Decantation examples of mixtures. Topic: "Methods for separating mixtures" (grade 8). More complex tasks

Theoretical block.

The definition of the concept "mixture" was given in the 17th century. English scientist Robert Boyle: "A mixture is a complete system consisting of dissimilar components."

Comparative characteristics of the mixture and the pure substance

Comparison criteria	Pure substance	Mixture
	Constant	Fickle
Substances	Same	Various
Physical properties	Permanent	Fickle
Energy change during education	Is happening	Not happening
Separation	Through chemical reactions	Physical methods

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).

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.

Various methods of mixture separation are used to purify substances.

Evaporation - the separation of solids dissolved in a liquid by means of its transformation into steam.

Distillation- distillation, separation of substances contained in liquid mixtures according to boiling points, followed by cooling of steam.

In nature, pure water (without salts) is not found. Oceanic, sea, river, well and spring water are varieties of salt solutions in water. However, people often need clean water that does not contain salts (it is used in car engines; in chemical production to obtain various solutions and substances; in the production of photographs). This water is called distilled, and the way it is obtained is distillation.

Filtration - filtering 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 ways to split heterogeneousand homogeneous mixtures.

Mix example	Separation method
Suspension - a mixture of river sand with water	Upholding Separation upholding based on different densities of substances. The heavier sand settles to the bottom. It is also possible to separate the emulsion: to separate oil or vegetable oil from water. In the laboratory, this can be done using a separating funnel. Oil or vegetable oil forms the upper, lighter layer. As a result of sedimentation, dew falls out of the fog, soot is deposited from the smoke, cream is settled in milk. Separation of a mixture of water and vegetable oil by settling
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. So you can separate a heterogeneous mixture of table salt and river sand. Various porous substances can be used as filters: cotton wool, coal, fired clay, pressed glass and others. The filtering method is the basis for the operation of household appliances such as vacuum cleaners. It is used by surgeons - gauze bandages; drillers and elevator workers - respiratory masks. With the help of a tea strainer to filter the tea leaves, Ostap Bender, the hero of the work by Ilf and Petrov, managed to take one of the chairs from Ellochka the Cannibal ("The Twelve Chairs"). Separation of a mixture of starch and water by filtration
Iron and Sulfur Powder Blend	Magnet or water action 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. Separation of a mixture of sulfur and iron using a magnet and water
Salt in water solution - homogeneous mixture	Evaporation or crystallization The water evaporates and the salt crystals remain in the porcelain cup. By evaporation of water from lakes Elton and Baskunchak, table salt is obtained. This separation method is based on the difference in the boiling points of the solvent and the solute. If a substance, for example sugar, decomposes on heating, then the water is evaporated incompletely - the solution is evaporated, and then sugar crystals are precipitated from the saturated solution. Sometimes it is required to remove impurities from solvents with a lower boiling point, for example, water from salt. In this case, the vapors of the substance must be collected and then condensed upon cooling. This method of separating a homogeneous mixture is called distillation, or distillation... Distilled water is obtained in special devices - distillers, which is used for the needs of pharmacology, laboratories, and automobile cooling systems. At home, you can design such a distiller: If you separate a mixture of alcohol and water, then alcohol with tboil = 78 ° C will be distilled off (collected in the receiving tube) first, and water will remain in the test tube. Distillation is used to obtain gasoline, kerosene, gas oil from oil. Separation of homogeneous mixtures

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

Using chromatography, a Russian botanist 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 stand the 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 per cent, are used in electronics, semiconductor, nuclear technology and other precision industries.

Ways 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"] = mcomponent / mmixture

· Mole fraction of a component in a mixture- the ratio of the number of moles (amount of substance) of the component to the total number of moles of all substances in the mixture. For example, if the mixture includes substances A, B and C, then:

χ ["chi"] component A = n component A / (n (A) + n (B) + n (C))

· The molar ratio of the components. Sometimes in problems for a mixture, the molar ratio of its constituents is indicated. For instance:

ncomponent A: ncomponent B = 2: 3

· Volume fraction of a component in a mixture (for gases only)- the ratio of the volume of substance A to the total volume of the entire gas mixture.

φ ["phi"] = Vcomponent / Vmixture

Practical block.

Consider three examples of problems in which mixtures of metals react with saline acid:

Example 1.When a mixture of copper and iron weighing 20 g was exposed to an excess of hydrochloric acid, 5.6 liters of gas (n.u.) were released. Determine the mass fraction 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 of example 1.

n = V / Vm = 5.6 / 22.4 = 0.25 mol.

