Metal nitrites in the +2 oxidation state form crystal hydrates with one, two or four water molecules. Nitrites form double and triple salts, for example. CsNO2. AgNO 2 or Ba(NO 2) 2. Ni(NO2)2. 2KNO 2 , as well as complex compounds, such as Na 3 .
Crystal structures are known only for a few anhydrous nitrites. The NO2 anion has a nonlinear configuration; ONO angle 115°, H–O bond length 0.115 nm; the type of bond M—NO 2 is ionic-covalent.
K, Na, Ba nitrites are well soluble in water, Ag, Hg, Cu nitrites are poorly soluble. With increasing temperature, the solubility of nitrites increases. Almost all nitrites are poorly soluble in alcohols, ethers, and low-polarity solvents.
Nitrites are thermally unstable; melt without decomposition only nitrites of alkali metals, 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 ones are metal oxide or elemental metal. The release of a large amount 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 medium 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 contribute to the decomposition of nitrogen-containing organic substances, in particular amines, amides, etc. With organic halides RXH. react to form both RONO nitrites and RNO 2 nitro compounds.
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 successive crystallization of NaNO 2; nitrites of other metals in industry and laboratories are obtained 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 and reducing agents in the rubber, textile and metalworking industries, as food preservatives. Nitrites such as NaNO 2 and KNO 2 are toxic, causing headache, vomiting, respiratory depression, etc. When NaNO 2 is poisoned, methemoglobin is formed in the blood, erythrocyte membranes are damaged. Perhaps the formation of nitrosamines from NaNO 2 and amines directly in the gastrointestinal tract.
6.Sulfates, salts of sulfuric acid. Medium sulfates with the anion SO 4 2- are known, acidic, or hydrosulfates, with the anion HSO 4 -, basic, containing along with the anion SO 4 2- - OH groups, for example Zn 2 (OH) 2 SO 4. There are also double sulfates, which include two different cations. These include two large groups of sulfates - alum, as well as chenites 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. Known triple sulfate K 2 SO 4 . MgSO4. 2CaSO4. 2H 2 O (mineral polyhalite), double basic sulfates, such as 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 they are highly soluble in water. Slightly soluble sulfates of calcium, strontium, lead and some others, practically insoluble BaSO 4 , RaSO 4 . Basic sulfates are usually sparingly soluble or practically insoluble, or hydrolyzed by water. Sulfates can crystallize from aqueous solutions in the form of crystalline hydrates. The crystalline hydrates of some heavy metals are called vitriol; copper sulphate СuSO 4. 5H 2 O, ferrous sulfate FeSO 4. 7H 2 O.
Medium alkali metal sulfates are thermally stable, while acid sulfates decompose when heated, turning into pyrosulfates: 2KHSO 4 \u003d H 2 O + K 2 S 2 O 7. Average 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 as 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 salts of volatile acids with sulfuric acid.
Inorganic sulfates are widely used. For example, ammonium sulfate is a nitrogen fertilizer, sodium sulfate is used in the glass, paper industry, 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 anion SO 3 2- and acidic (hydrosulfites) with the anion HSO 3 -. 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). In aqueous solutions they form hydrosulfites. Sulfites of alkaline earth and some other metals are practically insoluble in water; solubility of MgSO 3 1 g in 100 g (40°C). Crystal 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, disproportionate into sulfides and sulfates, when heated in a stream of N 2 they lose SO 2, and when heated in air, they are easily oxidized to sulfates. With SO 2 in the aquatic 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 are decomposed by strong acids (for example, HC1) with the release of SO 2.
Crystalline hydrosulfites are known for K, Rb, Cs, NH 4 +, they are unstable. Other hydrosulfites exist only in aqueous solutions. Density NH 4 HSO 3 2.03 g/cm3; solubility in water (g per 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 slurry solution of the pulp M 2 SO 3 is saturated with SO 2, pyrosulfites (obsolete - metabisulfites) M 2 S 2 O 5 are formed - salts of pyrosulfurous acid unknown in the free state 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 °С they decompose with the release of SO 2; dissolve in water (with decomposition to HSO 3 -), solubility (g per 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 ZK 2 S 2 O 5 . 2H 2 O; reducing agents.
