The solubility table for salts, acids and bases is the foundation without which it is impossible to fully master chemical knowledge. The solubility of bases and salts helps in learning not only for schoolchildren, but also for professional people. The creation of many life products cannot do without this knowledge.
Table of solubility of acids, salts and bases in water
The table of solubility of salts and bases in water is a guide that helps in mastering the basics of chemistry. The following notes will help you understand the table below.
- P – indicates a soluble substance;
- H – insoluble substance;
- M – the substance is slightly soluble in an aqueous environment;
- RK - a substance that can dissolve only when exposed to strong organic acids;
- A dash will indicate that such a creature does not exist in nature;
- NK – does not dissolve in either acids or water;
- ? – a question mark indicates that today there is no accurate information about the dissolution of the substance.
Often, the table is used by chemists and schoolchildren, students to conduct laboratory research, during which it is necessary to establish the conditions for the occurrence of certain reactions. Using the table, it is possible to determine how a substance will behave in a salt or acidic environment, and whether a precipitate may appear. A precipitate during research and experiments indicates the irreversibility of the reaction. This is a significant point that can affect the course of all laboratory work.
SALT, a class of chemical compounds. There is currently no generally accepted definition of the concept of “Salts,” as well as the terms “acids and bases,” the reaction products of which salts are. Salts can be considered as products of the replacement of acid hydrogen protons with metal ions, NH 4 +, CH 3 NH 3 + and other cations or OH groups of the base with acid anions (for example, Cl -, SO 4 2-).
Classification
The products of complete substitution are medium salts, for example. Na 2 SO 4, MgCl 2, partially acidic or basic salts, for example KHSO 4, СuСlОН. There are also simple salts, including one type of cations and one type of anions (for example, NaCl), double salts containing two types of cations (for example, KAl(SO 4) 2 12H 2 O), mixed salts, which contain two types of acid residues ( for example AgClBr). Complex salts contain complex ions, such as K4.
Physical properties
Typical salts are crystalline substances with an ionic structure, for example CsF. There are also covalent salts, for example AlCl 3. In fact, the nature of the chemical bond of many salts is mixed.
Based on their solubility in water, they distinguish between soluble, slightly soluble and practically insoluble salts. Soluble salts include almost all sodium, potassium and ammonium salts, many nitrates, acetates and chlorides, with the exception of polyvalent metal salts that hydrolyze in water, and many acidic salts.
Solubility of salts in water at room temperature
| Cations | Anions | |||||||||
| F- | Cl- | Br- | I - | S 2- | NO 3 - | CO 3 2- | SiO 3 2- | SO 4 2- | PO 4 3- | |
| Na+ | R | R | R | R | R | R | R | R | R | R |
| K+ | R | R | R | R | R | R | R | R | R | R |
| NH4+ | R | R | R | R | R | R | R | R | R | R |
| Mg 2+ | RK | R | R | R | M | R | N | RK | R | RK |
| Ca2+ | NK | R | R | R | M | R | N | RK | M | RK |
| Sr 2+ | NK | R | R | R | R | R | N | RK | RK | RK |
| Ba 2+ | RK | R | R | R | R | R | N | RK | NK | RK |
| Sn 2+ | R | R | R | M | RK | R | N | N | R | N |
| Pb 2+ | N | M | M | M | RK | R | N | N | N | N |
| Al 3+ | M | R | R | R | G | R | G | NK | R | RK |
| Cr 3+ | R | R | R | R | G | R | G | N | R | RK |
| Mn 2+ | R | R | R | R | N | R | N | N | R | N |
| Fe 2+ | M | R | R | R | N | R | N | N | R | N |
| Fe 3+ | R | R | R | - | - | R | G | N | R | RK |
| Co2+ | M | R | R | R | N | R | N | N | R | N |
| Ni 2+ | M | R | R | R | RK | R | N | N | R | N |
| Cu 2+ | M | R | R | - | N | R | G | N | R | N |
| Zn 2+ | M | R | R | R | RK | R | N | N | R | N |
| Cd 2+ | R | R | R | R | RK | R | N | N | R | N |
| Hg 2+ | R | R | M | NK | NK | R | N | N | R | N |
| Hg 2 2+ | R | NK | NK | NK | RK | R | N | N | M | N |
| Ag+ | R | NK | NK | NK | NK | R | N | N | M | N |
Legend:
P - the substance is highly soluble in water; M - slightly soluble; H - practically insoluble in water, but easily soluble in weak or dilute acids; RK - insoluble in water and soluble only in strong inorganic acids; NK - insoluble in either water or acids; G - completely hydrolyzes when dissolved and does not exist in contact with water. A dash means that such a substance does not exist at all.
