In water solution, orthophosphoric acid and its three derived anions coexist according to the dissociation and recombination equilibria below
Values are at 25°C and 0 ionic strength.
The pK values are the pH values where the concentration of each species is equal to that of its conjugate bases.  At pH 1 or lower, the phosphoric acid is practically undissociated.  Around pH 4.7 (mid-way between the first two pK values) the dihydrogen phosphate ion, , is practically the only species present.  Around pH 9.8 (mid-way between the second and third pK values) the monohydrogen phosphate ion, , is the only species present. At pH 13 or higher, the acid is completely dissociated as the phosphate ion, .
This means that salts of the mono- and di-phosphate ions can be selectively crystallised from aqueous solution by setting the pH value to either 4.7 or 9.8.
In effect, ,  and  behave as separate weak acids because the successive pK differ by more than 4.
Phosphate can form many polymeric ions such as pyrophosphate, , and triphosphate, . The various metaphosphate ions (which are usually long linear polymers) have an empirical formula of  and are found in many compounds.