Methods for cleaning homogeneous mixtures. Separation of mixtures

In our article we will consider what pure substances and mixtures are, methods of separating mixtures. V Everyday life each of us uses them. Are pure substances found in nature at all? And how can you tell them apart from mixtures?

Pure substances and mixtures: methods for separating mixtures

Pure substances are those that contain only a certain kind of particles. 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 water-soluble. Even if you immerse a silver ring in this liquid, for example, 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, the amount of energy changes. Moreover, it can both increase and decrease. It is possible to divide a pure substance into separate components only with the help of chemical reaction... For example, only distilled water has a typical boiling and freezing point for this substance, no taste or smell. And its oxygen and hydrogen can only be decomposed by electrolysis.

And how do their totality differ from pure substances? Chemistry will help us to answer this question. The separation methods of mixtures are physical, since they do not lead to a change chemical composition substances. Unlike pure substances, mixtures have variable composition and properties, and they can be separated by physical methods.

What is a mixture

A mixture is a collection of individual substances. An example of this is sea water. Unlike disillated, it has a bitter or salty taste, boils at a higher temperature, and freezes at a lower temperature. The methods for separating mixtures of substances are physical. Thus, pure salt can be extracted from seawater by evaporation and subsequent crystallization.

Types of mixtures

If you add sugar to the water, after a while its particles will dissolve and become invisible. As a result, it will be impossible to distinguish them with the naked eye. Such mixtures are called homogeneous or homogeneous. They are also examples of air, gasoline, broth, perfume, sweet and salty water, an alloy of copper and aluminum. As you can see, they can be in different aggregate states, but the most common are liquids. 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 their typical examples... Inhomogeneous mixtures are also called suspensions. Among them, suspensions and emulsions are distinguished. The former include a liquid and a solid. So, the 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, and aerosols include fog, smoke, deodorants, air fresheners, antistatic agents.

Methods for separating mixtures

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

Now let's see if there is such a thing as chemical methods for separating mixtures. Let's say from aqueous solution salt, we need to get pure substances. For this, the mixture must be heated. As a result, the water turns into steam and the salt crystallizes. But this will not happen the 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, 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.

Upholding

Some methods of separating mixtures are based on the action of gravity. Thus, suspensions and emulsions can be decomposed. If vegetable oil gets into the water, shake this mixture first. Then leave it for a while. As a result, the water will be at the bottom of the vessel, and the oil in the form of a film will cover it.

In laboratory conditions, it is used for settling. As a result of its work, a denser liquid is poured into a vessel, and a light one remains.

Deposition is characterized by a low rate of the process. It takes a certain amount of time for the sediment to form. In an 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, to separate the iron and But do all metals have such 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, erbium.

Distillation

This name is translated from Latin means "dripping". Distillation is a method for 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, alcohol vapors condense, turning into liquid state.

In industry, in this way, oil refined products, fragrances, and pure metals are obtained.

Evaporation and crystallization

These separation methods are suitable for liquid solutions. The substances that make up their composition differ in boiling point. Thus, it is possible to obtain crystals of salt or sugar from the water in which they are dissolved. For this, the solutions are heated and evaporated until saturated. In this case, crystals are deposited. If it is necessary to obtain pure 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. The raw materials of natural origin are air, coke oven gas, generator gas, associated gas and natural gas, which is a combination of hydrocarbons.

Physical methods of separation of mixtures in a gaseous state are as follows:

• Condensation is the process of gradual cooling of a mixture, during which condensation of its constituents occurs. In this case, first of all, high-boiling substances that are collected in separators pass into the liquid state. Thus, 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 in the course of the reaction. For the forward and reverse process, different conditions are required. 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 in which the property of semi-permeable partitions is used to selectively pass molecules of various substances.
• Reflux is 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 individual components should differ significantly.

Chromatography

The name of this method can be translated as "writing in color". Imagine adding ink to the water. If you dip the end of the filter paper into this mixture, it will begin to absorb. In this case, water will be absorbed faster than ink, which is associated with varying degrees 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 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, magnetism and chromatography.

