The sulfurous acid is an oxacid that is formed by the dissolution of sulfur dioxide, SOtwo, in water. It is a weak and unstable inorganic acid, which has not been detected in solution, since the reaction of its formation is reversible and the acid rapidly decomposes in the reagents that produced it (SOtwo and HtwoOR).
The sulfurous acid molecule has so far only been detected in the gas phase. The conjugated bases of this acid are common anions in the forms of sulfites and bisulfites..
SWtwo + HtwoOR <=> HSO3- + H+
This indicates that using the Raman spectrum it is not possible to detect the presence of sulfurous acid in a solution of sulfur dioxide in water..
When exposed to the atmosphere, it quickly turns into sulfuric acid. Sulfurous acid is reduced to hydrogen sulfide by the action of dilute sulfuric acid and zinc.
The attempt to concentrate an OS solutiontwo by evaporating water to obtain water-free sulfurous acid, it did not produce results, since the acid decomposes rapidly (reversing the formation reaction), so the acid cannot be isolated.
Article index
Sulfurous acid is formed in nature by the combination of sulfur dioxide, a product of the activity of large factories, with atmospheric water. For this reason, it is considered an intermediate product of acid rain, causing great damage to agriculture and the environment..
Its acid form is not usable in nature, but it is usually prepared in its salts, sodium and potassium sulphite and bisulphite..
Sulfite is endogenously generated in the body as a result of the metabolism of sulfur-containing amino acids. Likewise, sulfite is produced as a product of the fermentation of foods and beverages. Sulfite is allergenic, neurotoxic, and metabolic. It is metabolized by the enzyme sulfite oxidase that converts it into sulfate, a harmless compound.
In the image you can see the structure of an isolated molecule of sulfurous acid in the gaseous state. The yellow sphere in the center corresponds to the sulfur atom, the red ones to the oxygen atoms, and the white ones to the hydrogens. Its molecular geometry around the S atom is a trigonal pyramid, with the O atoms drawing the base.
Then, in the gaseous state, the molecules of HtwoSW3 can be thought of as tiny trigonal pyramids floating in the air, assuming it is stable enough to last for a while without reacting.
The structure makes it clear where the two acidic hydrogens come from: from the sulfur-bonded hydroxyl groups, HO-SO-OH. Therefore, for this compound, it is not correct to assume that one of the acidic protons, H+, is released from the sulfur atom, H-SOtwo(OH).
The two OH groups allow the sulfurous acid to interact through hydrogen bonds and in addition, the oxygen of the S = O bond is a hydrogen acceptor, which converts HtwoSW3 both a good donor and acceptor of these bridges.
According to the above, the HtwoSW3 should be able to condense into a liquid, just like sulfuric acid does, HtwoSW4. Nevertheless, that's not how it happens.
To date, it has not been possible to obtain anhydrous sulfurous acid, that is, HtwoSW3(l); while the HtwoSW4(ac), on the other hand, after dehydration, it transforms into its anhydrous form, HtwoSW4(l), which is a dense and viscous liquid.
If it is assumed that the molecule of HtwoSW3 remains unchanged, then it will be able to dissolve largely in water. The interactions that would govern in said aqueous solutions would again be hydrogen bonds; However, electrostatic interactions would also exist as a result of the hydrolysis equilibrium:
HtwoSW3(ac) + HtwoO (l) <=> HSO3-(ac) + H3OR+(ac)
HSO3-(ac) + HtwoO (l) <=> SW3two-(ac) + H3OR+
The sulfite ion, SO3two- It would be the same molecule as above, but without the white spheres; and the hydrogen sulfite (or bisulfite) ion, HSO3-, retains a white sphere. Infinities of salts can arise from both anions, some more unstable than others.
In reality, it has been confirmed that an extremely small portion of the solutions consists of HtwoSW3; that is, the molecule explained is not the one that interacts directly with the water molecules. The reason for this is because it undergoes decomposition causing SOtwo and HtwoOr, which is thermodynamically favored.
