TPR Chemistry Buffer - Potential Mistake

[5words]

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The buffering capacity of the sample solution is maximum:

A. when the pKa equals the pKb.
B. when [conjugate base] equals [conjugate acid].
C. when the concentration of the solution is very low.
D. at or near pH 7

I chose C by using POE, however the answer is B, isnt this a mistake since any buffer needs to have [HA] = [A-]? And their explanation is a bit sketchy as well..because it posit that the maximal buffer capacity ought to occur when [base] = [Acid] which isn't necessarily true.

Feedback would be appreciated..

 

[theonlytycrane]

Buffers resist pH change, and a good buffer has some acid and some base. This is because if you add some acid, the base will neutralize it. And if you add some base, the acid will neutralize it. By being able to react with what's added in this way, a buffer can resist drastic changes in pH.

Let me know if this helps clarify things, or if it's still unclear.

 

[5words]

Buffers resist pH change, and a good buffer has some acid and some base. This is because if you add some acid, the base will neutralize it. And if you add some base, the acid will neutralize it. By being able to react with what's added in this way, a buffer can resist drastic changes in pH.

Let me know if this helps clarify things, or if it's still unclear.

yes, in order to have a great buffer [Acid] = [Conjugate base], but the TPR answer says [Conjugate Acid] = [ Conjugate base] so not [HA]={A-] but [H2A+]=[A-], so is that a mistake on their part, since buffer are ALWAYS Conjugate Acid/Base pair or Conjugate Base/ Acid Pair.

 

[aldol16]

There's no such thing as conjugate acid/conjugate base - it's usually referred to as conjugate acid/base pair. But the meaning of the answer choice is obvious - that is, when pH = pKa, or when the log term in the Henderson-Hasselbalch equation drops out.

 

[5words]

There's no such thing as conjugate acid/conjugate base - it's usually referred to as conjugate acid/base pair. But the meaning of the answer choice is obvious - that is, when pH = pKa, or when the log term in the Henderson-Hasselbalch equation drops out.

So mistake on their part right? And I am not missing anything right?

Probably a typo?

 

[aldol16]

Probably a typo?

Yes, typo. I wouldn't get nit-picky about minor details like this. You might even notice some things like this on the real MCAT, although they will be very rare.