Solutions. How and when do liquids turn into gases? The main scientists who contributed to the development of the study of gases

You take a very hot shower for a long time, the bathroom mirror becomes covered in steam. You forget a pot of water on the window, and then you discover that the water has boiled away and the pan has burnt. You might think that water likes to change from gas to liquid, then from liquid to gas. But when does this happen?

In a ventilated space, water gradually evaporates at any temperature. But it boils only under certain conditions. The boiling point depends on the pressure above the liquid. At normal atmospheric pressure the boiling point will be 100 degrees. With altitude, the pressure will decrease as well as the boiling point. At the top of Mont Blanc it will be 85 degrees, and you won’t be able to make delicious tea there! But in a pressure cooker, when the whistle sounds, the water temperature is already 130 degrees, and the pressure is 4 times higher than atmospheric pressure. At this temperature, food cooks faster and the flavors don't escape with the guy because the valve is closed.

Changes in the state of aggregation of a substance with temperature changes.

Any liquid can turn into a gaseous state if it is heated enough, and any gas can turn into a liquid state if it is cooled. Therefore, butane, which is used in gas stoves and in the country, is stored in closed cylinders. It is liquid and under pressure, like a pressure cooker. And in the open air, at a temperature just below 0 degrees, methane boils and evaporates very quickly. Liquefied methane is stored in giant reservoirs called tanks. At normal atmospheric pressure, methane boils at a temperature of 160 degrees below zero. To prevent the gas from escaping during transportation, the tanks are carefully touched like thermoses.

Changes in the aggregative states of a substance with changes in pressure.

There is a dependence between the liquid and gaseous states of a substance on temperature and pressure. Since a substance is more saturated in the liquid state than in the gaseous state, you might think that if you increase the pressure, the gas will immediately turn into a liquid. But that's not true. However, if you start to compress air with a bicycle pump, you will find that it heats up. It accumulates the energy that you transfer to it by pressing on the piston. Gas can be compressed into liquid only if it is cooled at the same time. On the contrary, liquids need to receive heat in order to turn into gas. That is why evaporating alcohol or ether takes away heat from our body, creating a feeling of cold on the skin. The evaporation of sea water under the influence of the wind cools the water surface, and sweating cools the body.

Mixtures may differ from each other not only in composition, but also by appearance. According to what this mixture looks like and what properties it has, it can be classified as either homogeneous (homogeneous), or to heterogeneous (heterogeneous) mixtures.

Homogeneous (homogeneous) These are mixtures in which particles of other substances cannot be detected even with a microscope.

The composition and physical properties in all parts of such a mixture are the same, since there are no interfaces between its individual components.

TO homogeneous mixtures relate:

mixtures of gases;
solutions;
alloys

Gas mixtures

An example of such a homogeneous mixture is air.

Clean air contains various gaseous substances:

nitrogen (its volume fraction in clean air is \(78\)%));
oxygen (\(21\)%));
noble gases - argon and others (\(0.96\)%));
carbon dioxide (\(0.04\)%).

The gaseous mixture is natural gas And associated petroleum gas. The main components of these mixtures are gaseous hydrocarbons: methane, ethane, propane and butane.

Also a gaseous mixture is a renewable resource such as biogas, formed when bacteria process organic residues in landfills, in wastewater treatment tanks and in special installations. The main component of biogas is methane, which contains an admixture of carbon dioxide, hydrogen sulfide and a number of other gaseous substances.

Gas mixtures: air and biogas. The air can be sold to curious tourists, and biogas obtained from green mass in special containers can be used as fuel

Solutions

This is usually the name given to liquid mixtures of substances, although this term in science has a broader meaning: a solution is usually called any(including gaseous and solid) homogeneous mixture substances. So, about liquid solutions.

An important solution found in nature is oil. Liquid products obtained during its processing: gasoline, kerosene, diesel fuel, fuel oil, lubricating oils- are also a mixture of different hydrocarbons.

Pay attention!

To prepare a solution, you need to mix a gaseous, liquid or solid substance with a solvent (water, alcohol, acetone, etc.).

For example, ammonia obtained by dissolving ammonia gas in the input. In turn, for cooking iodine tinctures Crystalline iodine is dissolved in ethyl alcohol (ethanol).

Liquid homogeneous mixtures (solutions): oil and ammonia

The alloy (solid solution) can be obtained based on any metal, and its composition may include many different substances.

The most important ones at present are iron alloys- cast iron and steel.

Cast irons are iron alloys containing more than \(2\)% carbon, and steels are iron alloys containing less carbon.

What is commonly called "iron" is actually low carbon steel. Except carbon iron alloys may contain silicon, phosphorus, sulfur.

Today, the existence of more than 3 million different substances is known. And this figure is growing every year, as synthetic chemists and other scientists are constantly conducting experiments to obtain new compounds that have some useful properties.

Some substances are natural inhabitants, formed naturally. The other half are artificial and synthetic. However, in both the first and second cases, a significant part is made up of gaseous substances, examples and characteristics of which we will consider in this article.

