If dispersed particles are released slowly from the medium or it is necessary to pre-clarify a heterogeneous system, methods such as flocculation, flotation, classification, coagulation, etc. are used.
Coagulation is the process of particle adhesion in colloidal systems (emulsions or suspensions) with the formation of aggregates. Adhesion occurs due to the collision of particles during Brownian motion. Coagulation refers to a spontaneous process that tends to enter a state that has a lower free energy. The coagulation threshold is the minimum concentration of the administered substance that causes coagulation. Artificially, coagulation can be accelerated by adding special substances - coagulators - to the colloidal system, as well as by applying an electric field to the system (electrocoagulation), mechanical action (vibration, stirring), etc.
During coagulation, coagulant chemicals are often added to the separated heterogeneous mixture, which destroy the solvated shells, while reducing the diffusion part of the double electrical layer located at the surface of the particles. This facilitates the agglomeration of particles and the formation of aggregates. Thus, due to the formation of larger fractions of the dispersed phase, particle deposition is accelerated. Salts of iron, aluminum or salts of other polyvalent metals are used as coagulants.
Peptization is a reverse coagulation process, which is the decomposition of aggregates into primary particles. Peptization is carried out by adding peptizing substances to the dispersion medium. This process promotes the disaggregation of substances into primary particles. Peptizing agents can be surfactants or electrolytes, such as humic acids or ferric chloride. The peptization process is used to obtain liquid dispersed systems from pastes or powders.
Flocculation, in turn, is a type of coagulation. In this process, small particles that are suspended in gas or liquid media form flocculent aggregates called flocs. Soluble polymers, for example, polyelectrolytes, are used as flocculants. Substances that form flocs during flocculation can be easily removed by filtration or settling. Flocculation is used for water treatment and the separation of valuable substances from wastewater, as well as for the enrichment of minerals. In the case of water treatment, flocculants are used in low concentrations (from 0.1 to 5 mg/l).
In order to destroy aggregates in liquid systems, additives are used that induce charges on particles that prevent them from approaching each other. This effect can also be achieved by changing the pH of the environment. This method is called deflocculation.
Flotation is the process of separating solid hydrophobic particles from a liquid continuous phase by selectively fixing them at the interface between the liquid and gaseous phases (the contact surface of liquid and gas or the surface of bubbles in the liquid phase). The resulting system of solid particles and gas inclusions is removed from the surface of the liquid phase. This process is used not only to remove particles of the dispersed phase, but also to separate different particles due to differences in their wettability. In this process, hydrophobic particles are fixed at the interface and separated from hydrophilic particles that settle to the bottom. The best flotation results occur when the particle size is between 0.1 and 0.04 mm.
There are several types of flotation: foam, oil, film, etc. The most common is froth flotation. This process allows particles treated with reagents to be carried to the surface of the water using air bubbles. This allows the formation of a foam layer, the stability of which is adjusted using a foam concentrate.
The classification is used in devices of variable cross-section. With its help, it is possible to separate a certain number of small particles from the main product, consisting of large particles. Classification is carried out using centrifuges and hydrocyclones due to the effect of centrifugal force.
Separation of suspensions using magnetic treatment of the system is a very promising method. Water that has been treated in a magnetic field retains altered properties for a long time, for example, reduced wetting ability. This process makes it possible to intensify the separation of suspensions.
Topic: “Methods of separating mixtures” (8th grade)
Theoretical block.
The definition of the concept “mixture” was given in the 17th century. English scientist Robert Boyle: “A mixture is an integral system consisting of heterogeneous components.”
Comparative characteristics of the mixture and pure substance
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Signs of comparison |
Pure substance |
Mixture |
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Constant |
Fickle |
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Substances |
Same |
Various |
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Physical properties |
Permanent |
Fickle |
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Energy change during formation |
Happening |
Not happening |
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Separation |
Through chemical reactions |
By physical methods |
The mixtures differ from each other in appearance.
The classification of mixtures is shown in the table:
Let us give examples of suspensions (river sand + water), emulsions (vegetable oil + water) and solutions (air in a flask, table salt + water, small change: aluminum + copper or nickel + copper).
Methods for separating mixtures
In nature, substances exist in the form of mixtures. For laboratory research, industrial production, and for the needs of pharmacology and medicine, pure substances are needed.
