Strong Acid/Strong Base Titration

[JP2740]

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For SA/SB titrations, is there a buffering region with pH=pKa? In the Berkeley book it seems like there isn't.

 

[ap594]

That seems to make sense to me. A "buffer" is termed as a solution that compensates for increases or decreases in [H+] due to the reversibility of the acid<->base reaction. If an acid/base is strong, the conj base/acid (respectively) doesn't convert back to the original compound. Therefore, there is no region where the pH changes slightly due to the effects of the conj base/acid since it's essentially inactive after it donated or accepted H+.

I hope that makes sense. lol

 

[IntelInside]

There isnt because of this reason:

the reaction of an acid with a base goes as follows:

HA + H2O <--> A- + H3O+

As we can see here we can restate this as:

Acid + H2O <--> Conjugate base + H+

You can also notice that this is an equilibrium reaction. This holds true for weak acids and bases because of only partial dissociation. Therefore we can have a mixture of conjugate base and acid to form a buffer (remember that it has to be within a 10:1 ration in either direction). However, for a strong acid we have complete dissociation and can say that this reaction runs to completion. Therefore we can never have this ratio of acid to conj. base almost exact amounts. Therefore there will be no 1/2 equivalence point (pH = pKa) for strong acids/bases because only weak acids and bases have Ka's and Kb's (both of which are a type of equilbrium constant), and thus strong acids have no Ka's/Kb's and pKa's/pKb's

 

[JP2740]

That makes sense, but we could probably say that there is a slight buffering region, right? I mean technically speaking.

 

[Phantastic]

That makes sense, but we could probably say that there is a slight buffering region, right? I mean technically speaking.

Not in my opinion. The conjugate base/acid (e.g. Cl-, Na+) are so stable in the solution that they will essentially be useless for any buffering ability. To have any buffering occur, you must have something that does not completely dissociate (the conjugate must have some reactivity!). If strong acid/base had any buffering capacity, you'd also notice the equivalence point would be slightly higher or lower than 7, due to the interactions with the conjugate.

 

[BerkReviewTeach]

For SA/SB titrations, is there a buffering region with pH=pKa? In the Berkeley book it seems like there isn't.

There have been excellent answers so far. But let me offer up a slightly different way of looking at your question.

Buffer regions fall within the titration curve, where the pH is typically between 0-14 (if not a smaller range, depending on the concentrations of the components). Strong acids have pKas that are less than 0 (they have negative pKas because their Kas are so large). No where does the curve hit a negative number, so the pH never equals the pKa of the strong acid. A point where pH = pKa is only seen on weak acid curves and weak base curves.

 

[MedalHead15]

because only weak acids and bases have Ka's and Kb's (both of which are a type of equilbrium constant), and thus strong acids have no Ka's/Kb's and pKa's/pKb's

Just because their pKa (and likewise pKb for strong bases) is a negative value obviously discounts that statement since they would have to have a Ka/Kb as well to calculate their value on the log scale.