Sulfur is a fairly common chemical element in nature (sixteenth in content in the earth's crust and sixth in natural waters). There are both native sulfur (the free state of an element) and its compounds.
Sulfur in nature
Among the most important natural sulfur minerals are iron pyrite, sphalerite, galena, cinnabar, antimonite. In the oceans, it is mainly found in the form of calcium, magnesium and sodium sulfates, which determine the hardness of natural waters.
How do you get sulfur?
Sulfur ore is produced by various methods. The main way to obtain sulfur is its smelting directly in the places of occurrence.
An open-pit mining method involves the use of excavators that remove rock formations that cover sulfur ore. After crushing the ore layers by explosions, they are sent to a smelter.
In industry, sulfur is obtained as a by-product of processes in smelters for oil refining. In large quantities, it is present in natural gas (in the form of sulfur dioxide or hydrogen sulfide), which is deposited on the walls of the equipment used during production. Fine sulfur captured from gas is used in the chemical industry as a raw material for the production of various products.
This substance can also be obtained from natural sulfur dioxide. For this, the Klaus method is used. It consists in the use of "sulfur pits" in which sulfur is degassed. The result is modified sulfur, widely used in the production of asphalt.
Basic allotropic modifications of sulfur
Sulfur is characterized by allotropy. A large number of allotropic modifications are known. The most famous are rhombic (crystalline), monoclinic (needle) and plastic sulfur. The first two modifications are stable; the third, when hardened, turns into a rhombic one.
Physical properties characterizing sulfur
Molecules of rhombic (α-S) and monoclinic (β-S) modifications contain 8 sulfur atoms, which are connected in a closed cycle by single covalent bonds.
Under normal conditions, sulfur has a rhombic modification. It is a yellow solid crystalline substance with a density of 2.07 g / cm 3 . Melts at 113 ° C. The density of monoclinic sulfur is 1.96 g / cm 3 , its melting point is 119.3 ° C.
Upon melting, sulfur increases in volume and becomes a yellow liquid, which turns brown at a temperature of 160 ° C and turns into a viscous dark brown mass when it reaches about 190 ° C. At temperatures exceeding this value, the viscosity of sulfur decreases. At about 300 ° C, it reverts to a liquid fluid state. This is because in the process of heating, sulfur polymerizes, increasing the chain length with increasing temperature. And when a temperature value of over 190 ° C is reached, the destruction of polymer units is observed.
When the sulfur melt is cooled naturally in cylindrical crucibles, the so-called lump sulfur is formed — large-sized rhombic crystals that have a distorted shape in the form of octahedra with partially “cut off” faces or corners.
If the molten substance is subjected to rapid cooling (for example, using cold water), it is possible to obtain plastic sulfur, which is an elastic rubbery mass of brownish or dark red color with a density of 2.046 g / cm 3 . This modification, in contrast to the rhombic and monoclinic, is unstable. Gradually (within a few hours) it changes color to yellow, becomes fragile and turns into a rhombic one.
When sulfur vapor (strongly heated) is frozen with liquid nitrogen, its purple modification forms, which is stable at temperatures below minus 80 ° C.
Sulfur practically does not dissolve in an aqueous medium. However, it is characterized by good solubility in organic solvents. It conducts electricity and heat poorly.
The boiling point of sulfur is 444.6 ° C. The boiling process is accompanied by the release of orange-yellow vapors, consisting mainly of S 8 molecules, which dissociate upon subsequent heating, resulting in the formation of equilibrium S 6 , S 4 and S 2 forms. Then, when heated, large molecules decompose, and at temperatures above 900 degrees, the vapors consist almost exclusively of S 2 molecules that dissociate into atoms at 1500 ° C.
What chemical properties does sulfur have?
Sulfur is a typical non-metal. Chemically active. The redox properties of sulfur are manifested in relation to many elements. When heated, it easily connects with almost all elements, which explains its mandatory presence in metal ores. The exceptions are Pt, Au, I 2 , N 2 and inert gases. The oxidation states that sulfur exhibits in the compounds are -2, +4, +6.
The properties of sulfur and oxygen determine its combustion in air. The result of this interaction is the formation of sulfur (SO 2 ) and sulfuric (SO 3 ) anhydrides, which are used to produce sulfur and sulfuric acids.
At room temperature, the reducing properties of sulfur are manifested only in relation to fluorine, in the reaction with which sulfur hexafluoride is formed :
When heated (in the form of a melt) it interacts with chlorine, phosphorus, silicon, carbon. As a result of reactions with hydrogen, in addition to hydrogen sulfide, it forms sulfanes, united by the general formula H 2 S X.
The oxidizing properties of sulfur are observed in the interaction with metals. In some cases, quite violent reactions can be observed. As a result of interaction with metals, sulfides (sulfur compounds) and polysulfides ( sulphurous metals) are formed.