Various methods for separating mixtures are used to purify substances.
Evaporation is the separation of solids dissolved in a liquid by converting it into steam.
Distillation- distillation, separation of substances contained in liquid mixtures according to boiling points, followed by cooling of the steam.
In nature, water does not occur in its pure form (without salts). Ocean, sea, river, well and spring water are types of solutions of salts in water. However, people often need clean water that does not contain salts (used in car engines; in chemical production to obtain various solutions and substances; in making photographs). Such water is called distilled, and the method of obtaining it is called distillation.
Filtration - straining liquids (gases) through a filter in order to clean them from solid impurities.
These methods are based on differences in the physical properties of the components of the mixture.
Consider separation methods heterogeneous and homogeneous mixtures.
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Example of a mixture |
Separation method |
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Suspension - a mixture of river sand and water |
Advocacy Separation defending based on different densities of substances. Heavier sand settles to the bottom. You can also separate the emulsion: separate the oil or vegetable oil from the water. In the laboratory this can be done using a separatory funnel. Petroleum or vegetable oil forms the top, lighter layer. As a result of settling, dew falls out of the fog, soot settles out of the smoke, and cream settles in the milk. Separation of a mixture of water and vegetable oil by settling |
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A mixture of sand and table salt in water |
Filtration What is the basis for the separation of heterogeneous mixtures using filtering?On different solubility of substances in water and on different particle sizes. Only particles of substances comparable to them pass through the pores of the filter, while larger particles are retained on the filter. This way you can separate a heterogeneous mixture of table salt and river sand. Various porous substances can be used as filters: cotton wool, coal, baked clay, pressed glass and others. The filtration method is the basis for the operation of household appliances, such as vacuum cleaners. It is used by surgeons - gauze bandages; drillers and elevator workers - respiratory masks. Using a tea strainer to filter tea leaves, Ostap Bender, the hero of the work by Ilf and Petrov, managed to take one of the chairs from Ellochka the Ogress (“Twelve Chairs”). Separation of a mixture of starch and water by filtration |
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Mixture of iron and sulfur powder |
Action by magnet or water Iron powder was attracted by a magnet, but sulfur powder was not. Non-wettable sulfur powder floated to the surface of the water, and heavy wettable iron powder settled to the bottom. Separating a mixture of sulfur and iron using a magnet and water
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A solution of salt in water is a homogeneous mixture |
Evaporation or crystallization The water evaporates, leaving salt crystals in the porcelain cup. When water is evaporated from lakes Elton and Baskunchak, table salt is obtained. This separation method is based on the difference in boiling points of the solvent and the solute. If a substance, for example sugar, decomposes when heated, then the water is not completely evaporated - the solution is evaporated, and then sugar crystals are precipitated from the saturated solution. Sometimes it is necessary to remove impurities from solvents with a lower temperature boiling, for example water from salt. In this case, the vapors of the substance must be collected and then condensed upon cooling. This method of separating a homogeneous mixture is called distillation or distillation. In special devices - distillers, distilled water is obtained, which is used for the needs of pharmacology, laboratories, and car cooling systems. At home, you can construct such a distiller: If you separate a mixture of alcohol and water, then the alcohol with boiling point = 78 °C will be distilled off first (collected in a receiving test tube), and water will remain in the test tube. Distillation is used to produce gasoline, kerosene, and gas oil from oil. Separation of homogeneous mixtures |
A special method for separating components, based on their different absorption by a certain substance, is chromatography.
Using chromatography, the Russian botanist M. S. Tsvet was the first to isolate chlorophyll from the green parts of plants. In industry and laboratories, starch, coal, limestone, and aluminum oxide are used instead of filter paper for chromatography. Are substances with the same degree of purification always required?
For different purposes, substances with varying degrees of purification are required. Cooking water should be left to stand sufficiently to remove impurities and chlorine used to disinfect it. Water for drinking must first be boiled. And in chemical laboratories for preparing solutions and conducting experiments, in medicine, distilled water is needed, purified as much as possible from substances dissolved in it. Particularly 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.
Methods of expressing the composition of mixtures.
Mass fraction of the component in the mixture- the ratio of the mass of the component to the mass of the entire mixture. Usually the mass fraction is expressed in %, but not necessarily.
