Draeger
Hazard to Others
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Location: North-Rhine Westfalia, Germany
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Weird smell from Zn + FeSO4 reaction vessel?
Hello. About a week ago I put some lightly purified FeSO4 and a stoichiometric amount of zinc shavings in a beaker and heated it in hopes it would
speed up the reaction. All it did was generate a pungent smell which smelled tar-like and also reminded me of rubber. I thought it might just be zinc
living up to it's volatile title, but the smell hasn't stopped since then.
What could it be?
Collected elements:
Al, Cu, Ga, C (coal), S, Zn, Na
Collected compounds:
Inorganic:
NaOH; NaHCO3; MnCl2; MnCO3; CuSO4; FeSO4; aq. 30-33% HCl; aq. NaClO; aq. 9,5% ammonia; aq. 94-96% H2SO4; aq. 3% H2O2
Organic:
citric acid, sodium acetate, sodium citrate, petroleum, mineral oil
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Metacelsus
International Hazard
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It could be SO2 or H2S (reaction product of FeS and moisture).
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AJKOER
Radically Dubious
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Agree with Metacelsus, could be SO2/H2S in the presence of a sulfur compound, or possibly something more problematic.
My suggested mechanics starting with aqueous FeSO4 in the presence of Zn, where more advanced chemistry (see https://pubs.geoscienceworld.org/msa/ammin/article-abstract/... ) suggests how ferrous sulfate lowers pH introducing H+. Then, Zn in the presence
of acid creates surface hydrogen atoms (or equivalently, the hydrogen radical (.H)). This is followed by the possible slow breakdown of the sulfate
anion:
.H + SO4(2-) = OH- + .SO3-
.H + .SO3- = HSO3-
H+ + HSO3- = H2O + SO2 (g)
and, I would speculate further breakdown products could arise as NO3- can be broken down all the way, apparently, to NH3, or, in the current context,
H2S (my speculation based on this work https://digital.library.unt.edu/ark:/67531/metadc725872/m2/1... is as follows: .H + SO2 = .HOSO then .HOSO + .H = H2O + SO and .H + SO = .HSO,
also .H + .HSO = H2O + S and .H + S = .HS with finally, .HS + .HS = H2S2 -> H2S + S).
However, I did NOT write this reply solely for the presentation of the above chemistry. Actually, more for safety concerns, as the intentional or
accidental generation of this active hydrogen radical should be avoided, in my opinion, in heterogeneous compositions (like impure metal alloys with
small amount of, for example, Sb or As) per Hodges comment at https://www.sciencemadness.org/whisper/viewthread.php?tid=15... , and found that he had managed to stumble into something serious. As a possible
source, see https://www.citycollegiate.com/atomichydrogen.htm , and also, commentary in Bretherick, Volume 1, page 23-24, to quote:
"A student mixed aluminium foil and drain cleaner in a soft drink bottle, which started emitting gas. Another student carried the bottle outside and
was claimed to have been overcome by the toxic fumes [1]. Most drain cleaners are alkalis, so that aluminium will dissolve to produce hydrogen. The
bleach that it is is suggested may have been present will produce no toxic fumes in alkali, and one would be surprised to find arsenic or antimony
compounds present. If the collapse was not purely hysterical, the remaining, though remote, possibility would be phosphine. The soft drink the bottle
had contained was one of the many perhaps best described as impure dilute phosphoric acid [2]. "
A related comment attributing the formation of deadly gases like arsine and stibine from nascent hydrogen at https://pubs.acs.org/doi/pdf/10.1021/ed011p308
[Edited on 7-7-2020 by AJKOER]
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woelen
Super Administrator
Posts: 7976
Registered: 20-8-2005
Location: Netherlands
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Mood: interested
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I think that there are impurities in either the zinc, or the FeSO4, or both, which produce smelly compounds in the redox reaction. Sulfurous compounds
(especially organic ones) can be quite smelly, phosphorus compounds also can be smelly. Pure FeSO4 and Zn should not produce a strong smell, as long
as no acid is present. In the presence of acid, some H2S may be formed, but that does not have a smell like tar or rubber.
Try adding the zinc metal to some clean dilute hydrochloric acid (e.g. 10% acid) and smell this. With pure zinc and pure acid, the produced hydrogen
gas has no smell. Just let it bubble for a while, remove the piece of zinc, and then smell.
