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What is the best indicator to use to see the end-point of a weak acid/weak alkali reaction? Thanks.

Ulex says
No indicator is really satisfactory, as there is no sharp change in pH at the equivalence point in such titrations. The only hope is to pick one whose pKa value is the same as the pH at the mid-point of the inflection on the titration curve. Any indicator is likely to change colour over a range of volumes added rather than to change sharply with one drop of titrant, which is what you would get if either of the solutions were strong.
 
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updated: 28 January 2007

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