Salt is a complex substance that is formed as a result of the replacement of one or more hydrogen atoms in an acid with a metal (or NHJ group) and dissociates in aqueous solutions with positively charged metal ions (or NH4 +) and negatively charged ions - acid residues. There are salts medium, sour, basic, double, mixed and complex.
As already mentioned, acids are one-, two-, three- or more basic (the basicity of the acid is determined by the number of hydrogen atoms capable of being replaced by a metal). If in an acid all hydrogen atoms are replaced by a metal, then the resulting salt is called a middle salt, for example, sodium sulfite Na2SO3, potassium sulfate K2SO4.
Acid salts are obtained by incomplete substitution of hydrogen atoms in acid. Acid salts form only two or more basic acids. In the name of the salt formed by replacing one hydrogen in dibasic acid, the word “acidic” is added, for example, sodium hydrogen sulfide NaHSO3, potassium hydrogen sulfate KHSO4. Salts formed during the partial replacement of hydrogen by a metal in tribasic acids are commonly referred to as mono-, di- and tri-substituted.
So, the orthophosphoric acid salt H3PO4, formed by the replacement of one hydrogen atom with sodium, is called sodium phosphate monosubstituted NaH2PO4, when two hydrogen atoms are replaced, sodium phosphate disubstituted Na2HPO4, and three hydrogen atoms - sodium phosphate trisubstituted Na3 (O or average).
Basic salts are those salts in the molecule of which the metal is connected not only with an acid residue, but also with hydroxyl.
For example, the formula Bi (NO3) 3 corresponds to the average bismuth nitrate, while the composition of the main bismuth nitrate is expressed by the formula Bi (OH) 2NO3. Typically, the basic salts contain one or two hydroxyl groups in the metal: Mg (OH) Cl, Fe (OH) 2Cl, Al (OH) S04, etc. The basic salts are formed by the interaction of acids with weak bases, and the acid should be less than required to get medium salt.
Double salts are those salts in which the acid residue of the same acid is connected to two metal atoms or a metal atom and an ammonium group, for example, potassium carbonate KNaCO3, Mohr's salt (NH4) 2Fe (SO4) 2 * 6H2O, etc. .
Double salts exist only in solid crystalline form; when dissolved, they decompose into their simple salts. This is proved, for example, by the fact that K + and Al3 + ions can be detected in an aqueous solution of alum-potassium alum
Mixed salts are salts whose molecules are made up of one metal combined with two different acid residues. Like double salts, they can be obtained by crystallization of a saturated solution of two salts of one metal, but with different acid residues, for example:
CaCl2 + Ca (NO3) 2 = 2 CaClNO3
Complex salts differ from double salts in that in an aqueous solution they do not dissociate into the ions of the salts from which they are formed, but give specific complex ions.
For example, potassium ferruginous K3 [Fe (CN) 6] forms K + ions, and barium platinum synergistic Ba [Pt (CN) 4], respectively, Ba2 +; iron ion in the first case and platinum ion in the other cannot be detected in an aqueous solution.
The salt group is the largest in the assortment of inorganic reagents, and their number exceeds 1000 items. Taking into account the chemical properties, the location of salt-forming elements in the periodic system of elements of D. I. Mendeleev and, according to some other signs, inorganic salts are divided into nine subgroups .
1. Salts of alkali metals (lithium, sodium, potassium, rubidium, cesium), ammonium and thallium.
Alkali metal salts are white solid crystalline substances with the exception of thallium bromide and iodide (yellow) and salts having colored anions. Most salts are highly soluble in water; slightly soluble - potassium and ammonium perchlorate, potassium and sodium silicofluoride, sodium tetraborate, sodium acid pyro-antimony; very slightly soluble - carbonic, phosphate and fluoride lithium; insoluble - chloride, bromide and thallium iodide.
