![]() ![]() In biological systems, phosphorus can be found as free phosphate anions in solution ( inorganic phosphate) or bound to organic molecules as various organophosphates. The various metaphosphate ions (which are usually long linear polymers) have an empirical formula of (PO Phosphate can form many polymeric ions such as pyrophosphate, (P 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.īehave as separate weak acids because the successive p K a differ by more than 4. At pH 13 or higher, the acid is completely dissociated as the phosphate ion, (PO Around pH 9.8 (mid-way between the second and third p K a values) the monohydrogen phosphate ion, [HPO , is practically the only species present. Around pH 4.7 (mid-way between the first two p K a values) the dihydrogen phosphate ion, [H At pH 1 or lower, the phosphoric acid is practically undissociated. The p K a values are the pH values where the concentration of each species is equal to that of its conjugate bases. In water solution, orthophosphoric acid and its three derived anions coexist according to the dissociation and recombination equilibria below Equilibrium As a rule, the hydrogen and dihydrogen phosphates are slightly more soluble than the corresponding phosphates. Most other phosphates are only slightly soluble or are insoluble in water. The sodium, potassium, rubidium, caesium, and ammonium phosphates are all water-soluble. Many phosphates are soluble in water at standard temperature and pressure. , which in turn is the conjugate base of orthophosphoric acid, H ![]() ![]() , which in turn is the conjugate base of the dihydrogen phosphate ion H It is the conjugate base of the hydrogen phosphate ion H(PO The phosphate ion has a molar mass of 94.97 g/mol, and consists of a central phosphorus atom surrounded by four oxygen atoms in a tetrahedral arrangement. 1.4 Medical and biological research uses. ![]()
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