In aqueous solutions, salts completely or partially dissociate into ions. Salts of weak acids and/or weak bases undergo hydrolysis. Aqueous solutions of salts contain hydrated ions, ion pairs and more complex chemical forms, including hydrolysis products, etc. A number of salts are also soluble in alcohols, acetone, acid amides and other organic solvents.
From aqueous solutions, salts can crystallize in the form of crystal hydrates, from non-aqueous solutions - in the form of crystal solvates, for example CaBr 2 3C 2 H 5 OH.
Data on various processes occurring in water-salt systems, on the solubility of salts in their joint presence depending on temperature, pressure and concentration, on the composition of solid and liquid phases can be obtained by studying the solubility diagrams of water-salt systems.
General methods for the synthesis of salts.
1. Obtaining medium salts:
1) metal with non-metal: 2Na + Cl 2 = 2NaCl
2) metal with acid: Zn + 2HCl = ZnCl 2 + H 2
3) metal with a salt solution of a less active metal Fe + CuSO 4 = FeSO 4 + Cu
4) basic oxide with acidic oxide: MgO + CO 2 = MgCO 3
5) basic oxide with acid CuO + H 2 SO 4 = CuSO 4 + H 2 O
6) bases with acid oxide Ba(OH) 2 + CO 2 = BaCO 3 + H 2 O
7) bases with acid: Ca(OH) 2 + 2HCl = CaCl 2 + 2H 2 O
8) salts with acid: MgCO 3 + 2HCl = MgCl 2 + H 2 O + CO 2
BaCl 2 + H 2 SO 4 = BaSO 4 + 2HCl
9) base solution with salt solution: Ba(OH) 2 + Na 2 SO 4 = 2NaOH + BaSO 4
10) solutions of two salts 3CaCl 2 + 2Na 3 PO 4 = Ca 3 (PO 4) 2 + 6NaCl
2. Obtaining acid salts:
1. Interaction of an acid with a lack of base. KOH + H2SO4 = KHSO4 + H2O
2. Interaction of the base with excess acid oxide
Ca(OH) 2 + 2CO 2 = Ca(HCO 3) 2
3. Interaction of the average salt with the acid Ca 3 (PO 4) 2 + 4H 3 PO 4 = 3Ca(H 2 PO 4) 2
3. Obtaining basic salts:
1. Hydrolysis of salts formed by a weak base and a strong acid
ZnCl 2 + H 2 O = Cl + HCl
2. Adding (drop by drop) small amounts of alkalis to solutions of medium metal salts AlCl 3 + 2NaOH = Cl + 2NaCl
3. Interaction of salts of weak acids with medium salts
2MgCl 2 + 2Na 2 CO 3 + H 2 O = 2 CO 3 + CO 2 + 4NaCl
4. Preparation of complex salts:
1. Reactions of salts with ligands: AgCl + 2NH 3 = Cl
FeCl 3 + 6KCN] = K 3 + 3KCl
5. Preparation of double salts:
1. Joint crystallization of two salts:
Cr 2 (SO 4) 3 + K 2 SO 4 + 24H 2 O = 2 + NaCl
4. Redox reactions caused by the properties of the cation or anion. 2KMnO 4 + 16HCl = 2MnCl 2 + 2KCl + 5Cl 2 + 8H 2 O
2. Chemical properties of acid salts:
Thermal decomposition to form medium salt
Ca(HCO 3) 2 = CaCO 3 + CO 2 + H 2 O
Interaction with alkali. Getting medium salt.