ω ["omega"] = m component / m mixture
Mole fraction of the component in the mixture- the ratio of the number of moles (amount of substance) of a component to the total number of moles of all substances in the mixture. For example, if the mixture contains substances A, B and C, then:
χ ["chi"] component A = n component A / (n(A) + n(B) + n(C))
Molar ratio of components. Sometimes problems for a mixture indicate the molar ratio of its components. For example:
n component A: n component B = 2: 3
Volume fraction of the component in the mixture (only for gases)- the ratio of the volume of substance A to the total volume of the entire gas mixture.
φ ["phi"] = V component / V mixture
Practical block.
Let's look at three examples of problems in which mixtures of metals react with salt acid:
Example 1.When a mixture of copper and iron weighing 20 g was exposed to excess hydrochloric acid, 5.6 liters of gas (no.) were released. Determine the mass fractions of metals in the mixture.
In the first example, copper does not react with hydrochloric acid, that is, hydrogen is released when the acid reacts with iron. Thus, knowing the volume of hydrogen, we can immediately find the amount and mass of iron. And, accordingly, the mass fractions of substances in the mixture.
Solution to example 1.
Finding the amount of hydrogen:
n = V / V m = 5.6 / 22.4 = 0.25 mol.
According to the reaction equation:
The amount of iron is also 0.25 mol. You can find its mass:
m Fe = 0.25 56 = 14 g.
Answer: 70% iron, 30% copper.
Example 2.When a mixture of aluminum and iron weighing 11 g was exposed to excess hydrochloric acid, 8.96 liters of gas (n.s.) were released. Determine the mass fractions of metals in the mixture.
In the second example, the reaction is both metal Here, hydrogen is already released from the acid in both reactions. Therefore, direct calculation cannot be used here. In such cases, it is convenient to solve using a very simple system of equations, taking x to be the number of moles of one of the metals, and y to be the amount of substance of the second.
Solution to example 2.
2HCl = FeCl 2 +
It is much more convenient to solve such systems using the subtraction method, multiplying the first equation by 18:
27x + 18y = 7.2
and subtracting the first equation from the second:(56 − 18)y = 11 − 7.2
y = 3.8 / 38 = 0.1 mol (Fe)
x = 0.2 mol (Al)
Finding the amount of hydrogen:
n = V / V m = 8.96 / 22.4 = 0.4 mol.
Let the amount of aluminum be x moles, and the amount of iron be x moles. Then we can express the amount of hydrogen released in terms of x and y:
We know the total amount of hydrogen: 0.4 mol. Means,
1.5x + y = 0.4 (this is the first equation in the system).
For a mixture of metals we need to express masses through the amount of substances.
m = Mn
So, the mass of aluminum
m Al = 27x,
mass of iron
m Fe = 56у,
and the mass of the entire mixture
27x + 56y = 11 (this is the second equation in the system).
So, we have a system of two equations:
m Fe = n M = 0.1 56 = 5.6 g
m Al = 0.2 27 = 5.4 g
ω Fe = m Fe / m mixture = 5.6 / 11 = 0.50909 (50.91%),
respectively,
ω Al = 100% − 50.91% = 49.09%
Answer: 50.91% iron, 49.09% aluminum.
Example 3.16 g of a mixture of zinc, aluminum and copper were treated with an excess of hydrochloric acid solution. In this case, 5.6 liters of gas (n.s.) were released and 5 g of the substance did not dissolve. Determine the mass fractions of metals in the mixture.
In the third example, two metals react, but the third metal (copper) does not react. Therefore, the remainder of 5 g is the mass of copper. The amounts of the remaining two metals - zinc and aluminum (note that their total mass is 16 − 5 = 11 g) can be found using a system of equations, as in example No. 2.
Answer to Example 3: 56.25% zinc, 12.5% aluminum, 31.25% copper.
Example 4.A mixture of iron, aluminum and copper was treated with an excess of cold concentrated sulfuric acid. In this case, part of the mixture dissolved, and 5.6 liters of gas (n.s.) were released. The remaining mixture was treated with an excess of sodium hydroxide solution. 3.36 liters of gas were released and 3 g of undissolved residue remained. Determine the mass and composition of the initial mixture of metals.