Aggregate states of substances

Since the 17th century, it was generally accepted that all known compounds are capable of existing in three states of aggregation: solid, liquid, and gaseous substances. However, careful research in recent decades in the fields of astronomy, physics, chemistry, space biology and other sciences has proven that there is another form. This is plasma.

What is she? This is partially or completely. And it turns out that there is an overwhelming majority of such substances in the Universe. So, it is in the plasma state that the following are found:

interstellar matter;
cosmic matter;
upper layers of the atmosphere;
nebulae;
composition of many planets;
stars.

Therefore, today they say that there are solids, liquids, gases and plasma. By the way, every gas can be artificially transferred to this state if it is subjected to ionization, that is, forced to turn into ions.

Gaseous substances: examples

There are a lot of examples of the substances under consideration. After all, gases have been known since the 17th century, when van Helmont, a natural scientist, first obtained carbon dioxide and began to study its properties. By the way, he also gave the name to this group of compounds, since, in his opinion, gases are something disordered, chaotic, associated with spirits and something invisible, but tangible. This name has taken root in Russia.

It is possible to classify all gaseous substances, then it will be easier to give examples. After all, it is difficult to cover all the diversity.

According to the composition they are distinguished:

simple,
complex molecules.

The first group includes those that consist of identical atoms in any quantity. Example: oxygen - O 2, ozone - O 3, hydrogen - H 2, chlorine - CL 2, fluorine - F 2, nitrogen - N 2 and others.

hydrogen sulfide - H 2 S;
hydrogen chloride - HCL;
methane - CH 4;
sulfur dioxide - SO 2;
brown gas - NO 2;
freon - CF 2 CL 2;
ammonia - NH 3 and others.

Classification by nature of substances

You can also classify the types of gaseous substances according to their belonging to the organic and inorganic world. That is, by the nature of the atoms that make up it. Organic gases are:

the first five representatives (methane, ethane, propane, butane, pentane). General formula C n H 2n+2 ;
ethylene - C 2 H 4;
acetylene or ethylene - C 2 H 2;
methylamine - CH 3 NH 2 and others.

Another classification that can be applied to the compounds in question is division based on the particles they contain. Not all gaseous substances are made of atoms. Examples of structures in which ions, molecules, photons, electrons, Brownian particles, and plasma are present also refer to compounds in this state of aggregation.

Properties of gases

The characteristics of substances in the state under consideration differ from those of solid or liquid compounds. The thing is that the properties of gaseous substances are special. Their particles are easily and quickly mobile, the substance as a whole is isotropic, that is, the properties are not determined by the direction of movement of the structures included in the composition.

It is possible to identify the most important physical properties of gaseous substances, which will distinguish them from all other forms of existence of matter.

These are connections that cannot be seen, controlled, or felt by ordinary human means. To understand the properties and identify a particular gas, they rely on four parameters that describe them all: pressure, temperature, amount of substance (mol), volume.
Unlike liquids, gases are capable of occupying the entire space without a trace, limited only by the size of the vessel or room.
All gases easily mix with each other, and these compounds do not have an interface.
There are lighter and heavier representatives, so under the influence of gravity and time, it is possible to see their separation.
Diffusion is one of the most important properties of these compounds. The ability to penetrate other substances and saturate them from the inside, while performing completely disordered movements within its structure.
Real gases cannot conduct electric current, but if we talk about rarefied and ionized substances, then the conductivity increases sharply.
The heat capacity and thermal conductivity of gases is low and varies among different species.
Viscosity increases with increasing pressure and temperature.
There are two options for interphase transition: evaporation - a liquid turns into vapor, sublimation - a solid substance, bypassing the liquid one, becomes gaseous.

A distinctive feature of vapors from true gases is that the former, under certain conditions, are capable of turning into a liquid or solid phase, while the latter are not. It should also be noted that the compounds in question are able to resist deformation and be fluid.

Such properties of gaseous substances allow them to be widely used in various fields of science and technology, industry and the national economy. In addition, specific characteristics are strictly individual for each representative. We considered only the features common to all real structures.

Compressibility

At different temperatures, as well as under the influence of pressure, gases are able to compress, increasing their concentration and reducing their occupied volume. At elevated temperatures they expand, at low temperatures they contract.

Changes also occur under pressure. The density of gaseous substances increases and, upon reaching a critical point, which is different for each representative, a transition to another state of aggregation may occur.

The main scientists who contributed to the development of the study of gases

There are many such people, because the study of gases is a labor-intensive and historically long process. Let us dwell on the most famous personalities who managed to make the most significant discoveries.

made a discovery in 1811. It doesn’t matter what kind of gases, the main thing is that under the same conditions, one volume contains an equal amount of them in terms of the number of molecules. There is a calculated value named after the name of the scientist. It is equal to 6.03 * 10 23 molecules for 1 mole of any gas.
Fermi - created the theory of an ideal quantum gas.
Gay-Lussac, Boyle-Marriott - the names of the scientists who created the basic kinetic equations for calculations.
Robert Boyle.
John Dalton.
Jacques Charles and many other scientists.

