Chemistry_Keegan
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What Will Dissolve These Five Substances
I have some scrap aluminium, iron, copper, zinc and iron two disulphide that I would like to dissolve together, but it seems that each chemical I
think of can't dissolve at least one of them.
First, I thought of hydrochloric acid, but then I realized it can't react with copper under normal conditions.
6 HCl + 2 Al = 2 AlCl3 + 3 H2
2 HCl + Fe = FeCl2 + H2
2 HCl + 2 Cu ≠ 2 CuCl + H2
2 HCl + Zn = ZnCl2 + H2
2 HCl + FeS2 = S + FeCl2 + H2S
The same goes with sulphuric acid.
3 H2SO4 + 2 Al = Al2(SO4)3 + 3 H2
H2SO4 + Fe = FeSO4 + H2
H2SO4 + 2 Cu ≠ Cu2SO4 + H2
H2SO4 + Zn = ZnSO4 + H2
H2SO4 + FeS2 = S + FeSO4 + H2S
So then I figured that nitric acid would probably work, because it is well known for its ability to dissolve copper. But to my surprise, I learnt
that, out of all the five substances, the amphoteric metal aluminium would not dissolve in it because of the way nitric acid reacts with metals.
Nitric acid is a very strong oxidizer, so it oxidizes metals first, and then proceeds to dissolve there oxides. Since aluminium oxide (also known as
corundum) is very strong and resistant to corrosion, once the nitric acid forms the oxide layer on the aluminium, it protects the metal from further
attack.
2 Al + 2 HNO3 = Al2O3 + H2O + 2 NO
Al2O3 + 6 HNO3 ≠ 2 Al(NO3)3 + 3 H2O
Al + 4 HNO3 ≠ Al(NO3)3 + 2 H2O + NO
2 Fe + 2 HNO3 = Fe2O3 + H2O + 2 NO
Fe2O3 + 6 HNO3 = 2 Fe(NO3)3 + 3 H2O
Fe + 4 HNO3 = Fe(NO3)3 + 2 H2O + NO
3 Cu + 2 HNO3 = 3 CuO + H2O + 2 NO
CuO + 2 HNO3 = Cu(NO3)2 + H2O
3 Cu + 8 HNO3 = 3 Cu(NO3)2 + 4 H2O + 2 NO
3 Zn + 2 HNO3 = 3 ZnO + H2O + 2 NO
ZnO + 2 HNO3 = Zn(NO3)2 + H2O
3 Zn + 8 HNO3 = 3 Zn(NO3)2 + 4 H2O + 2 NO
2 FeS2 + 10 HNO3 = Fe2O3 + 4 H2SO4 + H2O + 10 NO
Fe2O3 + 6 HNO3 = 2 Fe(NO3)3 + 3 H2O
FeS2 + 8 HNO3 = Fe(NO3)3 + 2 H2SO4 + 2 H2O + 5 NO
First reaction is the oxidation reaction.
Second reaction is the dissolving reaction.
Third reaction is the overall reaction.
So, if anyone knows of an acid (or possibly another kind of liquid) that will dissolve all five of these substances together, please tell me.
[Edited on 18-2-2013 by Chemistry_Keegan]
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Ephesian
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Aqua Regia
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blogfast25
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Quote: Originally posted by Chemistry_Keegan  | I have some scrap aluminium, iron, copper, zinc and iron two disulfide that I would like to dissolve together, but it seems that each chemical I think
of can't dissolve at least one of them.
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Is there any particular reason why you want to dissolve this into a witch's brew? For most chemists, this is counter-intuitive and the fact that some
of these materials dissolve in one solvent but not another, would be considered a bonus! 
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Chemistry_Keegan
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I really have no use for them, and it is barely anything (the scrap just fills the bottom of a test tube). I understand it is quite rediculous that I
want to do this, but I like dissolving things, so I figured I would give it a shot. 
[Edited on 18-2-2013 by Chemistry_Keegan]
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woelen
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I found that FeS2 is amazingly hard to dissolve in anything. I treated this with nitric acid, sulphuric acid and hydrochloric acid, hot and cold. It
can be dissolved, but the process is very slow. Even after days of soaking in concentrated acids only a tiny fraction of the FeS2 dissolved.
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Chemistry_Keegan
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Thank you very much for that information! I didn't realize that iron two disulphide was so resistant to acid attack. I guess patience will be the key
to dissolving it.
And by the way, does anyone know why one part sulphur and one part hydrogen sulphide is formed instead of two parts sulphur and one part hydrogen when
dissolving it? In other words, why does this happen:
2 HCl + FeS2 = S + FeCl2 + H2S
Instead of this:
2 HCl + FeS2 = 2 S + FeCl2 + H2
[Edited on 18-2-2013 by Chemistry_Keegan]
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Mixell
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Because the Gibbs free energy for that specific temperature and pressure is negative. So it more favorable for H2S to form instead of S (mostly as S8)
and H2.
Woelen, how about trying to dissolve in hot concentrated sodium/potassium hydroxide solution? Or even fusing it with one of those.
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Vargouille
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Because it is unfavorable for the disulfide to be oxidized by protons, as the second reaction implies. The procedure for making a disulfide (mixing
sulfur and a sulfide salt) means that without an oxidant in the mix, the acid will merely break the disulfide bond.
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AJKOER
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Perhaps heating dry FeS2 in a stream of air may work:
2 FeS2 + 5 O2 --> 2 FeO + 4 SO2
Let it seat in vinegar/NaOCl, and see it any bubbles are formed.
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AndersHoveland
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A mixture of concentrated hydrochloric acid and hydrogen peroxide rapidly attacks copper.
I think I also read somewhere that FeS2 can be dissolved with acid in the presence of an additional supply of Fe+3.
| Quote: |
FeS2 + 14Fe3+ + 8H2O → 15Fe2+ + SO42- + 16 H+
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Not sure about this reaction.
[Edited on 20-2-2013 by AndersHoveland]
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Hexavalent
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| Quote: Originally posted by woelen | | I found that FeS2 is amazingly hard to dissolve in anything. I treated this with nitric acid, sulphuric acid and hydrochloric acid, hot and cold. It
can be dissolved, but the process is very slow. Even after days of soaking in concentrated acids only a tiny fraction of the FeS2 dissolved.
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Why does the FeS2 not liberate hydrogen sulfide gas when treated with these acids?
"Success is going from failure to failure without loss of enthusiasm." Winston Churchill
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Chemistry_Keegan
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| Quote: Originally posted by AndersHoveland | A mixture of concentrated hydrochloric acid and hydrogen peroxide rapidly attacks copper.
I think I also read somewhere that ferrous disulphide can be dissolved with acid in the presence of an additional supply of ferric ions.
| Quote: |
FeS2 + 14Fe3+ + 8H2O → 15Fe2+ + SO42- + 16 H+
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Not sure about this reaction.
[Edited on 20-2-2013 by AndersHoveland] |
Wouldn't this make more sense (I added a two before the sulphate ion)?
FeS2 + 14 Fe3+ + 8 H2O → 15 Fe2+ + 2 SO42- + 16 H+
If so, and the source of my ferric ions where from ferric chloride, would the following reaction make sense:
FeS2 + 14 FeCl3 + 8 H2O = 15 FeCl2 + 2 H2SO4 + 12 HCl
[Edited on 24-7-2013 by Chemistry_Keegan]
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