In this example, we must remember that cold concentrated sulfuric acid does not react with iron and aluminum (passivation), but does react with copper. This releases sulfur (IV) oxide.
With alkali reacts only aluminum- amphoteric metal (in addition to aluminum, zinc and tin also dissolve in alkalis, and beryllium can also be dissolved in hot concentrated alkali).
Solution to example 4.
(don’t forget that such reactions must be equalized using an electronic balance)
Since the molar ratio of copper and sulfur dioxide is 1:1, then copper is also 0.25 mol. You can find a mass of copper:
m Cu = n M = 0.25 64 = 16 g.Aluminum reacts with an alkali solution, resulting in the formation of a hydroxo complex of aluminum and hydrogen:
2Al + 2NaOH + 6H 2 O = 2Na + 3H 2Al 0 − 3e = Al 3+
2H + + 2e = H 2
Number of moles of hydrogen:
n H3 = 3.36 / 22.4 = 0.15 mol,
the molar ratio of aluminum and hydrogen is 2:3 and, therefore,
n Al = 0.15 / 1.5 = 0.1 mol.
Aluminum weight:
m Al = n M = 0.1 27 = 2.7 gThe remainder is iron, weighing 3 g. You can find the mass of the mixture:
m mixture = 16 + 2.7 + 3 = 21.7 g.Mass fractions of metals:
Only copper reacts with concentrated sulfuric acid, the number of moles of gas is:
n SO2 = V / Vm = 5.6 / 22.4 = 0.25 mol
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2H 2 SO 4 (conc.) = CuSO 4 + |
ω Cu = m Cu / m mixture = 16 / 21.7 = 0.7373 (73.73%)
ω Al = 2.7 / 21.7 = 0.1244 (12.44%)
ω Fe = 13.83%
Answer: 73.73% copper, 12.44% aluminum, 13.83% iron.
Example 5.21.1 g of a mixture of zinc and aluminum was dissolved in 565 ml of nitric acid solution containing 20 wt. %HNO 3 and having a density of 1.115 g/ml. The volume of the released gas, which is a simple substance and the only product of the reduction of nitric acid, was 2.912 l (n.s.). Determine the composition of the resulting solution in mass percent. (RHTU)
The text of this problem clearly indicates the product of nitrogen reduction - a “simple substance”. Since nitric acid with metals does not produce hydrogen, it is nitrogen. Both metals dissolved in the acid.
The problem asks not the composition of the initial mixture of metals, but the composition of the resulting solution after the reactions. This makes the task more difficult.
Solution to example 5.
Determine the amount of gas substance:
n N2 = V / Vm = 2.912 / 22.4 = 0.13 mol.
Determine the mass of the nitric acid solution, the mass and amount of dissolved HNO3:
m solution = ρ V = 1.115 565 = 630.3 g
m HNO3 = ω m solution = 0.2 630.3 = 126.06 g
n HNO3 = m / M = 126.06 / 63 = 2 mol
Please note that since the metals have completely dissolved, it means - there was definitely enough acid(these metals do not react with water). Accordingly, it will be necessary to check Is there too much acid?, and how much of it remains after the reaction in the resulting solution.
We compose reaction equations ( don't forget about your electronic balance) and, for the convenience of calculations, we take 5x to be the amount of zinc, and 10y to be the amount of aluminum. Then, in accordance with the coefficients in the equations, nitrogen in the first reaction will be x mol, and in the second - 3y mol:
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12HNO 3 = 5Zn(NO 3) 2 + |
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Zn 0 − 2e = Zn 2+ |
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2N +5 + 10e = N 2 |
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36HNO3 = 10Al(NO3)3 + |
It is convenient to solve this system by multiplying the first equation by 90 and subtracting the first equation from the second.
x = 0.04, which means n Zn = 0.04 5 = 0.2 mol
y = 0.03, which means n Al = 0.03 10 = 0.3 mol
Let's check the mass of the mixture:
0.2 65 + 0.3 27 = 21.1 g.
Now let's move on to the composition of the solution. It will be convenient to rewrite the reactions again and write down above the reactions the amounts of all reacted and formed substances (except water):
The next question is: is there any nitric acid left in the solution and how much is left?