2. According to the reaction equation:

3. The amount of iron is also 0.25 mol. You can find its mass:
mFe = 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 an excess of hydrochloric acid, 8.96 liters of gas (n.u.) were released. Determine the mass fraction of metals in the mixture.

In the second example, both metal. Here, hydrogen is already liberated from the acid in both reactions. Therefore, direct calculation cannot be used here. In such cases, it is convenient to solve with the help of a very simple system of equations, taking for x - the number of moles of one of the metals, and for y - the amount of substance of the second.

Solution of example 2.

1. Find the amount of hydrogen:
n = V / Vm = 8.96 / 22.4 = 0.4 mol.

2. Let the amount of aluminum - x mol, and iron - by mol. Then you can express the amount of released hydrogen in terms of x and y:


	2HCl = FeCl2 +

4. We know the total amount of hydrogen: 0.4 mol. Means,
1.5x + y = 0.4 (this is the first equation in the system).

5. For a mixture of metals, you need to express masses through the quantities of substances.
m = M n
Hence, the mass of aluminum
mAl = 27x,
iron mass
mFe = 56y,
and the mass of the whole mixture
27x + 56y = 11 (this is the second equation in the system).

6. So, we have a system of two equations:

7. It is much more convenient to solve such systems by the subtraction method, multiplying the first equation by 18:
27x + 18y = 7.2
and subtracting the first equation from the second:

8. (56 - 18) y = 11 - 7.2
y = 3.8 / 38 = 0.1 mol (Fe)
x = 0.2 mol (Al)

mFe = n M = 0.1 56 = 5.6 g
mAl = 0.2 27 = 5.4 g
ωFe = mFe / mmixture = 5.6 / 11 = 0.50.91%),

respectively,
ωAl = 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.u.) were released and 5 g of the substance did not dissolve. Determine the mass fraction of metals in the mixture.

In the third example, two metals react and 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 the system of equations, as in example # 2.

Answer to Example 3: 56.25% zinc, 12.5% aluminum, 31.25% copper.

Example 4.The 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.u.) were released. The remaining mixture was treated with an excess of sodium hydroxide solution. Released 3.36 liters of gas and remained 3 g of undissolved residue. Determine the mass and composition of the initial mixture of metals.

In this example, remember that cold concentrated sulfuric acid does not react with iron and aluminum (passivation), but does react with copper. This produces sulfur (IV) oxide.
With alkali reacts only aluminum- amphoteric metal (in addition to aluminum, zinc and tin also dissolve in alkalis, in hot concentrated alkali - beryllium can still be dissolved).

Solution example 4.

1.Only copper reacts with concentrated sulfuric acid, the number of moles of gas:
nSO2 = V / Vm = 5.6 / 22.4 = 0.25 mol


	2H2SO4 (conc.) = CuSO4 +

2. (do not forget that such reactions must be balanced using electronic balance)

3. Since the molar ratio of copper and sulfur dioxide is 1: 1, then copper is also 0.25 mol. You can find the mass of copper:
mCu = n M = 0.25 64 = 16 g.

4. Aluminum enters into a reaction with an alkali solution, thus forming a hydroxo complex of aluminum and hydrogen:
2Al + 2NaOH + 6H2O = 2Na + 3H2

Al0 - 3e = Al3 +

5. Number of moles of hydrogen:
nH2 = 3.36 / 22.4 = 0.15 mol,
the molar ratio of aluminum and hydrogen is 2: 3 and, therefore,
nAl = 0.15 / 1.5 = 0.1 mol.
Aluminum weight:
mAl = n M = 0.1 27 = 2.7 g

6. The remainder is iron, weighing 3 g. You can find the mass of the mixture:
mmixture = 16 + 2.7 + 3 = 21.7 g.

7. Mass fractions of metals:

ωCu = mCu / mmixture = 16 / 21.7 = 0.7.73%)
ωAl = 2.7 / 21.7 = 0.1.44%)
ωFe = 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 a nitric acid solution containing 20 wt. % HNO3 and having a density of 1.115 g / ml. The volume of the evolved gas, which is a simple substance and the only product of the reduction of nitric acid, was 2.912 L (standard). Determine the composition of the resulting solution in mass percent. (RCTU)

The text of this problem clearly indicates the product of nitrogen reduction - “simple substance”. Since nitric acid does not give hydrogen with metals, this is nitrogen. Both metals are dissolved in acid.
The problem does not ask for the composition of the initial mixture of metals, but for the composition of the solution obtained after the reactions. This makes the task more difficult.