Structure of gaseous substances

The most important feature in the construction of the crystal lattice of the substances under consideration is that its nodes contain either atoms or molecules that are connected to each other by weak covalent bonds. Van der Waals forces are also present when it comes to ions, electrons and other quantum systems.

Therefore, the main types of structure of gas lattices are:

atomic;
molecular.

The connections inside are easily broken, so these connections do not have a constant shape, but fill the entire spatial volume. This also explains the lack of electrical conductivity and poor thermal conductivity. But gases have good thermal insulation, because, thanks to diffusion, they are able to penetrate into solids and occupy free cluster spaces inside them. At the same time, air is not passed through, heat is retained. This is the basis for the combined use of gases and solids for construction purposes.

Simple substances among gases

We have already discussed above which gases belong to this category in terms of structure and structure. These are those that consist of identical atoms. Many examples can be given, because a significant part of non-metals from the entire periodic table under normal conditions exists in precisely this state of aggregation. For example:

white phosphorus - one of this element;
nitrogen;
oxygen;
fluorine;
chlorine;
helium;
neon;
argon;
krypton;
xenon.

The molecules of these gases can be either monatomic (noble gases) or polyatomic (ozone - O 3). The type of bond is covalent nonpolar, in most cases it is quite weak, but not in all of them. The crystal lattice is of a molecular type, which allows these substances to easily move from one state of aggregation to another. For example, iodine under normal conditions is dark purple crystals with a metallic luster. However, when heated, they sublimate into clouds of bright purple gas - I 2.

By the way, any substance, including metals, can exist in a gaseous state under certain conditions.

Complex compounds of gaseous nature

Such gases, of course, are the majority. Various combinations of atoms in molecules, united by covalent bonds and van der Waals interactions, allow the formation of hundreds of different representatives of the considered state of aggregation.

Examples of complex substances among gases can be all compounds consisting of two or more different elements. This may include:

propane;
butane;
acetylene;
ammonia;
silane;
phosphine;
methane;
carbon disulfide;
sulphur dioxide;
brown gas;
freon;
ethylene and others.

Crystal lattice of molecular type. Many of the representatives easily dissolve in water, forming the corresponding acids. Most of these compounds are an important part of chemical syntheses carried out in industry.

Methane and its homologues

Sometimes the general concept of “gas” refers to a natural mineral, which is a whole mixture of gaseous products of predominantly organic nature. It contains substances such as:

methane;
ethane;
propane;
butane;
ethylene;
acetylene;
pentane and some others.

In industry, they are very important, because the propane-butane mixture is the household gas with which people cook, which is used as a source of energy and heat.

Many of them are used for the synthesis of alcohols, aldehydes, acids and other organic substances. Annual consumption of natural gas amounts to trillions of cubic meters, and this is quite justified.

Oxygen and carbon dioxide

What gaseous substances can be called the most widespread and known even to first-graders? The answer is obvious - oxygen and carbon dioxide. After all, they are the direct participants in the gas exchange that occurs in all living beings on the planet.

It is known that it is thanks to oxygen that life is possible, since only some types of anaerobic bacteria can exist without it. And carbon dioxide is a necessary “food” product for all plants that absorb it in order to carry out the process of photosynthesis.

From a chemical point of view, both oxygen and carbon dioxide are important substances for carrying out syntheses of compounds. The first is a strong oxidizing agent, the second is more often a reducing agent.

Halogens

This is a group of compounds in which the atoms are particles of a gaseous substance, connected in pairs to each other through a covalent non-polar bond. However, not all halogens are gases. Bromine is a liquid under ordinary conditions, and iodine is an easily sublimated solid. Fluorine and chlorine are toxic substances that are dangerous to the health of living beings, which are strong oxidizing agents and are used very widely in syntheses.

3. Hydrocarbons

HYDROCARBONS, organic compounds whose molecules consist only of carbon and hydrogen atoms.

The simplest representative is methane CH 4. Hydrocarbons are the founders of all other organic compounds, a huge variety of which can be obtained by introducing functional groups into the hydrocarbon molecule; Therefore, organic chemistry is often defined as the chemistry of hydrocarbons and their derivatives.

Hydrocarbons, depending on their molecular weight, can be gaseous, liquid or solid (but plastic) substances. Compounds containing up to four carbon atoms in a molecule, under normal conditions - gases, for example methane, ethane, propane, butane, isobutane; These hydrocarbons are part of the combustible natural and associated petroleum gases. Liquid hydrocarbons are part of oil and petroleum products; they typically contain up to sixteen carbon atoms. Some waxes, paraffin, asphalts, bitumen, and tar contain even heavier hydrocarbons; Thus, paraffin contains solid hydrocarbons containing from 16 to 30 carbon atoms.

Hydrocarbons are divided into compounds with an open chain - aliphatic, or non-cyclic, compounds with a closed cyclic structure - alicyclic (do not have the property of aromaticity) and aromatic (their molecules contain a benzene ring or fragments built from fused benzene rings). Aromatic hydrocarbons are classified as a separate class because, due to the presence of a closed conjugated system of HS bonds, they have specific properties.

