[willy.Jonathan.12]

Hello
My task is to express dissociation degree for fully dissociated form of diprotoic acid in general as a function of Ka1 Ka2 and [H+].

I know that
Ka1=[H+]*[HA-]/[H2A]
Ka2=[H+]*[A2-]/[HA-]
[HA-]+[A2-]=[H+]

diss degree=[A2-]/(HA-]+[H2A]+[A2-])

But I have no idea how to exchange all this things with only Ka1 Ka2 and [H+]
Can someone help me with that ?

[Borek]

See

http://www.chembuddy.com/?left=pH-calculation&right=pH-polyprotic-acid-base

(while it aims at something else, it contains all formulas you need).