Solution example 5.

1. Determine the amount of gas substance:
nN2 = V / Vm = 2.912 / 22.4 = 0.13 mol.

2. Determine the mass of the nitric acid solution, the mass and amount of the substance of the dissolved HNO3:

m solution = ρ V = 1.115 565 = 630.3 g
mHNO3 = ω m solution = 0.2 630.3 = 126.06 g
nHNO3 = m / M = 126.06 / 63 = 2 mol

Please note that since the metals have completely dissolved, it means - acid is definitely enough(these metals do not react with water). Accordingly, it will be necessary to check was there an excess of acid, and how much of it remained after the reaction in the resulting solution.

3. We compose the reaction equations ( do not forget about electronic balance) and, for convenience of calculations, we take for 5x - the amount of zinc, and for 10y - 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:


	12HNO3 = 5Zn (NO3) 2 +

Zn0 - 2e = Zn2 +


	36HNO3 = 10Al (NO3) 3 +

Al0 - 3e = Al3 +

5. Then, taking into account that the mass of the mixture of metals is 21.1 g, their molar masses are 65 g / mol for zinc and 27 g / mol for aluminum, we obtain the following system of equations:

6. It is convenient to solve this system by multiplying the first equation by 90 and subtracting the first equation from the second.

7.x = 0.04, which means nZn = 0.04 5 = 0.2 mol
y = 0.03, which means nAl = 0.03 10 = 0.3 mol

8. Check the mass of the mixture:
0.2 65 + 0.3 27 = 21.1 g.

9. Now we turn to the composition of the solution. It will be convenient to rewrite the reactions again and write over the reactions the amounts of all reacted and formed substances (except for water):

10. The next question: is there any nitric acid left in the solution and how much is left?
According to the reaction equations, the amount of acid that has reacted is:
nHNO3 = 0.48 + 1.08 = 1.56 mol,
that is, the acid was in excess and you can calculate its remainder in solution:
nHNO3st. = 2 - 1.56 = 0.44 mol.

11. So, in final solution contains:

zinc nitrate in an amount of 0.2 mol:
mZn (NO3) 2 = n M = 0.2 189 = 37.8 g
aluminum nitrate in an amount of 0.3 mol:
mAl (NO3) 3 = n M = 0.3 213 = 63.9 g
excess nitric acid in the amount of 0.44 mol:
mHNO3 = n M = 0.44 63 = 27.72 g

12. What is the mass of the final solution?
Recall 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):

13.
Then for our task:

14.min. solution = mass of acid solution + mass of metal alloy - mass of nitrogen
mN2 = n M = 28 (0.03 + 0.09) = 3.36 g
mnew solution = 630.3 + 21.1 - 3.36 = 648.04 g

ωZn (NO3) 2 = mv-va / mr-pa = 37.8 / 648.04 = 0.0583
ωAl (NO3) 3 = mv-va / mr-pa = 63.9 / 648.04 = 0.0986
ωHNO3res. = mv-va / mr-ra = 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 were treated with an excess of concentrated nitric acid, 4.48 liters of gas (n.u.) were released, and when this mixture was exposed to the same mass of excess hydrochloric acid, 8.96 liters of gas (n.a.) was released. y.). Determine the composition of the original mixture. (RCTU)

When solving this problem, one must remember, firstly, that concentrated nitric acid with an inactive metal (copper) gives NO2, and iron and aluminum do not react with it. In contrast, hydrochloric acid does not react with copper.

The answer for example 6: 36.8% copper, 32.2% iron, 31% aluminum.

Tasks for an independent solution.

1. Simple problems with two components of the mixture.

1-1. A mixture of copper and aluminum weighing 20 g was treated with a 96% solution of nitric acid, while 8.96 liters of gas (n.u.) were evolved. Determine the mass fraction of aluminum in the mixture.

1-2. A mixture of copper and zinc weighing 10 g was treated with a concentrated alkali solution. At the same time, 2.24 liters of gas (n.y.) were released. Calculate the mass fraction of zinc in the original mixture.

1-3. A mixture of magnesium and magnesium oxide weighing 6.4 g was treated with a sufficient amount of dilute sulfuric acid. At the same time, 2.24 liters of gas (n.u.) were released. Find the mass fraction of magnesium in the mixture.

