Acids and Ionizable Hydrogens
How do acids like phosphoric acid, phosphorous acid, and hypophosphorous acid differ in terms of ionizable protons?
Phosphoric acid H₃PO₄ is a triprotic acid, phosphorous acid H₃PO₃ is a diprotic acid, and hypophosphorous acid H₃PO₂ is a monoprotic acid. What causes this difference?
Explanation:
The terms monoprotic, diprotic, and triprotic correspond to the number of ionizable hydrogen atoms (protons) in an acid. In these cases, H₃PO₄, H₃PO₃, and H₃PO₂ have 3, 2, and 1 ionizable protons respectively.
The phenomenon you're asking about is related to the number of ionizable hydrogens (protons) in each acid. Phosphoric Acid (H₃PO₄), having three ionizable (donatable) protons, is termed a triprotic acid. Phosphorous acid (H₃PO₃) only has two ionizable protons, making it a diprotic acid, and Hypophosphorous acid (H₃PO₂), having a single ionizable proton, is known as a monoprotic acid.
When these acids dissolve in water, they can donate these protons to water molecules to form hydronium ions (H₃O⁺), with the number of protons able to be donated defining whether the acid is mono, di or triprotic.