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kilowatt
Hazard to Others
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Registered: 11-10-2007
Location: Montana
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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.
The mind cannot decide the truth; it can only find the truth.
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Daddy
Harmless
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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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hissingnoise
International Hazard
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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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entropy51
Gone, but not forgotten
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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. . .
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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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hissingnoise
International Hazard
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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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woelen
Super Administrator
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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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