According to the reaction equations, the amount of acid that reacted:
n HNO3 = 0.48 + 1.08 = 1.56 mol,
those. the acid was in excess and you can calculate its remainder in the solution:
n HNO3 rest. = 2 − 1.56 = 0.44 mol.
So, in final solution contains:
zinc nitrate in an amount of 0.2 mol:
m Zn(NO3)2 = n M = 0.2 189 = 37.8 g
aluminum nitrate in an amount of 0.3 mol:
m Al(NO3)3 = n M = 0.3 213 = 63.9 g
excess nitric acid in an amount of 0.44 mol:
m HNO3 rest. = n M = 0.44 63 = 27.72 g
What is the mass of the final solution?
Let us remember that the mass of the final solution consists of those components that we mixed (solutions and substances) minus those reaction products that left the solution (precipitates and gases):
Then for our task:
m new solution = mass of acid solution + mass of metal alloy - mass of nitrogen
m N2 = n M = 28 (0.03 + 0.09) = 3.36 g
m new solution = 630.3 + 21.1 − 3.36 = 648.04 g
ωZn(NO 3) 2 = m quantity / m solution = 37.8 / 648.04 = 0.0583
ωAl(NO 3) 3 = m volume / m solution = 63.9 / 648.04 = 0.0986
ω HNO3 rest. = m water / m solution = 27.72 / 648.04 = 0.0428
Answer: 5.83% zinc nitrate, 9.86% aluminum nitrate, 4.28% nitric acid.
Example 6.When 17.4 g of a mixture of copper, iron and aluminum was treated with an excess of concentrated nitric acid, 4.48 liters of gas (n.o.) were released, and when this mixture was exposed to the same mass of excess hydrochloric acid, 8.96 liters of gas (n.o.) were released. y.). Determine the composition of the initial mixture. (RHTU)
When solving this problem, we must remember, firstly, that concentrated nitric acid with an inactive metal (copper) produces NO 2, and iron and aluminum do not react with it. Hydrochloric acid, on the contrary, does not react with copper.
Answer for example 6: 36.8% copper, 32.2% iron, 31% aluminum.
Explanatory note
Pure substances and mixtures. Methods separation mixtures. Develop an understanding of pure substances and mixtures. Methods purification of substances: ... substances to various classes organic compounds. Characterize: basic classes organic compounds...
Order of 2013 No. Work program for the academic subject "Chemistry" 8th grade (basic level 2 hours)
Working programmAssessing students' knowledge of opportunities and ways separation mixtures substances; formation of appropriate experimental skills... classification and chemical properties of basic substances classes inorganic compounds, the formation of ideas about...
... mixtures, ways separation mixtures. Objectives: To give the concept of pure substances and mixtures; Consider classification mixtures; Introduce students to ways separation mixtures... student and raises in front class card with the formula of an inorganic substance...
Do you know what methods there are to separate mixtures? Don't be too quick to give a negative answer. You use many of them in your daily activities.
Pure substance: what is it?
Atoms, molecules, substances and mixtures are basic chemical concepts. What do they mean? There are 118 chemical elements in D.I. Mendeleev’s table. These are different types of elementary particles - atoms. They differ from each other in mass.
By connecting with each other, atoms form molecules, or substances. The latter, connecting with each other, form mixtures. Pure substances have constant composition and properties. These are homogeneous structures. But they can be separated into components through chemical reactions.
Scientists claim that pure substances practically do not exist in nature. There is a small amount of impurities in each of them. This happens because most substances are different in activity. Even metals immersed in water dissolve in it at the ion level.
The composition of pure substances is always constant. It is simply impossible to change it. So, if you increase the amount of carbon or oxygen in a carbon dioxide molecule, it will be a completely different substance. And in the mixture you can increase or decrease the number of components. This will change its composition, but not the fact of its existence.
What is a mixture
A combination of several substances is called a mixture. They can be of two types. If the individual components in a mixture are indistinguishable, it is called uniform, or homogeneous. There is another name that is most often used in everyday life - solution. The components of such a mixture cannot be separated by physical methods. For example, it is not possible to mechanically extract crystals that are dissolved in it from a saline solution. Not only liquid solutions are found in nature. So, air is a gaseous homogeneous mixture, and a metal alloy is a solid.