Application. Salts of sodium, potassium and ammonium of reactive purity are widely used as technological raw materials in chemical, medical, metallurgical and other industries, as well as in analytical chemistry as starting materials for titrimetric analysis and for the preparation of buffer solutions. Some salts of potassium and sodium are used as oxidizing agents, fluxes, complexing agents, etc. ammonium salts - for colorimetric determinations and as ashless reagents in gravimetric analysis; potassium sour antimony acid - for the discovery and determination of sodium.
Salts of cesium and rubidium are used in electrical engineering and instrumentation in the manufacture of batteries, photocells and luminescent materials; thallium salts - in the production of single crystals, lithium - in the synthesis of drugs. In analytical chemistry, cesium, rubidium, and thallium salts are used for microcrystalloscopic reactions to a number of cations and anions, and lithium sulfate is used to separate calcium and magnesium.
2. Salts of alkaline earth metals (calcium, strontium, barium "magnesium) and beryllium .
Alkaline earth metal salts are white crystalline solids, with the exception of salts having colored anions. Unlike alkali metal salts, many salts of this subgroup are very little or practically insoluble in water, for example, all carbonic and phosphate salts (except for beryllium), sulfate and fluoride salts of calcium, strontium and magnesium. Magnesium salts have a bitter taste, and beryllium salts are sweet. Halides of calcium and magnesium are hygroscopic and spread out in air.
Application. Salts of alkaline earth metals of reactive purity are used in the following industries: barium and strontium salts - in radio electronics and aircraft industry; salts of magnesium, barium, calcium - in the production of medicines; beryllium salts - in the manufacture of gas heating nets; crystalline calcium chloride - in metallurgy, etc. In laboratory practice, anhydrous calcium chloride is widely used for drying gases, dehydrating ethers and other organic liquids; Anhydrous magnesium peroxide is also used for drying and dehydration. As analytical preparations, magnesium sulfate is used to precipitate lead, calcium carbonate is used to determine manganese, barium chloride is used to determine sulfates, etc.
3. Salts of cadmium, copper, mercury, lead and zinc.
Zinc salts are white substances, soluble salts of mercury and lead are colorless. The carbonic, phosphate and sulfur salts of zinc, cadmium and copper are insoluble in water. Most salts of mercury and lead are also insoluble in water; their nitric salts and perchloric mercury (mercuric chloride) are readily soluble.
Application. Salts of cadmium, copper, mercury, zinc of reactive purity are quite widely used in industry and technology, for example, zinc chloride and sulfate - in the medical industry, radio electronics, metallurgy and in special branches of technology; cadmium sulfate in the chemical industry, and cadmium chloride in agriculture; copper sulfate - in the chemical industry and radio electronics; mercury chloride (calomel) and perchloric - in medicine.
From this subgroup of salts, cadmium nitrate and sulfate are used for analytical purposes to determine hydrogen sulfide in water; zinc nitrate - with nephelometric determination of sulfur in the blood; zinc chloride - for the detection of secondary alcohols; mercury (1) nitric acid — as a precipitant in gravimetric analysis, and mercury (P) nitric acid — as an integral part of the reagent for protein; crystalline copper sulfate - as a catalyst in the determination of nitrogen by Kjeldahl, and anhydrous - as a desiccant.
Iodine mercury serves as the basis for the preparation of the so-called "heavy liquids" used in mineralogical analysis to separate the grains of minerals according to their densities. These include Rohrbach liquid - BaHgl4 solution - yellow liquid with a density of 3.40-3.50 g / cm3 and Thule liquid - K2Hgl4 solution containing potassium iodide, - a light yellow liquid with a density of 3.19-3.20 g / cm3, miscible with water without decomposition.
4. Salts of aluminum, vanadium, iron, cobalt, manganese, nickel, titanium and chromium.
Aluminum salts are crystalline or amorphous substances that are colored only with colored anions. Ferrous salts are green or bluish, cobalt is dark pink and red, chromium is dark purple or dark green, nickel is green. Many salts are highly soluble in water, carbonic and phosphate salts are insoluble, and fluoride salts are slightly or completely insoluble.
