fusso
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Remove Na impurities in K salts?
I suspect my KOH is impure and the impurity is NaOH. I flame tested the KOH and see orange colour in addition to the characteristic lilac colour so I
suspect some Na is in it. How much Na is in it, and how to remove most of them so at least the flame test can give a pure lilac colour?
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Bedlasky
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If you only want colorful flames, try this:
Dissolve some KOH in water, add HCl, evaporate some water, cool it in the fridge and let stand for 24 hours. On the bottom you'll have crystals of
pure KCl.
[Edited on 10-7-2019 by Bedlasky]
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fusso
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But how pure will the KCl be? Will it still contain enough Na to contaminate flames?
[Edited on 190711 by fusso]
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teodor2
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The best thing is to try. Also make sure you use appropriate material to introduce the sample into the flame. For analytical purposes most books
recommend Pt wire.
The best separation of K and Na you can achieve, with help of not expensive chemicals, probably, with perchloric acid. Chlorates, carbonates,
dichromates and permanganates also have a big difference in solubility (with K and N cations). You can check https://en.wikipedia.org/wiki/Solubility_table and find what will work for you.
If your question is "how pure should be K to make a good lilac flame" I think it is better to make a different experiment. Buy a very pure K salt and
make different mixes with Na. So, you will definitely know how pure K salt should be.
An interesting multi-stage experiment with K and Na separation you can find in http://library.sciencemadness.org/library/books/synthetic_in... , page 52 (KNO3 from NaNO3 and KCl). It is not so practical of course but will
give your some idea how to separate salts with different solubility.
[Edited on 11-7-2019 by teodor2]
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fusso
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But why are you using a new account?
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teodor2
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Sorry, I just unable to login with the old one. Pressing "forget password" doesn't send any email to my gmail. Possible I should catch some admin
here.
Also, you can find a very good description of the method of K and Na separation in Treadwell, Vol II (actually, he recommends to use 97% alcohol for
that purpose). Also it contains the receipt of HClO4 preparation in a case you don't have it.
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teodor2
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@fusso, but why are you asking if you have a solubility table in your signature 
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nezza
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KOH is much more soluble in alcohol than NaOH so dissolving it in alcohol and decanting off from any solids or filtering through sintered glass should
remove most of the NaOH.
If you're not part of the solution, you're part of the precipitate.
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fusso
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Why wiki say NaOH solubility in EtOH is <<139 g/L?
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unionised
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Quote: Originally posted by fusso  | | I flame tested the KOH and see orange colour in addition to the characteristic lilac colour so I suspect some Na is in it. How much Na is in it, ...
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If you can actually see the lilac colour then there's very little sodium.
The orange flame of sodium is extraordinarily sensitive. Even traces of it will wash out the potassium colour. (Partly because the emission is very
intense and partly because the human eye is much more sensitive to yellow light).
Unless you have access to very pure water and equipment that's not made of glass you are probably not going to make your KOH any more pure.
If anything you are likely to add more sodium.
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