Some substances dissolve better in a particular solvent, others worse. It is believed that absolutely insoluble substances do not exist. Every substance is capable of solubility, even if in some cases in very small quantities (for example, mercury in water, benzene in water).
Unfortunately, to date, there is no theory by which one could predict and calculate the solubility of any substance in the corresponding solvent. This is due to the complexity and diversity of the interaction of the components of the solution with each other and the lack of a general theory of solutions (especially concentrated ones). In this regard, the necessary data on the solubility of substances are obtained, as a rule, empirically.
Quantitatively, the ability of a substance to dissolve is most often characterized by solubility or solubility coefficient (S).
Solubility (S) shows how many grams of a substance can dissolve as much as possible under given conditions (temperature, pressure) in 100 g of a solvent to form a saturated solution.
If necessary, the solubility coefficient is also determined for a different amount of solvent (for example, for 1000 g, 100 cm 3 , 1000 cm 3 , etc.).
By solubility, all substances, depending on their nature, are divided into 3 groups: 1) highly soluble; 2) slightly soluble; 3) poorly soluble or insoluble.
The solubility coefficient for substances of the first group is more than 1 g (per 100 g of solvent), for substances of the second group lies in the range of 0.01 - 1.0 g and for substances of the third group S< 0,01 г.
The solubility of substances is influenced by many factors, the main of which are the nature of the solvent and the solute, temperature, pressure, and the presence of other substances (especially electrolytes) in the solution.
Influence of the nature of substances on solubility
It has been experimentally established that in a solvent whose molecules are polar, substances formed by ionic or covalent polar bonds. And in a solvent whose molecules are non-polar, substances formed by weakly polar or non-polar covalent bonds dissolve better. In another way, this revealed regularity can be formulated as follows: "Like dissolves into like."
The solubility of substances is largely determined by the strength and nature of their interaction with solvent molecules. The more pronounced this interaction, the greater the solubility and vice versa.
It is known that the forces acting between nonpolar and weakly polar molecules are small and nonspecific; in quantitative terms do not significantly depend on the type of substance.
If similar nonpolar molecules A are introduced into a nonpolar liquid B, then the energy of interaction between particles A and B will not differ significantly from the energy of interaction between particles A and A or particles B and B. Therefore, just as any amount of the same substance is mixed , with a high probability will mix with each other indefinitely (i.e., dissolve in each other) and various non-polar liquids.
For the same reason, molecular crystals usually dissolve better in non-polar liquids.
If the interaction energy of molecules A and A or B and B is greater than A and B, then the same molecules of each component will preferentially bind to each other and their solubility in each other will decrease (Table 6).
The polarity of any solvent is often characterized by the value of its permittivity (ε), which is easily determined empirically. The larger it is, the more polar the substance is.
Table 6. Solubility of KI (wt%) in solvents of different polarity
A solution is a homogeneous system consisting of two or more substances, the content of which can be changed within certain limits without violating homogeneity.
Aquatic solutions are made up of water(solvent) and solute. The state of substances in an aqueous solution, if necessary, is indicated by a subscript (p), for example, KNO 3 in solution - KNO 3 (p) .
Solutions that contain a small amount of solute are often referred to as diluted while solutions with high solute content concentrated. A solution in which further dissolution of a substance is possible is called unsaturated and a solution in which a substance ceases to dissolve under given conditions is saturated. The last solution is always in contact (in heterogeneous equilibrium) with the undissolved substance (one or more crystals).
V special conditions, for example, when carefully (without stirring) cooling a hot unsaturated solution solid substances can form supersaturated solution. When a crystal of a substance is introduced, such a solution is separated into a saturated solution and a precipitate of the substance.
In accordance with chemical theory of solutions D. I. Mendeleev, the dissolution of a substance in water is accompanied, firstly, destruction chemical bonds between molecules (intermolecular bonds in covalent substances) or between ions (in ionic substances), and thus the particles of the substance mix with water (in which some of the hydrogen bonds between molecules are also destroyed). Chemical bonds are broken due to the thermal energy of the movement of water molecules, and in this case cost energy in the form of heat.
Secondly, once in the water, the particles (molecules or ions) of the substance are subjected to hydration. As a result, hydrates- compounds of indeterminate composition between particles of matter and water molecules ( internal composition the particles of the substance themselves do not change during dissolution). This process is accompanied highlighting energy in the form of heat due to the formation of new chemical bonds in hydrates.