The mixtures can be separated in different ways, among which the most common are settling, filtration, evaporation.

Defending. By settling, mixtures are separated, the components of which are easily separated, for example, a mixture of starch and water (Fig. 25, a).

Soon after preparing the mixture, we see that the starch settles to the bottom (Fig. 25, b), since it is insoluble and heavier than water. A layer of water is located above the starch. In fig. 25c shows how this mixture is separated by carefully draining the water.

However, complete separation of the components of the mixture by settling will not occur. Part of the water remains with the starch, or part of the starch is separated from the mixture with water.

Let's separate the mixture of vegetable oil and water (fig. 26). For separation we use laboratory equipment called a separating funnel. As in the first case, these substances do not dissolve in each other, but vegetable oil is lighter than water.

Place the mixture in a separating funnel. Soon, a layer of vegetable oil will be on top of the water. The dividing line of the two liquids is clearly visible. By turning the tap, a hole is opened in the funnel through which water is poured into the glass. After pouring out the water, the tap is closed. Vegetable oil is poured into a separate bowl through the upper opening of the funnel.

Upholding - one of the ways to separate mixtures. The components of the mixture stratify as a result of settling, so they are easy to separate.

Filtration. It is better to use a filtration method to separate the mixture of liquid and insoluble solid.

To carry out filtration, you will need additional equipment - an ordinary funnel, filter, glass rod. Filters are non-dense porous materials through which liquid seeps, but particles of the solid component of the mixture do not penetrate. Such properties are possessed by paper, fabric, a layer of sand, cotton wool.

Filtration Is a method of separating a mixture by passing it through filters capable of retaining particles of one of its components.

In fig. 27 shows how to separate a mixture of iron filings and water by filtration. A mixture of water and sawdust is carefully poured onto the filter using a glass rod attached to the side of the funnel, as shown in the figure. Water quickly penetrates through the pores in the filter and drains into the receptacle. We see how clear clean water enters the receptacle. The size of the iron filings is larger than the pores of the filter, so they settle on it.

As in the previous two experiments, the mixtures were separated, since one component of the mixture did not dissolve in the other.

Evaporation. In nature and in everyday life, there are quite a lot of mixtures in which the particles of substances are so mixed and small in size that they cannot be separated by settling or filtering. For example, a mixture of water and table salt passes through the filter completely, none of its components remains on the filter. How do you split this mixture? In this case, another method is used - evaporation.

Evaporation Is the removal of the liquid component of the mixture by heating.

In fig. 28, a shows the preparation of a mixture of boiled salt and water, as well as its separation by evaporation. Material from the site

When evaporated, the water evaporates and turns into water vapor (Fig. 28, b). At the bottom of the vessel, in which the evaporation took place, there remains a solid substance - table salt (Fig. 28, c).

In addition to those considered, there are also other methods of separation of mixtures... For example, the property of substances to be attracted to a magnet. This method of separating mixtures can be used if one of the substances reacts to the action of the magnet, and the other does not.

Magnetization is characteristic of iron and is absent in sulfur. If you bring a magnet to the mixture of these substances (this can be done through a thin sheet of paper), then the mixture will separate, the iron filings will be attracted to the magnet, then it can be easily cleaned of them.

Using large magnets in metal recycling plants, scrap iron is separated from other components.

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Separation methods

Heterogeneous mixtures of gas-liquid, liquid-solid, gas-solid types are unstable in time under the influence of gravity. In such mixtures, composite components with a lower density gradually rise up (float), and with a higher density, they fall down (settle). This process of spontaneous separation of mixtures over time is called upholding... So, for example, a mixture of fine sand and water quickly spontaneously divides into two parts:

To accelerate the process of sedimentation of a substance with a higher density from a liquid in laboratory conditions, they often resort to a more advanced version of the sedimentation method - centrifugation... The role of gravity in centrifuges is played by centrifugal force, always appearing when rotating. Since the centrifugal force directly depends on the speed of rotation, it can be done many times more than the force of gravity, simply by increasing the number of revolutions of the centrifuge per unit of time. This achieves a much faster separation of the mixture compared to settling.