Ba(HCO 3) 2 + Ba(OH) 2 = 2BaCO 3 + 2H 2 O
3. Chemical properties of basic salts:
Thermal decomposition. 2 CO 3 = 2CuO + CO 2 + H 2 O
Interaction with acid: formation of medium salt.
Sn(OH)Cl + HCl = SnCl 2 + H 2 O
4. Chemical properties of complex salts:
1. Destruction of complexes due to the formation of poorly soluble compounds:
2Cl + K2S = CuS + 2KCl + 4NH3
2. Exchange of ligands between the outer and inner spheres.
K 2 + 6H 2 O = Cl 2 + 2KCl
5. Chemical properties of double salts:
Interaction with alkali solutions: KCr(SO 4) 2 + 3KOH = Cr(OH) 3 + 2K 2 SO 4
2. Reduction: KCr(SO 4) 2 + 2H°(Zn, dil. H 2 SO 4) = 2CrSO 4 + H 2 SO 4 + K 2 SO 4
The raw materials for the industrial production of a number of salts - chlorides, sulfates, carbonates, borates Na, K, Ca, Mg are sea and ocean water, natural brines formed during its evaporation, and solid salt deposits. For the group of minerals that form sedimentary salt deposits (sulfates and chlorides of Na, K and Mg), the conventional name “natural salts” is used. The largest deposits of potassium salts are located in Russia (Solikamsk), Canada and Germany, powerful deposits of phosphate ores are in North Africa, Russia and Kazakhstan, NaNO3 is in Chile.
Salts are used in the food, chemical, metallurgical, glass, leather, textile industries, agriculture, medicine, etc.
Main types of salts
1. Borats(oxoborates), salts of boric acids: metaboric HBO 2, orthoboric H3 BO 3 and polyboronic acids not isolated in a free state. Based on the number of boron atoms in the molecule, they are divided into mono-, di, tetra-, hexaborates, etc. Borates are also called by the acids that form them and by the number of moles of B 2 O 3 per 1 mole of the main oxide. Thus, various metaborates can be called monoborates if they contain the B(OH) 4 anion or a chain anion (BO 2) n n-diborates - if they contain a chain double anion (B 2 O 3 (OH) 2) n 2n-triborates - if they contain ring anion (B 3 O 6) 3-.
Table salt is sodium chloride used as a food additive and food preservative. It is also used in the chemical industry and medicine. It serves as the most important raw material for the production of caustic soda, soda and other substances. The formula for table salt is NaCl.
Formation of an ionic bond between sodium and chlorine
The chemical composition of sodium chloride is reflected by the conventional formula NaCl, which gives an idea of the equal number of sodium and chlorine atoms. But the substance is not formed by diatomic molecules, but consists of crystals. When an alkali metal reacts with a strong nonmetal, each sodium atom gives up the more electronegative chlorine. Sodium cations Na + and anions of the acidic residue of hydrochloric acid Cl - appear. Oppositely charged particles attract each other, forming a substance with an ionic crystal lattice. Small sodium cations are located between large chlorine anions. The number of positive particles in the composition of sodium chloride is equal to the number of negative ones; the substance as a whole is neutral.
Chemical formula. Table salt and halite
Salts are complex substances of ionic structure, the names of which begin with the name of the acidic residue. The formula for table salt is NaCl. Geologists call a mineral of this composition “halite,” and a sedimentary rock “rock salt.” An outdated chemical term that is often used in manufacturing is “sodium chloride.” This substance has been known to people since ancient times; it was once considered “white gold”. Modern schoolchildren and students, when reading reaction equations involving sodium chloride, use chemical symbols (“sodium chlorine”).
Let's carry out simple calculations using the formula of the substance:
1) Mr (NaCl) = Ar (Na) + Ar (Cl) = 22.99 + 35.45 = 58.44.