In general, a solution cools down(if the cost of heat exceeds its release), or heats up (otherwise); sometimes - if the cost of heat and its release are equal - the temperature of the solution remains unchanged.
Many hydrates are so stable that they do not break down even when the solution is completely evaporated. So, solid crystal hydrates of salts CuSO 4 5H 2 O, Na 2 CO 3 10H 2 O, KAl (SO 4) 2 12H 2 O, etc. are known.
The content of a substance in a saturated solution at T= const quantifies solubility this substance. Solubility is usually expressed as the mass of solute per 100 g of water, for example 65.2 g KBr/100 g H 2 O at 20 °C. Therefore, if 70 g of solid potassium bromide is introduced into 100 g of water at 20 °C, then 65.2 g of salt will go into solution (which will be saturated), and 4.8 g of solid KBr (excess) will remain at the bottom of the beaker.
It should be remembered that the solute content in rich solution equals, v unsaturated solution less and in supersaturated solution more its solubility at a given temperature. So, a solution prepared at 20 ° C from 100 g of water and sodium sulfate Na 2 SO 4 (solubility 19.2 g / 100 g H 2 O), with a content
15.7 g of salt - unsaturated;
19.2 g salt - saturated;
2O.3 g of salt is supersaturated.
The solubility of solids (Table 14) usually increases with increasing temperature (KBr, NaCl), and only for some substances (CaSO 4 , Li 2 CO 3) is the opposite observed.
The solubility of gases decreases with increasing temperature, and increases with increasing pressure; for example, at a pressure of 1 atm, the solubility of ammonia is 52.6 (20 ° C) and 15.4 g / 100 g H 2 O (80 ° C), and at 20 ° C and 9 atm it is 93.5 g / 100 g H 2 O.
In accordance with the solubility values, substances are distinguished:
– well soluble, the mass of which in a saturated solution is commensurate with the mass of water (for example, KBr - at 20 ° C the solubility is 65.2 g / 100 g H 2 O; 4.6 M solution), they form saturated solutions with a molarity of more than 0.1 M;
– sparingly soluble, the mass of which in a saturated solution is much less than the mass of water (for example, CaSO 4 - at 20 ° C the solubility is 0.206 g / 100 g H 2 O; 0.015 M solution), they form saturated solutions with a molarity of 0.1–0.001 M;
– practically insoluble the mass of which in a saturated solution is negligible compared to the mass of the solvent (for example, AgCl - at 20 ° C, the solubility is 0.00019 g per 100 g of H 2 O; 0.0000134 M solution), they form saturated solutions with a molarity of less than 0.001 M.
Compiled according to reference data solubility table common acids, bases and salts (Table 15), in which the type of solubility is indicated, substances are noted that are not known to science (not obtained) or completely decomposed by water.
Conventions used in the table:
"r" is a highly soluble substance
"m" - poorly soluble substance
"n" - practically insoluble substance
"-" - the substance is not received (does not exist)
» - the substance is miscible with water indefinitely
Note. This table corresponds to the preparation of a saturated solution at room temperature by introducing a substance (in the appropriate state of aggregation) in water. It should be noted that it is not always possible to obtain precipitates of poorly soluble substances using ion exchange reactions (for details, see 13.4).
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All topics in this section:
Common elements. structure of atoms. Electronic shells. Orbitals
Chemical element - certain kind atoms, denoted by name and symbol and characterized by serial number and relative atomic mass. In table. 1 list
Each orbital can hold at most two electrons.
One electron in an orbital is called unpaired, two electrons are called an electron pair:
The properties of the elements are in a periodic dependence on the ordinal number.
The periodically recurring nature of the change in the composition of the electron shell of the atoms of elements explains the periodic change in the properties of elements when moving through periods and groups Pe
Molecules. Chemical bond. The structure of substances
Chemical particles formed from two or more atoms are called molecules (real or conditional formula units of polyatomic substances). Atoms in a mol
Calcium
Calcium is an element of the 4th period and IIA‑group Periodic system, serial number 2O. Electronic formula of the atom 4s2, oxidation state
Aluminum
Aluminum is an element of the 3rd period and IIIA group of the Periodic system, serial number 13. The electronic formula of the atom is 3s23p1,
Manganese
Manganese is an element of the 4th period and VIIB-group of the Periodic system, serial number 25. The electronic formula of the atom is 3d54s2;
General properties of metals. Corrosion
Elements with metallic properties are located in the IA - VIA groups of the Periodic Table (Table 7).