Application . Salts of aluminum, vanadium, iron, cobalt, nickel and chromium are used as catalysts or they serve as feedstock for their preparation. Salts of higher valencies, namely potassium permanganate and potassium dichromate or sodium, are used as strong oxidizing agents, and salts of titanium, nickel and ferrous iron are used as reducing agents.
The salts of ferrous iron are of analytical value as reducing agents for nitro and nitroso compounds; ferric salts - as indicators of thiocyanates, cobalt salts - during the precipitation of potassium in the form of cobaltinitrite and for the preparation of non-fading color standards; nickel salts for iodometric determination of tin; titanium salts - in the analysis of azo compounds; chromium salts - for perimetric determination of iron and as a fixative in microscopy.
5. Salts of lanthanides, yttrium and scandium.
Lanthanides are called 14 elements occupying serial numbers 58–71 in the periodic system of D. I. Mendeleev. Together with yttrium and scandium, they make up the so-called subgroup of rare-earth elements. In nature, they are not widespread and are usually found in mixtures with each other. Distinguish between cerium and yttrium groups of rare earths. The first includes five elements: lanthanum, cerium, praseodymium, neodymium and samarium; the second is eleven: gadolinium, holmium, dysprosium, europium, ytterbium, yttrium, lutetium, scandium, terbium, thulium and erbium.
Samarium salts are light yellow in color, holmium is yellow, neodymium is lilac, thulium is greenish, praseodymium is green. Salts of the remaining rare earth metals are colorless crystals or white crystalline powders. Nitric acid, sulfate, chloride, bromide and iodide salts are highly soluble in water; carbonic and fluoride salts in water are insoluble. All of these salts, except fluoride, crystallize from solutions in the form of crystalline hydrates. Iodide and most chloride and bromide salts are very hygroscopic and diffuse in air.
Application. Salts of rare earth metals are used in technology so far to a limited extent, since they are relatively little studied. In analytical chemistry, lanthanum nitrate is used as a reagent for acetates in the drip analysis and for the gravimetric determination of fluorine; yttrium nitrate - for titrimetric determination of fluorine; cerium sulfate - in the perimetry for the oximetric determination of ferrous iron, ferric antimony and many others.
6. Salts of gallium, hafnium, indium, niobium and tantalum.
Application. Gallium and hafnium salts are used as catalysts in organic synthesis. Gallium chloride, soluble in organic solvents, as a catalyst has a significant advantage over aluminum chloride. Niobates and tantalates of potassium, sodium and other metals are used for the manufacture of piezoelectric transducers, ceramic ferro capacitors and image signal amplifiers in TVs. Tantalum-potassium fluoride is used to produce pure tantalum preparations that do not contain niobium.
7. Salts of bismuth, germanium, silicon, arsenic, tin, selenium, antimony and tellurium.
Oxygen compounds of bismuth, antimony, arsenic, germanium and tin have amphoteric properties.
The salts of the strong mineral acids of these metals are soluble in water, but with significant dilution or heating, they hydrolyze and produce insoluble precipitates of the basic salts. The oxides of the higher valencies of these elements form acids: arsenic, arsenic, ortho-, meta-antimony, tin, and others. Some of these acids in the free state were not obtained, but their salts are well known.
Silicon is an analogue of carbon, but its nonmetallic properties are less pronounced than that of carbon. With chlorine, it forms silicon tetrachloride - a liquid that decomposes by water into silicic and hydrochloric acids, and with fluorine - silicon tetrafluoride - a gas that forms hydrofluoric acid with water. Silicic acid salts are called silicates, and hydrofluoric acid are called fluorosilicates. Most of these salts are soluble in water.
Selenium and tellurium are close in properties to sulfur. Like sulfur, they form selenides and tellurides similar to sulfides, as well as salts of selenium H2SeO3 and selenium H2Se04, telluric Н2ТеО3 and telluric Н2ТеО4 acids, similar to salts of sulfurous and sulfuric acids.
