Polyphosphoric acid

There are various kinds of phosphoric acids and phosphates. Of the many phosphorus oxoacids, the phosphoric acids constitute the largest and most diverse group. The simplest phosphoric acid series begins with monophosphoric (orthophosphoric) acid, continues with many oligophosphoric acids such as diphosphoric (pyrophosphoric) acid and concludes in the polyphosphoric acids. But, phosphoric acid units can bind together into rings or cyclic structures, chains (catenas), or branched structures, with various combinations possible. Each of these can form phosphates (salts or esters of phosphoric acids).

The simplest compound of a series of phosphoric acids is sometimes called by its common name, orthophosphoric acid, but more often called by its IUPAC name, simply phosphoric acid, by both non-technical people and even many chemists. It has also been called monophosphoric acid. The chemical formula of orthophosphoric acid is H₃PO₄ and its chemical structure is shown in the illustration below. Two or more orthophosphoric acid molecules can be joined by condensation into larger molecules by elimination of water. This way, a series of polyphosphoric acids can be obtained.

Orthophosphoric acid has three hydrogen atoms bonded to oxygen atoms in its structure. All three hydrogens are acidic to varying degrees and can be lost from the molecule as H⁺ ions (alternatively referred to as protons). When all three H⁺ ions are lost from orthophosphoric acid, an orthophosphate ion (PO₄³⁻) is formed. Orthophosphate is the simplest in a series of phosphates, and is usually just called phosphate by both non-technical people and many chemists alike; see a separate article on phosphate for details.

...
Wikipedia