Pka > 14 or < 1 and understanding the concept

[somuchwater]

---

Members don't see this ad.

So here is wht I understand about pKa.. kA is basically the ratio of H and A to HA.. so the larger your ratio of products, the larger your Ka, the smaller your Pka.

We know that for weak acid titrations, pH = pkA at the half equivalence point. What if pKa is not 0-14. What if it is like 17 or -3 or something, etc. Do those still work with that equation. I also know the pKa and pKb of a conjugate acid and base should = 14. Is that still valid if the values are not in the 0-14 range?

 

[erythrocyte666]

If you had an acid with a pKa of -3, it'd be a really strong acid like HCl. In such a case you ASSUME it fully dissociates without having to deal with Ka and Henderson-Hasselbalch eqn; HH eqn won't apply, in fact, because it applies to small pH changes that you see in weak acid titrations - weak acid titrations DO HAVE a buffering region, strong acid titrations DO NOT have a buffering region. And yes to the last question.

 

[azor ahai]

it won't work. half-equivalence point only exists for weak acids, so something whose pKa < 2 is a strong acid. pKb > 12 I believe is a strong base, so it won't work for that either.

generally, for strong acids/bases you don't need to concern yourself with henderson-hasselbalch. the pH will just equal the pKa.