The relative value is 58.44 (in amu).
2) Molar mass is numerically equal to molecular weight, but this quantity has units of measurement g/mol: M (NaCl) = 58.44 g/mol.
3) A 100 g sample of salt contains 60.663 g of chlorine atoms and 39.337 g of sodium.
Physical properties of table salt
Fragile halite crystals are colorless or white. In nature, there are also deposits of rock salt, colored grey, yellow or blue. Sometimes a mineral substance has a red tint, which is due to the types and amount of impurities. The hardness of halite is only 2-2.5, glass leaves a line on its surface.
Other physical parameters of sodium chloride:
- smell - absent;
- taste - salty;
- density - 2.165 g/cm3 (20 °C);
- melting point - 801 °C;
- boiling point - 1413 °C;
- solubility in water - 359 g/l (25 °C);
Preparation of sodium chloride in the laboratory
When metallic sodium reacts with chlorine gas in a test tube, a white substance is formed - sodium chloride NaCl (formula of table salt).
Chemistry provides insight into different ways of producing the same compound. Here are some examples:
NaOH (aq) + HCl = NaCl + H 2 O.
Redox reaction between a metal and an acid:
2Na + 2HCl = 2NaCl + H2.
Effect of acid on metal oxide: Na 2 O + 2HCl (aq) = 2NaCl + H 2 O
Displacement of a weak acid from a solution of its salt by a stronger one:
Na 2 CO 3 + 2HCl (aq) = 2NaCl + H 2 O + CO 2 (gas).
All these methods are too expensive and complex for use on an industrial scale.
Production of table salt
Even at the dawn of civilization, people knew that salting meat and fish lasts longer. Transparent, regularly shaped halite crystals were used in some ancient countries instead of money and were worth their weight in gold. The search and development of halite deposits made it possible to satisfy the growing needs of the population and industry. The most important natural sources of table salt:
- deposits of the mineral halite in different countries;
- water of seas, oceans and salt lakes;
- layers and crusts of rock salt on the banks of salty reservoirs;
- halite crystals on the walls of volcanic craters;
- salt marshes.
The industry uses four main methods for producing table salt:
- leaching of halite from the underground layer, evaporation of the resulting brine;
- mining in ;
- evaporation or brine of salt lakes (77% of the mass of the dry residue is sodium chloride);
- using a by-product of salt water desalination.
Chemical properties of sodium chloride
In terms of its composition, NaCl is an average salt formed by an alkali and a soluble acid. Sodium chloride is a strong electrolyte. The attraction between ions is so strong that only highly polar solvents can break it. In water, the substance disintegrates, cations and anions (Na +, Cl -) are released. Their presence is due to the electrical conductivity possessed by a solution of table salt. The formula in this case is written in the same way as for dry matter - NaCl. One of the qualitative reactions to the sodium cation is the yellow color of the burner flame. To obtain the result of the experiment, you need to collect a little solid salt on a clean wire loop and add it to the middle part of the flame. The properties of table salt are also associated with the peculiarity of the anion, which consists in a qualitative reaction to the chloride ion. When interacting with silver nitrate, a white precipitate of silver chloride precipitates in the solution (photo). Hydrogen chloride is displaced from the salt by stronger acids than hydrochloric acid: 2NaCl + H 2 SO 4 = Na 2 SO 4 + 2HCl. Under normal conditions, sodium chloride does not undergo hydrolysis.
Areas of application of rock salt
Sodium chloride lowers the melting point of ice, so in winter a mixture of salt and sand is used on roads and sidewalks. It absorbs a large amount of impurities and, when melting, pollutes rivers and streams. Road salt also accelerates the corrosion process of car bodies and damages trees planted next to roads. In the chemical industry, sodium chloride is used as a raw material for the production of a large group of chemicals:
- of hydrochloric acid;
- sodium metal;
- chlorine gas;
- caustic soda and other compounds.
