Dihydrogen phosphate
Dihydrogen phosphate or dihydrogenphosphate ion is an inorganic ion with the formula −. Its formula can also be written as −, which shows the presence of two O-H bonds. Together with hydrogen phosphate, dihydrogen phosphate occurs widely in natural systems. Their salts are used in fertilizers and in cooking. Most dihydrogen phosphate salts are colorless, water soluble, and nontoxic.
Structure
The dihydrogen phosphate anion consists of a central phosphorus atom surrounded by 2 equivalent oxygen atoms and 2 hydroxy groups in a tetrahedral arrangement. The phosphorus atom is in the 5+ oxidation state. The dihydrogen phosphate ion carries an overall charge of −1 and it is the conjugate base of phosphoric acid.Acid-base equilibria
Dihydrogenphosphate is an intermediate in the multistep conversion of phosphoric acid to phosphate:| Equilibrium | Disassociation constant, pKa |
| H3PO4 + H+ | pKa1 = 2.14 |
| + H+ | pKa2 = 7.20 |
| + H+ | pKa3 = 12.37 |