Medium alkali metal sulfites are obtained 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 ; mainly SO 2 is used from the off-gases of contact sulfuric acid production. Sulfites are used in bleaching, dyeing and printing of fabrics, fibers, leather for grain conservation, green fodder, industrial feed waste (NaHSO 3 ,Na 2 S 2 O 5). CaSO 3 and Ca(HSO 3) 2 - disinfectants in winemaking and sugar industry. NaНSO 3 , MgSO 3 , NH 4 НSO 3 - components of sulfite liquor during pulping; (NH 4) 2SO 3 - SO 2 absorber; NaHSO 3 is an H 2 S absorber from production waste gases, a reducing agent in the production of sulfur dyes. K 2 S 2 O 5 - component of acid fixers in photography, antioxidant, antiseptic.
A salt can be defined as a compound that is formed by the reaction between an acid and a base, but is not water. In this section, those properties of salts that are associated with ionic equilibria will be considered.
salt reactions in water
Somewhat later it will be shown that solubility is a relative concept. However, for the purposes of the following discussion, we can roughly classify all salts into water-soluble and water-insoluble salts.
Some salts, when dissolved in water, form neutral solutions. 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 a salt solution is 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's 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 determines 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:
An excess 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 is equal to the concentration of Cl- ions. Since neither ion enters into acid-base reactions with water, there is no formation of an excess amount of H3O + or OH ions in the solution. Therefore, the solution is neutral.
Salts formed by weak acids and weak bases. An example of salts of this type is ammonium acetate. When dissolved in water, the ammonium ion reacts with water as an acid, and the 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, slightly alkaline, or neutral, depending on the relative concentrations of H3O+ and OH- ions formed as a result of the reactions of cations and anions of the salt with water. It depends on the ratio between the values of the dissociation constants of the cation and anion.
SALT, a class of chemical compounds. A generally accepted definition of the concept of “Salts”, as well as the terms “acids and bases”, the products of the interaction of which salts are, currently does not exist. Salts can be considered as products of substitution of acid hydrogen protons for metal ions, NH 4 + , CH 3 NH 3 + and other cations or OH groups of the base for acid anions (eg, 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 , СuСlOH. 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 include two types of acid residues ( e.g. AgClBr). Complex salts contain complex ions such as K 4 .
Physical Properties
Typical salts are crystalline substances with an ionic structure, such as CsF. There are also covalent salts, such as AlCl 3 . In fact, the nature of the chemical bond v of many salts is mixed.
By solubility in water, soluble, slightly soluble and practically insoluble salts are distinguished. Soluble include almost all salts of sodium, potassium and ammonium, many nitrates, acetates and chlorides, with the exception of salts of polyvalent metals that hydrolyze in water, many acidic salts.