You could do the same with adding zinc metal to some dilute H2SO4. That will produce some smell of rotten eggs. No need to worry high toxicity, the
amount of H2S formed is very low with a small piece of zinc and some clean acid.
[Edited on 7-7-20 by woelen]
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Draeger
Hazard to Others
Posts: 185
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Location: North-Rhine Westfalia, Germany
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Mood: Slowly getting ready for new projects
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The FeSO4 is technical grade so I think I'm going to cancel the reaction, just to be sure. How can I safely do it? Would a respirator that blocks
general Inorganic gasses be enough for a short while? I can only gravity filter, though, so that might be a problem.
Collected elements:
Al, Cu, Ga, C (coal), S, Zn, Na
Collected compounds:
Inorganic:
NaOH; NaHCO3; MnCl2; MnCO3; CuSO4; FeSO4; aq. 30-33% HCl; aq. NaClO; aq. 9,5% ammonia; aq. 94-96% H2SO4; aq. 3% H2O2
Organic:
citric acid, sodium acetate, sodium citrate, petroleum, mineral oil
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woelen
Super Administrator
Posts: 7976
Registered: 20-8-2005
Location: Netherlands
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Pick out the metal pieces of zinc from the mix and then just dump the remaining liquid mix in the toilet, unless you have huge quantities of the mix.
Iron and zinc are not really toxic. Actually, they are even used as food supplements in fairly large quantities (e.g. iron fumarate in 200 mg
quantities).
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AJKOER
Radically Dubious
Posts: 3026
Registered: 7-5-2011
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Just came across in another forum someone asking seemingly an innocent question about the decomposition of SF6 especially in the presence of
electrical sparks.
Upon further research per Atomistry (http://sulphur.atomistry.com/sulphur_hexafluoride.html ) on SF6 to quote:
"Mixed with hydrogen it withstands a high temperature, but under the influence of powerful electric sparks formation of hydrogen sulphide and hydrogen
fluoride can be effected. At a red heat copper and silver are without action on the gas, although magnesium and sodium effect its decomposition; at
lower temperatures, however, it resists even these two metals and sodium can be melted unchanged in an atmosphere of the gas, as also can the
hydroxides of the alkali metals. Hydrogen chloride and ammonia are unaffected by sulphur hexafluoride, but hydrogen sulphide reacts rapidly according
to the equation:
SF6+3H2S=6HF+4S "
So, with heating and also with hydrogen in the presence of electric sparks (atomic hydrogen), some H2S formation also followed by HF. Note, electric
arc generated atomic hydrogen is more powerful than the hydrogen radical (⋅H), albeit the latter is more ubiquitously created, and I would avoid
scenarios involving its potential introduction in the possible event, it also attacks SF6, speculatively (see relatedly, Eq (5) here https://aip.scitation.org/doi/am-pdf/10.1063/1.5034568?class... ) as follows (which could involve the extremely problematic formation of a deadly
chemical weapon, disulfur decafluoride):
SF6 + ⋅H ⟶? ⋅SF5 + HF
⋅SF5 + ⋅SF5 ⟶ S2F10 (Source: See https://books.google.com/books?id=srM3BQAAQBAJ&pg=PA200&... )
However, as:
⋅H = H+ + e-
And, per this source https://iopscience.iop.org/article/10.1088/1742-6596/115/1/0... :
e- + SF6 = F- + .SF5
So, upon adding H+ to both sides of the above equation, my apparently speculative reaction with ⋅H on SF6 is more likely, and so is the really
problematic self-reaction product (even if formed to a limited extent).
So yet another compound to avoid in the presence of hydrogen radicals.
[Edited on 9-7-2020 by AJKOER]
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woelen
Super Administrator
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@AJKOER: I think that all of this is nitpicking in reverse. Theoretical issues, far from the practical question, asked by Draeger. There can indeed be
some side reactions besides formation of hydrogen (e.g. formation of H2S and/or SO2 when reducing an acidic sulfate solution with zinc), or formation
of NH3 when reducing an alkaline nitrate solution with Al. Calling this a severe safety issue, however, is a far stretch in my opinion. Maybe with
arsenic-containing compounds . . .
The amounts of side-products formed are low, very low. But their smell can be noticeable clearly.
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