1-4. A mixture of zinc and zinc oxide weighing 3.08 g was dissolved in dilute sulfuric acid. Received zinc sulfate weighing 6.44, Calculate the mass fraction of zinc in the original mixture.

1-5. Under the action of a mixture of iron and zinc powders weighing 9.3 g on an excess of copper (II) chloride solution, 9.6 g of copper was formed. Determine the composition of the original mixture.

1-6. What mass of a 20% hydrochloric acid solution is required for the complete dissolution of 20 g of a mixture of zinc and zinc oxide, if 4.48 L of hydrogen is released in this case?

1-7. When 3.04 g of a mixture of iron and copper are dissolved in dilute nitric acid, nitric oxide (II) with a volume of 0.896 l (n.u.) is released. Determine the composition of the original mixture.

1-8. When 1.11 g of a mixture of iron and aluminum sawdust was dissolved in a 16% solution of hydrochloric acid (ρ = 1.09 g / ml), 0.672 liters of hydrogen (n.u.) were released. Find the mass fraction of metals in the mixture and determine the volume of consumed hydrochloric acid.

2. The tasks are more complex.

2-1. A mixture of calcium and aluminum weighing 18.8 g was calcined in the absence of air with an excess of graphite powder. The reaction product was treated with dilute hydrochloric acid, while 11.2 liters of gas (n.u.) were evolved. Determine the mass fraction of metals in the mixture.

2-2. To dissolve 1.26 g of an alloy of magnesium with aluminum, 35 ml of a 19.6% sulfuric acid solution (ρ = 1.1 g / ml) were used. The excess acid reacted with 28.6 ml of a 1.4 mol / L potassium hydrogen carbonate solution. Determine the mass fractions of metals in the alloy and the volume of gas (n.a.) released during the dissolution of the alloy.

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; its taste is bitter-salty. The Black Sea water freezes at a lower temperature and boils at a higher temperature than the Baltic Sea water. Why? The fact is that seawater contains other substances, for example, dissolved salts, i.e. it is a mixture of various substances, the composition of which varies within wide limits, 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 of the mixture and the 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.

Various methods of mixture separation are used to purify substances.

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

Consider ways to split heterogeneous and homogeneous mixtures .

Mix example	Separation method
Suspension - a mixture of river sand with water	Upholding The separation by settling is based on different densities of substances. The heavier sand settles to the bottom. It is also possible to separate the emulsion: to separate oil or vegetable oil from water. In the laboratory, this can be done using a separating funnel. Oil or vegetable oil forms the upper, lighter layer.As a result of sedimentation, dew falls out of the fog, soot is deposited from the smoke, cream is settled in milk. Separation of a mixture of water and vegetable oil by settling
A mixture of sand and table salt in water	Filtration What is the basis for the separation of heterogeneous mixtures using filtration? On the different solubility of substances in water and on different particle sizes. Across The filter pores pass only particles of substances commensurate with them, while larger particles are retained on the filter. So you can separate a heterogeneous mixture of table salt and river sand.Various porous substances can be used as filters: cotton wool, coal, fired clay, pressed glass and others. The filtering method is the basis for the operation of household appliances such as vacuum cleaners. It is used by surgeons - gauze bandages; drillers and elevator workers - respiratory masks. With the help of a tea strainer to filter the tea leaves, Ostap Bender, the hero of the work by Ilf and Petrov, managed to take one of the chairs from Ellochka the Cannibal ("The Twelve Chairs"). Separation of a mixture of starch and water by filtration
Iron and Sulfur Powder Blend	Magnet or water action 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... Separation of a mixture of sulfur and iron using a magnet and water
Salt in water solution - homogeneous mixture	Evaporation or crystallization The water evaporates and the salt crystals remain in the porcelain cup. By evaporation of water from lakes Elton and Baskunchak, table salt is obtained. This separation method is based on the difference in the boiling points of the solvent and the solute. If a substance, 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, such as 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. Distilled water is obtained in special devices - distillers, which is used for the needs of pharmacology, laboratories, and automobile cooling systems. At home, you can design such a distiller: If you separate a mixture of alcohol and water, then the first will be distilled off (collected in the receiving tube) alcohol with t bip = 78 ° C, and water will remain in the test tube. Distillation is used to obtain gasoline, kerosene, gas oil from oil. Separation of 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 paint lags behind the border of the rise of water. This is how the separation of two substances occurs: water and a dye in 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 stand the 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
Not to 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!

