Selecting an indicator

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Armo_Derbarsegian_3K
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Joined: Sat Jul 09, 2016 3:00 am

Selecting an indicator

Postby Armo_Derbarsegian_3K » Wed Nov 30, 2016 3:50 am

Why does pKin. (pKA) have to be close to pH at stoichiometric point to be an effective indicator?

Chem_Mod
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Re: Selecting an indicator

Postby Chem_Mod » Wed Nov 30, 2016 12:23 pm

I'm not exactly sure about your question. In general, though, indicators should be as close as possible to the expected equivalence point of a given titration. For example, we would use an indicator that changes color between pH 4.6-5.1 for a titration with an expected equivalence point around pH = 8.

Armo_Derbarsegian_3K
Posts: 35
Joined: Sat Jul 09, 2016 3:00 am

Re: Selecting an indicator

Postby Armo_Derbarsegian_3K » Wed Nov 30, 2016 6:58 pm

So if the equivalence point is near pH 8, why wouldn't we want one that changes color near pH 8? How exactly did you get that range of pHs for the indicator?

nicknavejas1B
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Re: Selecting an indicator

Postby nicknavejas1B » Sun Jul 28, 2019 5:49 pm

I had trouble particularly understanding the relationship with the indicator and pH

Chem_Mod
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Re: Selecting an indicator

Postby Chem_Mod » Sun Jul 28, 2019 7:54 pm

First, the understanding of indicators is applied more in 14BL. Indicators are used to find the equivalence point in titrations, which are experimentally found. Also, because pretty much the only thing about weak acids and bases that we cover in 14A is they do not fully dissociate, and because we cover strong acids and bases which have an equivalence point of 7, so an indicator with strong acids and bases is not that useful.


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