woelen
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Detection of perchlorate in chlorate
I have a nice anode and cathode set of decent size, for making an electrolysis cell. I bought this, together with a nice power supply (the 5V/60A
version).
https://www.ebay.nl/itm/174883976295
https://www.amazon.nl/dp/B0F47T3RD1?ref=ppx_yo2ov_dt_b_fed_a...
With these, and an added PVC lid and some M6 nuts and ring terminals for cable ends, I could set up a reliable electrolysis cell, running at 11.5 A
for days. I used KCl (appr. 500 grams in 1.5 liters of water) and 5 grams of K2S2O8 for keeping cell efficiency decent. Over the days, a nice thick
layer of crystals of KClO3 settled at the bottom. Every few days, I top up with 150 ml of boilingly hot water, saturated with more KCl. After a week I
added another gram or so of K2S2O8.
I collected the solid KClO3 a few times, before the level of solid goes so high that the bottom part of the electrodes become covered by it.
This KClO3 was filtered and pressed dry, such that nearly all adhering water was removed from it. Then it was rinsed with 200 ml of ice cold water and
again it was pressed dry in filter paper, surrounded by absorbing tissue to remove the water again. After that, I dissolved all of it in as little as
possible of boiling water, added 10% more water to assure that no crust is formed on the water, while boiling. Then I put all of the boilingly hot
concentrated solution in a big jar and allowed it to cool down. Finally, when it reached room temperature, it was put in a fridge, allowing it to cool
down to around 0 degrees. Nearly all of the KClO3 then is recovered.
Again, I took out all of the crystals and pressed them dry in a filter with paper tissue around them (actually, I used big coffee filters, with paper
tissue around it). Finally, I let it dry in an oven at 120 degrees C.
I obtained two big jars full of KClO3, snow white, coarse crystals. I had done all this treatment, because I want it to be really pure. This is not
needed for pyro-purposes, but I want to use it for other kinds of experiments, and I just want it to be very pure.
Tests with solution of AgNO3 shows that hardly any detectable level of chloride is present. A fairly concentrated, somewhat heated solution of KClO3
(50 C or so), mixed with a few drops of concentrated solution of AgNO3, only shows the faintest opalescence. You only see this, if you look through
the liquid, with bright light shining from the side and a black piece of paper behind it. This means that it only contains traces of chloride.
Tests with a solution of Ba(NO3)2 show no opalescence at all. I could not detect any sulfate in the crystals. Sulfate could be in them, because I use
K2S2O8 for cell efficiency, and this decomposes to KHSO4/K2SO4 over time in the hot liquor during electrolysis and also during boiling of the solution
of the KClO3 when recrystallizing it.
So, I am convinced that my KClO3 at most contains trace levels of chloride and sulfate. Not enough to have any influence in chemistry experiments. The
only other concern I have is the possible presence of perchlorate. The MMO-anode I used is an IrO2/RuO2 mixed oxide anode on titanium substrate.
According to documentation of Feanor Forges (the seller of the anodes) these anodes are not useful for making perchlorates, but when the chloride
concentration becomes low in your cell and voltage goes up (the power supply I use is configured as a current source, not a voltage source), then some
perchlorate may be formed.
I tested for perchlorate with methylene blue (a well known test, used by people who want to make perchlorate with electrolysis), but this test is not
sufficiently sensitive. It only is suitable for detecting correct working of a perchlorate cell, it is not useful for detecting small amounts of
perchlorate in chlorate. I did a search on internet, and found tests for perchlorate at micrograms per ml sensitivities, but these require expensive
equipment. I could not find a chemical test for perchlorate, which is sufficiently sensitive for my purpose. If I could know for sure that my chlorate
has at most a few tenths of percent of perchlorate in it, then I would be happy with it. I think that my chlorate is very low in perchlorate, but I
would like to confirm this with a test, just like I did for chloride and sulfate. Anyone knows about a sensitive chemical test, which works in the
presence of a much larger amount of chlorate as well?
[Edited on 7-8-25 by woelen]
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teodor
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There is some method I have read about but have no idea does it really work. KClO4 crystalls are isomorphic with KMnO4 and KClO3 are not. So, when you
have some saturated solution of KClO3/KClO4 with crystalls and drop a bit of KMnO4 solution into it all KClO4 crysalls become red due to forming solid
solution with KMnO4.
[Edited on 8-8-2025 by teodor]
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Boffis
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Looking at Feigl and Anger's "Spot tests in inorganic chemistry" page 183, it looks like the best test for perchlorate in the presence of chlorate is
with the basic dye brilliant green. Apparently this forms a salt that is soluble in organic solvents were as the chlorate salt isn't.
There is another test with triphenylselenium chloride which gives a very insoluble ppt with perchlorate but not chlorate but this reaction appears
less sensitive and the reagent pretty hard to get.
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yobbo II
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You could concentrate the suspected perchlorate.
PPT the (I presume) sodium chlorate with K chloride. This will leave the perchlorate behind in the liquid because it is at a very low conc.
The wet K chlorate will have some perchlorate in the water sticking to the crystals. Wash the K chlorate and add the washings to the original. You can
now boil down the original solution to concentrate the perchlorate and measure.
Yob
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moviez
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I was browsing through literature and found this paper: https://pubs.acs.org/doi/10.1021/es047935q
The author used HPLC-MS and the detection limit for perchlorate is 0.021 μg/L. Admittedly, HPLC-MS is probably not readily available for home
scientists. I haven’t read through it yet - Maybe this paper has referenced to some other research papers that report a different method.
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Mateo_swe
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woelen, any chance you could show some pics of your DIY cell?
I think many would be intrested and inspired by seeing some pics.
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RU_KLO
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Location: Argentina
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Found this
Determination of Chlorate and Perchlorate in the Presence of One Another
G. P. HAIGHT, JR.’
Department of Chemistry, The George Washington C‘niversity, Washington 6, D. C.
Attachment: ac60076a029_copia.pdf (304kB)
This file has been downloaded 151 times
found more information:
PERCHLORIC ACID AND PERCHLORATEI
by
ALFRED A. SCHILT
Department of Chemistry
Northern Illinois University
DeKalb, Illinois 60115
(maybe you could get info here)
[Edited on 25-8-2025 by RU_KLO]
Attachment: HClO4 - Alfred A. Schilt - Perchloric Acid and Perchlorates (1979).pdf (4MB)
This file has been downloaded 97 times
Go SAFE, because stupidity and bad Luck exist.
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