Phosphate ions carry a formal charge of -3 and are bound by covalent bonds. The pi bonds of the ion are delocalised. It forms salts with metallic and ammonium ions. Only ammonium and alkali metal phosphates dissolve well in water.
Occurrence and production
The phosphate ion is formed from phosphoric acid through the dissociation of three protons. It occurs in soil and certain minerals.
It is an important component in fertilisers. The manufacturing process of superphosphate consists of making tricalcium phosphate soluble by adding sulphuric acid and then adding gypsum powder. Trisodium phosphate is used in softening water.