Lara N.

asked • 09/27/16

TITRATION PROBLEM AND SOLVING pH

The problem deals with the titration of 441 mL of 0.501 M carbonic acid (H2CO3) (Ka1 = 4.3 x 10-7, Ka2 = 5.6 x 10-11) with 1.3 M NaOH.
 
What will the pH of the solution be when 0.2294 L of 1.3 M NaOH are added to the 441 mL of 0.501 M carbonic acid?

1 Expert Answer

By:

Nasr B. answered • 09/30/16

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Julie S.

I don't think you can say that the pH of the solution "anywhere between the two equivalence points" will be the average of their pKa values... 
 
I believe you have to do some more detailed calculations, recognizing that you have titrated the first H+ fully but you have not titrated the second equivalent of H+.  Therefore, at that point in the titration you are dealing with a HCO3-/CO32- buffer system. This would be analyzed by focusing on that equilibrium and the related Ka and pKa, which would be pKa2 for carbonic acid (Ka2 = 5.6 x 10-11, pKa = 10.25).
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09/30/16

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