In addition, table salt is used in the production of soap and dyes. It is used as a food antiseptic for canning and pickling mushrooms, fish and vegetables. To combat thyroid dysfunction in the population, the table salt formula is enriched by adding safe iodine compounds, for example, KIO 3, KI, NaI. Such supplements support the production of thyroid hormone and prevent endemic goiter.
The importance of sodium chloride for the human body
The formula of table salt, its composition has acquired vital importance for human health. Sodium ions are involved in the transmission of nerve impulses. Chlorine anions are necessary for the production of hydrochloric acid in the stomach. But too much salt in food can lead to high blood pressure and an increased risk of developing heart and vascular diseases. In medicine, when there is a large blood loss, patients are given physiological saline solution. To obtain it, 9 g of sodium chloride are dissolved in one liter of distilled water. The human body needs a continuous supply of this substance from food. Salt is excreted through the excretory organs and skin. The average sodium chloride content in the human body is approximately 200 g. Europeans consume about 2-6 g of table salt per day; in hot countries this figure is higher due to higher sweating.
A salt can be defined as a compound that is formed by the reaction between an acid and a base, but is not water. This section will consider those properties of salts that are associated with ionic equilibria.
reactions of salts in water
It will be shown a little later that solubility is a relative concept. However, for the purposes of the discussion ahead, we can roughly divide all salts into those that are soluble and those that are insoluble in water.
Some salts form neutral solutions when dissolved in water. Other salts form acidic or alkaline solutions. This is due to the occurrence of a reversible reaction between salt ions and water, as a result of which conjugate acids or bases are formed. Whether the salt solution turns out to be neutral, acidic or alkaline depends on the type of salt. In this sense, there are four types of salts.
Salts formed by strong acids and weak bases. Salts of this type, when dissolved in water, form an acidic solution. Let us take ammonium chloride NH4Cl as an example. When this salt is dissolved in water, the ammonium ion acts as
The excess amount of H3O+ ions formed in this process causes the acidic properties of the solution.
Salts formed by a weak acid and a strong base. Salts of this type, when dissolved in water, form an alkaline solution. As an example, let's take sodium acetate CH3COONa1. The acetate ion acts as a base, accepting a proton from water, which in this case acts as an acid:
The excess amount of OH- ions formed in this process determines the alkaline properties of the solution.
Salts formed by strong acids and strong bases. When salts of this type are dissolved in water, a neutral solution is formed. Let's take sodium chloride NaCl as an example. When dissolved in water, this salt is completely ionized, and, therefore, the concentration of Na+ ions turns out to be equal to the concentration of Cl- ions. Since neither one nor the other ion enters into acid-base reactions with water, an excess amount of H3O+ or OH ions does not form in the solution. Therefore, the solution turns out to be neutral.
Salts formed by weak acids and weak bases. An example of this type of salt is ammonium acetate. When dissolved in water, ammonium ion reacts with water as an acid, and acetate ion reacts with water as a base. Both of these reactions are described above. An aqueous solution of a salt formed by a weak acid and a weak base can be weakly acidic, weakly alkaline, or neutral, depending on the relative concentrations of the H3O+ and OH- ions formed as a result of the reactions of the salt's cations and anions with water. This depends on the relationship between the values of the dissociation constants of the cation and anion.
5.Nitrites, salts of nitrous acid HNO 2. Nitrites of alkali metals and ammonium are used primarily, and less - of alkaline earth and Zd metals, Pb and Ag. There is only fragmentary information about nitrites of other metals.Metal nitrites in the +2 oxidation state form crystal hydrates with one, two or four water molecules. Nitrites form double and triple salts, e.g. CsNO2. AgNO 2 or Ba(NO 2) 2. Ni(NO2)2. 2KNO 2, as well as complex compounds, for example Na 3.
Crystal structures are known for only a few anhydrous nitrites. The NO2 anion has a nonlinear configuration; ONO angle 115°, H–O bond length 0.115 nm; the type of M-NO 2 bond is ionic-covalent.
