pH of Polyprotic Acids

[Kathryn Go - 1A]

How and why are polyprotic acids treated differently when it comes to finding the pH? Are there any exceptions of the polyprotic acids that maybe require a different approach that's more similar to a regular acid/base?

[Rishi Parikh 1E]

Polyprotic acids release protons (H⁺) in multiple steps, so their pH is typically determined step-by-step, considering the dissociation constants for each proton release. The first dissociation usually dominates, and subsequent dissociations often contribute less to the overall pH, especially for weak polyprotic acids. However, for strong polyprotic acids like H₂SO₄ (sulfuric acid), the first dissociation is very strong, and the second dissociation is weaker, so the acid can behave more like a monoprotic acid in practice, where the second dissociation doesn't significantly affect pH. In such cases, it’s treated more like a strong acid, with the pH largely determined by the first dissociation. Since they have multiple protons that they can lose, polyprotic acids are overall typically treated very differently from monoprotic acids. Hope this answer helps! I think the dissociation topics are more Chem 14B material, but it should help answer your question.