MagicJigPipe
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Silver Tarnish Cleaning
I have some heavily tarnished silver. I know that silver reacts with H2S to produce the tarnish (Ag2S). Now, if a strong mineral acid such as HCl is
used to clean this, will it produce H2S?
2HCl + 2Ag2S ---> 2AgCl + H2S
However, silver is below H on the "reactivity series" (I was never really introduced to this properly). I'm thinking that the reaction will still
occur if the acid is concentrated enough (AgCl will form a precipitate?) I haven't been through inorganic chemistry yet.
I ask because when I attempt to clean a piece of silver with dilute HCl it produces an odor that is so foul I don't even know how to describe it
except to say: piss, shit, rotten dick dump. Not only does it smell bad but it causes one to recoil in horror if one gets a "good" whiff of it. I
can't think of any other reaction that would produce such a pungent compound from Ag2S, Ag and HCl so that must be it, right?
Also, I bought a bottle of "Tarn-X" and on the back says "CAUTION: Contains thiourea, sulforric acid, corrosion inhibitors and
detergent." What the hell is sulforric acid? Please don't tell me this is an accidental, or even deliberate, misspelling of sulfuric acid. I have
never heard of this compound, EVER and a quick Google search reveals nothing (surprisingly).
Thanks, in advance.
EDIT:
Nevermind about the "sulforric acid". I looked at the Spanish version on the other side and it says, "ácido sulfámico", which is sulfamic acid.
Makes perfect sense now.
[Edited on 10-31-2010 by MagicJigPipe]
"There must be no barriers to freedom of inquiry ... There is no place for dogma in science. The scientist is free, and must be free to ask any
question, to doubt any assertion, to seek for any evidence, to correct any errors. ... We know that the only way to avoid error is to detect it and
that the only way to detect it is to be free to inquire. And we know that as long as men are free to ask what they must, free to say what they think,
free to think what they will, freedom can never be lost, and science can never regress." -J. Robert Oppenheimer
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not_important
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Easier way with a lot less corrosion inducement in the surrounds :
Line a pot, glass ceramic or metal with Al foil - one big sheet. Put the silver into the pot, touching the foil. Cover with water, add enough sodium
bicarbonate that some doesn't dissolve. Heat, watch what happens.
The smell was indeed was likely H2S plus a bit of other gases including HCl.
'sulforric acid' is a typo, currend MSDS sez:
1. Water 7732-18-5 No 85-95
2. Thiourea 62-56-6 Yes 5 - 7
3. Sulfamic Acid 5329-14-6 Yes 3 – 5
4. Disodium Cocoampho Diproprionate 68604-71-7 No <1.0
5. Methanol 67-56-1 Yes <0.05
Sulfamic acid is a strongish acid whos salts with many/most metals are soluble.
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madscientist
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I think "sulforric acid" was supposed to be "sulfonic acid." Don't quote me on that though.
Silver chloride is very insoluble in water, though I guess it's possible there's a bit of H2S being produced. You can smell that stuff around 0.2 ppm,
I believe. What happens when you use acetic acid?
Having been exposed to volcanic bathroom blasts of H2S myself, I wouldn't say it smells like a "rotten dick dump"  but more along the lines of skunk, natural gas, or a huge fart.
[Edit: Loaded the page to write this before the above reply was posted; the reason I said sulfonic was because I found a lot of hits where google
misinterpreted pdfs, changing "sulfonic" to "sulforric" in the HTML version.]
[Edited on 31-10-2010 by madscientist]
I weep at the sight of flaming acetic anhydride.
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MagicJigPipe
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Unfortunately most of the pieces are too large for submerging in pots and pans. However, a 5 gal bucket should do. I remember when I used to clean
silver with NaHCO3 and boiling water.
Speaking of which. One thing that I learned (didn't realize until recently) is that a solution of NaHCO3 will slowly evolve CO2 even without heat.
Now that I think about it it makes sense.
I had sat. NaHCO3 solution sitting in a wash bottle and it slowly drips water due to the CO2 pressure.
Oh yeah, the Tarn-X produces the exact same smell.
"There must be no barriers to freedom of inquiry ... There is no place for dogma in science. The scientist is free, and must be free to ask any
question, to doubt any assertion, to seek for any evidence, to correct any errors. ... We know that the only way to avoid error is to detect it and
that the only way to detect it is to be free to inquire. And we know that as long as men are free to ask what they must, free to say what they think,
free to think what they will, freedom can never be lost, and science can never regress." -J. Robert Oppenheimer
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Random
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Check the nurdrage video about that:
http://www.youtube.com/watch?v=vGCx9HZwYBo
You won't even destroy the tarnished layer of silver, it will be recovered to metal again.
