The phosphate ion is a polyatomic ion with the empirical formula PO43- and a molar mass of 94.973 g/mol; it consists of one central phosphorus atom surrounded by four identical oxygen atoms in a tetrahedral arrangement. The phosphate ion carries a negative three formal charge and is the conjugate base of the hydrogenphosphate ion, HPO₄²-, which is the conjugate base of H₂PO₄-, the dihydrogen phosphate ion, which in turn is the conjugate base of H₃PO₄, phosphoric acid.

- Ammonium Hydrogen Phosphate - Sodium Hydrogen Phosphate - Magnesium Hydrogen Phosphate

- Calcium Hydrogen Phosphate - Potassium Hydrogen Phosphate