phosphate

phosphate, any of numerous chemical compounds related to phosphoric acid (H₃PO₄). One group of these derivatives is composed of salts containing the phosphate ion (PO₄³⁻), the hydrogen phosphate ion (HPO₄²⁻), or the dihydrogen phosphate ion (H₂PO₄⁻), and positively charged ions such as those of sodium or calcium; a second group is composed of esters, in which the hydrogen atoms of phosphoric acid have been replaced by organic combining groups such as ethyl (C₂H₅) or phenyl (C₆H₅).