In inhomogeneous or heterogeneous mixtures, individual particles are visible to the naked eye. They differ from each other in composition and properties. This means that they can be separated from each other purely mechanically. Cinderella, who was forced by her evil stepmother to separate the beans from the peas, coped with this task perfectly.
Chemistry: methods for separating mixtures
There are a huge number of mixtures found in everyday life and nature. How to choose the right way to separate them? It must be based on the physical properties of the individual components. If substances have different boiling points, then evaporation followed by crystallization, as well as distillation, will be effective. Such methods are used to separate homogeneous solutions. To separate heterogeneous mixtures, differences in other properties of their components are used: density, wettability, solubility, size, magnetism, etc.
Physical methods for separating mixtures
When separating the components of the mixture, the composition of the substances themselves does not change. Therefore, methods for separating mixtures cannot be called a chemical process. Thus, by settling, filtering and exposure to a magnet, the individual components can be separated mechanically. In the laboratory, various instruments are used: separating funnel, filter paper, magnetic strips. These are methods for separating heterogeneous mixtures.
Screening
This method is perhaps the simplest. Every housewife is familiar with it. It is based on the difference in size of the solid components of the mixture. Sifting is used in everyday life to separate flour from impurities, insect larvae and various contaminants. In agricultural production, cereal grains are cleaned of foreign debris in this way. Construction workers sift through a mixture of sand and gravel.
Advocacy
This method of separating mixtures is used for components with different densities. If sand gets into the water, the resulting solution must be mixed well and left for a while. The same can be done with a mixture of water and vegetable oil or petroleum. The sand will settle to the bottom. But the oil, on the contrary, will collect from above. This method is observed in everyday life and nature. For example, soot settles from smoke, and individual dew drops from fog. And if you leave homemade milk overnight, you can collect the cream by morning.
Filtration
Brewed tea lovers use this method daily. We are talking about filtration - a method of separating mixtures based on the different solubilities of the components. Imagine that iron filings and salt got into the water. Large insoluble particles will remain on the filter. And the dissolved salt will pass through it. The principle of this method underlies the operation of vacuum cleaners, the action of respiratory masks and gauze bandages.
Action by magnet
Suggest a method for separating mixtures of sulfur and iron powders. Naturally, this is the action of a magnet. Are all metals capable of this? Not at all. Based on the degree of susceptibility, three groups of substances are distinguished. For example, gold, copper and zinc will not attach to a magnet. They belong to the group of diamagnetic materials. Magnesium, platinum and aluminum have weak perception. But if the mixture contains ferromagnets, then this method will be the most effective. These include, for example, iron, cobalt, nickel, terbium, holmium, thulium.
Evaporation
Which method of separating mixtures is suitable for an aqueous homogeneous solution? This is evaporation. If you only have salt water, but need clean water, don’t get upset right away. You need to heat the mixture to boiling point. As a result, the water will evaporate. And crystals of the dissolved substance will be visible at the bottom of the dish. To collect water, it must be condensed - transferred from a gaseous state to a liquid. To do this, the vapors are cooled, touching a surface with a lower temperature, and flow into the prepared container.
Crystallization
In science, this term is considered in a broader meaning. This is not just a method for obtaining pure substances. Crystals in nature include icebergs, minerals, bones and tooth enamel.
Their growth occurs under the same conditions. Crystals form as a result of cooling liquids or supersaturation of steam, and then the temperature should no longer change. Thus, some limiting conditions are first reached. As a result, a crystallization center appears, around which atoms of liquid, melt, gas or glass gather.
Distillation
Surely you have heard about water, which is called distilled. This purified liquid is necessary for the manufacture of medicines, laboratory research, and cooling systems. And they get it in special devices. They are called distillers.
Distillation is a method of separating mixtures of substances with different boiling points. Translated from Latin, the term means “dripping down.” Using this method, for example, you can separate alcohol and water from a solution. The first substance will begin to boil at a temperature of +78 o C. The alcohol vapor will subsequently condense. The water will remain in liquid form.
