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hkparker
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catching H2S
Hey everyone, I'm going to be doing a reaction soon that produces a quantity of H2S, what's the best way to absorb it? I don't want it floating
around so I want to absorb it with something. Some solution I can pass it through or some salt that will react with? Thanks!
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NurdRage
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bubble it into a concentrated solution of sodium hydroxide.
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hkparker
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Yea I figured neuralizing it with something would do it, just didn't know what was most effective, thanks!
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Magpie
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It could also be bubbled into one of the many heavy metal soluble salts that form insoluble sulfides. Eg, Zn or Fe. That way you would have a
sulfide as a byproduct if you wanted it.
Use an intermediate trap to avoid suckback.
The single most important condition for a successful synthesis is good mixing - Nicodem
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mnick12
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I have seen alot of people use lead nitrate to absorb hydrogen sulfide, but then you have to deal with lead. Just out of curiosity what reaction are
you going to do?
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hkparker
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Thanks, making an insoluble sulfide could be useful, though id rather deal with zinc then lead lol. I'm going to be trying to synthesize carbon
disulfide by passing acetylene through molten sulfur.
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aonomus
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From my experience the easiest and cheapest way to deal with H2S and other thiols is to run it through 1-2 basic bleach traps. Then you don't have to
deal with heavy metal sulfides, etc; the waste stream is simply a solution of sulfonic acids (or rather their sodium salts). A bit of sodium hydroxide
and commercial/household bleach makes for an easy trap to get rid of thiols, especially volatile gaseous ones (MeSH, EtSH, nBuSH, AcSH, etc).
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woelen
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A mix of a solution of NaOH and bleach indeed is the best I can think of. The NaOH binds the free H2S and the bleach destroys the sulfide by means of
oxidation. You might get a turbid liquid, containing finely dispersed sulphur. But certainly part of the sulfide will be oxidized further, all the way
up to sulfate. Dissolve the NaOH in plain household bleach (4% active chlorine) and use that as the scrubbing solution.
Put a flask between your reaction vessel and the scrubbing bottle. If production of H2S stops or becomes very slow, then there may be suck-back.
[Edited on 23-12-10 by woelen]
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hkparker
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Awesome info, thanks. What's the problem with sodium sulfide though? If I don't have bleach on hand
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woelen
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Sodium sulfide still releases quite some H2S. The compound H2S is such a weak acid that even from alkaline solutions still quite some H2S can escape.
A solution of Na2S has a strong smell of rotten eggs.
Instead of bleach, you can also use dilute H2O2 (e.g. 3% H2O2 mixed with a solution of NaOH).
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aeacfm
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a month ago i was going to make a post like that but asking about if the sample contain sulfides how can determine the sulfide it self not
through the metal (stoitiometric) , and no loss in sulfides occure
[Edited on 23-12-2010 by aeacfm]
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blogfast25
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Beware also that H2S is seriously toxic, more toxic than HCN apparently.
There's a thread about someone who managed to poison himself with it and ended up in hospital, you might want to look it up for inspiration... It was
member 'fluke' IIRW...
NaOH + hypochlorite is my choice also. Make sure your scrubbers contain enough chemicals to comfortably absorb the H2S you'll be generating and make
sure your apparatus is air tight!
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BromicAcid
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During one of my attempts at CS<sub>2</sub> I was trying to react sulfur with carbon to get my desired product. I figured some
H<sub>2</sub>S would be generated from any other organics in my carbon so I put a trap in line just of a concentrated
CuSO<sub>4</sub> solution in water which I figured would make the sulfide and maybe some sulfuric. The fact that sulfides are not a fan
of acidic conditions didn't cross my mind since I added it at the last moment. The trap quickly turned dark and it became apparent I had grossly
underestimated the amount of toxic gas that would issue fourth from the reaction. The copper solution was being reduced to copper metal or some other
thick beautiful precipitate which began to collect.
