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Author: Subject: Chlorate or perchlorate?
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[*] posted on 16-2-2020 at 06:36
Chlorate or perchlorate?


Hi,
I guess one of the more energetic users here might know this...

I have inherited an old reagent bottle whose hand-written label says "Potassium Chlorate, KClO4". White sugar-like crystals, not hygroscopic, slight smell of chlorine.

Any way to make sure which one it is?
Thanks




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[*] posted on 16-2-2020 at 08:42
KClO4


The formula you specified is the perchlorate. To test for
chlorate, mix a tiny amount with sugar(sucrose) and place a
drop of concentrated H2SO4 on the pile. If it ignites, it contains
or is a chlorate. A test with a .3% solution of methylene
blue will turn purple if perchlorate is detected.




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[*] posted on 16-2-2020 at 09:42


Thanks for the quick reply.

The methylene blue test gave no color change.

The sugar/H2SO4 test resulted in rather impressive fireworks.

Guess it's the chlorate KClO3 then. Good to know, thank you!




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[*] posted on 16-2-2020 at 11:43


Another test for chlorate is to add a small spatula full of the solid to conc. HCl (take 1 ml of concentrated acid, then add a small amount of the solid). If the liquid turns deep yellow and a yellow gas/vapor is visible above the acid, then it is (or contains) KClO3. If it is pure KClO4, then nothing happens.



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[*] posted on 16-2-2020 at 11:47


Quote: Originally posted by woelen  
Another test for chlorate is to add a small spatula full of the solid to conc. HCl (take 1 ml of concentrated acid, then add a small amount of the solid). If the liquid turns deep yellow and a yellow gas/vapor is visible above the acid, then it is (or contains) KClO3. If it is pure KClO4, then nothing happens.


What would the yellow gas be - Chlorine?



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[*] posted on 16-2-2020 at 11:53


Quote: Originally posted by G-Coupled  


What would the yellow gas be - Chlorine?



Yes, chlorine.




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[*] posted on 16-2-2020 at 12:43


Quote: Originally posted by G-Coupled  
Quote: Originally posted by woelen  
Another test for chlorate is to add a small spatula full of the solid to conc. HCl (take 1 ml of concentrated acid, then add a small amount of the solid). If the liquid turns deep yellow and a yellow gas/vapor is visible above the acid, then it is (or contains) KClO3. If it is pure KClO4, then nothing happens.


What would the yellow gas be - Chlorine?



Depends on the stoichiometry. With a large excess of HCl, it should mostly just be chlorine and would be more greenish. With excess chlorate you will get yellow, explosive ClO2.

[Edited on 16-2-2020 by UC235]
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[*] posted on 16-2-2020 at 23:50


The yellow gas will be ClO2. That gas has a very intense color and totally overwhelms the faint green of the Cl2. Expect ClO2 : Cl2 in an approximate 2 : 1 molar ratio. ClO2, however, remains dissolved more in the liquid. If you use a small amount of KClO3 in a ml of conc. HCl, then there is no need to fear explosion. ClO2 can indeed explode, but only in the gaseous state or when pure. Solution in water or HCl cannot explode, dilute gas (a few tens of percent) also cannot explode.



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