Polyprotic acids

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ran2000
Posts: 66
Joined: Fri Sep 28, 2018 12:15 am

Polyprotic acids

Postby ran2000 » Wed Jan 23, 2019 1:11 pm

How do we calculate the pH of polyprotic acids with very small second or third Ka values? And how small should they be?

JacobHershenhouse3G
Posts: 32
Joined: Thu Jan 10, 2019 12:17 am

Re: Polyprotic acids

Postby JacobHershenhouse3G » Wed Jan 23, 2019 1:19 pm

Depending on how small the following ka's are, you may be able to approximate by only solving the equilibrium concentrations of the first ka, but only if the ka's are very small and you know the difference in equilibrium concentrations will be negligible. Otherwise, if you are told to go through the whole process, then it is basically just going through multiple ice tables, inserting previous equilibrium values in the initial box of the next. Then you use the same practices you would use in a single reaction as you solve for pH (-log[H3O+]) or whatever the problem is asking. Hope this helps!


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