About 45 minutes into the experiment my grandmother (whom I lived with at the time) came out of the house and yelled at me for making everything smell
like rotten eggs. I never smelled a thing, there was no wind, my sense of smell had died somewhere along the way. Traps don't fail suddenly... and
neither does the sense of smell, but the two can fail in step with one another and create a disastrous situation.
For safety prepare an indicator solution by dipping some paper in lead nitrate solution and drying, cut in strips and hang these papers around your
work area with more on hand. These will give you the visual you need if you have a leak or a trap fails, they can also be used to troubleshoot as the
response time can be rapid depending on preparation. Note that there are no commercial gas cartridges (at the time I last checked) that protect
against hydrogen sulfide except for emergency escape cartridges. This is a supplied air only issue and one of the elite groups of chemicals that
won't just injure you, it has the capacity to remove your conscious from this Earth with ease.
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hkparker
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Ok, I didnt know H2S was so toxic, or more worrisome that it numbs the nose. Tell me if this setup sounds safe then. A glass tube coming from my
reaction carrying all the H2S will be bubbled through bleach/NaOH then into CaCl2 soln. If I get the black ppt of CaS in the CaCl2 soln. then I know
the bleach/NaOH soln. isnt catching everything and I will have to add another bleach/NaOH gas washer.
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bbartlog
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CaS isn't black, and I don't think it exists as such in aqueous solution, and in any case with CaCl2 the reaction runs the other way (i.e. rather than
going CaCl2 + H2S -> CaS + 2HCl, it goes CaS + 2HCl -> CaCl2 + H2S). I don't know what the easiest/best indicator solution would be (lead
nitrate has been mentioned, I think copper acetate should also work), but CaCl2 isn't it.
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hkparker
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Ok thanks, yea my bad. Copper acetate I do have, so ill use that. I would go with lead if I had it, but I dont. Any other good indicators?
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blogfast25
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Quote: Originally posted by hkparker  | | Ok thanks, yea my bad. Copper acetate I do have, so ill use that. I would go with lead if I had it, but I dont. Any other good indicators?
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Yes, CaS hydrolyses immediately in water: CaS + 2 H2O === > Ca(OH)2 + H2S. Can't be used for capturing H2S. Solid it's white, BTW...
The reason why CaS hydrolyses has to do with solubility: CaS is quite soluble compared to most other sulphides, so you get:
CaS (s) (in water) === > Ca2+ (aq) + S2- (aq)
The S2- then reacts with the water, forming first HS-, then H2S and driving the first equilibrium to the right.
Lead really is your best bet, second to the even better silver (forms black Ag2S). Haven't you got a piece of lead from an old battery, pipe or (car
wheel) balancing weight you can dissolve in some nitric?
[Edited on 24-12-2010 by blogfast25]
[Edited on 24-12-2010 by blogfast25]
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Eclectic
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How about some kind of burner, followed by SO2 scrubber? It would also get rid of acetylene,CS2, and any other organics that make it past the
condenser.
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Jor
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| Quote: Originally posted by blogfast25 | | Quote: Originally posted by hkparker | | Ok thanks, yea my bad. Copper acetate I do have, so ill use that. I would go with lead if I had it, but I dont. Any other good indicators?
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Yes, CaS hydrolyses immediately in water: CaS + 2 H2O === > Ca(OH)2 + H2S. Can't be used for capturing H2S. Solid it's white, BTW...
The reason why CaS hydrolyses has to do with solubility: CaS is quite soluble compared to most other sulphides, so you get:
CaS (s) (in water) === > Ca2+ (aq) + S2- (aq)
The S2- then reacts with the water, forming first HS-, then H2S and driving the first equilibrium to the right.
Lead really is your best bet, second to the even better silver (forms black Ag2S). Haven't you got a piece of lead from an old battery, pipe or (car
wheel) balancing weight you can dissolve in some nitric?
[Edited on 24-12-2010 by blogfast25]
[Edited on 24-12-2010 by blogfast25] |
No, why use lead compounds when there so much better, safer compounds? Also lead is very environmentally unfriendly.
