## Ka2 and Ka1

Acidity $K_{a}$
Basicity $K_{b}$
The Conjugate Seesaw $K_{a}\times K_{b}=K_{w}$

Chu 3J
Posts: 19
Joined: Fri Sep 25, 2015 3:00 am

### Ka2 and Ka1

I know that Ka2 is typically smaller than Ka1, but why exactly is this the case? It was mentioned in the lecture that it was because it is harder for the molecule to lose another H atom, but I am not sure why it is harder for the molecule to lose another H atom.

Chem_Mod
Posts: 18878
Joined: Thu Aug 04, 2011 1:53 pm
Has upvoted: 714 times

### Re: Ka2 and Ka1

The first proton to dissociate from a polyprotic acid is the proton that is easiest for the molecule to lose. The second proton is the second easiest, etc. When a proton easily dissociates from a compound, it yields a high Ka because more conjugate base is produced as a result (remember, K = [products]/[reactants]). It follows that Ka1 > Ka2 > Ka3 etc.