TBR buffers question

[Pose]

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Hi all,

This refers to TBR G.C., Section V, PII, Q8...

Which mixture does NOT produce a buffer?

H3CCO2H with 2 equiv. H3CCO2K
NH3 with 2 equiv. NH4Cl
H2CO3 with 1.5 equiv. KOH
H3CNH2 with 1.5 equiv. HCl

The answer is the last one. How come?

My understanding is that you can buffer by either adding a weak acid with it's conjugate base in equal amounts, or by titration of a weak base or acid with half an equivalent of strong acid or base. The first two choices the book states are examples of a 1:1 ratio of a weak something with it's conjugate. But...aren't they in a 1:2 ratio??

I think I'm missing something...

Thanks!

 

[BestDoctorEver]

Hi all,

This refers to TBR G.C., Section V, PII, Q8...

Which mixture does NOT produce a buffer?

H3CCO2H with 2 equiv. H3CCO2K
NH3 with 2 equiv. NH4Cl
H2CO3 with 1.5 equiv. KOH
H3CNH2 with 1.5 equiv. HCl

The answer is the last one. How come?

My understanding is that you can buffer by either adding a weak acid with it's conjugate base in equal amounts, or by titration of a weak base or acid with half an equivalent of strong acid or base. The first two choices the book states are examples of a 1:1 ratio of a weak something with it's conjugate. But...aren't they in a 1:2 ratio??

I think I'm missing something...

Thanks!

I think TBR botch that question...I think they meant (I am not sure) two equivalents of each in A and B (acid/conjugate base and base/conjugate acid), which is 1:1 ratio. I only got the right answer because I know D is definitely wrong.