Just use something like bleach, that is very safe. If you decide to use a metal, don't use lead. I mean people should avoid using those toxic metals
if possible, so that means you are not going to use it for srubiing something right?
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DJF90
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Jor, the point of the lead nitrate was to make indicating strips. For detecting H2S in your workspace these would be indispensable. Bleach of course
would be fine for the wash trap, but it'd be unsafe not to be sure theres no leaks in the system. The amount of lead nitrate required to make such
indicating strips would be very small. I agree its nice to avoid toxic heavy metals wherever possible, but this is one case where theres no decent
substitute, at least to the best of my knowledge.
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Nicodem
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| Quote: Originally posted by hkparker | | Thanks, making an insoluble sulfide could be useful, though id rather deal with zinc then lead lol. I'm going to be trying to synthesize carbon
disulfide by passing acetylene through molten sulfur. |
In such case H2S is not the only thing to worry about! Acetylene can easily explode even without oxygen/air admixed. Passing a current of acetylene
through molten sulfur sounds extremely hazardous. Pure acetylene explodes if heated or compressed. I have seen it explode at normal pressure. The
explosion is much less violent than the explosion of acetylene/air mixtures, forms red flames and lot's of sooth, but is still violent enough to cause
damage and injuries.
I would recommend you to do what you should have done already in the first post, to provide the reference for this process so that other members can
evaluate the hazards involved.
Otherwise, aqueous sodium hypochlorite efficiently scrubs and oxidises H2S, but it is obviously not compatible with traces of unreacted acetylene.
…there is a human touch of the cultist “believer” in every theorist that he must struggle against as being
unworthy of the scientist. Some of the greatest men of science have publicly repudiated a theory which earlier they hotly defended. In this lies their
scientific temper, not in the scientific defense of the theory. - Weston La Barre (Ghost Dance, 1972)
Read the The ScienceMadness Guidelines!
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Jor
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| Quote: Originally posted by DJF90 | | Jor, the point of the lead nitrate was to make indicating strips. For detecting H2S in your workspace these would be indispensable. Bleach of course
would be fine for the wash trap, but it'd be unsafe not to be sure theres no leaks in the system. The amount of lead nitrate required to make such
indicating strips would be very small. I agree its nice to avoid toxic heavy metals wherever possible, but this is one case where theres no decent
substitute, at least to the best of my knowledge. |
Sorry, my fault, I didn't read all the posts well enough.
I was just suprised that someone was recommending the use of a lead nitrate scrubber, but this was not the case. My excuses.
Ofcourse for test strips you should use lead, it gives a very clear black color in contact with H2S.
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DJF90
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I thought so... don't worry about it! But yeah, I suspect a 0.01M solution (if not more dilute) of lead nitrate would make adequate test strips, the
colour change is very obvious and I suspect very sensitive also. Bear in mind the test strips would likely need to be moistened before use, to allow
good interaction with any H2S in the atmosphere.
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The WiZard is In
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Clorox Proresults Outdoor bleach (Lowe's among others)
in a strong bleach solution w/ sodium hydroxide.
The MSDS for their Proresults Deck Cleaner shows the same
ingredients/ %'s.
Attachment: Cloroxproresultsoutdoorbleachcleaner_6-07_.pdf (32kB)
This file has been downloaded 515 times
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The WiZard is In
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A short history of hydrogen sulfide
American Scientist
98:6-9 January-February 2010
http://tinyurl.com/2bv9d6f
Timing is everything. Just the other day a removed this
dis-bound article from the night stand to one of my file cabinets.
No sense saving the entire magazine when I can access it online,
however, like Nature, JAMA, The Lancet, &c., if I let my
subscriptions lapse I lose access.... 'bout 8-years back I took
my Bobcat dug a hole and filled it with 1200+ pounds of journals...
and never looked back.
The AAAS offered up a discount — so I renewed my membership
and now can access back issues of Science.
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