Non-cyclic hydrocarbons can have a non-branched chain of carbon atoms (molecules of normal structure) and a branched one (molecules of isostructure). Depending on the type of bonds between the carbon atoms, both aliphatic and cyclic hydrocarbons are divided into saturated ones, containing only simple bonds (alkanes, cycloalkanes) , and unsaturated, containing multiple bonds along with simple ones (alkenes, cycloalkenes, dienes, alkynes, cyclo-alkynes).

The classification of hydrocarbons is reflected in the diagram (see page 590), which also provides examples of the structures of representatives of each class of hydrocarbons.

Hydrocarbons are indispensable as a source of energy, since the main common property of all these compounds is the release of a significant amount of heat during combustion (for example, the heat of combustion of methane is 890 kJ/mol). Mixtures of hydrocarbons are used as fuel at thermal stations and boiler houses (natural gas, fuel oil, boiler fuel), as fuel for engines of cars, aircraft and other vehicles (gasoline, kerosene and diesel fuel). When hydrocarbons are completely burned, water and carbon dioxide are formed.

In terms of reactivity, different classes of hydrocarbons differ greatly from each other: saturated compounds are relatively inert, unsaturated compounds are characterized by addition reactions at multiple bonds, and aromatic compounds are characterized by substitution reactions (for example, nitration, sulfonation).

Hydrocarbons are used as starting and intermediate products in organic synthesis. In the chemical and petrochemical industries, not only hydrocarbons of natural origin are used, but also synthetic ones. Methods for obtaining the latter are based on the processing of natural gas (production and use of synthesis gas - a mixture of CO and H2), oil (cracking), coal (hydrogenation), and more recently biomass, in particular agricultural waste, wood processing and others production

3.1 Marginal hydrocarbons. Alkanes CnH3n+2

Features of the chemical structure

Basic physical and chemical properties:

CH4 gas is colorless and odorless, lighter than air, insoluble in water

С-С4 – gas;

C5-C16 - liquid;

C16 and more – solid

Examples of hydrocarbons used in cosmetology, their composition and properties (paraffin, petroleum jelly).

In cosmetics, hydrocarbons are used to create a film that provides a gliding effect (for example, in massage creams) and as structure-forming components of various preparations.

Gaseous hydrocarbons

Methone and ethane are components of natural gas. Propane and butane (in liquefied form) are fuels for transport.

Liquid hydrocarbons

Petrol. Transparent, flammable liquid with a typical odor, easily soluble in organic solvents (alcohol, ether, carbon tetrachloride). A mixture of gasoline and air is a strong explosive. Special gasoline is sometimes used to degrease and clean the skin, for example, from plaster residues.

Vaseline oil. A liquid, viscous hydrocarbon with a high boiling point and low viscosity. In cosmetics it is used as hair oil, skin oil, and is part of creams. Paraffin oil. Transparent, colorless, colorless, odorless, thick, oily substance, high viscosity, insoluble in water, almost insoluble in ethanol, soluble in ether and other organic solvents. Solid hydrocarbons

Paraffin. A mixture of solid hydrocarbons obtained by distillation of the paraffin fraction of oil. Paraffin is a crystalline mass with a specific odor and a neutral reaction. Paraffin is used in thermotherapy. Molten paraffin, which has a high heat capacity, cools slowly and, gradually releasing heat, maintains uniform warming of the body for a long time. As it cools, paraffin passes from a liquid to a solid state and, decreasing in volume, compresses the underlying tissue. By preventing hyperemia of superficial vessels, molten paraffin increases tissue temperature and sharply increases sweating. Indications for paraffin therapy are seborrhea of the facial skin, acne, especially indurative acne, infiltrated chronic eczema. It is advisable to prescribe facial cleansing after the paraffin mask.

Ceresin. A mixture of hydrocarbons obtained by processing ozokerite. It is used in decorative cosmetics as a thickener, as the coke mixes well with fats.

Petrolatum – a mixture of hydrocarbons. It is a good base for ointments, does not decompose the medicinal substances included in their composition, and is mixed with oils and fats in any quantities. All hydrocarbons are not saponified and cannot penetrate directly through the skin, therefore they are used in cosmetics as a surface protectant. All liquid, semi-solid and solid hydrocarbons do not go rancid (are not affected by microorganisms).

The hydrocarbons considered are called acyclic. They are contrasted with cyclic (having a benzene ring in the molecule) hydrocarbons, which are obtained during the distillation of coal tar - benzene (solvent), naphthalene, which was previously used as a moth repellent, anthracene and other substances.

3.2 Unsaturated hydrocarbons

Alkenes (ethylene hydrocarbons) are unsaturated hydrocarbons, the molecules of which have one double bond.

Features of the chemical structure

With 2 H 4 ethylene is a colorless gas with a weak sweetish odor, lighter than air, slightly soluble in water.

Principles for naming hydrocarbons:

Hydrocarbons containing a double bond end in –ene.

Ethane C 2 H 6 ethene C 2 H 4

3.3 Cyclic and aromatic hydrocarbons, principles of chemical structure, examples

Arenes (aromatic hydrocarbons), the molecules of which contain stable cyclic structures - benzene rings, with a special nature of bonds.

