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Author: Subject: Homemade HCL Bright Yellow
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[*] posted on 16-11-2009 at 18:51


No one has mentioned that you can buy 40lb or 50lb bags of NaCl (for water softener and ice melt) at almost any store for like $3-$5. This is much cheaper than KCl, or CaCl2, and has no intentionally added ingredients. There may be some mineral contaminants since it is derived from mined salt with minimal processing.



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Daddy
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[*] posted on 21-11-2009 at 15:13


Sorry if this is off-topic - but the 25% HCl I buy in the hardware store is also somewhat yellow. So it has impurities in it?
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[*] posted on 21-11-2009 at 16:11


Yes, HCl is often tinted slightly lemonish. . .
It may be that HCl undergoes some slight oxidation on standing, freeing small amounts of Cl2, as HOCl/HCl, but I'm just speculating. . .
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[*] posted on 21-11-2009 at 18:00


Quote: Originally posted by hissingnoise  
Yes, HCl is often tinted slightly lemonish. . .
It may be that HCl undergoes some slight oxidation on standing, freeing small amounts of Cl2, as HOCl/HCl, but I'm just speculating. . .
That's what I thought too, and I don't disagree. But I have a bottle of ACS reagent HCl that's 20 years old and it has no yellow tint. Some have said it's iron contamination, but I wonder? I think it's been cussed and discussed here before, with no resolution that I know of. All that being said, my hardware store HCl is not yellow either, so it seems to be a sometimes thing. If used for something such as preparing Cl2 it may not be problematic, but I wouldn't use yellow HCl in an analytical procedure.
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[*] posted on 22-11-2009 at 15:47


I was thinking that dissolved atmospheric oxygen might play a part---but HCl in a sealed container with little airspace might be more stable!
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[*] posted on 23-11-2009 at 00:35


No, HCl is not turning yellow due to dissolvedm atmospheric oxygen. The yellow/green contamination usually is due to traces of dissolved metal salts (mainly iron) and due to organics. I once did a test of yellow/green HCl with a solution of ammonium thiocyanate and the test was positive on iron, the solution turned red.

You can make very pure colorless HCl of around 20% concentration by distilling the yellow/green acid. If the concentration of the acid is higher than 20%, first dilute with some water and then distill at well above 100 C (the azeotrope comes over). In this way you can make very good quality, colorless HCl. If the concentration is lower than 20%, first boil off the water and when the temperature rises to well above 100 C, then start collecting the liquid. With this you also get 20% HCl.

I once did this procecure with an all-glass distillation setup. I stopped distilling when appr. 20% of the original acid remained, just to be sure that no crap goes over into the clean liquid. The dark green/yellow remains can be kept and is perfectly suitable for cleaning/rinsing dirty glassware.

[Edited on 23-11-09 by woelen]




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