WITH separation of mixtures (both heterogeneous and homogeneous) are based on the fact that the substances that make up the mixture retain their individual properties. Heterogeneous mixtures can differ in composition and phase state, for example: gas + liquid; solid + liquid; two immiscible liquids, etc. The main methods for separating mixtures are shown in the diagram below. Let's consider each method separately.
Separation of heterogeneous mixtures
For separation of heterogeneous mixtures, which are solid-liquid or solid-gas systems, there are three main ways:

filtration,
settling (decanting,
magnetic separation

FILTRATION
method based on different solubility of substances and different particle sizes of the mixture components. Filtration separates a solid from a liquid or gas.

To filter liquids, you can use filter paper, which is usually folded in four and inserted into a glass funnel. The funnel is placed in glasses, which accumulates filtrate- liquid that has passed through the filter.
The pore size in the filter paper is such that it allows water molecules and solute molecules to leak unhindered. Particles larger than 0.01mm are retained on the filter and are notpass through it, thus forming a layer of sediment.
Remember! Filtration cannot separate true solutions of substances, that is, solutions in which dissolution occurred at the level of molecules or ions.
In addition to filter paper, chemical laboratories use special filters with

different pore sizes.
Filtration of gas mixtures does not fundamentally differ from filtration of liquids. The only difference is that when filtering gases from solid suspended particles (HFC), filters of special designs (paper, coal) and pumps are used to forcibly pump the gas mixture through a filter, for example, filtering the air in the passenger compartment or exhaust hood above the stove.
Filtration can separate:

cereals and water,
chalk and water,
sand and water, etc.
dust and air (various designs of vacuum cleaners)

Lagging
The method is based on different settling rates of solid particles with different weight (density) in a liquid or air environment. The method is used to separate two or more solid insoluble substances in water (or other solvent). A mixture of insoluble substances is placed in water, mixed thoroughly. After some time, substances with a density greater than one settle to the bottom of the vessel, and substances with a density less than one float. If the mixture contains several substances with different gravity, then heavier substances will settle in the lower layer, and then lighter ones. Such layers can also be separated. Previously, grains of gold were isolated from crushed gold-bearing rock in this way. Gold-bearing sand was placed on an inclined trough, through which a stream of water was sent. The stream of water picked up and carried away the waste rock, and heavy grains of gold settled at the bottom of the trough. In the case of gas mixtures, solid particles settle on hard surfaces, for example, dust settles on furniture or plant leaves.
This method can also separate immiscible liquids. For this, a separating funnel is used.
For example, to separate gasoline and water, the mixture is placed in a separating funnel, waiting for a moment until a clear phase boundary appears. Then the tap is carefully opened and water flows into the glass.
By settling, mixtures can be separated:

river sand and clay,
heavy crystalline precipitate from solution
oil and water
vegetable oil and water, etc.

MAGNETIC SEPARATION
The method is based on different magnetic properties of the solid components of the mixture. This method is used in the presence of ferromagnetic substances in the mixture, that is, substances with magnetic properties, such as iron.
All substances, in relation to the magnetic field, can be conditionally divided into three large groups:

pheromagnetics: attracted by magnet-Fe, Co, Ni, Gd, Dy
paramagnets: weakly attracted-Al, Cr, Ti, V, W, Mo
diamagnetics: Rebound from magnet - Cu, Ag, Au, Bi, Sn, brass

Magnetic separation can be separated b:

sulfur and iron powder
soot and iron, etc.

Separation of homogeneous mixtures
For separation of liquid homogeneous mixtures (true solutions) use the following methods:

evaporation (crystallization),
distillation (distillation),
chromatography.

EVAPORATION. CRYSTALLIZATION.
The method is based on different boiling points of the solvent and solute. Used to separate soluble solids from solutions. Evaporation is usually carried out as follows: the solution is poured into a porcelain cup and heated, constantly stirring the solution. The water gradually evaporates and a solid remains at the bottom of the cup.
DEFINITION
Crystallization- phase transition of a substance from a gaseous (vapor), liquid or solid amorphous state to a crystalline one.
In this case, the evaporated substance (water or solvent) can be collected by condensation on a colder surface. For example, if you place a cold glass slide over an evaporation dish, water droplets will form on the surface. The distillation method is based on the same principle.
DISTILLATION. DISTILLATION.
If a substance, for example sugar, decomposes on heating, then the water is not completely evaporated - the solution is evaporated, and then sugar crystals are precipitated from the saturated solution. Sometimes it is required to clean solvents from impurities, for example, water from salt. In this case, the solvent must be evaporated, and then its vapors must be collected and condensed on cooling. This method of separating a homogeneous mixture is called distillation, or distillation.

