Phosphoric acid, the formula of which is H3PO4,is also called orthophosphoric. This compound under normal conditions has a solid state of aggregation. Small crystals of this substance are colorless. The acid is highly soluble in water, ethanol and other organic solvents. In the solid and liquid state, the molecules of a given substance are associated z
but due to hydrogen bonds, which is why concentrated H3PO4 has an increased viscosity. Boiling point 42.3 C, and when heated to 213 C it transforms into pyrophosphoric acid H4P2O7.
Phosphoric acid is an electrolyte of medium strength, and since it is a tribasic acid, it dissociates stepwise in three stages in aqueous solutions.
Orthophosphoric acid is usually obtained from its s alts contained in phosphate minerals - apatite and phosphorite, under the influence of sulfuric acid. Also by hydration of phosphorus (V) oxide or by hydrolysis of an inorganic compound -phosphorus pentachloride.
Phosphoric acid reacts with bases, metal oxides, s alts, active metals and strong acids. When interacting with hydroxides, a neutralization reaction occurs, the result of which is the formation of s alt and water. Reacting with metal oxides, it also forms s alt and water. When reacting with s alts, an exchange reaction occurs, in which a new s alt and acid are obtained. The interaction of phosphoric acid with silver nitrate (s alt) is a qualitative reaction that makes it possible to detect precisely its solutions. The result is a yellow precipitate - silver phosphate (Ag3PO4). With active metals, which stand in the Beketov series up to hydrogen, it enters into a substitution reaction. Interacting with strong acids (perchloric), it exhibits a dual nature (amphoteric) and forms complex s alts - phosphoryls. Also, this compound can be thermally decomposed to diphosphoric acid.
Phosphoric acid, which is widely used, is actively used in many industries. For example, in agriculture, in particular in the production of mineral fertilizers containing phosphorus. Such fertilizers can not only increase productivity, but also have a positive effect on 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 a food additive E 338, which is contained in a smallquantity in marmalade, syrup and carbonated drinks. It is because of the content of orthophosphoric and citric acids in drinks that, when they are consumed excessively, tooth decay occurs. This property to soften tooth enamel and dentin has been used by dentists. Thus, phosphoric acid, contained in a special paste, is applied to the tooth before its filling and contributes to the demineralization of its tissues. This substance is also used for etching wood and creating non-combustible paints and varnishes and building materials (non-combustible phosphate foam, phosphor wood boards). It is actively used in soldering copper, ferrous metal, stainless steel as a cleaner that removes various oxides from the metal surface. Also used in descaling, detergent manufacturing and molecular biology.
Phosphoric acid has found such an active and diverse application due to its physical and chemical properties and relatively inexpensive production.
