Polyprotic acids contain multiple ionizable protons, each dissociating differently, with each successive acid dissociation constant, being weaker than the previous one. For instance, consider an example of sulfurous acid with two protons. When titrated with a strong base like NaOH, the first proton is removed, generating a hydrogen sulfite ion. The titration curve mirrors those of a weak monoprotic acid with a strong base with an equivalence point, and the pH of the solution at the half-equivalence point equals pKa1. Further base addition neutralizes the second proton. Here, the same base amount is needed as the initial sulfurous acid concentration, indicating two moles of the base are required to neutralize one mole of acid. The titration curve for this process has a second half-equivalence point and a second equivalence point in the basic region. Similarly, the titration of triprotic phosphoric acid with a strong base reveals three equivalence points. In weak polyprotic acid titrations, equivalence points equal the number of ionizable protons, assuming Ka values differ by over ten thousand fold.