After settling or centrifugation, the supernatant can be separated from the sediment by the method decantation- by carefully draining the liquid from the sediment.

It is possible to separate a mixture of two liquids insoluble in each other (after settling) using a separating funnel, the principle of which is clear from the following illustration:

To separate mixtures of substances in different states of aggregation, in addition to sedimentation and centrifugation, filtration is also widely used. The method consists in the fact that the filter has different throughput in relation to the components of the mixture. Most often this is due to different particle sizes, but it can also be due to the fact that individual components of the mixture interact more strongly with the filter surface ( adsorbed them).

For example, a suspension of a solid insoluble powder with water can be separated using a porous filter paper. The solid remains on the filter, and the water passes through it and is collected in a container located below it:

In some cases, heterogeneous mixtures can be separated due to different magnetic properties components. For example, a mixture of powders of sulfur and metallic iron can be separated using a magnet. Iron particles, unlike sulfur particles, are attracted and held by a magnet:

Separation of mixture components using magnetic field are called magnetic separation.

If the mixture is a solution of a refractory solid in any liquid, this substance can be isolated from the liquid by evaporating the solution:

To separate liquid homogeneous mixtures, a method called distillation, or distillation... This method has a principle of operation similar to evaporation, but allows separating not only volatile components from non-volatile ones, but also substances with relatively close boiling points. One of the simplest options for distillation apparatus is shown in the figure below:

The meaning of the distillation process is that when a mixture of liquids boils, the vapor of the lighter-boiling component is the first to volatilize. Vapors of this substance, after passing through the refrigerator, condense and drain into the receiver. The distillation method is widely used in the oil industry in the primary refining of oil to separate oil into fractions (gasoline, kerosene, diesel, etc.).

By the same method of distillation, water purified from impurities (primarily salts) is obtained. Water purified by distillation is called distilled water.

What is the difference between pure substances and mixtures of substances?

An individual pure substance has a certain set of characteristic properties (constant physical properties). Only pure distilled water has a melting point = 0 ° C, boiling point = 100 ° C, and has no taste. Sea water freezes at a lower temperature and boils at a higher temperature; it tastes bitter-salty. The Black Sea water freezes at a lower temperature and boils at a higher temperature than the Baltic Sea water. Why? The point is that in sea ​​water contains other substances, such as dissolved salts, i.e. it is a mixture of various substances, the composition of which varies over a wide range, while the properties of the mixture are not constant. The definition of the concept "mixture" was given in the 17th century. by the English scientist Robert Boyle: "A mixture is a complete system consisting of dissimilar components."

Comparative characteristics mixture and pure substance

The mixtures differ from each other in appearance.

The classification of mixtures is shown in the table:

We will give examples of suspensions (river sand + water), emulsions (vegetable oil + water) and solutions (air in a flask, table salt + water, loose change: aluminum + copper or nickel + copper).

In suspensions, particles of a solid are visible, in emulsions - droplets of liquid, such mixtures are called inhomogeneous (heterogeneous), and in solutions the components are indistinguishable, they are homogeneous (homogeneous) mixtures.

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.

For cleaning substances used different ways separation of mixtures

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

Consider ways to split heterogeneous and homogeneous mixtures .

A special method of separating components, based on their different absorption by a certain substance, is chromatography.

At home, you can do the following experiment. Hang a strip of filter paper over a container of red ink, immersing only the end of the strip. 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 two substances are separated: water and the dye in the ink.

Using chromatography, the Russian botanist MS 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 with the same degree of purification always required?

For different purposes, substances with different degrees of purification are required. It is enough to settle water for cooking to remove impurities and chlorine used for its disinfection. Water for drinking must first be boiled. And in chemical laboratories for the preparation of solutions and conducting 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.

