Hey guys so the other day I was synthesizing some HCL from tap water and hydrogen chloride gas by sulfuric acid salt method. Well after the reaction I
was left with some reasonably strong and clear HCl. Now I have been away from my lab for about a week but open opening the chemical cabinet I saw that
the HCL had turned bright yellow. My first thought was that there was a contaminate in the water that reacted with the HCL turning the solution yellow
most likely iron. My question is does using yellow HCL in reactions especially washings effect the final product to a noticeable extent?1281371269 - 11-11-2009 at 10:46
It depends what the impurities are and how pure you need the final product to be - what sort of reactions will it be used for?.
I once left a molar solution of NaHCO3 / tap water in a glass bottle for a while and white flakes formed, which is presumably calcium carbonate and
calsium and magnesium bicarbonates.
It's very cheap to buy distilled water although it's almost as cheap to buy HCl - which might be the best option.
[Edited on 11-11-2009 by Mossydie]psychokinetic - 11-11-2009 at 11:33
Does your council fluoridate your water supply?Sedit - 11-11-2009 at 13:06
Jmneissa I know im just stating the obvious here but I feel it needs to be said. If you are going to attempt to perform any synthesis that uses H2O
other then using it for a wash that will be tossed any way why not use bottled water? When using spring water you can even get the test results
showing the percentage of contamination in the water if really needed. Its cheep enough that you should try to do another run with spring water and
see if the yellow color still presents itself.Lambda-Eyde - 11-11-2009 at 14:01
In what sort of vessel did you store your clear hydrochloric acid? Rubber stoppers are attacked by HCl, rendering the stoppers black and the acid
yellow-ish.Paddywhacker - 11-11-2009 at 14:28
Ferric chloride is a common contaminant in HCl. It distills with the HCl, so cannot be removed that way.hissingnoise - 11-11-2009 at 14:48
I think Lambda-Eyde is correct here. . .
FeCl3 imparts a greenish hue to HCl!
Tap water would need to be visibly contaminated to produce coloured HCl. . .jmneissa - 11-11-2009 at 15:01
Thanks for all the replies here are some answers. Firstly, yes my town does fluoridate there water. Secondly I did think about using bottled water but
isn't it the same as tap water? Isn't all that media about how we should save money by using filters at home blah blah blah. I stored the HCL in a
glass flask with a glass stopper. Thankshissingnoise - 11-11-2009 at 15:17
Some brands of table-salt contain various anti-caking agents---one is potassium ferricyanide possibly, though they would generally be in trace
amounts. . .Sedit - 11-11-2009 at 16:23
Quote:
Secondly I did think about using bottled water but isn't it the same as tap water? Isn't all that media about how we should save money by using
filters at home blah blah blah. I stored the HCL in a glass flask with a glass stopper. Thanks
As far as tap water being like bottled water the answer is no not a chance. Much of what you here is enviromentist hype scared of plastic bottles
being used and the rest is based on top notch water filters to remove the crap from tap water making it simular to bottled water. If this is a concern
to you then by distilled water at the store. Its not much more and ensures low contamination. It can be found in the baby isle if no where else albeit
at a higher cost. The fact that you mentioned your city fluoridating your drinking water should have answered your question as to wether or not it is
the same as bottled water.
Attempt to wash out your glass with HCl prior to storing the main portion to make sure you have no soluble reactants on the glass. I do not believe
your issue is a big one when it comes to using it for synthesis but since you asked for purity I thought I would mention some ways to ensure it.
~Sedit
Sedit - 11-11-2009 at 16:23
Quote:
Secondly I did think about using bottled water but isn't it the same as tap water? Isn't all that media about how we should save money by using
filters at home blah blah blah. I stored the HCL in a glass flask with a glass stopper. Thanks
As far as tap water being like bottled water the answer is no not a chance. Much of what you hear is enviromentist hype scared of plastic bottles
being used and the rest is based on top notch water filters to remove the crap from tap water making it simular to bottled water(which many companys
are ripping people off using the same filters and claiming spring water). If this is a concern to you then buy distilled water at the store. Its not
much more and ensures low contamination. It can be found in the baby isle if no where else albeit at a higher cost. The fact that you mentioned your
city fluoridating your drinking water should have answered your question as to wether or not it is the same as bottled water.
If you wish attempt to wash out your glass with HCl prior to storing the main portion to make sure you have no soluble reactants on the glass. I do
not believe your issue is a big one when it comes to using it for synthesis but since you asked for purity I thought I would mention some ways to
ensure it. If nothing else it will be a good excercise in cleanliness.
~Sedit
[Edited on 12-11-2009 by Sedit]not_important - 11-11-2009 at 17:30
hissingnoise had similar thoughts to mine. If you used table or kitchen salt, it often has both sodium ferrocyanide and iodides or iodates added to
it.
