Sulfur dioxide - physical properties, production and application

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Sulfur dioxide - physical properties, production and application
Sulfur dioxide - physical properties, production and application
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Sulfur dioxide has a molecular structure similar to ozone. The sulfur atom in the center of the molecule is bonded to two oxygen atoms. This gaseous product of sulfur oxidation is colorless, emits a pungent odor, easily condenses into a clear liquid under changing conditions. The substance is highly soluble in water, has antiseptic properties. SO2 is obtained in large quantities in the chemical industry, namely in the cycle of sulfuric acid production. The gas is widely used for processing agricultural and food products, bleaching fabrics in the textile industry.

Systematic and trivial names of substances

It is necessary to understand the variety of terms related to the same compound. The official name of the compound, whose chemical composition is reflected by the formula SO2, is sulfur dioxide. IUPAC recommends the use of this term and its English equivalent, Sulfur dioxide. Textbooks for schools and universities often mention another name - sulfur oxide (IV). The Roman numeral in brackets denotes the valency of the S atom. The oxygen in this oxide is bivalent, and the oxidation number of sulfur is +4. The technical literature uses obsolete terms such as sulfur dioxide, sulfurous anhydride (a product of its dehydration).

sulphur dioxide
sulphur dioxide

Composition and features of the molecular structure of SO2

The SO2 molecule is formed by one sulfur atom and two oxygen atoms. There is an angle of 120° between covalent bonds. Sp2-hybridization occurs in the sulfur atom - clouds of one s and two p-electrons are aligned in shape and energy. They are involved in the formation of a covalent bond between sulfur and oxygen. In the O-S pair, the distance between the atoms is 0.143 nm. Oxygen is more electronegative than sulfur, which means that the bonding pairs of electrons move from the center to the outer corners. The whole molecule is also polarized, negative pole - O atoms, positive - S atom.

sulfur dioxide formula
sulfur dioxide formula

Some physical parameters of sulfur dioxide

Tetravalent sulfur oxide, under normal environmental conditions, retains a gaseous state of aggregation. The formula for sulfur dioxide allows you to determine its relative molecular and molar masses: Mr(SO2)=64.066, M=64.066 g/mol (may be rounded up to 64 g/mol). This gas is almost 2.3 times heavier than air (M(air)=29 g/mol). Dioxide has a sharp specific smell of burning sulfur, which is difficult to confuse with any other. It is unpleasant, irritates the mucous membranes of the eyes, causes a cough. But sulfur(IV) oxide is not as poisonous as hydrogen sulfide.

Under pressure at room temperature, gaseous sulfur dioxide liquefies. At low temperatures, the substance is in a solid state, it melts at –72…–75.5 °C. With a further increase in temperature, a liquid appears, and at –10.1 °C, a gas is formed again. SO2 molecules are thermally stable, decomposition into atomic sulfur and molecular oxygen occurs at very high temperatures (about 2800 ºС).

sulfur dioxide production
sulfur dioxide production

Solubility and interaction with water

Sulfur dioxide, when dissolved in water, partially interacts with it to form a very weak sulfurous acid. At the time of receipt, it immediately decomposes into anhydride and water: SO2 + H2O ↔ H2 SO3 In fact, it is not sulfurous acid that is present in the solution, but hydrated molecules SO2 Gaseous dioxide interacts better with cool water, its solubility decreases with rise in temperature. Under normal conditions, it can dissolve in 1 volume of water up to 40 volumes of gas.

Sulfide gas in nature

Significant volumes of sulfur dioxide are released with volcanic gases and lava during eruptions. Many human activities also increase the concentration of SO2 in the atmosphere.

formation of sulfur dioxide in a volcano
formation of sulfur dioxide in a volcano

Sulfur dioxide is supplied to the air by metallurgical plants, where exhaust gases are not captured during the roasting of ore. Many types of fossil fuels contain sulfur, as a result, significant amounts of sulfur dioxide are released into the atmospheric air during the combustion of coal, oil, gas, and the fuel obtained from them. Sulfur dioxide becomes toxic to humans at concentrations in the air above 0.03%. A person begins shortness of breath, there may be phenomena resembling bronchitis and pneumonia. A very high concentration of sulfur dioxide in the atmosphere can lead to severe poisoning or death.