With prolonged heating, it reacts with concentrated oxidizing acids, oxidizing at the same time.
Next, we consider the main properties of sulfur compounds.
sulphur dioxide
Sulfur oxide (IV), also called sulfur dioxide and sulfur dioxide, is a gas (colorless) with a sharp asphyxiating odor. It has the property of liquefying under pressure at room temperature. SO 2 is an acid oxide. It is characterized by good solubility in water. In this case, a weak, unstable sulfuric acid is formed, which exists only in aqueous solution. As a result of the interaction of sulfur dioxide with alkalis, sulfites are formed.
It has a fairly high chemical activity. The most pronounced are the reducing chemical properties of sulfur oxide (IV). Such reactions are accompanied by an increase in the degree of oxidation of sulfur.
The oxidizing chemical properties of sulfur oxide are manifested in the presence of strong reducing agents (e.g., carbon monoxide).
Sulfur trioxide
Sulfur trioxide (sulfuric anhydride) is the highest sulfur oxide (VI). Under normal conditions, it is a colorless volatile liquid characterized by a choking odor. Tends to solidify at temperatures below 16.9 degrees. In this case, a mixture of different crystalline modifications of solid sulfur trioxide is formed. High hygroscopic properties of sulfur oxide determine its "smoke" in humid air. As a result, droplets of sulfuric acid are formed.
Hydrogen sulfide
Hydrogen sulfide is a binary chemical compound of hydrogen and sulfur. H 2 S is a toxic, colorless gas whose characteristic features are the sweetish taste and smell of rotten eggs. It melts at a temperature of minus 86 ° C, boils at a minus 60 ° C. Thermally unstable. At temperatures above 400 ° C, hydrogen sulfide decomposes into S and H 2 . It is characterized by good solubility in ethanol. It dissolves poorly in water. As a result of dissolution in water, weak hydrogen sulfide acid is formed. Hydrogen sulfide is a strong reducing agent.
Flammable. When it burns in the air, a blue flame can be observed. In high concentrations, it is able to react with many metals.
Sulfuric acid
Sulfuric acid (H 2 SO 4 ) can be of different concentration and purity. When anhydrous, it is a colorless, odorless, oily liquid.
The temperature at which the substance melts is 10 ° C. The boiling point is 296 ° C. It dissolves well in water. When sulfuric acid is dissolved, hydrates are formed, and a large amount of heat is released. The boiling point of all aqueous solutions at a pressure of 760 mm RT. Art. exceeds 100 ° C. Boiling points increase with increasing acid concentration.
The acidic properties of a substance are manifested in the interaction with basic oxides and bases. H 2 SO 4 is a dibasic acid, due to which it can form both sulfates (middle salts) and hydrosulfates (acid salts), most of which are soluble in water.
The most pronounced properties of sulfuric acid are manifested in redox reactions. This is explained by the fact that sulfur has a higher oxidation state (+6) in the composition of H 2 SO 4 . As an example of the manifestation of the oxidizing properties of sulfuric acid, we can give a reaction with copper:
- Cu + 2H 2 SO 4 = CuSO 4 + 2H 2 O + SO 2 .
Sulfur: useful properties
Sulfur is a trace element necessary for living organisms. It is an integral part of amino acids (methionine and cysteine), enzymes and vitamins. This element takes part in the formation of the tertiary structure of the protein. The amount of chemically bound sulfur contained in the proteins is by weight 0.8 to 2.4%. The content of an element in the human body is about 2 grams per 1 kg of weight (i.e., approximately 0.2% is sulfur).
The beneficial properties of the trace element are difficult to overestimate. Protecting the protoplasm of the blood, sulfur is an active assistant to the body in the fight against harmful bacteria. Blood coagulation depends on its quantity, that is, the element helps to maintain its sufficient level. Sulfur also plays an important role in maintaining normal values of the concentration of bile produced by the body.
It is often called the “mineral of beauty,” because it is simply necessary to maintain the health of the skin, nails and hair. Sulfur is inherent in the ability to protect the body from various types of negative environmental effects. This helps to slow down the aging process. Sulfur cleanses the body of toxins and protects against radiation, which is especially relevant at present, given the current environmental situation.
An insufficient amount of a microelement in the body can lead to poor elimination of toxins, a decrease in immunity and vitality.
Sulfur is a participant in bacterial photosynthesis. It is a component of bacteriochlorophyll, and hydrogen sulfide is a source of hydrogen.
Sulfur: properties and applications in industry
Sulfur is most widely used for the production of sulfuric acid. Also, the properties of this substance allow it to be used for vulcanization of rubber, as a fungicide in agriculture and even a medicinal product (colloidal sulfur). In addition, sulfur is used for the production of matches and pyrotechnic compositions, it is part of sulfur-bitumen compositions for the manufacture of sulfur asphalt.