What is the chemical composition of sulfur
At room temperature, pure sulfur is a non-metal with a lemon-yellow color and a characteristic odor that can easily irritate the respiratory tract. The thermal conductivity and also the electrical conductivity is poor. Sulfur is not soluble in water. Compact sulfur crystals drown in the water due to their higher density. Powdered sulfur can also swim due to the lack of wettability with water and with the help of the surface tension of the water. If sulfur is dissolved in carbon disulfide and the solution is left to stand in a Petri dish for a long time, rhombic sulfur crystals crystallize out after a while. On the other hand, when a sulfur melt cools down in air, monoclinic crystals form. When quenching molten sulfur in cold water, plastic sulfur is produced. Sulfur occurs in numerous modifications, of which only a selection is dealt with here. Orthorhombic or rhombic sulfur is stable at room temperature and forms lemon yellow crystals that can easily be broken and ground into a fine powder. The rods or threads available commercially contain rhombic sulfur.
Rhombic sulfur will also α-sulfur called, atomically it is composed of annularly corrugated S.8-Molecules built up. When heated from 95.2 ° C., it changes into a yellow, slightly liquid melt and is obtained λ-sulfur. If the temperature is continued, the melt turns orange; from 159 ° C it gradually becomes viscous and at 200 ° C it forms a dark brown, resinous mass, the μ-sulfur. The ring-shaped S.8Molecules and form long chains. The viscosity decreases above 250 ° C, and at the boiling point, at 444 ° C, the melt is again thin. If the molten sulfur is allowed to solidify on the surface in large crucibles, long, monoclinic crystal needles are formed. This modification is called monoclinic sulfur or as β-sulfur designated. When it cools down to below 115.2 ° C, it slowly converts back into rhombic sulfur. If you pour the liquid melt into a glass with cold water, elastic threads or a yellow-brown, viscous mass are formed, which as plastic sulfur referred to as. This, too, gradually changes back into rhombic sulfur.
|Heat the sulfur in the test tube|
|Various modifications occur when the sulfur is heated.|
Sulfur is very reactive and forms chemical compounds with many elements. The exceptions are gold, platinum, iridium, nitrogen, tellurium, iodine and the noble gases. In the air, sulfur burns in an oxidation with a bluish flame to the toxic and pungent smelling gas sulfur dioxide SO2, which also contains sulfur trioxide SO3 can be mixed:
S + O2 SO2 ΔHR. = −297 kJ / mol
|Sulfur burns in the air|
|Sulfur burns with a bluish flame, the heat melts it into a brownish mass.|
When the sulfur dioxide is dissolved in water, a sulfur dioxide solution and, in small amounts, sulfurous acid are formed. The salts of this acid are the sulfites. If mixtures of sulfur and metal powder are ignited, the corresponding metal sulfides are usually formed with strong heat development and lighting:
Fe + S FeS ΔHR. = −100 kJ / mol
Zn + S ZnS ΔHR. = −201 kJ / mol
Cu + S CuS ΔHR. = −53 kJ / mol
|Zinc powder reacts with sulfur|
|Reaction of zinc and sulfur in a school experiment: initial mixture, reaction, product|
With methane and an aluminum oxide catalyst, carbon disulfide is obtained at 700 ° C, a poisonous, colorless liquid:
CH4 + 4 p CS2 + 2 H.2S.
Through the reaction of sulfur and hydrogen at 350 ° C with the help of catalysts, the poisonous gas hydrogen sulfide is obtained:
S + H2 H2S.ΔHR. = −21 kJ / mol
Sulfur is not attacked by hydrochloric acid, but by oxidizing acids such as concentrated nitric acid. Other important compounds of sulfur are sulfuric acid and its salts, the sulfates. If the oxygen atom of the hydroxyl group is replaced by a sulfur atom in the alcohols, a thiol is obtained (outdated: mercaptan or thioalcohol). This group of substances is characterized by a very unpleasant odor.
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