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When I see demonstrations of titration of acid solutions of unknown concentration with phenolphthalein as the indicator, when the last drop of NaOH went in the analyte solution became permanently pink. This means that more than enough NaOH was used and the recorded endpoint has some error (by 1 drop?). If we use a diluted titrant, the error is still 1 drop but it is diluted so could the margin of error be lower?

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The use of a burette in titration, once considered an art, has nearly disappeared from modern educational practice in schools and universities. This decline is due in part to the lack of expertise in classical analytical techniques among current teaching assistants. In precise titration, even an extra drop of titrant can significantly skew results i.e., an extra drop is too much! Experienced chemists could accurately dispense fractional volumes of liquid (e.g., 0.05 mL) with practice and would rinse the burette tip upon observing a slight pink tinge during acid-base titrations.

If you are really keen, then search Vogel's textbook of Quantitative Analysis. It is available on Internet Archive (free for reading). Search the sections on burette usage.

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  • $\begingroup$ Is not a "standard drop" rather 0.03 mL? Using hydrophobic PE burette tips can lead to even smaller drops. $\endgroup$
    – Poutnik
    Sep 1, 2023 at 5:08
  • $\begingroup$ I have not seen any documentation from standard sources about the volumes of the so-called standard drop because who is going to standardize a drop :-) Even 0.05 mL was a guess. Do you recall a good quality reference for 0.03 mL? $\endgroup$
    – AChem
    Sep 1, 2023 at 12:21
  • $\begingroup$ I have used it quoted. I am not sure if it is any standard nor official value, but seeing the value 0.03 mL over the years many many dozen times. Few time also 0.02 mL. All probably from weighting the drops. $\endgroup$
    – Poutnik
    Sep 1, 2023 at 12:34
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    $\begingroup$ @Poutnik Now you have done it: the various standards organizations will form committees to study and propose standards for the standard drop, then the disparate proposals will be studied by harmonization committees. After 20 years or so, we will have a standard drop definition, complete with turgid footnotes and provisos. Of course, no one will follow it. ;-) $\endgroup$
    – Ed V
    Sep 1, 2023 at 12:56
  • $\begingroup$ @EdV you understand the system too well :-) $\endgroup$
    – AChem
    Sep 1, 2023 at 12:58

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