Sulphides and hydrosulphides. Hydrosulfide and ammonium sulphide

Sulphides include organic and inorganic chemical compounds, the sulfur atom in their molecule is connected to metals or some non-metals. For inorganic sulfides, the characteristic compounds are hydrogen sulphide (H2S), belonging to the class of acids, and ammonium sulphide (formula (NH4) 2S), belonging to the class of salts. Also, the sulfides of metals and nonmetals with the general formula KxSy (where K is the metal or nonmetal cation and S is the acid residue of hydrogen sulfide, x and y is the number of metal cations and anions of the acid residue in the molecule, respectively) belong to the class of salts. For example, iron (II) FeS sulfide. Organic sulphides are chemical substances, the sulfur atom in their molecule is bound to hydrocarbon radicals. These are mercaptides (thioethers), their general formula is RSR ', and R and R' are hydrocarbon radicals.

All chemical compounds in which the metal atom, as well as the atoms of some nonmetals (Boron B, phosphorus P, silicon Si, arsenic As), are bound to a sulfur atom (S) with an oxidation degree of minus 2, are usually considered as salts of hydrogen sulfide H2S . Inorganic sulphides (except H2S), for example, ammonium sulfide or boron sulphide, should be referred to as average salts, since in hydrogen sulphide, both hydrogen atoms are replaced by other cations. If in hydrogen sulphide only one atom is replaced by cations (which is characteristic of alkaline earth and alkali metals), the salt formed will be an acid salt. Examples of inorganic hydrosulfides (otherwise bisulfides) may be compounds such as ammonium hydrosulfide (formula NH4HS) or sodium hydrogensulfide (NaHS). In hydrosulfide molecules, unlike sulphides, the acid residue or anion is HS-. Organic hydrosulfides include mercaptans (thiosparts and thiols) with the general formula RSH, where R is a hydrocarbon radical. Mercaptides and mercaptans are characterized by extensive nomenclature, so they require additional consideration.

Most sulphides have a bright color. Only ammonium sulfide and alkali metal sulphides are readily soluble in water . Almost all other metals are not soluble in water. Since sulphides are salts of weak hydrogen sulfide, their water-soluble representatives can undergo hydrolysis. For sulfides formed by metals with a high degree of oxidation or, if their hydroxides belong to weak bases (for example, Cr2S3, Al2S3 and others), more often hydrolysis proceeds irreversibly. Sulphides are moderate reducing agents, react with oxygen in air at elevated temperatures to form salts in which the sulfur atom has a higher oxidation state, for example, sulfates and sulfur dioxide. Ammonium sulphide is used in photography, in textile production. Sulphides are used as semiconductor materials, phosphors, in medicine, in agriculture.

Sulphides can be obtained by various methods. Ammonium sulphide (also known as another name for this salt is diammonium sulfide) is obtained by reacting hydrogen sulphide with an excess of ammonia: H2S + 2 NH3 → (NH4) 2S. The more stable salt of hydrosulphuric acid is iron sulphide FeS, which can decompose only when heated in a vacuum, it turns out (this is one of many known methods) as a result of irreversible reaction of sulfur with iron: Fe + S → FeS.

The molecular weight of ammonium sulphide is 68.14 a. The gross formula for the Hill system is written as: H8N2S. In appearance salt resembles colorless crystals. Ammonium sulphide at 20 ° C is readily soluble in water. Soluble in ethyl alcohol. It is a hygroscopic substance capable of absorbing moisture. Ammonium sulphide is not obtained in the free state. Since (NH4) 2S is an unstable salt, its aqueous solutions are approximated by hydrosulfide and, therefore, consist mainly of a mixture of NH3 and NH4HS, and aqueous solutions of (NH4) 2S are a colorless liquid with the smell of ammonia and hydrogen sulphide. The reaction of the solution is alkaline with a pH of 9.3. Crystals of solid salt can not be isolated, even with strong cooling of the solution. As a result of oxidation by air oxygen and the formation of polysulphides, the solution of ammonium sulphide quickly turns yellow. Therefore, the sulphide solution should be stored in a bottle filled up to the plug itself, as well as tightly clogged.

The molecular weight of ammonium hydrosulfide is 51.11 a. The gross formula for the Hill system is written as: H5NS. Salt in appearance is a colorless crystals of rhombic form. The salt density is 0.89 g / cm3. The melting point is 120 ° C (under pressure). At room temperature, evaporation and sublimation of reagent vapors are observed. This compound is volatile at room temperature. The substance is readily soluble in ethyl alcohol and cold water, in hot water or with slight heating decomposes. The reaction of the aqueous solution of the salt is alkaline. In air, ammonium hydrosulfide can oxidize, so its solution from colorless during storage rapidly becomes yellow due to the formation of polysulphides. Ammonium hydrosulfide can be obtained by direct reaction of ammonia with hydrogen sulphide in diethyl ether or by passing through an ammonia solution of hydrogen sulphide excess at 0 ° C according to the reaction equation: NH3 + H2S → NH4HS.