Problem

[405996618]

Calculate the pH of 0.15 M H2SO4(aq) at 25 degrees C.

For this question, even though I have the answer, I don't know why the HSO4 AND the H3O are BOTH 0.15 for the second protonation, or how are we supposed to know there is going to be 2?

[Nicole Mazaheri 1F]

You know there is going to be two deprotonations as H2SO4 is a strong acid, meaning its first deprotonation has complete dissociation, and a very high Ka value. Thus, you will analyze the Ka value of the second deprotonation. Since the first deprotonation goes to completion, 0.15 is completely used up by the reactants and is gained for each of the two products, HSO4- and H3O+. These values are then the initial values for the next deprotonation.