There are no single (C - O and double (C = C) bonds in the benzene molecule. All bonds are equivalent, their lengths are equal. This is a special type of bond - a circular p-conjugation.

Hybridization - ;s p 2 Bond angle -120°

Six non-hybrid bonds form a single -electron system (aromatic ring), which is located perpendicular to the plane of the benzene ring.

Chemical properties:

Benzene occupies an intermediate position between saturated and unsaturated hydrocarbons, because enters into a substitution reaction (easy) and addition reaction (difficult).

Azulene. This is a cyclic hydrocarbon obtained synthetically (the natural analogue of chamazulene is obtained from chamomile and yarrow flowers). Azulene has anti-allergic and anti-inflammatory properties, relieves spasms of smooth muscles, accelerates the processes of tissue regeneration and healing. It is used in cosmetics in concentrated form (dark blue liquid) and in the form of a 25% solution in children's creams, toothpaste and decorative products, as well as in resins for biomechanical depilation.

4. Alcohols

4.1 Definition

Alcohols are organic compounds in which one hydrogen atom (H) is replaced by a hydroxyl group (OH).

4.2 Functional groups. Classification of alcohols into monohydric and polyhydric alcohols, examples. Principles for naming alcohols

According to the number of OH groups, mono- and polyhydric alcohols are distinguished.

Depending on the location of the OH group, alcohols are divided into primary, secondary and tertiary. Unlike paraffin hydrocarbons, they have a relatively high boiling point. All polyhydric alcohols have a sweetish taste.

Short chain alcohols are hydrophilic, i.e. mix with water and dissolve hydrophilic substances well. Monohydric alcohols with long chains are almost or completely insoluble in water, i.e. hydrophobic.

Alcohols with large molecular masses (fatty alcohols) are solid at room temperature (for example, myristyl or cetyl alcohol). An alcohol containing more than 24 carbon atoms is called waxed alcohol.

As the number of hydroxyl groups increases, the sweet taste and solubility of alcohol in water increase. Therefore, glycerin (3-hydric alcohol), similar to oil, dissolves well in water. Solid 6-atomic alcohol sorbitol is used as a sugar substitute for diabetic patients.

4.3 Basic chemical and physical properties of alcohols, their use in cosmetology (methanol, ethanol, isopropanol, glycerin)

Monohydric alcohols

Methanol (methyl alcohol, wood alcohol) is a clear, colorless liquid, easily mixed with water, alcohol and ether. This extremely toxic substance is not used in cosmetics.

Ethanol (ethyl alcohol, wine alcohol, food alcohol) is a transparent, colorless, volatile liquid, can be mixed with water and organic solvents, is much less toxic than methanol, is widely used in medicine and cosmetics as a solvent for biologically active substances (essential oils , resins, iodine, etc.). Ethanol is produced by fermentation of substances containing sugar and starch. The fermentation process occurs due to yeast enzymes. After fermentation, the alcohol is isolated by distillation. Then purification from undesirable substances and impurities is carried out (rectification). Ethanol is supplied to pharmacies mainly at 96° strength. Other mixtures of ethanol and water contain 90, 80, 70, 40% alcohol. Almost pure alcohol (with very minor impurities of water) is called absolute alcohol.

Depending on the purpose of using alcohol, it is flavored with various additives (essential oils, camphor). Ethanol promotes the expansion of subcutaneous capillaries and has a disinfectant effect.

Eau de toilette for the face can contain from 0 to 30% alcohol, hair lotion - about 50%, cologne - at least 70%. Lavender water contains about 3% essential oil. Perfumes contain from 12 to 20% essential oils and a fixative, colognes - about 9% essential oils and a little fixative. Isopropanol (isopropyl alcohol) is a complete and inexpensive substitute for ethanol and belongs to secondary alcohols. Even purified isopropyl alcohol has a characteristic odor that cannot be eliminated. The disinfecting and degreasing properties of isopropanol are stronger than those of ethyl alcohol. It is used only externally, as part of eau de toilette for hair, in fixatives, etc. Vodka should not contain isopropanol, and a small amount of it is allowed in an alcohol tincture of pine needles (pine concentrate).

Polyhydric alcohols

Dihydric alcohols have a standard ending to their name - glycol. In cosmetic preparations, propylene glycol, which has low toxicity, is used as a solvent and humectant. Dihydric alcohols, or glycols, are called diols according to substitutive nomenclature. Trihydric alcohol - glycerin - is widely used in medicine and pharmaceuticals. The consistency of glycerin is similar to syrup, almost odorless, hygroscopic, has a sweet taste, soluble in all other substances containing an OH group, insoluble in ether, gasoline, chloroform, fatty and essential oils. 86 - 88% glycerin and dehydrated 98% glycerin are supplied to trade. In diluted form, glycerin is included in skin creams, facial eau de toilette, toothpastes, shaving soap, and hand gel. Diluted in appropriate proportions, it softens the skin, makes it elastic, replacing the natural moisture factor of the skin. It is not used in its pure form in skin care products because it dries it out. and human health organic chemistry USSR Academy of Sciences, one of the organizers... to several areas organic chemistry - chemistry alicyclic compounds, chemistry heterocycles, organic catalysis, chemistry protein and amino acids. ...

