Ka2 and Ka1

The Conjugate Seesaw

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

Ka2 and Ka1

Postby Chu 3J » Sun Nov 29, 2015 11:39 pm

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.

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Re: Ka2 and Ka1

Postby Chem_Mod » Mon Nov 30, 2015 9:03 am

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.

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