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Modern studies in the field of chemistry have opposed the theory that was put forward by Lavoisier’s acid-base reaction. It has been inferred that acids are of two types –oxoacids and hydro acids that contain oxygen and hydrogen atoms respectively. Oxyacid compounds maintain the chemical structure as X – O – H. Here, X is the central atom forming the compound. Its electronegative degree determines the acidic strength of the acid. As the oxygen atoms keep on increasing, the electronegativity goes up. Oxoacids are unstable compounds so it is not possible to isolate the individual elements. Some popular examples of oxoacids are sulphuric acid, phosphorus acid, and hypochlorous acid.
Inorganic variants of oxoacids depict the formula: HaXOb. The denotations a and b state the oxidation state of primary constituent atom X. Primarily, X is a nonmetallic element but there are exceptional cases when the central atom is a metal for example manganese and chromium. Chemical disintegration of oxoacids into anhydrides and water takes place when they are subjected to high temperatures. For example, when carbonic acid is treated at a high temperature it dissociates into anhydride – CO2 and water. Inorganic oxyacids have a simple molecular structure as compared to phenols and carboxylic acids. Phenols are oxoacids that have carbon as the central atom. While carboxylic acids are compounds where a generalized carboxyl group (CO2H) is attached to an R-group. This R signifies aryl, alkyl, alkenyl, or some other functional groups.
Oxoacids of phosphorus
One of the core elements involved in the formation of oxoacids is phosphorus. Oxoacids of phosphorus are majorly represented by phosphorus acid (H3PO4) and orthophosphoric acid (H3PO4). In the oxoacids of phosphorus, the phosphorus atom is surrounded from all four sides by other participating atoms to form the bond. There are three types of co-existent bonds in the oxoacids of phosphorus. These are the P – P or P – H links that occur alongside the P-OH bond and the P=O bond. As the phosphorus atom’s oxidation number is not more than 5, the oxidation states of these acids shift from high to low.
Oxoacids of phosphorus depict the varying degree of acidic strength which is given in the following order:
H3PO2>H3PO3 > H3PO4 (in terms of acidity)
Phosphorus Acid (H3PO2): This compound is received as an intermediate product in other reactions involving phosphorus. It is a diprotic acid that enables it to disintegrate into ions when combined with water. This oxoacid is produced by the mechanism of hydroxylation.
Phosphoric Acid (H3PO4): It constitutes three hydrogen molecules and is therefore referred to as atricroticacid. This acid is produced by combining sulphuric acid and solid tricalcium phosphate.
Meta phosphoric Acid (HPO3) n: This oxoacid cannot exist as a monomer. H3PO4 is heated to around 850°C to receive metaphosphoric acid. When the protons are disintegrated it breaks down to produce anions in the form of metaphosphates.
Pyrophosphoric acid (H4P2O7): It is a tetrabasic variant of oxoacids of phosphorus. H3PO4 forms pyrophosphoric acid when it is thermally treated at around 250°C.
Another form of phosphorus acid–hypophosphoric acid, is formed by oxidation of red-hot phosphorus. The reaction involves the usage of sodium chlorite.
Oxoacids of chlorine
There are four primary sorts of oxoacids that can be prepared from chlorine. Their names are hypochlorous acid, chlorous acid, perchloric acid, and chloric acid. The purpose of producing them is associated with the industrial processes of glucose and chlorine production. These acids are indispensable ingredients in modern medicinal chemistry.
Hydrolytic disproportion is a chemical reaction that happens when gaseous chlorine is allowed to flow through water. This reaction is reversible and produces HClO or hypochlorous acid.
Chlorous acid is one of the most abundant oxoacids of chlorine that is prepared by oxidizing lead chloride or barium. Diluted sulphuric acid facilitates the reaction.
The concentrated form of sulphuric acid is utilized to carry out the oxidation of barium chlorate. This produces chloric acid. Its formula is HClO3. If we execute the oxidation of barium perchlorate instead of barium chlorate, this same procedure will lead to the formation of HOClO3 or perchloric acid. All the oxoacids of chlorine are dissolved in water.
Oxoacids of halogens
The family of chlorine oxoacids discussed above represents a class of oxoacids of halogens. Halogens are the elements that appear in group 17 of the classical periodic table. Some examples of halogens are bromine, iodine, chlorine, and fluorine. Bromine and iodine form three types of oxoacids each. We notice sp3 hybridization in the central atom of halogen oxoacids. The X=O bonds in halogen oxoacids exhibit the d pi-pi characteristic. The acidity is directly proportional to the constituent halogen element’s oxidation state.
Conclusion
Oxoacid is an acidic compound that includes elements chemically linked with hydrogen and oxygen. These elements can potentially be phosphorus or halogens. They exhibit varying acidity and some of them are produced as intermediaries in reversible chemical reactions.