Hydrogen
Hydrogen is the first element of the Periodic Table (1st period, serial number 1). Does not have a complete analogy with the rest chemical elements and does not belong to any
Chlorine. Hydrogen chloride
Chlorine is an element of the 3rd period and VII A-group of the Periodic system, serial number 17. The electronic formula of the atom is 3s23p5, ha
chlorides
Sodium chloride NaCl. Anoxic salt. The common name is table salt. White, slightly hygroscopic. Melts and boils without decomposition. Dissolve moderately
Hypochlorites. Chlorates
Calcium hypochlorite Ca(ClO)2. Salt of hypochlorous acid HClO. White, decomposes without melting when heated. Well soluble in cold water(arr.
Bromides. iodides
Potassium bromide KBr. Anoxic salt. White, non-hygroscopic, melts without decomposition. Let's well dissolve in water, there is no hydrolysis. Reducing agent (weaker, h
Oxygen
Oxygen - an element of the 2nd period and the VIA group of the Periodic Table, serial number 8, belongs to chalcogens (but is more often considered separately). Electronic pho
Sulfur. Hydrogen sulfide. Sulfides
Sulfur is an element of the 3rd period and VIA‑group of the Periodic system, serial number 16, belongs to chalcogens. The electronic formula of the atom is 3s
Sulphur dioxide. Sulfites
Sulfur dioxide SO2. Acid oxide. A colorless gas with a pungent odor. The molecule has the structure of an incomplete triangle [: S(O)2] (sp
Sulphuric acid. sulfates
Sulfuric acid H2SO4. Oxoacid. Colorless liquid, very viscous (oily), very hygroscopic. Molek
Nitrogen. Ammonia
Nitrogen is an element of the 2nd period and the VA group of the Periodic Table, serial number 7. The electronic formula of the atom is 2s22p3, character
nitrogen oxides. Nitric acid
Nitrogen monoxide NO. Non-salt forming oxide. colorless gas. The radical contains a covalent σπ-bond (N=O), in the solid state the N2 dimer
Nitrites. Nitrates
Potassium nitriteKNO2. Oksosol. White, hygroscopic. Melts without decomposition. Stable in dry air. Very soluble in water (forming colorless
Free carbon
Carbon is an element of the 2nd period and IVA group of the Periodic Table, serial number 6. The chemistry of carbon is mainly the chemistry of organic compounds; inorganic
Oxides of carbon
Carbon monoxide CO. Non-salt forming oxide. Colorless gas, odorless, lighter than air. The molecule is weakly polar, contains a covalent triple σππ
Carbonates
Sodium carbonate Na2CO3. Oksosol. The technical name is soda ash. White, melts and decomposes when heated. Feelings
Silicon
Silicon is an element of the 3rd period and IVA group of the Periodic system, serial number 14. The electronic formula of the atom is 3s23p2. X
Alkanes. Cycloalkanes
Alkanes (paraffins) are compounds of carbon and hydrogen, in the molecules of which the carbon atoms are interconnected by a single bond (limiting hydrocarbons).
Alkenes. Alkadienes
Alkenes (olefins) are hydrocarbons whose molecules contain carbon atoms linked by a double bond ( unsaturated hydrocarbons row
Alcohols. Ethers. Phenols
Alcohols are derivatives of hydrocarbons containing the functional group OH (hydroxyl). Alcohols that have one OH group are called monoat
Aldehydes and ketones
Aldehydes and ketones are derivatives of hydrocarbons containing a CO functional carbonyl group. In aldehydes, the carbonyl group is bonded to a
carboxylic acids. Complex ethers. Fats
Carboxylic acids are derivatives of hydrocarbons containing the functional group COOH (carboxyl). Formulas and names of some common
Carbohydrates
Carbohydrates (sugars) are the most important natural compounds consisting of carbon, hydrogen and oxygen. Carbohydrates are divided into monosaccharides, disaccharides and polysaccharides.
