Buffer question

[September24]

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This is in reference to the Buffers chapter (section 5) of Berkeley review. Passage 6, question 43. No need to have the question ready as I will try to ask in a generic fashion.


When looking at a WEAK ACID and WEAK BASE titration (with a strong base/strong acid), there is a 1/2 equivalence point. Is this point the pkA for the weak acid titration AND the weak base titration. Or is it the pkA for weak acid and pkB for weak base. Berkeley review tries to argue the former.

 

[deh2ase]

For weak acid + strong base titration, when the pKa = pH that is your 1/2 equivalence point.

For weak base + strong acid, when pKb = pOH that is your 1/2 equivalence point. Since the titration curves are usually by pH scale, the 1/2 equivalence point is also when the pKa = pH of your conjugate acid from the weak base. To find this it would just be 14 - pKb (weak base) = pKa (conjugate acid)