Dihydrogen phosphate is an inorganic ion with the formula [H2PO4]−. Phosphates occur widely in natural systems. Perhaps the most common salt of dihydrogen phosphate is sodium dihydrogen phosphate. It is used in animal feed, fertilizer, buffer (in food), and treating metal surfaces.
Structure The dihydrogen phosphate anion consists of a central phosphorus atom bonded two oxides and two hydroxy groups in a tetrahedral arrangement.
Acid-base equilibria Dihydrogen phosphate can be both a hydrogen donor and acceptor. Equilibrium Disassociation constant, pKa H3PO4 + H+ pKa1 = 2.14 + H+ pKa2 = 7.20 + H+ pKa3 = 12.37
Examples Ammonium dihydrogen phosphate ((NH4)(H2PO4)) Monocalcium phosphate (Ca(H2PO4)2)
Safety Many foods including milk, eggs, poultry, and nuts contain these sodium phosphates.
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