Effects of ion association in organic chemistry

Abstract >> Chemistry

Stereochemical direction of the process. IN organic chemistry interest in ion pairs arose... the most striking achievements of physical organic chemistry. Reaction studies, in... the concept of ion pairs in organic chemistry has undergone significant changes; were...

single-phase systems consisting of two or more components. According to their state of aggregation, solutions can be solid, liquid or gaseous. So, air is a gaseous solution, a homogeneous mixture of gases; vodka- liquid solution, a mixture of several substances forming one liquid phase; sea water- liquid solution, a mixture of solid (salt) and liquid (water) substances forming one liquid phase; brass- solid solution, a mixture of two solids (copper and zinc) forming one solid phase. A mixture of gasoline and water is not a solution because these liquids do not dissolve in each other, remaining as two liquid phases with an interface. The components of the solutions retain their unique properties and do not enter into chemical reactions with each other to form new compounds. Thus, when two volumes of hydrogen are mixed with one volume of oxygen, a gaseous solution is obtained. If this gas mixture is ignited, a new substance is formed- water, which in itself is not a solution. The component present in the solution in larger quantities is usually called a solvent, the remaining components- dissolved substances.

However, sometimes it is difficult to draw the line between the physical mixing of substances and their chemical interaction. For example, when mixing hydrogen chloride gas HCl with water

H2O H ions are formed 3 O+ and Cl - . They attract neighboring water molecules to themselves, forming hydrates. Thus, the starting components are HCl and H 2 O - undergo significant changes after mixing. Nevertheless, ionization and hydration (in the general case, solvation) are considered as physical processes that occur during the formation of solutions.

One of the most important types of mixtures that represent a homogeneous phase are colloidal solutions: gels, sols, emulsions and aerosols. The particle size in colloidal solutions is 1-1000 nm, in true solutions

~ 0.1 nm (on the order of molecular size).Basic Concepts. Two substances that dissolve in each other in any proportions to form true solutions are called completely mutually soluble. Such substances are all gases, many liquids (for example, ethyl alcohol- water, glycerin - water, benzene - gasoline), some solids (for example, silver - gold). To obtain solid solutions, you must first melt the starting substances, then mix them and allow them to solidify. When they are completely mutually soluble, one solid phase is formed; if the solubility is partial, then small crystals of one of the original components are retained in the resulting solid.

If two components form one phase when mixed only in certain proportions, and in other cases two phases appear, then they are called partially mutually soluble. These are, for example, water and benzene: true solutions are obtained from them only by adding a small amount of water to a large volume of benzene or a small amount of benzene to a large volume of water. If you mix equal amounts of water and benzene, a two-phase liquid system is formed. Its lower layer is water with a small amount of benzene, and the upper

- benzene with a small amount of water. There are also known substances that do not dissolve in one another at all, for example, water and mercury. If two substances are only partially mutually soluble, then at a given temperature and pressure there is a limit to the amount of one substance that can form a true solution with the other under equilibrium conditions. A solution with a maximum concentration of solute is called saturated. You can also prepare a so-called supersaturated solution, in which the concentration of the dissolved substance is even greater than in a saturated one. However, supersaturated solutions are unstable, and with the slightest change in conditions, for example, with stirring, the ingress of dust particles, or the addition of crystals of a solute, the excess solute precipitates.

Any liquid begins to boil at the temperature at which its saturated vapor pressure reaches the external pressure. For example, water under a pressure of 101.3 kPa boils at 100

° C because at this temperature the water vapor pressure is exactly 101.3 kPa. If you dissolve some non-volatile substance in water, its vapor pressure will decrease. To bring the vapor pressure of the resulting solution to 101.3 kPa, you need to heat the solution above 100° C. It follows that the boiling point of the solution is always higher than the boiling point of the pure solvent. The decrease in the freezing point of solutions is explained in a similar way.Raoult's law. In 1887, the French physicist F. Raoult, studying solutions of various non-volatile liquids and solids, established a law relating the decrease in vapor pressure over dilute solutions of non-electrolytes with concentration: the relative decrease in the saturated vapor pressure of the solvent above the solution is equal to the mole fraction of the dissolved substance. Raoult's law states that the increase in boiling point or decrease in freezing point of a dilute solution compared to a pure solvent is proportional to the molar concentration (or mole fraction) of the solute and can be used to determine its molecular weight.

A solution whose behavior obeys Raoult's law is called ideal. Solutions of nonpolar gases and liquids (the molecules of which do not change orientation in an electric field) are closest to ideal. In this case, the heat of solution is zero, and the properties of solutions can be directly predicted by knowing the properties of the original components and the proportions in which they are mixed. For real solutions such a prediction cannot be made. When real solutions are formed, heat is usually released or absorbed. Processes with heat release are called exothermic, and processes with absorption are called endothermic.

