KA2<KA1

[BoparaiAdeshsurjit2F]

What do you do if KA2 is less than KA1. Does that mean the pH of the first reaction is equal to the second reaction also.

[Brittney Nguyen 2L]

Hi!

I don't think it's physically possible for Ka2 to be less than Ka1, since the effective nuclear charge would be stronger after the loss of a proton. The central atom would have to hold onto less stuff, so it can hold onto that stuff a little stronger, and thus it'd be harder to take away another proton (thus contributing to a higher Ka2).

I hope this helps!

[Marcus Lagman 2A]

Hello!

Yes, you are correct! Since the Ka of the 2nd deprotonation of polyprotic acid is extremely less than the Ka of the 1st deprotonation (Ka2 << Ka1/1000), we can say that the pH of the 1st deprotonation is approximately equal to the pH of the 2nd deprotonation. Therefore, solving for the first pH is enough and we do not need any further work.

I hope this helps!