GC concept quesiton

[hope_to_match]

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I came across a question in bootcamp which asks for the best ph indicator for a given acid/base buffer.

from what I understand:

-if a buffer consists of a strong base/weak acid--> then the ph indicator should be a weak base
- if a buffer consists of a strong acid/weak base--> then the ph indicator should be a weak acid
- if a buffer is weak acid/conjugate base--> will the indicator be a strong base? if so, why?

 

[Dark Blue]

Indicators are usually weak acids or bases, I don't think we can have strong acid or base as indicator, the reason is if it is strong, then it can protonate/deprotonate the reagents which is not good!

 

[Dark Blue]

by the way, a buffer is usually is a weak acid with its c.b. or a weak base and its c.a. a strong acid/base is not part of the buffer. you probably talk about titration.

 

[aznriptide859]

If buffer is strong base/weak acid, then equivalence point pH >7, therefore indicator should have a pH range just >7.
If buffer is weak base/strong acid, then equivalence point pH <7, therefore indicator should have a pH range just <7.
If buffer is strong base/strong acid, then equivalence point pH=7, therefore indicator should have a pH range just ~ 7.

I do not believe questions ask for the actual ACIDITY or BASICITY of the indicator, rather simply the pH range it's meant to detect.