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blogfast25
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Quote: Originally posted by Melgar  | For generating hydrogen from aluminum economically, the cheapest way to do it is muriatic acid. It has to be diluted down a lot (like half water,
half muriatic) though, or else your "hydrogen" gas ends up containing a whole lot of HCl gas. You can't eliminate the HCl entirely, so if this is a
problem, the next cheapest way is with NaOH. H2SO4 doesn't work that well though, since some of it is reduced by aluminum to SO2.
[Edited on 9/24/11 by Melgar] |
Do you have evidence for that? I’ve dissolved Al in fairly strong (up to 50 %) H2SO4 many times and will testify that it is harder to do than with
HCl or NaOH/KOH and that it is quite a smelly activity. But I’ve never identified the smell as part SO2. I could be wrong on that, of course…
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Melgar
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I remember reading somewhere that in low concentrations sulfuric acid acts more like a typical acid toward metals, forming the sulfate salt and
hydrogen, and that at higher concentrations it acts more like an oxidizer, forming water, metal oxides, and SO2. And also, that you can't really
supress either reaction entirely. But sulfuric acid is definitely an oxidizing acid, which is why you get some elemental bromine when you mix it with
a bromide salt.
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blogfast25
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| Quote: Originally posted by Melgar | | I remember reading somewhere that in low concentrations sulfuric acid acts more like a typical acid toward metals, forming the sulfate salt and
hydrogen, and that at higher concentrations it acts more like an oxidizer, forming water, metal oxides, and SO2. And also, that you can't really
supress either reaction entirely. But sulfuric acid is definitely an oxidizing acid, which is why you get some elemental bromine when you mix it with
a bromide salt. |
Yes, no one disputes it is an oxidising acid but with metals that are easily oxidised (like Al) I'd have expected all oxidising to be done by H3O+.
I'll be keeping an eye and a nose out next time I dissolve some Al in faitly strong H2SO4...
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Melgar
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| Quote: Originally posted by blogfast25 | | Quote: Originally posted by Melgar | | I remember reading somewhere that in low concentrations sulfuric acid acts more like a typical acid toward metals, forming the sulfate salt and
hydrogen, and that at higher concentrations it acts more like an oxidizer, forming water, metal oxides, and SO2. And also, that you can't really
supress either reaction entirely. But sulfuric acid is definitely an oxidizing acid, which is why you get some elemental bromine when you mix it with
a bromide salt. |
Yes, no one disputes it is an oxidising acid but with metals that are easily oxidised (like Al) I'd have expected all oxidising to be done by H3O+.
I'll be keeping an eye and a nose out next time I dissolve some Al in faitly strong H2SO4... |
Well, the smell is definitely a sulfur smell, so the H2SO4 is being reduced to something, for sure. There could even be some H2S formed as part of
the reaction, if Al is a strong enough reducing agent. Anyway, the reaction isn't a clean one, producing several different products, and is certainly
not an ideal way to generate hydrogen. :p
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FrankRizzo
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| Quote: Originally posted by IrC | "The idea your gallium stays behind unaffected is a complete nonsense." - symboom
The idea? How about the experience....[snip]
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IrC - No, you were quoting blogfast25. Symboom was simply quoting blogfast25's post, then replying in the line below, basically agreeing with you. He
didn't use the quote feature, which made things confusing. Also, his English and punctuation could use a bit of work, but the gist was there. 
| Quote: Originally posted by blogfast25 |
Gallium is more reactive than aluminium in many ways. The idea your gallium stays behind unaffected is a complete nonsense.
YAAaawwnn...
[Edited on 20-9-2011 by blogfast25] |
| Quote: Originally posted by symboom |
Gallium is more reactive than aluminium in many ways. The idea your gallium stays behind unaffected is a complete nonsense.
what were you using Gallium is more reactive than aluminium thats nonsense. aluminum without the oxide disolves in water i
am putting it in water |
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AJKOER
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If a product requires more energy to produce from currently available paths, than it does not make economic sense to manufacture. However, the key
phrase here is ‘currently available’ as for limited time spans and setup costs, one may be able to obtain ‘free’ energy. Examples of the
latter could include electricity generated from the sun or tides or dams or nuclear power plants or drilling/transporting oil/gas or by tapping in
natural occurring heat sources (like volcanoes,...).
As the cost of tapping into 'free energy' based on technological process changes over time, one cannot assert that a product that normally requires
more energy to produce from current conventional paths is not deemed forever to be economically unfeasible.
[Edited on 19-11-2018 by AJKOER]
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Sulaiman
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In a global sense the above is true,
but I personally get nothing from my used aluminium that I put in the recycling bin,
so to me (and most SM members) aluminium is a FREE resource.
CAUTION : Hobby Chemist, not Professional or even Amateur
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AJKOER
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As the value of recycled Aluminum is baked into the sale price of Al, if everyone (or enough of us so that the cost of collecting makes it unecomical)
stopped recycling due to newly invented alternative uses, then the current sale price of Aluminum increases for everyone!
---------------------------------
Here is my suggested more fruitful path to hydrogen, the electrolysis of methanol! Apparently, the energy required is but a fraction of the energy
required to liberate H2 from H2O (see https://www.techbriefs.com/component/content/article/tb/tech...)!
To quote another source (https://www.researchgate.net/publication/288690690_Hydrogen_... ):
"An economical method to produce hydrogen by direct electrolysis of methanol is developed. It is demonstrated that the hydrogen produced by the
electrolysis of methanol can considerably reduce the consumption of electricity. The novelty of this technique is the inherent simplicity and the
substantially lowered cost. Using these modified proton exchange membrane fuel cell membrane electrode assembly (PEMFC-MEA) as an electrolyzer, any
scale requirements can be easily achieved. The combination of this electrolyzer concept with the concept of solar cells would economically produce
hydrogen for storage and subsequent use in, or for in situ use in, fuel cells and chemical engineering applications."
Still not a totally great idea given the energy needed to make the CH3OH.
[Edited on 20-11-2018 by AJKOER]
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