Solubility of salts in water at room temperature
| Cations | Anions | |||||||||
| F- | Cl- | br- | I- | S2- | 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 |
| Mg2+ | RK | R | R | R | M | R | H | RK | R | RK |
| Ca2+ | NK | R | R | R | M | R | H | RK | M | RK |
| Sr2+ | NK | R | R | R | R | R | H | RK | RK | RK |
| Ba 2+ | RK | R | R | R | R | R | H | RK | NK | RK |
| sn 2+ | R | R | R | M | RK | R | H | H | R | H |
| Pb 2+ | H | M | M | M | RK | R | H | H | H | H |
| Al 3+ | M | R | R | R | G | R | G | NK | R | RK |
| Cr3+ | R | R | R | R | G | R | G | H | R | RK |
| Mn2+ | R | R | R | R | H | R | H | H | R | H |
| Fe2+ | M | R | R | R | H | R | H | H | R | H |
| Fe3+ | R | R | R | - | - | R | G | H | R | RK |
| Co2+ | M | R | R | R | H | R | H | H | R | H |
| Ni2+ | M | R | R | R | RK | R | H | H | R | H |
| Cu2+ | M | R | R | - | H | R | G | H | R | H |
| Zn2+ | M | R | R | R | RK | R | H | H | R | H |
| CD 2+ | R | R | R | R | RK | R | H | H | R | H |
| Hg2+ | R | R | M | NK | NK | R | H | H | R | H |
| Hg 2 2+ | R | NK | NK | NK | RK | R | H | H | M | H |
| Ag+ | R | NK | NK | NK | NK | R | H | H | M | H |
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 neither in water nor in acids; G - completely hydrolyzes upon dissolution 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 salt solutions 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 crystalline hydrates, from non-aqueous solutions - in the form of crystalline 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 acid oxide: MgO + CO 2 = MgCO 3
5) basic oxide with acid CuO + H 2 SO 4 \u003d CuSO 4 + H 2 O
6) bases with acidic oxide Ba (OH) 2 + CO 2 = BaCO 3 + H 2 O
7) bases with acid: Ca (OH) 2 + 2HCl \u003d CaCl 2 + 2H 2 O
8) acid salts: MgCO 3 + 2HCl = MgCl 2 + H 2 O + CO 2
BaCl 2 + H 2 SO 4 \u003d BaSO 4 + 2HCl
9) a base solution with a salt solution: Ba (OH) 2 + Na 2 SO 4 \u003d 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 a base. KOH + H 2 SO 4 \u003d KHSO 4 + H 2 O
2. Interaction of a base with an excess of acid oxide
Ca(OH) 2 + 2CO 2 = Ca(HCO 3) 2
3. Interaction of an average salt with acid Ca 3 (PO 4) 2 + 4H 3 PO 4 \u003d 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 \u003d Cl + HCl
2. Addition (drop by drop) of 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 \u003d 2 CO 3 + CO 2 + 4NaCl
4. Obtaining complex salts:
1. Reactions of salts with ligands: AgCl + 2NH 3 = Cl
FeCl 3 + 6KCN] = K 3 + 3KCl
5. Getting double salts:
1. Joint crystallization of two salts:
Cr 2 (SO 4) 3 + K 2 SO 4 + 24H 2 O \u003d 2 + NaCl
4. Redox reactions due to 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 medium salt
Ca (HCO 3) 2 \u003d CaCO 3 + CO 2 + H 2 O
Interaction with alkali. Obtaining 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 \u003d 2CuO + CO 2 + H 2 O
Interaction with acid: formation of an average 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 + K 2 S \u003d CuS + 2KCl + 4NH 3
2. Exchange of ligands between the outer and inner spheres.
K 2 + 6H 2 O \u003d 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. Recovery: KCr (SO 4) 2 + 2H ° (Zn, diluted H 2 SO 4) \u003d 2CrSO 4 + H 2 SO 4 + K 2 SO 4
The raw materials for the industrial production of a number of chloride salts, sulfates, carbonates, Na, K, Ca, Mg borates are sea and ocean water, natural brines formed during its evaporation, and solid deposits of salts. For a group of minerals that form sedimentary salt deposits (sulfates and chlorides of Na, K and Mg), the code name “natural salts” is used. The largest deposits of potassium salts are located in Russia (Solikamsk), Canada and Germany, powerful deposits of phosphate ores - in North Africa, Russia and Kazakhstan, NaNO3 - in Chile.
Salts are used in food, chemical, metallurgical, glass, leather, textile industries, agriculture, medicine, etc.
The main types of salts
1. Borates(oxoborates), salts of boric acids: metaboric HBO 2, orthoboric H 3 BO 3 and polyboric acids not isolated in the free state. According to the number of boron atoms in the molecule, they are divided into mono-, di, tetra-, hexaborates, etc. Borates are also called according to the acids that form them and according to the number of moles of B 2 O 3 per 1 mole of the basic oxide. So various metaborates can be called monoborates if they contain an anion B (OH) 4 or a chain anion (BO 2) n n-diborates - if they contain a double chain anion (B 2 O 3 (OH) 2) n 2n-triborates - if they contain ring anion (B 3 O 6) 3-.
