tom haggen
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Acid mixtures
Well I have heard about the fabled mixture of HCl and HNO3, and how it is supposed to be a very strong combination. But know that I'm learning
chemistry, and have realized that HBr and HI are stronger acids than HCl, I have a new question. Would you be able to have a mixture of HI and HNO3 in
order to create a strong combination of acids? Or would the HNO3 simply oxidize the HI acid destroying the Hydrogen Iodine bond? If that is the case
what about a HNO3 and HBr combination?
[Edited on 31-3-2005 by tom haggen]
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runlabrun
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i think yes nitric acid would oxidise HI to iodine, as sulphuric acid does. But i dont know to what extent this would occur.
2HNO3 + 2HI --> I2 + 2NO2 + 2H2O
As for HBr, i dont think this would happen due to the ability to make HBr from H2SO4 + NaBr with no hassels.
This may be a very potent acid mix so if you try it be very bloody carefull.... aqua regia is very powerful so anything with higher power acids in it
would be highly highly corrosive.
-rlr
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neutrino
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Nitric and hydrochloric acids are strong acids (complete dissociation), so mixing them doesn’t make them any stronger. Rather, they become more
corrosive. You can find the reasons for this on the internet, but here is the basic explanation: HNO<sub>3</sub> oxidizes the top layer of
a metal, HCl dissolves off the oxide, and so on. Neither one does this alone for some reason.
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sparkgap
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In the case of aqua regia, its ability to dissolve the "noble" metals stems from 1) ionization of the metal to the corresponding cation; and
2) subsequent complexation by chloride ions.
sparky (^_^)
"What's UTFSE? I keep hearing about it, but I can't be arsed to search for the answer..."
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cyclonite4
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I recall hearing an explanation saying that it formed other compounds such as nitrosyl chloride, but I can't remember where, and whether its
reputable or not.
[Edited on 31-3-2005 by cyclonite4]
\"It is dangerous to be right, when your government is wrong.\" - Voltaire
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JohnWW
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I would have thought that the mechanism of action of aqua regia on metals would be through the oxidation of the HCl by HNO3 to chlorine gas in
solution. Once metal cations start going into solution, they should catalyze further reactions, not necessarily the initial reaction. NO and NO2 would
be major byproducts, along with small amounts of NOCl.
BTW has anyone experimented with mixtures of HF and HNO3?
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sparkgap
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People, keep in mind that nitric acid is a nice oxidizer. Metals of any sort are all fair game. The trouble is that the metal to cation equilibrium
for the "noble" metals is unfavorable, i.e. they tend to go back to being metal.
This is where HCl comes in. The chloride ions produced tend to form nice complexes with the metal cations (e.g. chloroaurate and chloroplatinate).
Since the cations keep being depleted, the equilibrium is pushed to the metals being tranformed to their cationic forms, which will then be complexed,
and so forth...
Le Chatelier's, I'd say.
sparky (^_^)
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chloric1
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sparky, your statement is quite valid but realize that the free chlorine produced in solution plays a major role. I can't afford noble metal but
I had nickel and dissolves in acid with great difficulty. But, when aqua regia is prepared and the nickel is added loads of nickel chloride are
produced and nitrous fumes AND chlorine are evolved.
[Edited on 3/31/2005 by chloric1]
Fellow molecular manipulator
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tom haggen
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I think I might have explained my thoughts a little incorrectly. I didn't mean that mixing HCl and HNO3 would make them stronger acids. I just
meant that HBr is a stronger acid than HCl because bromine falls lower on the periodic table. Because of this I was just curious if a combinatioin of
HBr and HNO3 would make an even more powerful combination? When I get my glassware I will do some experimentation on report back.
[Edited on 31-3-2005 by tom haggen]
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runlabrun
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As a general acid i would say HBr/HNO3 would be stronger than HCl/HNO3 due to the increased ionisation of HBr in solution... however as a acid with
specific properties such as aqua regia to dissolve precious metals due to one reason or another i cant say how HBr/HNO3 will compare....
But like i said, as a general acid, i belive HBr/HNO3 will be more corrosive than HCl/HNO3.
-rlr
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Borek
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My textbooks state that:
3HCl + HNO3 --> Cl2 + NOCl + 2H2O
Cl2 and NOCl are strong oxidizers, Cl- is - as it was already pointed out - complexing agent.
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