Ka1 Ka2

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Jose Torres
Posts: 31
Joined: Fri Sep 28, 2018 12:22 am

Ka1 Ka2

Postby Jose Torres » Mon Jan 21, 2019 8:36 pm

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
Posts: 66
Joined: Fri Sep 28, 2018 12:27 am

Re: Ka1 Ka2

Postby Hedi Zappacosta 1E » Mon Jan 21, 2019 8:51 pm

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
Posts: 65
Joined: Fri Sep 28, 2018 12:25 am

Re: Ka1 Ka2

Postby Mindy Kim 4C » Mon Jan 21, 2019 8:54 pm

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
Posts: 90
Joined: Fri Sep 28, 2018 12:15 am

Re: Ka1 Ka2

Postby Ray Guo 4C » Mon Jan 21, 2019 9:17 pm

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

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