In a similar way, refined products are obtained from oil: gasoline, kerosene, gas oil. This process is not a chemical reaction. Oil is divided into separate fractions, each of which has its own boiling point. This happens in several stages. First, primary oil separation is carried out. It is purified from associated gas, mechanical impurities and water vapor. At the next stage, the resulting product is placed in distillation columns and begins to be heated. This is atmospheric distillation of oil. At temperatures below 62 degrees, the remaining associated gas evaporates. By heating the mixture to 180 degrees, gasoline fractions are obtained, up to 240 - kerosene, up to 350 - diesel fuel. The residue from thermal oil refining is fuel oil, which is used as a lubricant.
Chromatography
This method was named after the scientist who first used it. His name was Mikhail Semenovich Tsvet. Initially, the method was used to separate plant pigments. And chromatography is literally translated from Greek as “I write with color.” Dip the filter paper into the water and ink mixture. The first one will immediately begin to be absorbed. This is due to different degrees of adsorbing properties. This also takes into account diffusion and the degree of solubility.
Adsorption
Some substances have the ability to attract molecules of other types. For example, we take activated carbon when poisoning to get rid of toxins. This process requires an interface that lies between the two phases.
This method is used in the chemical industry for separating benzene from gaseous mixtures, purifying liquid products of oil refining, and purifying them from impurities.
So, in our article we looked at the main ways to separate mixtures. People use them both at home and on an industrial scale. The choice of method depends on the type of mixture. An important factor is the specific physical properties of its components. To separate solutions in which the individual parts are visually indistinguishable, methods of evaporation, crystallization, chromatography and distillation are used. If the individual components can be identified, such mixtures are called heterogeneous. To separate them, methods of settling, filtering and magnetic action are used.
Pure substances and mixtures. Methods for separating mixtures.In order to establish the properties of a substance, it is necessary to have it in its pure form, but substances do not occur in nature in their pure form. Each substance always contains a certain amount of impurities. A substance in which there are almost no impurities is called pure. They work with such substances in a scientific laboratory or school chemistry lab. Note that absolutely pure substances do not exist.
Mixtures include almost all natural substances, food (except salt, sugar, and some others), building materials, household chemicals, and many medicines and cosmetics.
Natural substances are mixtures, sometimes consisting of a very large number of different substances. For example, natural water always contains salts and gases dissolved in it. Sometimes a very small amount of an impurity can lead to a very strong change in some properties of the substance. For example, the content of only hundredths of iron or copper in zinc accelerates its interaction with hydrochloric acid hundreds of times. When one of the substances is in a predominant amount in a mixture, the entire mixture usually bears its name.
A component is each substance contained in a mixture.
Homogeneous mixtures.
Add a small portion of sugar to a glass of water and stir until all the sugar has dissolved. The liquid will taste sweet. Thus, the sugar did not disappear, but remained in the mixture. But we will not see its crystals, even when examining a drop of liquid through a powerful microscope.
Rice. 3. Homogeneous mixture (aqueous sugar solution)
The prepared mixture of sugar and water is homogeneous (Fig. 3); the smallest particles of these substances are evenly mixed in it.
Mixtures in which components cannot be detected with the naked eye are called homogeneous.
Water mixed with sand, chalk or clay freezes at a temperature of O 0 C and boils at 100 0 C.
Some types of heterogeneous mixtures have special names: foam (for example, polystyrene foam, soap suds), suspension (a mixture of water with a small amount of flour), emulsion (milk, well-shaken vegetable oil and water), aerosol (smoke, fog).
Rice. 5. Heterogeneous mixtures:
a - a mixture of water and sulfur;
b - a mixture of vegetable oil and water;
c - a mixture of air and water
There are different ways to separate mixtures. The choice of method for separating a mixture is influenced by the properties of the substances forming the mixture.
Let's take a closer look at each method:
Advocacy- a common method of purifying liquids from mechanical impurities insoluble in water, or liquid substances that are insoluble in each other and have different densities.
Sedimentation is used in the preparation of water for technological and domestic needs, treatment of sewage, dehydration and desalting of crude oil, and in many chemical technology processes. It is an important stage in the natural self-purification of natural and artificial reservoirs.
Filtration– separation of liquid from solid insoluble impurities; Liquid molecules pass through the pores of the filter, and large particles of impurities are retained.
Imagine that in front of you is a mixture of river sand and water. Determine the type of mixture. ( heterogeneous). Compare the physical properties of river sand and water. (These are substances that are insoluble in each other and have different densities). Suggest a method for separating this mixture ( filtering).
