chemkid
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White gas?
Hi all, i am new to this forum and sort of new to chemistry. Anyway, a few weeks ago i was making hydrogen gas by aluminium and HCl. I was using HCl
in the form of muriatic acid that you get at the hardware store, 30% water dilute or so, and some basic aluminium foil you get at the supermarket. I
tossed the aluminium foil into a flask and a mysterious white gas rose off. I say rose as in went up, distinctly rose to the ceiling of my lab. SO i
really don't think it was chlorine gas. I did hours of research and came up with this:
Al + HCl + H2O--> AlCl +H2 + H2O
then...
AlCl + H2O --> AlCl2OH + HCl (vapor)
Well, if anyone has any insight it would be greatly appreciated.
Bob
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Furch
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The reaction between aqueous hydrochloric acid and aluminium is very exothermic, so there's no doubt some water will evaporate from the solution. Also
when the already fairly concentrated hydrochloric acid solution is heated, the water solubility of the HCl decreases, meaning it goes out of solution
and into the air and subsequently the moisture in it, forming a white mist.
\"Those who say do not know, those who know do not say.\" -Lao Tzu
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Magpie
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2Al + 6HCl ---> 2AlCl3 + 3H2
(Your AlCl shows a valence of +1 for aluminum, which is incorrect)
I agree with Furch that probably what you saw was an HCl/water mist generated by the heat of reaction, possibly aided by the turbulence of escaping H2
gas. I would definitely not breathe any of this gas.
[Edited on by Magpie]
The single most important condition for a successful synthesis is good mixing - Nicodem
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chemkid
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I hope it didn't corode the pipes to badly. I quickly evacuated my lab (the basement) and turned on the ventialtion fan and opend the windows. I don't
think i was exposed at all if any to the gas.
Thank you for the correction on my formula. I am new to chemistry and have't quite got my head around the whole orbitals, valency, p, s, d etc. thing.
Bob
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12AX7
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Exposure isn't a problem... you choke on it long before your lungs burn from it. It's only an acute hazard; once it stops hurting, you're okay.
What is a hazard is being confined and unable to escape the gas (big clouds of nastiness on a battlefield, for example).
So yeah, muriatic is already pretty strong. It tends to fume around any humidity. Extra heat from the aluminum "burning" is definetly going to cook
off some HCl vapors and steam.
You'll notice a brown haze on everything made of steel. It's only cosmetic, though would be quite annoying around precision surfaces.
Tim
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woelen
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The white material is not a gas. A gas is invisible, or if it has a color, it still is transparent. The white stuff either is smoke (consisting of
solid particles), or a fog (consisting of very fine droplets).
As stated before, the reaction between Al and HCl (30%) is very exothermic and hence really hot. I've done the reaction several times myself and the
intensely thick fumes/smoke seem to consist of HCl-gas, which becomes humid by presence of water from the air, forming small droplets, but this
reaction also gives smoke of AlCl3. If you capture some of the white material (e.g. by bubbling through a liter of water), then you'll notice that
quite some Al(3+) ion is contained in the water. So, I think that the white 'gas' actually is a fog, mixed with some smoke.
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chemkid
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How exactly would i "notice that quite some Al(3+) ion is contained in the water.'?
Bob
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12AX7
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Test for Al(3+), obviously 
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chemkid
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Would the test be something like this (i just did a google search):
Aluminum ion reacts with aqueous ammonia to produce a white gelatinous precipitate of Al(OH)3:
Al3+(aq) + 3NH3(aq)+ 3H2O(aq) <==> Al(OH)3(s) + 3NH4+(aq)
Bob
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Levi
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| Quote: | Originally posted by chemkid
Would the test be something like this (i just did a google search):
Aluminum ion reacts with aqueous ammonia to produce a white gelatinous precipitate of Al(OH)3:
Al3+(aq) + 3NH3(aq)+ 3H2O(aq) <==> Al(OH)3(s) + 3NH4+(aq)
Bob |
I wouldn't expect to find Al<sup>+++</sup> ions without a halogen to go with them. Since you prepared the solution with HCl, the halogen
in this case would be chlorine and I think the equation would look more like the following:
AlCl<sub>3</sub> + 3NH<sub>4</sub>OH --> Al(OH)<sub>3</sub> + 3NH<sub>4</sub>Cl
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unionised
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I don't think NH4OH exists in any meaningful sense. Also, I think that most of the Al+++ ions on earth are stuck in oxide or silicate minerals and
don't have a halogen associated with them.
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chemkid
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That still doesn't leave me with a test for Al (3+) ions. (or am i just being stupid?)