Nitrites K, Na, Ba are well soluble in water, nitrites Ag, Hg, Cu are poorly soluble. With increasing temperature, the solubility of nitrites increases. Almost all nitrites are poorly soluble in alcohols, ethers and low-polar solvents.
Nitrites are thermally unstable; Only nitrites of alkali metals melt without decomposition; nitrites of other metals decompose at 25-300 °C. The mechanism of nitrite decomposition is complex and includes a number of parallel-sequential reactions. The main gaseous decomposition products are NO, NO 2, N 2 and O 2, solid - metal oxide or elemental metal. The release of large amounts of gases causes the explosive decomposition of some nitrites, for example NH 4 NO 2, which decomposes into N 2 and H 2 O.
The characteristic features of nitrites are associated with their thermal instability and the ability of the nitrite ion to be both an oxidizing agent and a reducing agent, depending on the environment and the nature of the reagents. In a neutral environment, nitrites are usually reduced to NO; in an acidic environment, they are oxidized to nitrates. Oxygen and CO 2 do not interact with solid nitrites and their aqueous solutions. Nitrites promote the decomposition of nitrogen-containing organic substances, in particular amines, amides, etc. With organic halides RXH. react to form both nitrites RONO and nitro compounds RNO 2 .
The industrial production of nitrites is based on the absorption of nitrous gas (a mixture of NO + NO 2) with solutions of Na 2 CO 3 or NaOH with sequential crystallization of NaNO 2; Nitrites of other metals are obtained in industry and laboratories by the exchange reaction of metal salts with NaNO 2 or by the reduction of nitrates of these metals.
Nitrites are used for the synthesis of azo dyes, in the production of caprolactam, as oxidizing agents and reducing agents in the rubber, textile and metalworking industries, as food preservatives. Nitrites, such as NaNO 2 and KNO 2, are toxic, causing headaches, vomiting, depressing breathing, etc. When NaNO 2 is poisoned, methemoglobin is formed in the blood and red blood cell membranes are damaged. It is possible to form nitrosamines from NaNO 2 and amines directly in the gastrointestinal tract.
6.Sulfates, salts of sulfuric acid. Medium sulfates with the SO 4 2- anion are known, or hydrosulfates, with the HSO 4 - anion, basic, containing, along with the SO 4 2- anion, OH groups, for example Zn 2 (OH) 2 SO 4. There are also double sulfates containing two different cations. These include two large groups of sulfates - alum, as well as schenites M 2 E (SO 4) 2. 6H 2 O, where M is a singly charged cation, E is Mg, Zn and other doubly charged cations. Triple sulfate K 2 SO 4 is known. MgSO4. 2CaSO4. 2H 2 O (polyhalite mineral), double basic sulfates, for example minerals of the alunite and jarosite groups M 2 SO 4. Al 2 (SO 4) 3 . 4Al(OH 3 and M 2 SO 4. Fe 2 (SO 4) 3. 4Fe(OH) 3, where M is a singly charged cation. Sulfates can be part of mixed salts, for example 2Na 2 SO 4. Na 2 CO 3 ( mineral berkeite), MgSO 4 . KCl . 3H 2 O (kainite).
Sulfates are crystalline substances, medium and acidic in most cases, highly soluble in water. Sulfates of calcium, strontium, lead and some others are slightly soluble; BaSO 4 and RaSO 4 are practically insoluble. Basic sulfates are usually poorly soluble or practically insoluble, or are hydrolyzed by water. From aqueous solutions, sulfates can crystallize in the form of crystalline hydrates. Crystal hydrates of some heavy metals are called vitriols; copper sulfate CuSO 4. 5H 2 O, iron sulfate FeSO 4. 7H 2 O.
Medium alkali metal sulfates are thermally stable, while acid sulfates decompose when heated, turning into pyrosulfates: 2KHSO 4 = H 2 O + K 2 S 2 O 7. Medium sulfates of other metals, as well as basic sulfates, when heated to sufficiently high temperatures, as a rule, decompose with the formation of metal oxides and the release of SO 3.
