Answer:
Sure, the equilibrium equation for the ionization of the third proton in phosphoric acid (H3PO4) can be written as follows:
H3PO4 + H2O ⇌ H2PO4- + H3O+
This is the equilibrium equation associated with the third dissociation constant (Ka3) for phosphoric acid. In this equation, H3PO4 donates a proton (H+) to water, forming the dihydrogen phosphate ion (H2PO4-) and a hydronium ion (H3O+). The value of Ka3 represents the equilibrium constant for this reaction and describes the degree of ionization of the third proton in phosphoric acid.