Textbook Problem 6E.3

[Andres Medrano 1I]

Hello! I have a conceptual question regarding this textbook problem. It asks us to Calculate the pH of each solution of diprotic acids, ignoring second deprotonations only when the approximations are justified.

The answer key states that, "Since Ka2 << Ka1, then we can ignore second deprotonations." Can someone explain why this is the case and also do we have a chance at seeing this on the midterm because I never remember going over this (correct me if I'm wrong pls). Thanks!

[Kenneth Vu 3B]

In a polyprotic acid, the second H+ is a lot harder to dissociate, so the Ka2 is a lot smaller than the Ka1. When it is much much smaller, the amount of H3O+ ions becomes negligible since there will be too little of it to make a difference to the pH.
Not sure if it's gonna be on the exam tho