In nature, pure water (without salts) is not found. Oceanic, sea, river, well and spring water are varieties of salt solutions in water. However, people often need clean water that does not contain salts (it is used in car engines; in chemical production to obtain various solutions and substances; in the production of photographs). This water is called distilled, it is it that is used in the laboratory for conducting chemical experiments.
Distillation can be divided into:

water and alcohol
oil (for various fractions)
acetone and water, etc.

CHROMATOGRAPHY
Method of separation and analysis of mixtures of substances. Based on different rates of distribution of the test substance between two phases - stationary and mobile (eluent). The stationary phase, as a rule, is a sorbent (fine powder, for example, aluminum oxide or zinc oxide or filter paper) with a developed surface, and the mobile phase is a gas or liquid flow. The flow of the mobile phase is filtered through the sorbent layer or moves along the sorbent layer, for example, over the surface of filter paper.

You can independently obtain a chromatogram and see the essence of the method in practice. It is necessary to mix several inks and apply a drop of the resulting mixture to filter paper. Then, exactly in the middle of the colored speck, we begin to pour clean water drop by drop. Each drop should be applied only after the previous one has been absorbed. Water plays the role of an eluent that carries the test substance along the sorbent - porous paper. The substances that make up the mixture are retained by the paper in different ways: some are well retained by it, while others are absorbed more slowly and continue to spread out with water for some time. Soon, a real colorful chromatogram will begin to creep across the sheet of paper: a spot of the same color in the center, surrounded by multi-colored concentric rings.
Thin-layer chromatography has become especially widespread in organic analysis. The advantages of thin layer chromatography are that you can use the simplest and very sensitive detection method - visual control. It is possible to reveal spots invisible to the eye with various reagents, as well as using ultraviolet light or autoradiography.
In the analysis of organic and inorganic substances, chromatography on paper is used. Numerous methods have been developed for the separation of complex mixtures of ions, for example, mixtures of rare earth elements, uranium fission products, elements of the platinum group.
METHODS OF MIXTURE SEPARATION USED IN INDUSTRY.
The methods for separating mixtures used in the industry are not much different from the laboratory methods described above.
For oil separation, rectification (distillation) is most often used. This process is described in more detail in the topic. "Oil refining".
The most common methods of purification and separation of substances in industry are sedimentation, filtration, sorption and extraction. Filtration and settling methods are carried out similarly to the laboratory method, with the difference that settling tanks and filters of large volumes are used. Most often, these methods are used for wastewater treatment. Therefore, let's take a closer look at the methods extraction and sorption.
The term "extraction" can be applied to various phase equilibria (liquid - liquid, gas - liquid, liquid - solid, etc.), but more often it is applied to liquid - liquid systems, so the following definition can most often be found:
DEFINITION
Extraction i is a method of separation, purification and isolation of substances, based on the process of distributing a substance between two immiscible solvents.
One of the immiscible solvents is usually water, the other is an organic solvent, but this is not required. The extraction method is versatile, it is suitable for the isolation of almost all elements in various concentrations. Extraction allows complex multicomponent mixtures to be separated often more efficiently and faster than other methods. The extraction separation or separation does not require complex and expensive equipment. The process can be automated, if necessary, it can be controlled from a distance.
DEFINITION
Sorption- a method for the isolation and purification of substances based on the absorption by a solid (adsorption) or liquid sorbent (absorption) of various substances (sorbates) from gas or liquid mixtures.
Most often in the industry, absorption methods are used to clean gas-air emissions from dust or smoke particles, as well as toxic gaseous substances. In the case of absorption of gaseous substances, a chemical reaction can occur between the sorbent and the solute. For example, when absorbing gaseous ammoniaNH 3with a solution of nitric acid HNO 3, ammonium nitrate NH 4 NO 3 is formed(ammonium nitrate), which can be used as a highly effective nitrogen fertilizer.

Do you know what methods exist for separating mixtures? Take your time with 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? DI Mendeleev's table contains 118 chemical elements. These are different types of elementary particles - atoms. They differ in mass.

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 broken down into their constituents through chemical reactions.

