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Bedlasky
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I think you looking at this in a wrong way. You try to find mixture which dissolve as many elements as possible, but this is nonsense. You must work
with every sample in a different way. Depending on what components you try to analyse, what method do you plan to use etc. Stop solving general
problem, solve some particular problem.
I give you simple example. I want to analyse stainless steel. There are several components in stainless steel, some types don't have certain
components, some do (for example molybdenum), but I just want to determine main components - Fe, Cr, Ni. I prefer volumetric analysis (gravimetry took
more effort and time), so I stick to that. And I want procedure to be simple as possible (so idealy from one solution, more steps = more possible
mistakes). You can dissolve stainless steel easily in HCl or H2SO4 - in that case I would have solution containing Fe2+, Ni2+ and Cr2+ (Cr2+ is very
unstable on air, so 1 hour on air should convert all Cr2+ to Cr3+). Easiest method for determination of Fe2+ is direct titration by K2Cr2O7 or KMnO4,
nickel can be directly titrated by EDTA at pH 10 using eriochrome black T indicator, all three metals than by boiling with excess of EDTA and than
re-titrating with CuSO4 using PAN indicator at pH 5.
HCl dissolve stainless steel quicker, but in that case I can't perform permanganometry because permanganate react with HCl at room temperature. If I
want to use permanganate instead of dichromate, I must dissolve sample in H2SO4. But because I am lazy, I have diphenylamine, want to dissolve
stainless steel quickly, don't want to standardize permanganate, I choose dichromatometry, thus I dissolve sample in HCl. That's how I choose acid for
dissolving my sample. The rest is pretty straightforward as I described above. The only thing I didn't mention is that before nickel determination I
must remove Fe(OH)3 from the solution. Without that I wouldn't be able to see colour change of indicator.
If you have some questions about analytical chemistry, just ask. Classical analysis is one of my main focuses in chemistry.
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Tsjerk
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I think we can safely conclude that if there was a single easy to perform way to dissolve all elements we would have known by now. There might be a
way to dissolve everything as atara mentioned but you are better off working like Bedlasky explains.
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teodor
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Dissolving metals in an acid always involves an oxidation step. That's why nitric acid is so popular in classical analysis. If you don't like this way
the alternative could be the solution of chlorisulphonic acid in acetic acid. In many cases it forms anhydrous chlorides which are soluble in organic
solvents. Different cations could be analized then by the methods of solvent extraction.
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Bedlasky
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HSO3Cl in acetic acid? This would form acetyl chloride and sulfuric acid. I don't see any benefits of this mixture for dissolving metals. Nitric acid
is good for dissolving noble metals, lead and nonmetals. HCl is better for dissolving base metals.
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BromicAcid
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I used to mainline 120V AC through flatware from the dollar store spaced about 5 inches apart in concentrated hydrochloric acid. Would heat it to
boiling in short order but you could quickly dissolve stainless that way. Of course beware the usual hazards of high voltage and stupidity.
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teodor
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Why do you think so? Of course, HSO3Cl is a powerful dehydrating agent but I don't think it is capable of splitting a water molecule from acetic acid.
[Edited on 6-9-2022 by teodor]
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Bedlasky
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Oh, my mistake, sorry Teodor. But still - what is benefit of this mixture? I don't see any. Chlorosulfuric acid is expensive and hard to obtain
reagent. It is waste of useful reagent, you have many far cheaper possibilities for dissolving metals. Moreover chlorosulfuric + acetic acids mixture
can be hardly call an alternative for nitric acid, considering that nitric acid is strong oxidant, while pure chlorosulfuric acid is just mild oxidant
(and dilute one would be even less oxidazing).
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teodor
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From a practical point of view, there is no alternative to HNO3. Also, it is quite easily prepared from nitrate salt and a strong acid in a home lab.
So, I believe the purpose of discussing "what else can we use to dissolve metals" could be driven only by a pure spirit of experimentation and looking
at well-known things from a different perspective.
The choice of acetic acid based on the "solubilities" of its salts in water solution looks like a doubtful step for me.
First of all, only a few metals have something similar to "true" acetates - they are Fe, Mn, Cu, Co, Cr, Pb, Cd, Hg, and alkali & alkali earths
metals. The rest of the metals forms either basic acetates, or acetates that are easily hydrolyzed in a water solution, or they don't react with
acetic acid without acetic anhydride or something else, or they form polymeric complexes. The chemistry of carboxylates is not uniform even for
members of one group of the periodic table.
So, for the purpose of analysis, I think the true power of acetic acid is not in dissolving metals but as a solvent.
Chlorosulphonic acid is oxidizing acid. It oxidizes Sn(0) to SnCl4, P to H3PO4, S to SO2, As and Sb to trichlorides, C to CO2, and so on. The reason
to dissolve it is that it passivates some metals in a concentrated state, is expensive and is not convenient to use in high concentrations. I
investigated its reaction with some metals in this thread: http://www.sciencemadness.org/talk/viewthread.php?tid=157951
So, I think for the purpose of looking at well-known things from a different perspective HClSO3 is OK because it allows investigating analytical
reactions in non-aqueous systems. And I doubt extending long-existing methods of qualitative analysis in aqueous systems is worth the effort.
Also, Bedlasky, the reaction of CH3COOH and HClSO3 seems to form some, at least, catalytical amount of acetyl chloride, I was not aware of it, thank
you for raising this question. So, probably acetyl chloride is a better solvent to study the chemistry of this acid.
Update:
The electrochemical oxidation of metals in acetic acid (with alkali metal acetate as electrolyte) is a way of getting anhydrous acetates of those
metals. By this method, you can get Hg(I), Zn, Fe(III), Cu(II), Co, Ni, Al, Ga, In acetates. But I think all of them are insoluble in acetic acid.
[Edited on 7-9-2022 by teodor]
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