Ka1 Ka2

[Jose Torres]

Can Ka1 and Ka2 of a polyprotic be the same? If so, would you find the pH the same as any other solution?

[Hedi Zappacosta 1E]

I think that Ka2 is always smaller than Ka1 and you have to do each dissociation as its own problem, using Ka1 for the first and Ka2 for the second dissociation.

[Mindy Kim 4C]

For most polyprotic acids you do not need to calculate the second dissociation because the Ka2 is typically so small that any H3O+ ions generated from the acid in solution will contribute insignificantly towards the pH. One exception to this is H2SO4, as the acid completely dissociates in the first reaction.

[Ray Guo 4C]

Ka2 would always be smaller than Ka1 because it's harder to lose a proton from an already positively charged molecule.