Salts are the product of substitution of hydrogen atoms in an acid for a metal. Soluble salts in soda dissociate into a metal cation and an acid residue anion. Salts are divided into:
Medium
Basic
Complex
Double
Mixed
Medium salts. These are products of complete replacement of hydrogen atoms in an acid with metal atoms, or with a group of atoms (NH 4 +): MgSO 4, Na 2 SO 4, NH 4 Cl, Al 2 (SO 4) 3.
The names of middle salts come from the names of metals and acids: CuSO 4 - copper sulfate, Na 3 PO 4 - sodium phosphate, NaNO 2 - sodium nitrite, NaClO - sodium hypochlorite, NaClO 2 - sodium chlorite, NaClO 3 - sodium chlorate, NaClO 4 - sodium perchlorate, CuI - copper (I) iodide, CaF 2 - calcium fluoride. You also need to remember a few trivial names: NaCl-table salt, KNO3-potassium nitrate, K2CO3-potash, Na2CO3-soda ash, Na2CO3∙10H2O-crystalline soda, CuSO4-copper sulfate,Na 2 B 4 O 7 . 10H 2 O- borax, Na 2 SO 4 . 10H 2 O-Glauber's salt. Double salts. This salt containing two types of cations (hydrogen atoms multibasic acids are replaced by two different cations): MgNH 4 PO 4 , KAl (SO 4 ) 2 , NaKSO 4 .Double salts as individual compounds exist only in crystalline form. When dissolved in water, they are completelydissociate into metal ions and acid residues (if the salts are soluble), for example:
NaKSO 4 ↔ Na + + K + + SO 4 2-
It is noteworthy that the dissociation of double salts in aqueous solutions takes place in 1 step. To name salts of this type, you need to know the names of the anion and two cations: MgNH4PO4 - magnesium ammonium phosphate.
complex salts.These are particles (neutral molecules orions ), which are formed as a result of joining this ion (or atom) ), called complexing agent, neutral molecules or other ions called ligands. Complex salts are divided into:
1) Cation complexes
Cl 2 - tetraamminzinc(II) dichloride
Cl2- di hexaamminecobalt(II) chloride
2) Anion complexes
K2- potassium tetrafluoroberyllate(II)
Li-lithium tetrahydridoaluminate(III)
K3-potassium hexacyanoferrate(III)
The theory of the structure of complex compounds was developed by the Swiss chemist A. Werner.
Acid salts are products of incomplete substitution of hydrogen atoms in polybasic acids for metal cations.
For example: NaHCO3
Chemical properties:
React with metals in the voltage series to the left of hydrogen.
2KHSO 4 + Mg → H 2 + Mg (SO) 4 + K 2 (SO) 4
Note that for such reactions it is dangerous to take alkali metals, because they will first react with water with a large release of energy, and an explosion will occur, since all reactions occur in solutions.
2NaHCO 3 + Fe → H 2 + Na 2 CO 3 + Fe 2 (CO 3) 3 ↓
Acid salts react with alkali solutions to form the middle salt(s) and water:
NaHCO 3 +NaOH→Na 2 CO 3 +H 2 O
2KHSO 4 +2NaOH→2H 2 O+K 2 SO 4 +Na 2 SO 4
Acid salts react with solutions of medium salts if gas is released, a precipitate forms, or water is released:
2KHSO 4 + MgCO 3 → MgSO 4 + K 2 SO 4 + CO 2 + H 2 O
2KHSO 4 +BaCl 2 →BaSO 4 ↓+K 2 SO 4 +2HCl
Acid salts react with acids if the acid product of the reaction is weaker or more volatile than the one added.