Sulfates are widely distributed in nature. They occur in the form of minerals, such as gypsum CaSO 4 . H 2 O, mirabilite Na 2 SO 4. 10H 2 O, and are also part of sea and river water.
Many sulfates can be obtained by the interaction of H 2 SO 4 with metals, their oxides and hydroxides, as well as the decomposition of volatile acid salts with sulfuric acid.
Inorganic sulfates are widely used. For example, ammonium sulfate is a nitrogen fertilizer, sodium sulfate is used in the glass, paper industries, viscose production, etc. Natural sulfate minerals are raw materials for the industrial production of compounds of various metals, building materials, etc.
7.Sulfites, salts of sulfurous acid H 2 SO 3. There are medium sulfites with the SO 3 2- anion and acidic (hydrosulfites) with the HSO 3 - anion. Medium sulfites are crystalline substances. Ammonium and alkali metal sulfites are highly soluble in water; solubility (g in 100 g): (NH 4) 2 SO 3 40.0 (13 ° C), K 2 SO 3 106.7 (20 ° C). Hydrosulfites are formed in aqueous solutions. Sulfites of alkaline earth and some other metals are practically insoluble in water; solubility of MgSO 3 1 g in 100 g (40°C). Crystalline hydrates (NH 4) 2 SO 3 are known. H 2 O, Na 2 SO 3. 7H 2 O, K 2 SO 3. 2H 2 O, MgSO 3. 6H 2 O, etc.
Anhydrous sulfites, when heated without access to air in sealed vessels, are disproportionately divided into sulfides and sulfates; when heated in a current of N 2, they lose SO 2, and when heated in air, they are easily oxidized to sulfates. With SO 2 in an aqueous environment, medium sulfites form hydrosulfites. Sulfites are relatively strong reducing agents; they are oxidized in solutions with chlorine, bromine, H 2 O 2, etc. to sulfates. They decompose with strong acids (for example, HC1) with the release of SO 2.
Crystalline hydrosulfites are known for K, Rb, Cs, NH 4 +, they are unstable. The remaining hydrosulfites exist only in aqueous solutions. Density of NH 4 HSO 3 2.03 g/cm3; solubility in water (g in 100 g): NH 4 HSO 3 71.8 (0 ° C), KHSO 3 49 (20 ° C).
When crystalline hydrosulfites Na or K are heated or when the teeming pulp solution is saturated with SO 2 M 2 SO 3, pyrosulfites (obsolete - metabisulfites) M 2 S 2 O 5 are formed - salts of the unknown free pyrosulfuric acid H 2 S 2 O 5; crystals, unstable; density (g/cm3): Na 2 S 2 O 5 1.48, K 2 S 2 O 5 2.34; above ~ 160 °C they decompose with the release of SO 2; dissolve in water (with decomposition to HSO 3 -), solubility (g in 100 g): Na 2 S2O 5 64.4, K 2 S 2 O 5 44.7; form Na 2 S 2 O 5 hydrates. 7H 2 O and 3K 2 S 2 O 5. 2H 2 O; reducing agents.
Medium alkali metal sulfites are prepared by reacting an aqueous solution of M 2 CO 3 (or MOH) with SO 2, and MSO 3 by passing SO 2 through an aqueous suspension of MCO 3; They mainly use SO 2 from the exhaust gases of contact sulfuric acid production. Sulfites are used in bleaching, dyeing and printing of fabrics, fibers, leather for grain conservation, green feed, feed industrial waste (NaHSO 3,Na 2 S 2 O 5). CaSO 3 and Ca(HSO 3) 2 are disinfectants in the winemaking and sugar industries. NaHSO 3, MgSO 3, NH 4 HSO 3 - components of sulfite liquor during pulping; (NH 4) 2SO 3 - SO 2 absorber; NaHSO 3 is an absorber of H 2 S from industrial waste gases, a reducing agent in the production of sulfur dyes. K 2 S 2 O 5 - a component of acidic fixatives in photography, an antioxidant, an antiseptic.