Dihydrogen phosphate ion (H₂PO₄⁻)

Dihydrogen phosphate is a phosphate group that still holds two hydrogen atoms: two hydrogen, one phosphorus and four oxygen atoms with a 1− charge. Phosphoric acid, H₃PO₄, has three hydrogen ions to give, and this ion forms when it loses just one of them. You meet it in fertilizers, baking powder and the buffers that keep the pH of cells and lab solutions steady.

• The prefix di- counts two hydrogens; each H⁺ added to phosphate, PO₄³⁻, makes the charge one step less negative, so 3− becomes 1−.
• Together with hydrogen phosphate, HPO₄²⁻, it forms the phosphate buffer used inside cells and in many biology labs.
• Monocalcium phosphate, Ca(H₂PO₄)₂, is the acid ingredient in many baking powders.

Compounds that contain dihydrogen phosphate

Other ions with a −1 charge