Nitro compounds. Amines
Very important in national economy nitrogen-containing organic matter. Nitrogen can be included in organic compounds in the form of the nitro group NO2, the amino group NH2 and a
Amino acids. Squirrels
Amino acids are organic compounds that contain two functional groups– acid COOH and amine NH2
Reaction rate
Quantitative characteristic of the speed of the flow chemical reaction A + B → D + E is its speed, i.e. the speed of interaction of particles of reagents A
The rate of a chemical reaction is directly proportional to the product of the molar concentrations of the reactants
when a reaction requires two reacting molecules to collide. This dependence is called the kinetic law of acting masses (K. Gullberg, P. Vog
Energy of reactions
Any reaction is accompanied by the release or absorption of energy in the form of heat. In the initial substances, chemical bonds are broken, and energy is spent on this (i.e., it is
Reversibility of reactions
A chemical reaction is called reversible if, under the given conditions, not only the direct reaction (→) proceeds, but also the reverse reaction, i.e., from the starting substances
When exposed to an equilibrium system, the chemical equilibrium shifts to the side that counteracts this effect.
Let us consider in more detail the influence of such factors as temperature, pressure, concentration on the equilibrium shift. 1. Temperature. temperature rise
Electrolytic dissociation
The dissolution of any substance in water is accompanied by the formation of hydrates. If, in this case, no formula changes occur in the particles of the dissolved substance in the solution, then such substances
dissociation of water. Solution medium
Water itself is a very weak electrolyte:
Ion exchange reactions
In dilute solutions of electrolytes (acids, bases, salts), chemical reactions usually proceed with the participation of ions. In this case, all elements of the reagents can be preserved.
Salt hydrolysis
Salt hydrolysis is the interaction of its ions with water, leading to the appearance of an acidic or alkaline environment, but not accompanied by the formation of a precipitate or gas (below
Oxidizing and reducing agents
Redox reactions proceed with a simultaneous increase and decrease in the oxidation states of elements and are accompanied by the transfer of electrons:
Selection of coefficients by the electronic balance method
The method consists of several stages. 1. Write down the reaction scheme; find elements that increase and decrease their oxidation states, and drink
A range of stress metals
In a series of metal stresses, the arrow corresponds to a decrease in the reducing ability of metals and an increase in the oxidizing ability of their cations in an aqueous solution (acidic environment):
Melt and solution electrolysis
Electrolysis is a redox process that occurs on the electrodes during the passage of a constant electric current through solutions or
Mass fraction of the dissolved substance. Dilution, concentration and mixing of solutions
The mass fraction of the dissolved substance B (ω in) is the ratio of the mass of substance B (t in) to the mass of the solution (m (p)
Volume ratio of gases
For a chemical reaction a A + b B = c C + d D, the relation
Mass (volume, amount of substance) of the product according to the reagent in excess or with impurities
Excess and lack of reagents. The quantities, masses and volumes (for gases) of the reactants are not always taken as stoichiometric, that is, in accordance with the reaction equations. H
Finding the molecular formula of an organic compound
When deriving formulas of substances, especially in organic chemistry, the relative density of a gas is often used. The relative density of the gas X is the ratio of the absolute
Solution is called a thermodynamically stable homogeneous (single-phase) system of variable composition, consisting of two or more components ( chemical substances). The components that make up a solution are a solvent and a solute. Typically, a solvent is considered to be a component that exists in its pure form in the same state of aggregation as the resulting solution (for example, in the case of an aqueous salt solution, the solvent is, of course, water). If both components before dissolution were in the same state of aggregation (for example, alcohol and water), then the component that is in a larger amount is considered the solvent.
Solutions are liquid, solid and gaseous.
Liquid solutions are solutions of salts, sugar, alcohol in water. Liquid solutions may be aqueous or non-aqueous. Aqueous solutions are solutions in which the solvent is water. Non-aqueous solutions are solutions in which organic liquids (benzene, alcohol, ether, etc.) are solvents. Solid solutions are metal alloys. Gaseous solutions - air and other mixtures of gases.
Dissolution process. Dissolution is a complex physical and chemical process. During the physical process, the structure of the dissolved substance is destroyed and its particles are distributed between the solvent molecules. chemical process is the interaction of solvent molecules with solute particles. As a result of this interaction, solvates. If the solvent is water, then the resulting solvates are called hydrates. The process of formation of solvates is called solvation, the process of formation of hydrates is called hydration. When aqueous solutions are evaporated, crystalline hydrates are formed - these are crystalline substances, which include a certain number of water molecules (water of crystallization). Examples of crystalline hydrates: CuSO 4 . 5H 2 O - copper (II) sulfate pentahydrate; FeSO4 . 7H 2 O - iron sulfate heptahydrate (II).
