phosphoric acid definition of phosphoric acid in the Free Online Encyclopedia.

phosphoric acid, any one of three chemical compounds made up of phosphorus phosphorus (fŏs`fərəs) [Gr.,=light-bearing], nonmetallic chemical element; symbol P; at. no. 15; at. wt. 30.97376; m.p. 44.
..... Click the link for more information. , oxygen, and hydrogen (see acids and bases acids and bases, two related classes of chemicals; the members of each class have a number of common properties when dissolved in a solvent, usually water.

Properties

..... Click the link for more information. ). The most common, orthophosphoric acid, H₃PO₄, is usually simply called phosphoric acid. Two molecules of it are formed by adding three molecules of water, H₂O, to one molecule of phosphorus pentoxide (phosphoric anhydride, P₂O₅). It occurs as rhombic crystals or as a viscous liquid; both are deliquescent. The crystals melt at about 42°C;. It has specific gravity 1.834 at 18°C;, is soluble in alcohol, and is very soluble in water. It is a tribasic acid and forms orthophosphate salts with either one, two, or all three of the hydrogens replaced by some other positive ion. When it is heated to about 225°C;, it dehydrates to form pyrophosphoric acid, H₄P₂O₇; at still higher temperatures metaphosphoric acid, HPO₃, is formed. Salts of pyrophosphoric acid are pyrophosphates; salts of metaphosphoric acid are metaphosphates. Phosphoric acid is prepared commercially by heating calcium phosphate rock with sulfuric acid; purer grades may be prepared by treating red phosphorus with nitric acid. It is used in pickling and rust-proofing metals, in acidifying jellies and beverages, and in preparing phosphate salts.

phosphoric acid [fä′sfȯr·ik ′as·əd]

(inorganic chemistry)

H₃PO₄Water-soluble, transparent crystals, melting at 42°C; used as a fertilizer, in soft drinks and flavor syrups, pharmaceuticals, water treatment, and animal feeds and to pickle and rust-proof metals. Also known as orthophosphoric acid.