The true structure of sulfurous acid consists of a molecule of sulfur dioxide surrounded by a sphere of water that is made up of n molecules..
Thus, the SOtwo, whose structure is angular (boomerang type), together with its watery sphere, is responsible for the acidic protons that characterize acidity:
SWtwo∙ nHtwoO (ac) + HtwoO (l) <=> H3OR+(ac) + HSO3-(ac) + nHtwoO (l)
HSO3-(ac) + HtwoO (l) <=> SW3two-(ac) + H3OR+
In addition to this balance, there is also a solubility balance for SOtwo, whose molecule can escape from water to the gas phase:
SWtwo(g) <=> SWtwo(ac)
HtwoSW3
82.073 g / mol.
It is a colorless liquid, with a pungent smell of sulfur.
1.03 g / ml.
2.3 (in relation to air taken as 1)
It is corrosive to metals and fabrics.
Miscible with water.
It is sensitive to air.
Stable, but incompatible with strong bases.
1.54 x 10-two
1.81
1.5 on the pH scale.
Not flammable.
When heated, sulfurous acid can decompose, emitting toxic sulfur oxide smoke..
Sulfur has the following valences: ± 2, +4 and +6. From the formula HtwoSW3, the valence or oxidation number of the sulfur in the compound can be calculated. To do this, just solve an algebraic sum:
2 (+1) + 1v + 3 (-2) = 0
As it is a neutral compound, the sum of the charges of the atoms that constitute it must be 0. Solving for v for the previous equation, we have:
v = (6-2) / 1
Thus, v is equal to +4. That is, sulfur participates with its second valence, and according to traditional nomenclature, the suffix -oso must be added to the name. For this reason at HtwoSW3 it is known as sulfur acidbear.
Another faster way to determine this valence is by comparing the HtwoSW3 with the HtwoSW4. In the HtwoSW4 sulfur has a valence of +6, so if an O is removed, the valence drops to +4; and if another one is removed, the valence drops to +2 (which would be the case for acid hiccupsulfurbear, HtwoSWtwo).
Although less known, to the HtwoSW3 It can also be called trioxosulfuric acid (IV), according to the stock nomenclature.
Technically it is formed by burning sulfur to form sulfur dioxide. This then dissolves in water to form sulfurous acid. However, the reaction is reversible and the acid rapidly decomposes back into the reactants..
This is an explanation of why sulfurous acid is not found in aqueous solution (as already mentioned in the section on its chemical structure).
Generally, the uses and applications of sulfur acid, since its presence cannot be detected, refer to the uses and applications of solutions of sulfur dioxide and the bases and salts of the acid..
In the sulfite process, wood pulp is produced in the form of almost pure cellulose fibers. Various salts of sulfurous acid are used to extract lignin from wood chips, using high pressure vessels called digistors..
The salts used in the process of obtaining the pulp of the wood are sulfite (SO3two-) or bisulfite (HSO3-), depending on the pH. The counter ion can be Na+, ACtwo+, K+ or NH4+.
-Sulfurous acid is used as a disinfectant. It is also used as a mild bleaching agent, especially for chlorine sensitive materials. In addition, it is used as a teeth whitener and food additive.
-It is an ingredient in various skin care cosmetics and was used as a pesticidal element in the elimination of rats. Eliminates stains caused by wine or fruit on different fabrics.
-It serves as an antiseptic, being effective in preventing skin infections. At times, it was used in fumigations to disinfect ships, belongings of sick victims of epidemics, etc..
Sulfurous acid is used as a preservative for fruits and vegetables and to prevent the fermentation of beverages such as wine and beer, being an antioxidant, antibacterial and fungicidal element..
-Sulfurous acid is used in the synthesis of drugs and chemicals; in the production of wine and beer; refining of petroleum products; and is used as an analytical reagent.
-The bisulfite reacts with the pyrimidine nucleosides and adds to the double bond between the 5 and 6 position of the pyrimidine, modifying the bond. Bisulfite transformation is used to test for secondary or higher structures of polynucleotides.
Yet No Comments