Bob
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bereal511
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You'll still precipitate aluminum hydroxide with the ammonia solution.
Al3+(aq) + 3NH3(aq)+ 3H2O(aq) <==> Al(OH)3(s) + 3NH4+(aq)
I don't see much problem with Bob's equation here, it's just a net ionic precipitation.
As an adolescent I aspired to lasting fame, I craved factual certainty, and I thirsted for a meaningful vision of human life -- so I became a
scientist. This is like becoming an archbishop so you can meet girls.
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chemkid
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Ok, i'll try it out when i get time, I tink i have an idea of what to do. I just need to run the fumes through glass tubing into an ammonia solution
and a gelatin like precipitant should precipitate out.
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Elawr
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Al is interesting metal to experiment with. It is extremely reactive, and if not for the presence of an adherent oxide film, Al would be all but
useless for making thing out of. It would act more like calcium or someting, reacting vigorously with water and quickly oxidizing in the air. You
may note that relatively dilute HCl - much weaker than 30%- will eat Al right up. The acid hydrolyzes the Al2O3 film and exposes the bare metal to
attack by ordinary H2O. You end up with a solution of hydrated aluminum ions and chloride ions. Similarly, in a strong alkali solution, such as NaOH,
the oxide is dissolved to form an aluminate ion and again baring the reactive metal to oxidation by water.
A spectacular demo involves metallic mercury ( DANGER - poisonous!!!) applied to a clean shiny aluminum surface. The mercury dissolves into and
penetrates the aluminum forming an amalgam, to which the protective Al2O3 layer cannot adhere. Atmospheric O2 goes to work, quickly converting the Al
into a pile of ashlike oxide.
To test for aluminum, use a little strong base NH4OH is fine and you should get the hydroxide Al(OH)3(H2O)3 as precipitate. Take some of this and add
some strong alkali such as NaOH ( be careful!) : the precipitate will dissolve, giving you a solution of NaAl(OH)4(H20)2 or sodium aluminate.
1
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Levi
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| Quote: | Originally posted by unionised
I don't think NH4OH exists in any meaningful sense. Also, I think that most of the Al+++ ions on earth are stuck in oxide or silicate minerals and
don't have a halogen associated with them. |
I was oversimplifying. His original equations had cations floating around in solution with no anion counterpart. And whether or not ammonium
hydroxide exists, it is extremely convenient to pretend it does when writing equations.
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12AX7
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| Quote: | Originally posted by Elawr
the precipitate will dissolve, giving you a solution of NaAl(OH)4(H20)2 or sodium aluminate. |
Incidentially, what hydration is this when crystallized? I noticed a solution of it formed well-hydrated crystals, efflorescent in dry air.
Tim
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16MillionEyes
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| Quote: | Originally posted by Magpie
2Al + 6HCl ---> 2AlCl3 + 3H2
(Your AlCl shows a valence of +1 for aluminum, which is incorrect)
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I'm also new to chemistry and I don't seem to understand what you mean. Valence electrons are those present in the most outer shell so it seems you're
saying that he's wrong because his equation would show Al as having 7 e- on the outer shell (thus the +1). But it seems to me (and based on what they
teach on basic chem) that Al having a charge of +3 would in fact make AlCl3 so I'm confused. Can you explain.
As for the original thread, why don't you try making the reaction inside a bucket of ice or some cooling substance so that the heat generated doesn't
evaporate the HCl nor the water and instead just get the evolution of H2?
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woelen
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| Quote: | Originally posted by Levi
I was oversimplifying. His original equations had cations floating around in solution with no anion counterpart. And whether or not ammonium
hydroxide exists, it is extremely convenient to pretend it does when writing equations. |
Well, actually I do this very often. If ions are involved in a reaction, I write down the reaction, without the spectator ions.
Something like Fe(3+) + 4Cl(-) ---> FeCl4(-)
Is this an illegal equation? I don't think so, it just leaves unspecified, which ions originally go with the iron, and which ions originally go with
the chloride.
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Magpie
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From ______:
| Quote: |
Valence electrons are those present in the most outer shell so it seems you're saying that he's wrong because his equation would show Al as having 7
e- on the outer shell (thus the +1). |
With a valence of +1 Al would be missing one of its 3 outer shell electrons. It would still have 2e-, not 7e-.
The single most important condition for a successful synthesis is good mixing - Nicodem
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16MillionEyes
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Yes, I was thinking octet rule. 
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Brie
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Once you get to the 3p elements, the octet rule gets... interesting. Even moreso with transition metals.
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16MillionEyes
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Yes, I'm actually doing that right now in class. I never thought there be such thing as "extended octets" or "incomplete octets".
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