Physical and chemical properties of sulfur

Sulfur is a fairly widespread chemical element in nature (the sixteenth in terms of its content in the earth's crust and the sixth in natural waters). There are both native sulfur (the free state of the element) and its compounds.

Sulfur in nature

Among the most important natural minerals of sulfur are iron pyrite, sphalerite, galena, cinnabar, antimonite. In the oceans, it is mainly contained in the form of sulfates of calcium, magnesium and sodium, which determine the rigidity of natural waters.

How do they get sulfur?

The extraction of sulfuric ores is carried out by different methods. The main way to produce sulfur is to smelt it directly in the ground.

The open method of mining involves the use of excavators, removing rock layers that cover sulfuric ore. After crushing layers of ore, explosions are sent to the smelter.

In industry, sulfur is produced as a by-product of processes in smelting furnaces, in oil refining. In large quantities, it is present in natural gas (in the form of sulfurous anhydride or hydrogen sulphide), during the extraction of which it is deposited on the walls of the equipment used. The fine-dispersed sulfur, which has been caught from the gas, is used in the chemical industry as raw material for the production of various products.

This substance can be obtained from natural sulfur dioxide. For this, the Claus method is used. It consists in the application of "sulfur pits" in which sulfur degasses. The result is a modified sulfur, widely used in the production of asphalt.

Basic allotropic sulfur modifications

Sulfur is inherent in allotropy. A large number of allotropic modifications are known. The most famous are rhombic (crystalline), monoclinic (acicular) and plastic sulfur. The first two modifications are stable, the third at solidification turns into a rhombic one.

Physical properties that characterize sulfur

The molecules of orthorhombic (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 . It melts at 113 ° C. The density of monoclinic sulfur is 1.96 g / cm ³ , its melting point is 119.3 ° C.

During melting, sulfur increases in volume and becomes a yellow liquid that ruptures 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 again turns into a liquid flowable state. This is because in the process of heating, sulfur is polymerized, increasing the length of the chain with increasing temperature. And when the temperature value exceeds 190 ° C, the polymer units are destroyed.

When the sulfur melt is cooled naturally, so-called gray-rhombic crystals of large sizes are formed in cylindrical crucibles, having a distorted shape in the form of octahedra with partially "cut off" faces or corners.

If the molten substance is quenched (for example, with cold water), it is possible to obtain plastic sulfur, which is an elastic, rubbery, 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 rhombic.

When sulfur vapor (strongly heated) is frozen with liquid nitrogen, its purple modification is formed, which is stable at temperatures below minus 80 ° C.

In the aqueous environment, sulfur is practically insoluble. However, it is characterized by good solubility in organic solvents. Poor conduct electricity and heat.

The boiling point of sulfur is 444.6 ° C. The boiling process is accompanied by the release of orange-yellow vapors consisting predominantly of S ₈ molecules, which dissociate upon subsequent heating, resulting in the formation of equilibrium forms S ₆ , S ₄ and S ₂ . Further, upon heating, large molecules decay, and at temperatures above 900 degrees, the pairs consist essentially of only S ₂ molecules _that dissociate into atoms at 1500 ° C.

What are the chemical properties of sulfur?

Sulfur is a typical non-metal. It is chemically active. Oxidation - reduction properties of sulfur are manifested in relation to the set of elements. When heated, it is easily connected with practically all elements, which explains its obligatory presence in metallic ores. The exceptions are Pt, Au, I ₂ , N ₂ and inert gases. Degree of oxidation, which shows sulfur in compounds, -2, +4, +6.

The properties of sulfur and oxygen cause its combustion in air. The result of this interaction is the formation of sulfur dioxide (SO ₂ ) and sulfuric (SO ₃ ) anhydrides used for the production of sulfuric and sulfuric acids.

At room temperature, the reducing properties of sulfur are manifested only with respect to fluorine, in the reaction with which sulfur hexafluoride is formed :

• S + 3F ₂ = SF ₆ .

When heated (in the form of a melt) interacts with chlorine, phosphorus, silicon, carbon. As a result of reactions with hydrogen, in addition to hydrogen sulphide, it forms sulfates combined by the general formula H ₂ S _X.

Oxidizing properties of sulfur are observed when interacting with metals. In some cases, quite violent reactions can be observed. As a result of interaction with metals, sulfides (sulfur compounds) and polysulfides (multi-sulfur metals) are formed.

