Ka/pKa of multi-protic acids

[Hemichordate]

In a multi-protic acid, is the Ka of the second ionization always going to be lower than the Ka for the first ionization step, and the Ka for the third step (if there is one) always going to be less than the Ka for the second step?

What is the reason for this?

---

Members don't see this ad.

 

[minutemen11]

yeah its based on stability mostly. H2CO3 is highly unstable so it really wants to get rid of one H, when it reaches HCO3^- i think its stabilized more as the H in solution will act as a buffer. Thus, the Ka for HCO3 is much lower than for H2CO3. Subsequently, Ka of CO3^-2 is even lower.

 

[Hemichordate]

So the acidity (from greatest to smallest) still goes from: H2CO3, HCO3-, CO3(2-)?

 

[minutemen11]

well yeah... high Ka= low pKa= very acidic

 

[RogueUnicorn]

As you progressively lose protons, the conjugate base becomes stronger and stronger, and thus much less willing to be an acid.