The physical process of dissolution proceeds with takeover energy, chemical highlighting. If as a result of hydration (solvation) more energy is released than it is absorbed during the destruction of the structure of a substance, then dissolution - exothermic process. Energy is released during the dissolution of NaOH, H 2 SO 4 , Na 2 CO 3 , ZnSO 4 and other substances. If more energy is needed to destroy the structure of a substance than it is released during hydration, then dissolution - endothermic process. Energy absorption occurs when NaNO 3 , KCl, NH 4 NO 3 , K 2 SO 4 , NH 4 Cl and some other substances are dissolved in water.
The amount of energy released or absorbed during dissolution is called thermal effect of dissolution.
Solubility substance is its ability to be distributed in another substance in the form of atoms, ions or molecules with the formation of a thermodynamically stable system of variable composition. The quantitative characteristic of solubility is solubility factor, which shows what is the maximum mass of a substance that can be dissolved in 1000 or 100 g of water at a given temperature. The solubility of a substance depends on the nature of the solvent and substance, on temperature and pressure (for gases). The solubility of solids generally increases with increasing temperature. The solubility of gases decreases with increasing temperature, but increases with increasing pressure.
According to their solubility in water, substances are divided into three groups:
1. Highly soluble (p.). The solubility of substances is more than 10 g in 1000 g of water. For example, 2000 g of sugar dissolves in 1000 g of water, or 1 liter of water.
2. Slightly soluble (m.). The solubility of substances is from 0.01 g to 10 g in 1000 g of water. For example, 2 g of gypsum (CaSO 4 . 2 H 2 O) dissolves in 1000 g of water.
3. Practically insoluble (n.). The solubility of substances is less than 0.01 g in 1000 g of water. For example, in 1000 g of water, 1.5 . 10 -3 g AgCl.
When substances are dissolved, saturated, unsaturated and supersaturated solutions can be formed.
saturated solution is the solution that contains the maximum amount of solute under given conditions. When a substance is added to such a solution, the substance no longer dissolves.
unsaturated solution A solution that contains less solute than a saturated solution under given conditions. When a substance is added to such a solution, the substance still dissolves.
Sometimes it is possible to obtain a solution in which the solute contains more than in a saturated solution at a given temperature. Such a solution is called supersaturated. This solution is obtained by carefully cooling the saturated solution to room temperature. Supersaturated solutions are very unstable. Crystallization of a substance in such a solution can be caused by rubbing the walls of the vessel in which the solution is located with a glass rod. This method is used when performing some qualitative reactions.
The solubility of a substance can also be expressed by the molar concentration of its saturated solution (section 2.2).
Solubility constant. Let us consider the processes that occur during the interaction of a poorly soluble but strong electrolyte of barium sulfate BaSO 4 with water. Under the action of water dipoles, Ba 2+ and SO 4 2 - ions from the crystal lattice of BaSO 4 will pass into the liquid phase. Simultaneously with this process, under the influence electrostatic field part of the Ba 2+ and SO 4 2 - ions will again be deposited in the crystal lattice (Fig. 3). At a given temperature, an equilibrium will finally be established in a heterogeneous system: the rate of the dissolution process (V 1) will be equal to the rate of the precipitation process (V 2), i.e.
BaSO 4 ⇄ Ba 2+ + SO 4 2 -
solid solution
Rice. 3. Saturated barium sulfate solution
A solution in equilibrium with the BaSO 4 solid phase is called rich relative to barium sulfate.
A saturated solution is an equilibrium heterogeneous system characterized by a constant chemical equilibrium:
, (1)
where a (Ba 2+) is the activity of barium ions; a(SO 4 2-) - activity of sulfate ions;
a (BaSO 4) is the activity of barium sulfate molecules.
The denominator of this fraction - the activity of crystalline BaSO 4 - is a constant value, equal to one. The product of two constants gives a new constant called thermodynamic solubility constant and denote K s °:
K s ° \u003d a (Ba 2+) . a(SO 4 2-). (2)
This value was previously called the solubility product and was designated PR.
Thus, in a saturated solution of a poorly soluble strong electrolyte, the product of the equilibrium activities of its ions is a constant value at a given temperature.
