Do triprotic titrations have a 3rd equivalence point?

[stester77s]

Advertisement - Members don't see this ad

I'm searching a lot of triprotic titrations such as this one: https://www.google.com/search?q=tri...edu%2F~toh%2Fmodels%2FTitration.html;1094;543


And the triprotic titrations look a lot like diprotic titrations... i.e. there is no third equivalence point. Why is this? Do triprotic titrations sometimes have a third equivalence point and sometimes not? Why is that?

 

[chenzt]

It does, it is just barely noticeable because of how weak of a pKa value it has.

 

[funtertaining15]

^^Ditto. the 1st Eq pt, H2A dominates, then the 2nd eq. point, HA dominates...then the last eq. pt, A- (all deprotonated) dominates...
#of protons is typically indicative of the number of eq. pts.

 

[ipmed]

Does this mean that the pkb is really strong for the third proton to remove or first proton to be added? For example co2 would have a really high tendency and a low pkb to turn into hco3 right? But a low tendency to become co2 from hco3