Application. Many salts of this subgroup are used in engineering and scientific research. Arsenic acid salts are used as vigorous reducing agents, and arsenic acid potassium is used in medicine; bismuth salts - in medicine and as catalysts in organic synthesis; germanium salts - in the manufacture of luminous screens and in special optics; silicon tetrachloride - for the synthesis of organosilicon compounds, etc.
In analytical chemistry, tin tetrachloride is used to separate rubidium and cesium from potassium by the chlorostannate method and for saponification of phenol ethers; bismuth salts - for microcrystalloscopic determination of potassium, sodium and other metals; potassium telluric acid - as a diagnostic tool in medicine; hydrofluoric sodium - for the deposition and separation of scandium.
8. Salts of tungsten, molybdenum, thorium, uranium and zirconium.
Tungsten and molybdenum in compounds can exhibit different electrochemical valencies - from 2 to 6. The most stable compounds are those where the metal is hexavalent, such as tungsten. H2WO4 and molybdenum H2MoO4 acid. With metals, these acids form salts - tungstates and molybdates, which are solid crystalline, mainly white substances. Tungstates and molybdates of alkali metals are soluble in water, the remaining salts are insoluble. Salts of complex acids are also known; phosphoric tungsten, phosphoric molybdenum, silicotungsten, silicomolybdenum, etc. The salts of these acids, painted in various colors, are readily soluble in water.
Tungsten and molybdenum also form salts in which they exhibit basic properties and act as cations: tungsten WCl6 hexachloride (blue-violet crystalline powder), MoCl5 pentachloride (black crystalline powder with a greenish tint), etc.
Oxides of thorium and zirconium with mineral acids give well crystallizing white salts, most of which are soluble in water. Zirconium exhibits amphoteric properties, forming zirconyls, for example, zirconyl nitrate ZrO (NO3) 2 and zirconium salts H2ZrO3 - zirconates.
Application . Compounds of tungsten and molybdenum are used in metallurgy for the production of special steels. In addition, molybdates are used as catalysts; some salts of tungsten and zirconium - for the manufacture of artistic paints; zirconium chloride - as a catalyst for the polymerization of ethylene and propylene; thorium nitrate - for the manufacture of gas-heating nets.
For analytical purposes, ammonium molybdenum acid is used to discover and quantify phosphoric acid; thorium nitrate - for gravimetric, titrimetric and colorimetric determination of fluorides; uranyl nitrate - for titrimetric determination of arsenic, gravimetric determination of vanadium and as a microchemical reagent for acetic acid and hydrogen peroxide; zirconium nitrate - for the deposition and separation of small amounts of phosphates.
9. Salts of precious metals.
The subgroup of salts of precious metals includes salts of silver, gold and metals of the so-called platinum group: ruthenium, rhodium, palladium, osmium, iridium and platinum.The listed metals are low-active elements that are very resistant to chemical influences. Silver is soluble only in nitric acid, others in aqua regia (a mixture of nitric and hydrochloric acids), and iridium, for example, is not affected by aqua regia.
Silver salts are solid crystalline substances. Silver nitrate and fluoride are soluble in water, the sulfate salt is slightly soluble, and the remaining salts are insoluble. Soluble silver salts are colorless crystals or white powders.
Of the metal salts of the platinum group, palladium nitrate - brownish-brown crystals, palladium chloride - a dark brown powder, and iridium tetrachloride - a black-brown powder, are most common. All of these salts, with the exception of palladium chloride, are extremely hygroscopic and disperse in air.
Application.Of the salts of precious metals, nitric silver, used in medicine, the photographic film industry, the production of mirrors and for electroplating, is of the greatest importance. Salts of the remaining elements, except electroforming, serve directly or as raw materials for the preparation of various catalysts.
For analytical purposes, silver nitrate is used for titrimetric determination of halides, cyanides and rhodanides, for the deposition of arsenic, thiosemicarbazides and purine bases; silver sulfate - for the precipitation of chlorides; palladium chloride - in a drop analysis as a reagent for hydroiodic acid.