My intuition says that the titration curve for titrating a $1:1$ mixture of the monoprotic acids $\ce{HA_1}$ and $\ce{HA_2}$ (having ionization constants $K_a = x$ and $K_a = y$ respectively) is identical to the titration curve obtained by titrating a diprotic acid $\ce{H2X}$, with successive ionization constants $Ka_1 = x$ and $Ka_2 = y$.

I feel that this should be correct because the "concentration" and "strength" of the acids are the same, but I am not sure how to prove if it is correct.

  • 1
    $\begingroup$ What is diuretic acid? You meant diprotic acid. $\endgroup$
    – AChem
    Apr 11, 2020 at 22:25

1 Answer 1


Your intuition is right, because a potentiometric sensor (a $\mathrm{pH}$ probe in your case) does not know the source of hydrogren ions, it only senses the presence of hydrogen ions. The same is true for any other detection mode. All we care is $\ce{H+ + OH- -> H2O}$.

It can come from two monoprotic acids or it can come from a diprotic acid. In order to make your wish true, $\mathrm{p}K_\mathrm{a}$ must be less than $\mathrm{p}K_\mathrm{b}$. They cannot vary randomly and they cannot be equal.

However intuition is not enough to prove a point. You have to pick numbers and simulate. Here is useful online tool to calculate titration curve and see how well they match.

pH Titration Curve Generator

Choose to add $\ce{HA}$ or $\ce{H2A}$ and $\ce{NaOH}$ as a base.


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