NaHCO 3 +HCl→NaCl+CO 2 +H 2 O
Acid salts react with basic oxides with the release of water and intermediate salts:
2NaHCO 3 + MgO → MgCO 3 ↓ + Na 2 CO 3 + H 2 O
2KHSO 4 + BeO → BeSO 4 + K 2 SO 4 + H 2 O
Acid salts (in particular hydrocarbonates) decompose under the influence of temperature:
2NaHCO 3 → Na 2 CO 3 + CO 2 + H 2 O
Receipt:
Acid salts are formed when alkali is exposed to an excess of a solution of a polybasic acid (neutralization reaction):
NaOH + H 2 SO 4 → NaHSO 4 + H 2 O
Mg (OH) 2 + 2H 2 SO 4 → Mg (HSO 4) 2 + 2H 2 O
Acid salts are formed by dissolving basic oxides in polybasic acids:
MgO + 2H 2 SO 4 → Mg (HSO 4) 2 + H 2 O
Acid salts are formed when metals are dissolved in an excess of a polybasic acid solution:
Mg + 2H 2 SO 4 → Mg (HSO 4) 2 + H 2
Acid salts are formed as a result of the interaction of the average salt and the acid, which formed the anion of the average salt:
Ca 3 (PO 4) 2 + H 3 PO 4 → 3CaHPO 4
Basic salts:
Basic salts are the product of incomplete substitution of the hydroxo group in the molecules of polyacid bases for acid residues.
Example: MgOHNO 3 ,FeOHCl.
Chemical properties:
Basic salts react with excess acid to form a medium salt and water.
MgOHNO 3 + HNO 3 → Mg (NO 3) 2 + H 2 O
Basic salts are decomposed by temperature:
2 CO 3 →2CuO + CO 2 + H 2 O
Obtaining basic salts:
The interaction of salts of weak acids with medium salts:
2MgCl 2 + 2Na 2 CO 3 + H 2 O → 2 CO 3 + CO 2 + 4NaCl
Hydrolysis of salts formed by a weak base and a strong acid:
ZnCl 2 + H 2 O → Cl + HCl
Most basic salts are sparingly soluble. Many of them are minerals, for example malachite Cu 2 CO 3 (OH) 2 and hydroxyapatite Ca 5 (PO 4) 3 OH.
The properties of mixed salts are not covered in the school chemistry course, but it is important to know the definition.
Mixed salts are salts in which acidic residues of two different acids are attached to one metal cation.
A good example is Ca(OCl)Cl bleach (bleach).
Nomenclature:
1. Salt contains a complex cation
First, the cation is named, then the ligands-anions entering the inner sphere, ending in "o" ( Cl - - chloro, OH - -hydroxo), then ligands, which are neutral molecules ( NH 3 -amine, H 2 O -aquo). If there are more than 1 identical ligands, their number is denoted by Greek numerals: 1 - mono, 2 - di, 3 - three, 4 - tetra, 5 - penta, 6 - hexa, 7 - hepta, 8 - octa, 9 - nona, 10 - deca. The latter is called the complexing ion, indicating its valency in brackets, if it is variable.
[ Ag (NH 3 ) 2 ](OH )-silver diamine hydroxide ( I)
[ Co (NH 3 ) 4 Cl 2 ] Cl 2 -chloride dichloro o cobalt tetraamine ( III)
2. Salt contains a complex anion.
First, the anion ligands are named, then the neutral molecules entering the inner sphere ending in "o", indicating their number with Greek numerals. The latter is called the complexing ion in Latin, with the suffix "at", indicating the valency in brackets. Next, the name of the cation located in the outer sphere is written, the number of cations is not indicated.
K 4 -hexacyanoferrate (II) potassium (reagent for Fe 3+ ions)
K 3 - potassium hexacyanoferrate (III) (reagent for Fe 2+ ions)
Na 2 -sodium tetrahydroxozincate
Most complexing ions are metals. The greatest tendency to complex formation is shown by d elements. Around the central complexing ion there are oppositely charged ions or neutral molecules - ligands or addends.
The complexing ion and ligands make up the inner sphere of the complex (in square brackets), the number of ligands coordinating around the central ion is called the coordination number.