If we accept that in a saturated solution of a sparingly soluble electrolyte, the activity coefficient f~1, then the activity of ions in this case can be replaced by their concentrations, since a( X) = f (X) . WITH( X). The thermodynamic solubility constant K s ° will turn into the concentration solubility constant K s:
K s \u003d C (Ba 2+) . C(SO 4 2-), (3)
where C(Ba 2+) and C(SO 4 2 -) are the equilibrium concentrations of Ba 2+ and SO 4 2 - ions (mol / l) in a saturated solution of barium sulfate.
To simplify calculations, the concentration solubility constant K s is usually used, taking f(X) = 1 (Appendix 2).
If a poorly soluble strong electrolyte forms several ions during dissociation, then the expression K s (or K s °) includes the corresponding powers equal to the stoichiometric coefficients:
PbCl 2 ⇄ Pb 2+ + 2 Cl-; K s \u003d C (Pb 2+) . C 2 (Cl -);
Ag3PO4 ⇄ 3 Ag + + PO 4 3 - ; K s \u003d C 3 (Ag +) . C (PO 4 3 -).
V general view expression of the concentration solubility constant for the electrolyte A m B n ⇄ m A n+ + n B m - has the form
K s \u003d C m (A n+) . C n (B m -),
where C are the concentrations of A n+ and B m ions in a saturated electrolyte solution in mol/l.
The value of K s is usually used only for electrolytes, the solubility of which in water does not exceed 0.01 mol/l.
Precipitation conditions
Suppose c is the actual concentration of ions of a sparingly soluble electrolyte in solution.
If C m (A n +) . With n (B m -) > K s , then a precipitate will form, because the solution becomes supersaturated.
If C m (A n +) . C n (B m -)< K s , то раствор является ненасыщенным и осадок не образуется.
Solution properties. Below we consider the properties of nonelectrolyte solutions. In the case of electrolytes, a correction isotonic coefficient is introduced into the above formulas.
If a non-volatile substance is dissolved in a liquid, then the saturation vapor pressure over the solution is less than the saturation vapor pressure over the pure solvent. Simultaneously with the decrease in vapor pressure over the solution, a change in its boiling and freezing point is observed; the boiling points of solutions increase, and the freezing points decrease in comparison with the temperatures characterizing pure solvents.
The relative decrease in the freezing point or the relative increase in the boiling point of a solution is proportional to its concentration.
SOLUBILITY called the ability of a substance to dissolve in a particular solvent. A measure of the solubility of a substance under given conditions is its content in a saturated solution . If more than 10 g of a substance dissolves in 100 g of water, then such a substance is called highly soluble. If less than 1 g of a substance dissolves, the substance sparingly soluble. Finally, the substance is considered practically insoluble if less than 0.01 g of the substance passes into the solution. There are no absolutely insoluble substances. Even when we pour water into glass vessel, a very small part of the glass molecules inevitably goes into solution.
Solubility, expressed as the mass of a substance that can be dissolved in 100 g of water at a given temperature, is also called solubility coefficient.
Solubility of some substances in water at room temperature.
The solubility of most (but not all!) solids increases with increasing temperature, while the solubility of gases, on the contrary, decreases. This is primarily due to the fact that gas molecules during thermal motion are able to leave the solution much more easily than molecules of solids.
If we measure the solubility of substances at different temperatures, it will be found that some substances noticeably change their solubility depending on temperature, others - not very much
When solids are dissolved in water the volume of the system usually changes slightly. Therefore, the solubility of substances in the solid state is practically independent of pressure.
Liquids can also dissolve in liquids.. Some of them are indefinitely soluble in one another, that is, they mix with each other in any proportions, such as alcohol and water, while others dissolve mutually only up to a certain limit. So if diethyl ether is shaken with water, two layers are formed: the upper one is a saturated solution of water in ether, and the lower one is a saturated solution of ether in water. In most such cases, as the temperature rises, the mutual solubility of the liquids increases until a temperature is reached at which both liquids are mixed in any proportions.
Dissolution of gases in water is an exothermic process. Therefore, the solubility of gases decreases with increasing temperature. If you leave a glass with cold water, then its inner walls are covered with gas bubbles - this is air that was dissolved in water, is released from it due to heating. Boiling can remove all the air dissolved in it from the water.