I've recently started getting into chemistry a bit as a hobby. Nothing serious, just amateur level stuff mostly, primarily just to educate myself.

Whenever I need to determine the pH level of a solution, I typically use either a pH meter I have, or sometimes the pH test strips. And while I do have a "universal indicator" solution, I've never used it before. Mainly because it seems to me that adding an additional chemical to the solution you're working with just to determine the pH seems a bit counter intuitive to me.

A couple of reasons I can think of off the top of my head:

  1. Even if the indicator seems somewhat benign, you've now added some extra volume that isn't essential to the reaction or solution.
  2. Some pH indicators use chemicals that are somewhat hazardous or carcinogenic.

Any time I've seen someone use a pH indicator reagent, it's always been in some type of demonstration of a reaction, where the yield or result of the reaction is just discarded in the end. This gives me the impression that pH indicator reagents are useful for neat chemistry tricks (like here, where the chemist uses bromophenol blue to demo dichromatism), but not so much for instances where one plans on utilizing the resulting solution for any reason.

Thanks in advance for any input!

  • 2
    $\begingroup$ If you are doing titrations you need a quick response to sometimes drop amounts that could be too much. That means you have to keep your sample under constant stirring so it mixes very well. If you had to stop after every drop and use a strip it would take for ages. And I don't know how fast pH-meters actually react to changes. They are also expensive and indicators are much older and well known. There are also indicators or titrations that do not base on pH but on redox-reactions for instance. $\endgroup$ Feb 1, 2019 at 17:10
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    $\begingroup$ In a general chemistry class giving every student a pH meter would be very expensive. Plus the pH electrode is expensive too and delicate. A pH electrode is easily smashed if banged against the side of a flask or with a stirring bar. Lastly a pH meter setup won't give any better results than the proper indicator. $\endgroup$
    – MaxW
    Feb 1, 2019 at 17:50
  • $\begingroup$ And you don't have to smash a pH electrode to break it. Too alkalic is bad, drying is bad, basically just using it isn't too good. And it doesn't turn green or purple if it wants to be left in a beaker with buffer solution for a few days to recuperate. $\endgroup$
    – Karl
    Feb 1, 2019 at 20:28
  • $\begingroup$ I should also add that while swirling a solution with an indicator you can get a good idea of how close you are to the end point due to the inhomogeneity of the solution. $\endgroup$
    – MaxW
    Feb 1, 2019 at 21:08
  • $\begingroup$ And each indicator has a particular looking at about equivalence point which tells a lot to an experienced operator. To get the same feeling one should plot real time the ph meter data. Now feasible of course but there is quite history here. You can image dedicated glasswares easy to swirl and incorporating micro electrodes etc but all will be expensive. Etc. $\endgroup$
    – Alchimista
    Feb 2, 2019 at 9:15


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