Ions that do not enter the inner sphere form the outer sphere. If a complex ion is a cation, then there are anions in the outer sphere and vice versa, if a complex ion is an anion, then there are cations in the outer sphere. Cations are usually alkali and alkaline earth metal ions, ammonium cation. When dissociated, complex compounds give complex complex ions, which are quite stable in solutions:
K 3 ↔3K + + 3-
If we are talking about acid salts, then when reading the formula, the prefix hydro- is pronounced, for example:
Sodium hydrosulfide NaHS
Sodium bicarbonate NaHCO 3
With basic salts, the prefix is \u200b\u200bused hydroxo- or dihydroxo-
(depends on the degree of oxidation of the metal in the salt), for example:
magnesium hydroxochlorideMg(OH)Cl, aluminum dihydroxochloride Al(OH) 2 Cl
Methods for obtaining salts:
1. Direct interaction of metal with non-metal . In this way, salts of anoxic acids can be obtained.
Zn+Cl 2 →ZnCl 2
2. Reaction between acid and base (neutralization reaction). Reactions of this type are of great practical importance (qualitative reactions to most cations), they are always accompanied by the release of water:
NaOH+HCl→NaCl+H 2 O
Ba(OH) 2 + H 2 SO 4 → BaSO 4 ↓ + 2H 2 O
3. The interaction of the basic oxide with the acid :
SO 3 +BaO→BaSO 4 ↓
4. Reaction of acid oxide and base :
2NaOH + 2NO 2 → NaNO 3 + NaNO 2 + H 2 O
NaOH + CO 2 →Na 2 CO 3 +H 2 O
5. Interaction of basic oxide and acid :
Na 2 O + 2HCl → 2NaCl + H 2 O
CuO + 2HNO 3 \u003d Cu (NO 3) 2 + H 2 O
6. Direct interaction of metal with acid. This reaction may be accompanied by the evolution of hydrogen. Whether hydrogen will be released or not depends on the activity of the metal, the chemical properties of the acid and its concentration (see Properties of concentrated sulfuric and nitric acids).
Zn + 2HCl \u003d ZnCl 2 + H 2
H 2 SO 4 + Zn \u003d ZnSO 4 + H 2
7. Reaction of salt with acid . This reaction will occur provided that the acid forming the salt is weaker or more volatile than the acid that reacted:
Na 2 CO 3 + 2HNO 3 \u003d 2NaNO 3 + CO 2 + H 2 O
8. Reaction of salt with acidic oxide. Reactions occur only when heated, therefore, the reacting oxide must be less volatile than the one formed after the reaction:
CaCO 3 + SiO 2 \u003d CaSiO 3 + CO 2
9. The interaction of a non-metal with an alkali . Halogens, sulfur and some other elements, interacting with alkalis, give oxygen-free and oxygen-containing salts:
Cl 2 + 2KOH \u003d KCl + KClO + H 2 O (the reaction proceeds without heating)
Cl 2 + 6KOH \u003d 5KCl + KClO 3 + 3H 2 O (the reaction proceeds with heating)
3S + 6NaOH \u003d 2Na 2 S + Na 2 SO 3 + 3H 2 O
10. interaction between two salts. This is the most common way to obtain salts. For this, both salts that have entered into the reaction must be highly soluble, and since this is an ion exchange reaction, in order for it to go to the end, one of the reaction products must be insoluble:
Na 2 CO 3 + CaCl 2 \u003d 2NaCl + CaCO 3 ↓
Na 2 SO 4 + BaCl 2 \u003d 2NaCl + BaSO 4 ↓
11. Interaction between salt and metal . The reaction proceeds if the metal is in the voltage series of metals to the left of that contained in the salt:
Zn + CuSO 4 \u003d ZnSO 4 + Cu ↓
12. Thermal decomposition of salts . When some oxygen-containing salts are heated, new ones are formed, with a lower oxygen content, or not containing it at all:
2KNO 3 → 2KNO 2 + O 2
4KClO 3 → 3KClO 4 +KCl
2KClO 3 → 3O 2 +2KCl
13. Interaction of non-metal with salt. Some non-metals are able to combine with salts to form new salts:
Cl 2 +2KI=2KCl+I 2 ↓
14. Reaction of base with salt . Since this is an ion exchange reaction, in order for it to go to the end, it is necessary that 1 of the reaction products be insoluble (this reaction is also used to convert acid salts into medium ones):
FeCl 3 + 3NaOH \u003d Fe (OH) 3 ↓ + 3NaCl
NaOH+ZnCl 2 = (ZnOH)Cl+NaCl