Scientists argue that there are practically no pure substances in nature. There is an insignificant amount of impurities in each of them. This is because most substances are active. 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

The 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 homogeneous, 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 from a brine solution that are dissolved in it. Not only liquid solutions are found in nature. So, air is a gaseous homogeneous mixture, and an alloy of metals is 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 it is possible to separate them from each other purely mechanically. Cinderella perfectly coped with this task, which the evil stepmother forced to separate the beans from the peas.

Chemistry: methods of separating mixtures

A huge number of mixtures are found in everyday life and nature. How to choose the right way to separate them? It must necessarily be based on the physical properties of the individual components. If the 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 inhomogeneous mixtures, the difference in other properties of their constituents is used: density, wettability, solubility, size, magnetism, etc.

Physical methods of separation of mixtures

When separating the components of the mixture, the composition of the substances themselves does not change. Therefore, the methods of separating mixtures cannot be called a chemical process. Thus, by settling, filtering and magnetising, the individual components can be separated mechanically. At the same time, various devices are used in the laboratory: separating funnel, filter paper, magnetic strips. These are methods for separating inhomogeneous mixtures.

Screening

This method is perhaps the simplest. Every housewife is familiar with him. It is based on the difference in the 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, in this way, cereal grains are cleaned from foreign debris. Builders are sifting through a mixture of sand and gravel.

Upholding

This method of separation of mixtures is used for components with different densities. If the 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 oil. The sand will settle to the bottom. But the oil, on the contrary, will collect from the top. This method is observed in everyday life and nature. For example, soot settles out of the smoke, and separate drops of dew from the fog. And if you leave homemade milk overnight, then by morning you can collect the cream.

Filtration

Brewed tea lovers use this method on a daily basis. We are talking about filtration - a method of separating mixtures based on the different solubility 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 operation of respiratory masks and gauze dressings.

Magnet action

Suggest a method for separating mixtures of sulfur and iron powders. Naturally, this is a magnet action. Are all metals capable of this? Not at all. According to the degree of susceptibility, three groups of substances are distinguished. For example, gold, copper and zinc will not attach to a magnet. They are included in the group of diamagnets. Magnesium, platinum and aluminum are distinguished by poor perception. But if the mixture includes ferromagnets, then this method will be the most effective. These include, for example, iron, cobalt, nickel, terbium, holmium, thulium.

Evaporation

What method of separating mixtures is suitable for an aqueous homogeneous solution? This is evaporation. If you only have salt water, and you need clean water, you shouldn't get upset right away. It is necessary to heat the mixture to boiling point. As a result, the water will evaporate. Crystals of the solute will be visible at the bottom of the dish. To collect water, it must be condensed - transferred from a gaseous state to a liquid. For 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 sense. This is not just a method for obtaining pure substances. By their nature, crystals are icebergs, minerals, bones and tooth enamel.

Their growth occurs under the same conditions. Crystals are formed 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 center of crystallization arises, around which atoms of a liquid, melt, gas or glass gather.

Distillation

You've probably heard about distilled water. 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 drops". Using this method, for example, you can isolate alcohol and water from a solution. The first substance will begin to boil at a temperature of +78 o C. Alcohol vapors will condense further. The water will remain in liquid form.

In a similar way, the products of its processing 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, the primary oil separation is carried out. It is cleaned of associated gas, mechanical impurities and water vapor. At the next stage, the resulting product is placed in distillation columns and heating is started. This is atmospheric distillation of oil. At temperatures below 62 degrees, the residues of associated gas volatilize. By heating the mixture to 180 degrees, gasoline fractions are obtained, up to 240 - kerosene, up to 350 - diesel fuel. The remainder of the thermal processing of oil is fuel oil, which is used as a lubricant.

Chromatography

This method was named after the name of the scientist who first used it. His name was Mikhail Semenovich Tsvet. The method was originally used to separate plant pigments. And literally chromatography is translated from Greek as "I write in color." Dip the filter paper into a mixture of water and ink. The first one will immediately begin to be absorbed. This is due to the varying degrees of adsorbing properties. This also takes into account diffusion and the degree of solubility.

Adsorption

Some substances have the ability to attract other types of molecules. For example, we take activated charcoal when poisoning to get rid of toxins. This process requires an interface between the two phases.

This method is used in the chemical industry for the separation of benzene from gaseous mixtures, purification of liquid products of oil refining, and their purification from impurities.