With prolonged heating, it reacts with concentrated acid-oxidizing agents, while oxidizing.

Next, we consider the main properties of sulfur compounds.

Sulphur dioxide

Sulfur (IV) oxide, also called sulfur dioxide and sulfurous anhydride, is a gas (colorless) with a sharp asphyxiating odor. It has the property of being liquefied under pressure at room temperature. SO ₂ is an acidic oxide. It is characterized by good solubility in water. This produces a weak, unstable sulfurous acid, which exists only in aqueous solution. As a result of the interaction of sulfurous anhydride with alkalis, sulfites are formed.

It has a rather high chemical activity. The most pronounced are the reducing chemical properties of sulfur (IV) oxide. Such reactions are accompanied by an increase in the degree of sulfur oxidation.

Oxidative chemical properties of sulfur oxide are manifested in the presence of strong reducing agents (for example, carbon monoxide).

Sulfur trioxide

Sulfur trioxide (sulfur anhydride) is the highest sulfur oxide (VI). Under normal conditions, it is a colorless, volatile liquid, characterized by a suffocating odor. It has the property of freezing at temperatures below 16.9 degrees. A mixture of different crystalline modifications of solid sulfur trioxide is formed. High hygroscopic properties of sulfur oxide cause it to "smoke" in moist air. As a result, droplets of sulfuric acid are formed.

Hydrogen sulfide

Hydrogen sulphide is a binary chemical compound of hydrogen and sulfur. H ₂ S is a poisonous colorless gas, the characteristic features of which are the sweetish taste and smell of rotten eggs. It melts at minus 86 ° С, boils at minus 60 ° С. Is thermally unstable. At temperature values above 400 ° C, hydrogen sulphide decomposes into S and H _{2 .} It is characterized by good solubility in ethanol. It dissolves badly in water. As a result of dissolution in water, weak hydrogen sulphide is formed. Hydrogen sulfide is a strong reducing agent.

Flammable. When it burns in the air, you can see a blue flame. 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. In the anhydrous state it is a colorless oily liquid that does not have an odor.

The temperature at which the substance melts is 10 ° C. The boiling point is 296 ° C. It dissolves well in water. When dissolving sulfuric acid hydrates are formed, while a large amount of heat is released. The boiling point of all aqueous solutions at a pressure of 760 mm Hg. Art. Exceeds 100 ° С. Boiling point increases with increasing acid concentration.

Acidic properties of the substance are manifested when interacting with basic oxides and bases. H ₂ SO ₄ is a dibasic acid, as a result of which it can form both sulfates (middle salts) and hydrogensulfates (acid salts), most of which are soluble in water.

The most pronounced properties of sulfuric acid appear in oxidation-reduction reactions. This is explained by the fact that in the composition of H ₂ SO ₄ , sulfur has a higher degree of oxidation (+6). As an example of the manifestation of the oxidizing properties of sulfuric acid, we can cite the reaction with copper:

• Cu + 2H ₂ SO ₄ = CuSO ₄ + 2H ₂ O + SO ₂ .

Sulfur: useful properties

Sulfur is a microelement 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 proteins is 0.8 to 2.4% by weight. The content of the element in the human body is about 2 grams per 1 kg of weight (that is, about 0.2% is sulfur).

Useful properties of the microelement can not be overestimated. Protecting the protoplasm of blood, sulfur is an active assistant of the body in the fight against harmful bacteria. The amount of blood coagulability depends on its amount, that is, the element helps maintain its sufficient level. Also, sulfur plays an important role in maintaining normal concentrations of bile produced by the body.

Often called "beauty mineral", because it is simply necessary to preserve the health of the skin, nails and hair. Sulfur has the ability to protect the body from various kinds of negative environmental effects. This helps slow the aging process. Sulfur cleanses the body of toxins and protects against radiation, which is especially important now, given the current environmental situation.

Insufficient amount of trace element in the body can lead to poor excretion of slags, reduced immunity and vitality.

Sulfur is a participant in bacterial photosynthesis. It is a constituent of bacteriochlorophyll, and hydrogen sulphide is a source of hydrogen.

Sulfur: properties and applications in industry

The most widely used sulfur is 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 for a drug (colloidal sulfur). In addition, sulfur is used for the production of matches and pyrotechnic compositions, it is part of the sulfur-bitumen compositions for the manufacture of sulfur asphalt.