Triprotic
Each proton loss changes the ion.
The next proton therefore sits in a different electrostatic environment.
Molecular compound · triprotic oxoacid
Phosphoric acid
H₃PO₄
Phosphoric acid is H₃PO₄. Three O–H groups can lose protons stepwise, generating dihydrogen phosphate, hydrogen phosphate and phosphate.
Do not flatten the equilibria: three acidic hydrogens does not mean three equally strong proton transfers.
Essentials
Three P–OH groups make the acid chemistry visible.
The conventional O=P(OH)₃ drawing is a useful first model because it shows the three proton-bearing oxygen atoms.
Detail
The reference 2D structure fixes connectivity.
The familiar P=O / P–OH Lewis picture is useful bookkeeping; the real electronic structure is more delocalized than one rigid bond-order cartoon.
Phosphate family
Deprotonation changes charge while retaining the P–O framework.
Think of the species as neighboring protonation states.
Understand
Phosphate speciation changes strongly with pH.
H₃PO₄, H₂PO₄⁻, HPO₄²⁻ and PO₄³⁻ are connected by three distinct equilibria.
Buffers
Neighboring phosphate species form useful buffer pairs.
The dominant pair depends on pH.
Reference identifiers
Names and identifiers that pin down the chemical identity.
| Formula | H₃PO₄ |
|---|---|
| CAS Registry Number | 7664-38-2 |
| PubChem CID | 1004 |
Advanced
Push past the first model without losing the simple picture.
Are all three protons equally acidic?
No. Successive deprotonations are progressively less favorable.
Is phosphate always PO₄³⁻ in water?
No. Protonated phosphate species dominate across many ordinary pH ranges.
Is O=P(OH)₃ the complete bonding description?
No. It is a Lewis representation, not a wavefunction-level description.
Constituent elements