TBR Titration Question.

[arosmom]

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From TBR Gen Chem 1, Chapter 5, Passage 2, Question 8. I swear there's a mistake here.

8) Which mixture does NOT produce a buffer

A. H3CCO2H with 2 equivalents of H3CCO2K
B. NH3 with 2 equivalents of NH4Cl
C. H2CO3 with 1.5 equivalents of KOH
D. H3CNH2 with 1.5 equivalents of HCL

The correct answer choice is D. which I understand. What I don't understand is how A. and B. are buffers. A buffer should be equal amounts of acid and conjugate base and A. has excess conjugate base while B. has excess conjugate acid. I'm so confused I'm starting to think TBR meant to put "1 equivalent" instead of "2 equivalents". Can anyone explain this to me?

Thanks!

 

[Raiden2012]

From TBR Gen Chem 1, Chapter 5, Passage 2, Question 8. I swear there's a mistake here.

8) Which mixture does NOT produce a buffer

A. H3CCO2H with 2 equivalents of H3CCO2K
B. NH3 with 2 equivalents of NH4Cl
C. H2CO3 with 1.5 equivalents of KOH
D. H3CNH2 with 1.5 equivalents of HCL

The correct answer choice is D. which I understand. What I don't understand is how A. and B. are buffers. A buffer should be equal amounts of acid and conjugate base and A. has excess conjugate base while B. has excess conjugate acid. I'm so confused I'm starting to think TBR meant to put "1 equivalent" instead of "2 equivalents". Can anyone explain this to me?

Thanks!

I may be wrong but I believe the one to one ratio is for max buffering capacity. Even if there is more conjugate base than the acid, it can still act as a buffer. Because if you add acid, the conjugate base will take up the H+ and vice versa for the acid.

 

[V5RED]

I may be wrong but I believe the one to one ratio is for max buffering capacity. Even if there is more conjugate base than the acid, it can still act as a buffer. Because if you add acid, the conjugate base will take up the H+ and vice versa for the acid.

You are correct. The system is still a useful buffer as long as the ratio of acid:base(or base:acid) doesn't exceed 10:1.

 

[arosmom]

Cool, thanks! I seem to recall them saying something about that 10:1 ratio now. Does that mean then if they put A. or B. in a 1:1/2 they would still be buffers?