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Author: Subject: Distinguishing between KCl and NaCl
HamiltonMaya
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[*] posted on 16-10-2020 at 23:27
Distinguishing between KCl and NaCl


I'm looking for an easy way to test if something is Potassium or Sodium Chloride.

I'm thinking of taking advantage of the different molar masses to react a known mass with a known number of moles of something else and seeing if the reaction uses all of the other reagent or not. But I thought first I should check if there's any easier ways.
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outer_limits
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[*] posted on 16-10-2020 at 23:50


For qualitative analysis you can use HClO4.
Potassium perchlorate has poor solubility and will precipitate

[Edited on 17-10-2020 by outer_limits]
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valeg96
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[*] posted on 16-10-2020 at 23:59


If it's telling apart two food supplements you can safely eat, just taste them: potassium salts taste horrible.

If you are doing this in a lab setting, you could use some sodium cobaltnitrite, which gives a yellow precipitate with the potassium cation.

If you have some cobalt chloride and sodium nitrite it's a very simple preparation.





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Fery
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[*] posted on 17-10-2020 at 00:31


If you have solid samples, solubility curve for NaCl is almost flat, KCl dissolves better at higher temperature and then crystallizes on cooling down. If you have diluted solutions, then flame tests if the solution contains only one cation. Also look into analytical chemistry how to precipitate them, for Na there is zinc uranyl acetate ZnUO2(CH3COO)4 which is hard to get for home lab and for K you already have the answer by outer_limits.
And yes, you can determine Cl content by gravimetry, e.g. by Ag.

[Edited on 17-10-2020 by Fery]




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brubei
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[*] posted on 17-10-2020 at 02:45


https://en.wikipedia.org/wiki/Flame_test

K Potassium Lilac; invisible through cobalt blue glass
Na Sodium Intense yellow; invisible through cobalt blue glass




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teodor
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[*] posted on 17-10-2020 at 04:34


Last time I used KSb(OH)6 as a reagent, sodium salt is insoluble and potassium is soluble. So, you can precipitate Na+ as well as other ions and what is left is K+ only.
This reagent could be prepared from pottery-grade antimony oxide, I wrote preparation somewhere on SM.
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HamiltonMaya
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[*] posted on 17-10-2020 at 05:04


Thanks for all the answers! I did the solubility test and then the taste test, and it's Sodium Chloride.
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MidLifeChemist
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[*] posted on 17-10-2020 at 05:28


Quote: Originally posted by Fery  
Also look into analytical chemistry how to precipitate them, for Na there is zinc uranyl acetate ZnUO2(CH3COO)4 which is hard to get for home lab and for K you already have the answer by outer_limits.

[Edited on 17-10-2020 by Fery]


Oh come on, most of us have a little zinc uranyl acetate on our shelf.

:)
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valeg96
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[*] posted on 17-10-2020 at 08:28


Quote: Originally posted by HamiltonMaya  
Thanks for all the answers! I did the solubility test and then the taste test, and it's Sodium Chloride.


That was the quickest way. Besides, the flame test is often ambiguous with potassium: sodium is virtually everywhere, and unless you have very clean equipment and a very pure potassium salt, you're bound to see yellow regardless of the salt.

Fery, don't take it the wrong way but I lol'd when I saw the zinc uranyl acetate suggestion lmao. HClO4 isn't exactly common in home labs either; argentometry is a nice idea but probably not worth it in this case, considering we're talking about chemicals that cost as low as 10 cents/kg.





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vibbzlab
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[*] posted on 17-10-2020 at 09:55


Theres something to test for potassium
its called sodium cobaltinitrite. It gives a yellow ppt with potassium salts. This is the video in which I have prepared that compound.Hope it helps

https://youtu.be/cit0A0OJiac





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Fery
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[*] posted on 17-10-2020 at 10:52


valeg96 I just wanted to tell HamiltonMaya that there is even something which could precipitate Na+ and info about "availability" in home lab followed...
it is also possible to substitute precious Ag with cheaper metal good enough for home "precision"... just various ways to go... chemistry is colorful...
vibbzlab - excelent hint for potassium !!!




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Bedlasky
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[*] posted on 20-10-2020 at 08:25


Quote: Originally posted by Fery  
Also look into analytical chemistry how to precipitate them, for Na there is zinc uranyl acetate ZnUO2(CH3COO)4 which is hard to get for home lab and for K you already have the answer by outer_limits.


Potassium salt is also insoluble. It's more soluble than sodium salt, but it also precipitates.




If you are interested in aqueous inorganic chemistry look at https://colourchem.wordpress.com/main-page/

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metalresearcher
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[*] posted on 20-10-2020 at 10:42


Quote: Originally posted by valeg96  

That was the quickest way. Besides, the flame test is often ambiguous with potassium: sodium is virtually everywhere, and unless you have very clean equipment and a very pure potassium salt, you're bound to see yellow regardless of the salt.


You can electrolyze a NaCl / KCl mixture and allow the reagents to mix which produces hypochlorite and finally chlorate.
KClO3 has a very poor solubility in ice-cold water while NaClO3 has a good solubility, so let the solution cool and then put it into the fridge, but better in the freezer. That precipitates the KClO3 and then filter it off. Then rinse the filtrate with ice cold (from the fridge) water repeatedly and you get rather clean KClO3. You can take a small sample after each rinse by holding a tiny crystal in a flame and no yellow tinge should be visible. Otherwise repeat the rinse.

I did this and there were no traces of yellow Na color: mixed with sugar it gave its traditiona purplish flame color.
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