Phosphoric acid, whose formula H 3 PO 4, is also called orthophosphoric acid. This compound under normal conditions has a solid aggregate state. The fine crystals of this substance are colorless. The acid is highly soluble in water, ethyl alcohol and other organic solvents. In the solid and liquid state, the molecules of a given substance are associated with But through hydrogen bonds, which is why concentrated H3PO4 has an increased viscosity. The boiling point is 42.3 ° C, and when heated to 213 ° C it passes into the pyrophosphoric acid H 4 P 2 O 7 .
Phosphoric acid is an electrolyte of medium strength, and since it is a tribasic acid, in aqueous solutions it dissociates stepwise in three stages.
Obtain orthophosphoric acid, usually from its salts contained in phosphate minerals - apatite and phosphorite, under the influence of sulfuric acid. Also by hydrating the phosphorus oxide (V) or by hydrolyzing the inorganic compound - phosphorus pentachloride.
Phosphoric acid interacts with bases, metal oxides, salts, active metals and strong acids. When reacting with hydroxides, a neutralization reaction occurs, the result of which is the formation of salt and water. Reacting with metal oxides also forms salt and water. When reacting with salts, an exchange reaction takes place, at which a new salt and acid are obtained. The interaction of orthophosphoric acid with silver nitrate (salt) is a qualitative reaction that makes it possible to detect its solutions. The result is a yellow precipitate - silver phosphate (Ag 3 PO 4 ). With active metals that stand in the Beketov series to hydrogen, it enters a substitution reaction. Interacting with strong acids (chloric acid), it manifests a dual nature (amphotericity) and forms complex salts - phosphoryl. Also, this compound can be thermally decomposed to diphosphoric acid.
Phosphoric acid, an application that is widely used, is widely used in many industries. For example, in agriculture, in particular in the production of fertilizers containing phosphorus. Such fertilizers can increase not only the yield, but also favorably influence the microbiological composition of the soil, promoting the reproduction and development of beneficial bacteria, as well as increasing the winter hardiness of crops. In the food industry, this acid is used as food additive E 338, which is contained in a small amount in marmalade, syrup and carbonated beverages. It is because of the content of orthophosphoric and citric acids in drinks, when they are used excessively, the tooth is destroyed. This property of softening tooth enamel and dentin was used by dentists. So, phosphoric acid, containing in a special paste, is applied to the tooth before it is sealed and promotes the demineralization of its tissues. This substance is also used to etch wood and create non-combustible paint and varnish products and building materials (non-combustible phosphate foam, phosphate wood plates). It is actively used in the brazing of copper, black metal, stainless steel as a cleaner, which removes various oxides from the surface of the metal. Also used in descaling, detergent production and molecular biology.
Phosphoric acid has found such an active and versatile application due to its physico-chemical properties and relatively inexpensive production.