Those characteristics of a solution that depend mainly on its concentration (the number of molecules of the solute per unit volume or mass of the solvent), and not on the nature of the solute, are called

colligative . For example, the boiling point of pure water at normal atmospheric pressure is 100° C, and the boiling point of a solution containing 1 mole of dissolved (non-dissociating) substance in 1000 g of water is already 100.52° C regardless of the nature of this substance. If the substance dissociates, forming ions, then the boiling point increases in proportion to the increase in the total number of particles of the solute, which, due to dissociation, exceeds the number of molecules of the substance added to the solution. Other important colligative quantities are the freezing point of a solution, osmotic pressure and partial pressure of solvent vapor.Solution concentration is a quantity that reflects the proportions between the solute and the solvent. Qualitative concepts such as “dilute” and “concentrated” only indicate that a solution contains little or a lot of solute. To quantify the concentration of solutions, percentages (mass or volume) are often used, and in the scientific literature - the number of moles or chemical equivalents (cm . EQUIVALENT MASS)solute per unit mass or volume of solvent or solution. To avoid confusion, the concentration units should always be specified accurately. Consider the following example. A solution consisting of 90 g of water (its volume is 90 ml, since the density of water is 1 g/ml) and 10 g of ethyl alcohol (its volume is 12.6 ml, since the density of alcohol is 0.794 g/ml) has a mass of 100 g , but the volume of this solution is 101.6 ml (and it would be equal to 102.6 ml if, when mixing water and alcohol, their volumes simply added up). The percentage concentration of a solution can be calculated in different ways: or

The units of concentration used in the scientific literature are based on concepts such as mole and equivalent, since all chemical calculations and equations of chemical reactions must be based on the fact that substances react with each other in certain proportions. For example, 1 eq. NaCl equal to 58.5 g reacts with 1 eq. AgNO 3 equal to 170 g. It is clear that solutions containing 1 eq. These substances have completely different percentage concentrations.Molarity (M or mol/l) - the number of moles of dissolved substances contained in 1 liter of solution.Molality (m) - the number of moles of solute contained in 1000 g of solvent.Normality (n.) - the number of chemical equivalents of a dissolved substance contained in 1 liter of solution.Mole fraction (dimensionless value) - the number of moles of a given component divided by the total number of moles of solute and solvent. (Mole percent - mole fraction multiplied by 100.)

The most common unit is molarity, but there are some ambiguities to consider when calculating it. For example, to obtain a 1M solution of a given substance, an exact weighed portion of it equal to mol. is dissolved in a known small amount of water. mass in grams, and bring the volume of the solution to 1 liter. The amount of water required to prepare this solution may vary slightly depending on temperature and pressure. Therefore, two one-molar solutions prepared under different conditions do not actually have exactly the same concentrations. Molality is calculated based on a certain mass of solvent (1000 g), which does not depend on temperature and pressure. In laboratory practice, it is much more convenient to measure certain volumes of liquids (for this there are burettes, pipettes, and volumetric flasks) than to weigh them, therefore, in the scientific literature, concentrations are often expressed in moles, and molality is usually used only for particularly precise measurements.

Normality is used to simplify calculations. As we have already said, substances interact with each other in quantities corresponding to their equivalents. By preparing solutions of different substances of the same normality and taking equal volumes, we can be sure that they contain the same number of equivalents.

In cases where it is difficult (or unnecessary) to distinguish between solvent and solute, concentration is measured in mole fractions. Mole fractions, like molality, do not depend on temperature and pressure.

Knowing the densities of the solute and solution, one can convert one concentration to another: molarity to molality, mole fraction and vice versa. For dilute solutions of a given solute and solvent, these three quantities are proportional to each other.

Solubility of a given substance is its ability to form solutions with other substances. Quantitatively, the solubility of a gas, liquid or solid is measured by the concentration of its saturated solution at a given temperature. This is an important characteristic of a substance, helping to understand its nature, as well as influence the course of reactions in which this substance is involved.Gases. In the absence of chemical interaction, gases mix with each other in any proportions, and in this case there is no point in talking about saturation. However, when a gas dissolves in a liquid, there is a certain limiting concentration, depending on pressure and temperature. The solubility of gases in some liquids correlates with their ability to liquefy. The most easily liquefied gases, such as NH 3, HCl, SO 2 , more soluble than difficult to liquefy gases, such as O 2 , H 2 and He. If there is a chemical interaction between the solvent and the gas (for example, between water and NH 3 or HCl) solubility increases. The solubility of a given gas varies with the nature of the solvent, but the order in which the gases are arranged according to increasing solubility remains approximately the same for different solvents.

The dissolution process obeys Le Chatelier's principle (1884): if a system in equilibrium is subject to any influence, then as a result of the processes occurring in it, the equilibrium will shift in such a direction that the effect will decrease. The dissolution of gases in liquids is usually accompanied by the release of heat. At the same time, in accordance with Le Chatelier's principle, the solubility of gases decreases. This decrease is more noticeable the higher the solubility of gases: such gases also have

greater heat of solution. The “soft” taste of boiled or distilled water is explained by the absence of air in it, since its solubility at high temperatures is very low.

