density - water or oil - is high.
It is clear that the lower layer is formed by water, and the upper layer by oil (Fig. 40a). Therefore, water will be the first to pour out of the separating funnel through the open edge (Fig. 40b). You just need to turn it off in time so that the oil remains in the funnel.
Recall
Just like in natural history lessons, you watch the teacher prepare mixtures; you yourself made and separated the mixtures. What methods of separating mixtures do you know?
Rice. 39. Separation of a mixture of insoluble solid and water by settling
Rice. 40. Separation of a heterogeneous mixture of liquid by settling
SEPARATION OF MIXTURES BY FILTERING This method is used to separate heterogeneous mixtures of liquid and insoluble solids, for example water and chalk (Fig. 41). A filter made of special porous paper is placed on the watering can, which is called a filter.
Remember! The edges of the filter should not extend beyond the funnel, but should be 0.2-0.5 cm below its edges. You should ensure that the filter fits tightly to the funnel (for this purpose, the inner wall of the funnel is pre-moistened with water).
The mixture is carefully poured onto the filter using a glass rod. Water penetrates through the pores of the filter into the receiving vessel, and the chalk insoluble in it remains on the filter. Everything that passes through the pores of the filter is called filtrate.
In everyday life, several layers of gauze or other fabric can serve as a filter. The filter can also be a loose bunch of cotton wool. By the way, at home, when the need for filtering arises, a cotton filter is most often used. Sand filters at water treatment plants (Fig. 42), which provide drinking water to large cities. Nowadays, at home, many people use household filters to purify water (Fig. 43).
Rice. 41. Separation of a heterogeneous mixture of water and chalk by filtration
Rice. 42. Use of filters in water treatment plants
Rice. 43. Household portable water filter
Rice. 44. Vacuum cleaner (a) and respirator (6) filter the air from dust
Filtration is the separation of a solid from a liquid by passing a mixture of substances through a porous material permeable only to the liquid. It is the most common method for separating heterogeneous mixtures of liquids and solids.
There are also filters that separate air mixtures with dust particles (Fig. 44).
SEPARATION OF MIXTURES BY EVAPORATION. Homogeneous mixtures cannot be separated by settling or filtering. The particles of all components in them are so small that they do not settle and pass through the pores of the filter without delay. To make sure that this is really the case, let's try to filter a homogeneous mixture made from water and copper sulfate (a blue solid) (Fig. 45). The same blue color of the mixture and the filtrate indicates that it was not possible to separate this mixture by filtration. There was no sediment left on the filter; all components of the mixture passed into the filtrate (Fig. 45a). A homogeneous mixture of table salt and water will behave similarly (Fig. 45(5). To separate such mixtures, another method should be used - evaporation.
Rice. 45. Passing homogeneous liquid mixtures through a filter
Rice. 46. Separation of a mixture of table salt and water by evaporation
For evaporation, you need an alcohol lamp or other heating device, a laboratory stand, and a porcelain cup.
When a mixture of water and salt is heated (Fig. 46a. (7), the liquid component (water) evaporates, and the solid substance (table salt) remains on the walls and bottom of the cup (Fig. 46.).
To separate a mixture means to isolate individual substances from it. Separation can be carried out by filtration, settling, evaporation and some other methods.
1. What is called a pure substance and a mixture?
2. What types of mixtures do you know?
3. How does a homogeneous mixture differ from a heterogeneous one?
4. Give 2-3 examples of natural mixtures, name their component.
5. What methods of separating mixtures do you know?
6. Fill out the table (you will find all the necessary information in the text of the paragraph). Also use stand-alone examples.
7. Match the right and left columns:
8. Which mixture can be separated by filtering and which by evaporation:
a) a mixture of chalk and salt;
b) sea water?
9. From the list above, write down separately the names of pure substances and mixtures: sugar, mineral water, honey, milk, carbon dioxide, vinegar, baking soda.
3 Geography you know that water, after evaporating from the seas and oceans, returns to the earth in the form of rain or snow. Then why aren't rainwater and snow salty?