[sn1sn2e1e2]

Hello!

According to some of my friends, pH= 0.5(pka1+pka2)

I have tried to derive that equation but it raises several questions:

Is it only for diprotic acids or can it be used for mono or triprotic acids?

[Borek]

Where do you plan to get pKa2 from for a monoprotic acid?

In some cases it will work for triprotic acid, for example it will work for a solution of NaH₂PO₄, it will also work for Na₂HPO₄ (but then it requires pKa2 and pKa3). But it works only if the separation of pKa values is large enough and pKa values are not too large nor too small.