Phosphoric acid, the formula of which is H 3 PO 4, is also called orthophosphoric. Under normal conditions, this compound has a solid state of aggregation. Small 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
and due to hydrogen bonds, that is why concentrated H3PO4 has an increased viscosity. The boiling point is 42.3 C, and when heated to 213 C, it passes into pyrophosphoric acid H
4 P
2 O
7 .
Phosphoric acid is an electrolyte of medium strength, and since it is a tribasic acid, it dissociates stepwise in aqueous solutions in three stages.
Orthophosphoric acid is usually obtained from its salts contained in phosphate minerals - apatite and phosphorite, under the influence of sulfuric acid. Also, by hydration of phosphorus oxide (V) or by hydrolysis of an inorganic compound - phosphorus pentachloride.
Phosphoric acid reacts with bases, metal oxides, salts, active metals and
strong acids. When interacting 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 occurs, in which a new salt and acid are obtained. The interaction of orthophosphoric acid with
silver nitrate (salt) is a qualitative reaction that allows one to detect precisely its solutions. The result is a yellow precipitate - silver phosphate (Ag
3 PO
4 ). With active metals, which stand in the Beketov series before hydrogen, enters the substitution reaction. Interacting with strong acids (perchloric), it exhibits a dual nature (amphotericity) and forms complex salts - phosphoryl. This compound can also be thermally decomposed to diphosphoric acid.
Phosphoric acid, a widely used application, is widely used in many industries. For example, in agriculture, in particular in the production of mineral fertilizers containing phosphorus. Such fertilizers can increase not only productivity, but also favorably affect the microbiological composition of the soil, contributing to the reproduction and development of beneficial bacteria, as well as increase the winter hardiness of crops. In the food industry, this acid is used as a food supplement E 338, which is found in small amounts in marmalade, syrup and carbonated drinks. It is because of the content of phosphoric and citric acids in drinks, when they are consumed excessively, tooth decay occurs. This property to soften tooth enamel and dentin began to be used by dentists. So, phosphoric acid, which is contained in a special paste, is applied to the tooth before filling and contributes to the demineralization of its tissues. This substance is also used to etch wood and create non-combustible paints and varnishes and building materials (non-combustible phosphate polystyrene foam, phosphate-wood slabs). It is actively used in the soldering of copper, ferrous metal, stainless steel as a cleaner that removes various oxides from the surface of the metal. Also used in descaling, production of detergents and molecular biology.
Phosphoric acid has found such an active and diverse application due to its physicochemical properties and relatively inexpensive preparation.