Sulfide gas - laboratory and industrial production

Laboratory methods:

  1. When sulfur is burned in a flask with oxygen or air, dioxide is obtained according to the formula: S + O2=SO2.
  2. It is possible to act on s alts of sulfurous acid with stronger inorganic acids, it is better to take hydrochloric acid, but you can use dilute sulfuric acid:
  • Na2SO3 + 2HCl=2NaCl + H2SO 3;
  • Na2SO3 + H2SO4(disassembled)=Na2SO4 + H2SO 3;
  • H2SO3=H2O + SO 2↑.

3. When copper reacts with concentrated sulfuric acid, not hydrogen is released, but sulfur dioxide:

2H2SO4 (conc.) + Cu=CuSO4 + 2H 2O + SO2↑.

Modern methods of industrial production of sulfur dioxide:

  1. Oxidation of natural sulfur during its combustion in special furnaces: S + O2=SO2.
  2. Roasting iron pyrite (pyrite).
raw materials
raw materials

Basic chemical properties of sulfur dioxide

Sulfur dioxide is a chemically active compound. In redox processes, this substance often acts as a reducing agent. For example, when molecular bromine interacts with sulfur dioxide, the reaction products are sulfuric acid and hydrogen bromide. The oxidizing properties of SO2 appear when this gas is passed through hydrogen sulfide water. As a result, sulfur is released, self-oxidation-self-healing occurs: SO2 + 2H2S=3S + 2H2 O.

Sulfur dioxide exhibits acidic properties. It corresponds to one of the weakest and most unstable acids - sulfurous. This compound does not exist in its pure form; it is possible to detect the acidic properties of a sulfur dioxide solution using indicators (litmus turns pink). Sulfurous acid gives medium s alts - sulfites and acidic - hydrosulfites. Among them are stable compounds.

The process of oxidation of sulfur in dioxide to a hexavalent state in sulfuric anhydride is catalytic. The resulting substance dissolves vigorously in water, reacts with H2O molecules. The reaction is exothermic, producing sulfuric acid, or rather its hydrated form.

Practical use of sour gas

The main process for the industrial production of sulfuric acid, which requires element dioxide, has four stages:

  1. Obtaining sulfur dioxide by burning sulfur in special furnaces.
  2. Purification of the resulting sulfur dioxide from all kinds of impurities.
  3. Further oxidation to hexavalent sulfur in the presence of a catalyst.
  4. Absorption of sulfur trioxide by water.

Previously, almost all the sulfur dioxide needed to produce sulfuric acid on an industrial scale was obtained by roasting pyrite as a by-product of steelmaking. New types of processing of metallurgical raw materials use less ore combustion. Therefore, natural sulfur has become the main starting material for sulfuric acid production in recent years. Significant world reserves of this raw material, its availability make it possible to organize large-scale processing.

sulfuric acid production
sulfuric acid production

Sulfur dioxide is widely used not only in the chemical industry, but also in other sectors of the economy. Textile mills use this substance and the products of its chemical interaction to bleach silk and woolen fabrics. This is a type of chlorine-free bleaching that does not break down the fibers.

Sulfur dioxide has excellent disinfectant properties, which is used in the fight against fungi and bacteria. Sulfur dioxide is used to fumigate agricultural storages, wine barrels and cellars. SO2 is used in the food industry as a preservative and antibacterial agent. Add it to syrups, soak fresh fruits in it. Sulfitizationsugar beet juice discolors and disinfects raw materials. Canned vegetable purees and juices also contain sulfur dioxide as an antioxidant and preservative agent.

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