So, in our article we examined the main methods for separating mixtures. A person uses them both at home and on an industrial scale. The choice of method depends on the type of mixture. An important factor is the features of the physical properties of its components. For the separation of solutions in which individual parts are visually indistinguishable, methods of evaporation, crystallization, chromatography and distillation are used. If the individual components can be identified, such mixtures are said to be heterogeneous. To separate them, methods of settling, filtering and magnetism are used.

I. New material

In preparing the lesson, the author's materials were used: N.K. Cheremisina,

chemistry teacher of secondary school number 43

(Kaliningrad),

We live among chemicals. We inhale air, and this is a mixture of gases ( nitrogen, oxygen and others), exhale carbon dioxide... We wash water- This is another substance most abundant on Earth. Drink milk- mix water with the smallest droplets of milk fat and more: there is also milk protein casein, mineral salt, vitamins and even sugar, but not the one with which they drink tea, but special, milk - lactose... We eat apples, which are composed of a whole range of chemicals - here and sugar, and Apple acid, and vitamins... When the chewed apple pieces enter the stomach, human digestive juices begin to act on them, which help to assimilate all the tasty and useful substances not only of the apple, but also of any other food. We not only live among chemicals, but we ourselves are made of them. Every person - his skin, muscles, blood, teeth, bones, hair - is built of chemicals, like a house is made of bricks. Nitrogen, oxygen, sugar, vitamins are substances of natural origin. Glass, rubber, steel is also substances, more precisely, materials(mixtures of substances). Both glass and rubber are of artificial origin, they did not exist in nature. Absolutely pure substances do not occur in nature or are very rare.

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; its taste is bitter-salty. The Black Sea water freezes at a lower temperature and boils at a higher temperature than the Baltic Sea water. Why? The fact is that seawater contains other substances, for example, dissolved salts, i.e. it is a mixture of various substances, the composition of which varies within wide limits, while the properties of the mixture are not constant. The definition of the concept "mixture" was given in the 17th century. English scientist Robert Boyle : "A mixture is a complete system consisting of dissimilar components."

Comparative characteristics of the mixture and the pure substance

Comparison criteria	Pure substance	Mixture
Compound	Constant	Fickle
Substances	Same	Various
Physical properties	Permanent	Fickle
Energy change during education	Is happening	Not happening
Separation	Through chemical reactions	Physical methods

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).

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.

Various methods of mixture separation are used to purify substances.

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

Consider waysdivisionheterogeneous and homogeneous mixtures .

Mix example	Separation method
Suspension - a mixture of river sand with water	Upholding Separation upholding based on different densities of substances. The heavier sand settles to the bottom. It is also possible to separate the emulsion: to separate oil or vegetable oil from water. In the laboratory, this can be done using a separating funnel. Oil or vegetable oil forms the upper, lighter layer.As a result of sedimentation, dew falls out of the fog, soot is deposited from the smoke, cream is settled in milk. Separation of a mixture of water and vegetable oil by settling
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. Across The filter pores pass only particles of substances commensurate with them, while larger particles are retained on the filter. So you can separate a heterogeneous mixture of table salt and river sand.Various porous substances can be used as filters: cotton wool, coal, fired clay, pressed glass and others. The filtering method is the basis for the operation of household appliances such as vacuum cleaners. It is used by surgeons - gauze bandages; drillers and elevator workers - respiratory masks. With the help of a tea strainer for filtering tea leaves, Ostap Bender, the hero of the work by Ilf and Petrov, managed to take one of the chairs from Ellochka the Cannibal ("The Twelve Chairs").
Iron and Sulfur Powder Blend	Magnet or water action 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. Separation of a mixture of sulfur and iron using a magnet and water
Salt in water solution - homogeneous mixture	Evaporation or crystallization The water evaporates and the salt crystals remain in the porcelain cup. By evaporation of water from lakes Elton and Baskunchak, table salt is obtained. This separation method is based on the difference in the boiling points of the solvent and the solute. If a substance, 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 purify solvents with a lower temperature from impurities. boiling, such as 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 receive distilled water whichused for the needs of pharmacology, laboratories, car cooling systems ... At home, you can design such a distiller: If you separate a mixture of alcohol and water, then the first will be distilled off (collected in the receiving tube) alcohol with t bip = 78 ° C, and water will remain in the test tube. Distillation is used to obtain gasoline, kerosene, gas oil from oil. Separation of homogeneous mixtures

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

For different purposes, substances with different degrees of purification are required. It is enough to stand the 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:

Distilled water application

II. Tasks for consolidation

1) Work with simulators number 1-4(necessarydownload the simulator, it will open in the Internet Explorer browser)