As pressure increases, the solubility of gases increases. According to Henry's law (1803), the mass of a gas that can dissolve in a given volume of liquid at a constant temperature is proportional to its pressure. This property is used to make carbonated drinks. Carbon dioxide is dissolved in liquid at a pressure of 3-4 atm; under these conditions, 3-4 times more gas (by mass) can dissolve in a given volume than at 1 atm. When a container with such a liquid is opened, the pressure in it drops, and part of the dissolved gas is released in the form of bubbles. A similar effect is observed when opening a bottle of champagne or reaching the surface of groundwater saturated with carbon dioxide at great depths.

When a mixture of gases is dissolved in one liquid, the solubility of each of them remains the same as in the absence of other components at the same pressure as in the case of the mixture (Dalton's law).

Liquids. The mutual solubility of two liquids is determined by how similar the structure of their molecules is (“like dissolves in like”). Non-polar liquids, such as hydrocarbons, are characterized by weak intermolecular interactions, so molecules of one liquid easily penetrate between the molecules of another, i.e. the liquids mix well. In contrast, polar and non-polar liquids, such as water and hydrocarbons, do not mix well with each other. Each water molecule must first escape from the environment of other similar molecules that strongly attract it to itself, and penetrate between the hydrocarbon molecules that weakly attract it. Conversely, hydrocarbon molecules, in order to dissolve in water, must squeeze between water molecules, overcoming their strong mutual attraction, and this requires energy. As the temperature rises, the kinetic energy of molecules increases, intermolecular interactions weaken, and the solubility of water and hydrocarbons increases. With a significant increase in temperature, their complete mutual solubility can be achieved. This temperature is called the upper critical solution temperature (UCST).

In some cases, the mutual solubility of two partially miscible liquids increases with decreasing temperature. This effect occurs when heat is generated during mixing, usually as a result of a chemical reaction. With a significant decrease in temperature, but not below the freezing point, the lower critical solution temperature (LCST) can be reached. It can be assumed that all systems that have LCTE also have HCTE (the reverse is not necessary). However, in most cases, one of the mixing liquids boils at a temperature below the HTST. The nicotine-water system has an LCTR of 61

° C, and VCTR is 208° C. Between 61-208° C, these liquids have limited solubility, and outside this range they have complete mutual solubility.Solids. All solids exhibit limited solubility in liquids. Their saturated solutions at a given temperature have a certain composition, which depends on the nature of the solute and solvent. Thus, the solubility of sodium chloride in water is several million times higher than the solubility of naphthalene in water, and when they are dissolved in benzene, the opposite picture is observed. This example illustrates the general rule that a solid will readily dissolve in a liquid having similar chemical and physical properties, but will not dissolve in a liquid with opposite properties.

Salts are usually easily soluble in water and less so in other polar solvents, such as alcohol and liquid ammonia. However, the solubility of salts also varies significantly: for example, ammonium nitrate is millions of times more soluble in water than silver chloride.

The dissolution of solids in liquids is usually accompanied by the absorption of heat, and according to Le Chatelier's principle, their solubility should increase with heating. This effect can be used to purify substances by recrystallization. To do this, they are dissolved at high temperature until a saturated solution is obtained, then the solution is cooled and after the dissolved substance precipitates, it is filtered. There are substances (for example, calcium hydroxide, sulfate and acetate), the solubility of which in water decreases with increasing temperature.

Solids, like liquids, can also completely dissolve in each other, forming a homogeneous mixture - a true solid solution, similar to a liquid solution. Partially soluble substances in each other form two equilibrium conjugate solid solutions, the compositions of which change with temperature.

Distribution coefficient. If a solution of a substance is added to an equilibrium system of two immiscible or partially miscible liquids, then it is distributed between the liquids in a certain proportion, independent of the total amount of the substance, in the absence of chemical interactions in the system. This rule is called the distribution law, and the ratio of the concentrations of a dissolved substance in liquids is called the distribution coefficient. The distribution coefficient is approximately equal to the ratio of the solubilities of a given substance in two liquids, i.e. the substance is distributed between liquids according to its solubility. This property is used to extract a given substance from its solution in one solvent using another solvent. Another example of its application is the process of extracting silver from ores, in which it is often included along with lead. To do this, zinc is added to the molten ore, which does not mix with lead. Silver is distributed between molten lead and zinc, mainly in the upper layer of the latter. This layer is collected and the silver is separated by zinc distillation.Solubility product (ETC ). Between excess (precipitate) solid matter M x B y and its saturated solution establishes a dynamic equilibrium described by the equationThe equilibrium constant of this reaction is

and is called the solubility product. It is constant at a given temperature and pressure and is the value on the basis of which the solubility of the precipitate is calculated and changed. If a compound is added to the solution that dissociates into ions of the same name as the ions of a slightly soluble salt, then, in accordance with the expression for PR, the solubility of the salt decreases. When adding a compound that reacts with one of the ions, it, on the contrary, will increase.On some properties of solutions of ionic compounds see also ELECTROLYTES. LITERATURE Shakhparonov M.I. Introduction to Molecular Theory of Solutions . M., 1956
Remy I. Inorganic chemistry course , vol. 1-2. M., 1963, 1966