Such salt may also have small amounts of organic substances, there are brands of salt that have sugar added to them for example. These could reduce
any Fe(III) to Fe(II), carry-over of that iron in spray (if a simple distillation setup was used) would give only a slight greenish tint to the
product, but air oxidation to Fe(III) would give the stronger yellowish colour of the chloride complex of ferric iron. woelen - 11-11-2009 at 23:40
Even clean-looking glass can give off quite some yellow color in HCl. I sometimes buy glassware from eBay and even when it looks clean I many times
see that colorless HCl turns yellow when I rinse the glassware with this acid. Apparently there is a very thin invisible film of crap inside the glass
which gives visible contamination to the HCl. It might be that your bottle suffered from the same issue. So, the best is to rinse the bottle before
storage of HCl with some dilute H2SO4/NaCl mix (or some of your yellow HCl) and then with some distilled water.jmneissa - 12-11-2009 at 08:17
Thanks for the info guys. Some notes for next time I guess. Firstly wash out glassware with HCL and then distilled water to remove unseen
contaminants. Secondly use bottled water or filtered water in reaction vessel. Thirdly, try and find some pure salt without additives. I wonder is the
kosher salt they sell at the store would work or sea salt I think would also work. Let me know if I missed anything.bbartlog - 12-11-2009 at 09:11
Quote:
or sea salt I think would also work
This would be pretty much the opposite of 'pure salt without additives'. Commercial salt may have some anti-caking agent and small amounts of iodine
compounds, but sea salt will have a multitude of compounds above and beyond that. Look at the composition of seawater to get an idea. Granted it's
still mostly chlorides, and if all you're doing is H2SO4+NaCl to produce HCl then having some MgCl in the mix won't matter, but there's also small
amounts of sulfur, bromine and many other things.jmneissa - 12-11-2009 at 09:40
yes while that is true it is mostly chlorides and does not have any the anti-caking agents that most likely caused the problem in the beginning. It is
sort of the least of all evils. hissingnoise - 12-11-2009 at 09:41
One of those other things being gold---extraction by electrolysis was seroiusly considered at one time by many eminent scientists who should have
known better.
I consider sea-salt the superior condiment though, possibly because it's so mineral-rich. . .not_important - 12-11-2009 at 10:02
Quote:
Secondly use bottled water or filtered water in reaction vessel
No, use deionised or distilled water. Bottled or filtered addresses stuff that might be harmful to you, not chemical purity. Distilled water isn't the
best water for drinking purposes, the WHO recommends that water for consumption contain a certain amount of calcium and magnesium salts.
Canning salt is non-iodised, in fact some table salt is also and wil be so labeled. Kosher salt is so named because of its use in making meats kosher
be pulling out the blood. The grain shape determines this, kosher salt has relatively large flat grains. It may or may not contain additives, read
the label.
hissingnoise - 12-11-2009 at 10:09
Canning salt too, may have added ingredients to help with the process of canning, but as I said upthread the amounts of anti-caking agents in
table-salt should be relatively minor and I would be surprised if they were the culprit. . .
KCl might be better for HCl, though. . .or. . .some other chloride salt!
[Edited on 12-11-2009 by hissingnoise]bbartlog - 12-11-2009 at 10:45
One advantage of using CaCl2 instead of NaCl or KCl is that excess remaining H2SO4 (that you might want to reuse) should be easily separated from the
precipitated gypsum. Separating Na2SO4 from H2SO4 would be a fair bit more difficult. Bulk CaCl2 is cheap, too, though it's probably even less pure
than table salt.
Not planning to try that myself, though. 31% HCl is very cheap at the local hardware store (given that it's basically a repurposed industrial waste,
that's not too surprising). hissingnoise - 12-11-2009 at 10:52
Of course, using the Na or K salt leaves you with the bi-sulphate which has other uses.
Na2SO4 isn't normally formed at the temperatures used for HCl preparation.jmneissa - 12-11-2009 at 14:38
Okay thank so I will use distilled or deionized water in my next experiment and try to fine some "pure" salt that is non iodized and contains no other
ingredients. The one place that has occurred to me to look for this is the water softening section of stores because I know they sell big bags of KCl
but do not know its relative purity. hissingnoise - 12-11-2009 at 14:43
Muriate of Potash fertiliser is cheap, comes in prills and the outer moisture-repelling layer is practically insoluble. . .
The prills can be dissolved, filtered and evaporated leaving the equivalent of tech. grade KCl!woelen - 16-11-2009 at 03:08
Buy the cheapest table salt you can find in a super market, which is a free flowing fine crystalline mass. That is very pure NaCl and the only
additive (if any) will be a tiny tiny amount of anticaking agent (appr. 0.001% of potassium ferricyanide is added for this purpose, sometimes simply
some tenths of percents of CaCO3 is added for this purpsoe). All the fancier and more expensive stuff contains a lot of other things like iodide,
other minerals and even some added flavors.not_important - 16-11-2009 at 18:10
Depends on which country you are in. I know from experience that in some the lowest priced food salt costs the same with or without added iodine in
some form, and contains the same anti-caking substances.
Course grain salts, such as kosher and canning, often have no additives but the trace of ferricyanide used to control crystal size and shape in the
crystallisation step. Finer grain forms of salt often have additional anti-caking additives, some such as the aluminosilicates won't cause problems
for making HCl, others might.
kilowatt - 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. Daddy - 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?hissingnoise - 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. . . entropy51 - 21-11-2009 at 18:00
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.hissingnoise - 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! woelen - 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.
