What is the conjugate acid of HPO4^2-? What is the conjugate base of HPO4^2-?

Answer 1

When a bronsted-lowry acid is in equilibrium, it will donate a proton (as acids do) in the form of a hydrogen ion, and will therefore become a base (willing to accept a proton). The resulting base is called the conjugate base. The same is true for bases-- when in equilibrium, it will accept a proton, and become a conjugate acid.

Here are the equilibrium expressions:

HPO₄^2- + H₂O ↔ PO₄^3- + H₃O⁺ (conjugate base)

HPO₄^2- + H₂O ↔ H₂PO₄^1- + OH^1- (conjugate acid)