KHSO 4 + KOH \u003d K 2 SO 4 + H 2 O
In the same way, double salts can be obtained:
NaOH + KHSO 4 \u003d KNaSO 4 + H 2 O
15. The interaction of metal with alkali. Metals that are amphoteric react with alkalis, forming complexes:
2Al+2NaOH+6H 2 O=2Na+3H 2
16. Interaction salts (oxides, hydroxides, metals) with ligands:
2Al+2NaOH+6H 2 O=2Na+3H 2
AgCl+3NH 4 OH=OH+NH 4 Cl+2H 2 O
3K 4 + 4FeCl 3 \u003d Fe 3 3 + 12KCl
AgCl+2NH 4 OH=Cl+2H 2 O
Editor: Kharlamova Galina Nikolaevna
In order to answer the question of what salt is, you usually don’t have to think for a long time. This chemical compound is quite common in everyday life. There is no need to talk about ordinary table salt. The detailed internal structure of salts and their compounds is studied by inorganic chemistry.
A clear answer to the question of what salt is can be found in the works of M. V. Lomonosov. He gave this name to fragile bodies that can dissolve in water and do not ignite under the influence of high temperatures or open flames. Later, the definition was derived not from their physical, but from the chemical properties of these substances.
An example of a mixed one is the calcium salt of hydrochloric and hypochlorous acid: CaOCl 2.
Salts formed by metals with variable valence have an additional designation: after the formula, the valency is written in brackets in Roman numerals. So, there is iron sulfate FeSO 4 (II) and Fe 2 (SO4) 3 (III). In the name of salts there is a prefix hydro-, if there are unsubstituted hydrogen atoms in its composition. For example, potassium hydrogen phosphate has the formula K 2 HPO 4 .
The theory of electrolytic dissociation gives its own interpretation of chemical properties. In the light of this theory, a salt can be defined as a weak electrolyte that, when dissolved, dissociates (breaks down) in water. Thus, a salt solution can be represented as a complex of positive negative ions, and the first ones are not H + hydrogen atoms, and the second ones are not OH - hydroxo group atoms. There are no ions that would be present in all types of salt solutions, so they do not have any common properties. The lower the charges of the ions that form the salt solution, the better they dissociate, the better the electrical conductivity of such a liquid mixture.
Acid salts in solution decompose into complex negative ions, which are an acid residue, and simple anions, which are positively charged metal particles.
For example, the dissolution reaction of sodium bicarbonate leads to the decomposition of the salt into sodium ions and the rest of HCO 3 -.
The full formula looks like this: NaHCO 3 \u003d Na + + HCO 3 -, HCO 3 - \u003d H + + CO 3 2-.
The dissociation of basic salts leads to the formation of acid anions and complex cations consisting of metals and hydroxogroups. These complex cations, in turn, are also able to decompose in the process of dissociation. Therefore, in any solution of a salt of the main group, there are OH - ions. For example, the dissociation of hydroxomagnesium chloride proceeds as follows:
What is salt? This element is one of the most common chemical compounds. Everyone knows table salt, chalk (calcium carbonate) and so on. Among the carbonate salts, the most common is calcium carbonate. It is an integral part of marble, limestone, dolomite. And calcium carbonate is the basis for the formation of pearls and corals. This chemical compound is essential for the formation of hard integuments in insects and skeletons in chordates.
Salt has been known to us since childhood. Doctors warn against its excessive use, but in moderation it is essential for the implementation of vital processes in the body. And it is needed to maintain the correct composition of the blood and the production of gastric juice. Saline solutions, an integral part of injections and droppers, are nothing more than a solution of table salt.