Action by magnet is a method of separating heterogeneous mixtures when one of the substances in the mixture is capable of being attracted by a magnet
Evaporation – this is a method of separating homogeneous mixtures, in which a solid soluble substance is released from a solution; when heated, the water evaporates, and crystals of the solid substance remain.
Distillation (Latin for "dropping") – This is a method of separating homogeneous mixtures, in which liquid mixtures are separated into fractions that differ in composition. It is carried out by partial evaporation of a liquid followed by condensation of steam. The distilled fraction (distillate) is enriched with relatively more volatile (low-boiling) substances, and the non-distilled liquid (bottoms) is enriched with relatively less volatile (high-boiling) substances.
In the laboratory, distillation is carried out using a special installation (Fig. 6). 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. 6. Laboratory installation for distillation: a - conventional; b - simplified
1 - a mixture of liquids with different boiling points;
2 - thermometer;
3 - water refrigerator;
4 - receiver
Let's look at how some use methods separation of mixtures.
The filtration process underlies the operation of a respirator - a device that protects the lungs of a person working in a very dusty room. The respirator has filters that prevent dust from entering the lungs (Fig. 7). The simplest respirator is a bandage made of several layers of gauze. A vacuum cleaner also has a filter that removes dust from the air.
Rice. 7. Worker in a respirator
Conclude by what methods you can separate a mixture of soluble and insoluble substances in water.
heterogeneous (heterogeneous) | homogeneous (homogeneous) |
| Heterogeneous mixtures are those in which the interface between the original components can be identified either with the naked eye or under a magnifying glass or microscope: | Substances in such mixtures are mixed with each other as much as possible, one might say, at the molecular level. In such mixtures, it is impossible to detect the interface between the original components even under a microscope: |
| Examples | |
| Suspension (solid + liquid) Emulsion (liquid + liquid) Smoke (solid + gas) Solid powder mixture (solid+solid) | True solutions (for example, a solution of table salt in water, a solution of alcohol in water) Solid solutions (metal alloys, crystalline salt hydrates) Gas solutions (a mixture of gases that do not react with each other) |
Methods for separating mixtures
Heterogeneous mixtures of the gas-liquid, liquid-solid, gas-solid types are unstable in time under the influence of gravity. In such mixtures, components with a lower density gradually rise upward (float), and with a higher density, they sink down (settle). This process of spontaneous separation of mixtures over time is called defending. For example, a mixture of fine sand and water quite quickly spontaneously divides into two parts:
To speed up the process of deposition of substances with a higher density from a liquid in laboratory conditions, they often resort to a more advanced version of the settling method - centrifugation. The role of gravity in centrifuges is played by centrifugal force, which always occurs during rotation. Since centrifugal force directly depends on the speed of rotation, it can be made many times greater than the force of gravity simply by increasing the number of revolutions of the centrifuge per unit time. Thanks to this, a much faster separation of the mixture is achieved compared to settling.
After settling or centrifugation, the supernatant can be separated from the sediment using the method decanting— by carefully draining the liquid from the sediment.
You can separate a mixture of two liquids that are insoluble in each other (after settling) using a separating funnel, the principle of operation 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 a different throughput in relation to the components of the mixture. Most often this is due to different particle sizes, but it may also be due to the fact that individual components of the mixture interact more strongly with the filter surface ( are adsorbed them).
For example, a suspension of solid insoluble powder with water can be separated using a porous paper filter. The solid remains on the filter, and the water passes through it and is collected in a container located underneath it:
In some cases, heterogeneous mixtures can be separated due to the different magnetic properties of the components. For example, a mixture of sulfur and metallic iron powders can be separated using a magnet. Iron particles, unlike sulfur particles, are attracted and held by a magnet:
The separation of mixture components using a magnetic field is called magnetic separation.
If the mixture is a solution of a refractory solid in a liquid, this substance can be separated 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 you to separate not only volatile components from nonvolatile 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 vapors of the lighter-boiling component evaporate first. The vapors of this substance, after passing through the refrigerator, condense and flow into the receiver. The distillation method is widely used in the oil industry during primary oil refining to separate oil into fractions (gasoline, kerosene, diesel, etc.).
The distillation method also produces water purified from impurities (primarily salts). Water that has been purified by distillation is called distilled water.
