pH indicators

[JMMTB]

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Just want to make sure I have this concept down. If I am running a titration of a weak acid with pKa of say 4.5 and a EQ point with a strong base that would yield a pH of 8 then I want an indicator with a range of 7-9 not 5.5-7.5. In other words the indicator pKa should center around the EQ point.
Thanks!

 

[Czarcasm]

Just want to make sure I have this concept down. If I am running a titration of a weak acid with pKa of say 4.5 and a EQ point with a strong base that would yield a pH of 8 then I want an indicator with a range of 7-9 not 5.5-7.5. In other words the indicator pKa should center around the EQ point.
Thanks!

An indicator basically functions as an acid and conjugate base pair at equivalence point (it's buffer region). Buffers operate maximally within +/- 1 of their pKa (best at pKa). Ideally you want an indicator with a pKa as close as possible to the predicted equivalence point. So in your example, 7-9 would be a good pKa for an indicator when the equivalence point is at or near pH of 8.