Read the poem "Distilled water" by L. Martynov:

Water
Favored
To pour!
She
Shone
So pure
No matter what to get drunk
No wash.
And it was not without reason.
She missed
Willows, tala
And the bitterness of flowering vines,
She lacked algae
And fish, oily from dragonflies.
She didn't have enough to be wavy
She missed flowing everywhere.
She lacked life
Clean -
Distilled water!

• Laboratory rules.
• Laboratory glassware and equipment.
• Safety rules when working with caustic, flammable and toxic substances, household chemicals.
• Scientific research methods chemical substances and transformations. Methods for separation of mixtures and purification of substances.

Laboratory rules

It is strictly forbidden to work alone in the laboratory, since in the event of an accident there will be no one to help the victim and eliminate the consequences of the accident.

When working in the laboratory, it is necessary to observe cleanliness, silence, order and safety rules, since haste and negligence often lead to serious accidents.

Everyone who works should know where the fire protection equipment and the first aid kit containing everything necessary for first aid are located in the laboratory.

You cannot start work until students have mastered all the techniques for doing it.

Experiments should be carried out only in clean chemical containers. After the end of the experiment, the dishes should be washed immediately.

In the process of work, it is necessary to observe cleanliness and accuracy, make sure that the substances do not get on the skin of the face and hands, since many substances cause irritation of the skin and mucous membranes.

No substance can be tasted in the laboratory. You can sniff the substances only by carefully directing vapors or gases towards yourself with a slight movement of the hand, and not bending over to the vessel and not inhaling deeply.

Any utensil containing reagents must be labeled with the name of the substance.

Vessels with substances or solutions must be taken by the neck with one hand, and the bottom must be supported with the other from below.

During heating of liquid and solid substances in test tubes and flasks, do not direct their holes at yourself and your neighbors. It is also impossible to look from above into openly heated vessels in order to avoid possible injury from the ejection of a hot mass.

After finishing work, you must turn off the gas, water, electricity.

It is strictly forbidden to pour concentrated solutions of acids and alkalis, as well as various organic solvents, strong smelling and flammable substances into sinks. All this waste must be poured into special bottles.

Each laboratory must have protective masks and goggles.

In each room of the laboratory, it is necessary to have fire protection equipment: a box with sifted sand and a scoop for it, a fire blanket (asbestos or thick felt), charged fire extinguishers.

Safety rules when working with caustic, flammable and toxic substances, household chemicals

To accelerate the dissolution of solids in the test tube, do not close its opening with your finger while shaking.

The dissolution of alkali should be carried out in porcelain dishes by adding small portions of the substance to the water, with continuous stirring.

When determining the smell of a substance, do not bend over it, inhale vapors or emitted gas. It is necessary to direct the vapor or gas to the nose with a slight movement of the hand over the throat of the vessel and inhale carefully.

Spilled acid or alkali should be covered with clean, dry sand and stirred until all liquid is completely absorbed. Remove wet sand with a scoop into a wide glass container for subsequent rinsing and neutralization.

Solutions from reactive flasks must be poured so that when tilted, the label is on top (the label is in the palm). In case of contact with the skin of solutions of alkalis or acids, it is necessary to wash them off after shaking the visible drops with a strong stream. cold water, and then treat with a neutralizing solution (2% solution acetic acid or 2% sodium bicarbonate solution) and rinse with water.

Methods for separation of mixtures and purification of substances. Pure substances and mixtures substances

A mixture is a material consisting of two or more substances randomly alternating with each other in space.

A pure substance is a physically and chemically homogeneous material with a certain set of permanent properties. The content of impurities in high-purity preparations is measured in millionths and billionths of a percent.

Settling is a method based on different densities of substances.

For example, a mixture of vegetable oil and water can be separated into oil and water by letting the mixture simply settle.

Filtration is a method based on the different ability of the filter to pass the substances that make up the mixture. For example, a filter can separate solids from liquids.

Evaporation is the separation of non-volatile solids from solution in a volatile solvent — particularly water. For example, to isolate salt dissolved in water, you just need to evaporate the water. The water will evaporate, but the salt will remain.