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psychokinetic
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I put mine in the oven. Roasted silver = clean silver 
“If Edison had a needle to find in a haystack, he would proceed at once with the diligence of the bee to examine straw after straw until he found
the object of his search.
I was a sorry witness of such doings, knowing that a little theory and calculation would have saved him ninety per cent of his labor.”
-Tesla
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MagicJigPipe
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Thanks Random, I didn't even think of that.
Will heating the silver decompose Ag2S? Is that what you mean psychokinetic?
"There must be no barriers to freedom of inquiry ... There is no place for dogma in science. The scientist is free, and must be free to ask any
question, to doubt any assertion, to seek for any evidence, to correct any errors. ... We know that the only way to avoid error is to detect it and
that the only way to detect it is to be free to inquire. And we know that as long as men are free to ask what they must, free to say what they think,
free to think what they will, freedom can never be lost, and science can never regress." -J. Robert Oppenheimer
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psychokinetic
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Hmm. Not sure about Ag2S in particular. . . Ag(II)O definitely.
Heat above 200c (but not more than 240, or you'll have a silver oxide liquid forming) and buh bai oxygen.
EDIT: Sure it's Ag(I) and not Ag(II)?
[Edited on 1-11-2010 by psychokinetic]
“If Edison had a needle to find in a haystack, he would proceed at once with the diligence of the bee to examine straw after straw until he found
the object of his search.
I was a sorry witness of such doings, knowing that a little theory and calculation would have saved him ninety per cent of his labor.”
-Tesla
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argyrium
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Quote: Originally posted by not_important  | Easier way with a lot less corrosion inducement in the surrounds :
Line a pot, glass ceramic or metal with Al foil - one big sheet. Put the silver into the pot, touching the foil. Cover with water, add enough sodium
bicarbonate that some doesn't dissolve. Heat, watch what happens.
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The suggestion by not_important is very good and will be the safest choice all around. Na2CO3 will work a bit faster but is a tad nastier to use.
Heat is an important issue; done around 80 - 90° c the tarnish disappears in seconds.
Anyone wanting to try this with knives is cautioned in that with most older silver, the blades are set into the handles with a shellac mixture and
will either melt-out, and/or be attacked by the high pH.
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not_important
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| Quote: Originally posted by psychokinetic | Hmm. Not sure about Ag2S in particular. . . Ag(II)O definitely.
Heat above 200c (but not more than 240, or you'll have a silver oxide liquid forming) and buh bai oxygen.
EDIT: Sure it's Ag(I) and not Ag(II)?
[Edited on 1-11-2010 by psychokinetic] |
Ag2S melts at 825 C. Ag(II) isn't very stable,and really is Ag(I)AG(III)O2; it decomposes below the boiling point of water. Ag2O forms when silver
is warmed in air, and decomposes in the 270 to 300 C range.
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psychokinetic
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Ok, makes sense. Any idea then what a favourable temperature for decomposition but not melting of Ag2S would be then?
“If Edison had a needle to find in a haystack, he would proceed at once with the diligence of the bee to examine straw after straw until he found
the object of his search.
I was a sorry witness of such doings, knowing that a little theory and calculation would have saved him ninety per cent of his labor.”
-Tesla
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not_important
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Above the melting point of silver, I believe.
However Ag2S will oxidise when heated in air ending up forming metallic silver at temperatures above 300. However this will not be compact metal, and
often appears black.
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psychokinetic
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If the mp of Ag2S is higher than that of silver, I'm guessing the silver metal will melt as it is formed, right?
“If Edison had a needle to find in a haystack, he would proceed at once with the diligence of the bee to examine straw after straw until he found
the object of his search.
I was a sorry witness of such doings, knowing that a little theory and calculation would have saved him ninety per cent of his labor.”
-Tesla
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not_important
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MP of Ag2S is lower than that of siliver, its decomp temp in an inert atmospere is higher (I think)
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metalresearcher
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| Quote: Originally posted by madscientist |
Having been exposed to volcanic bathroom blasts of H2S myself, I wouldn't say it smells like a "rotten dick dump" but more along the lines of skunk, natural gas, or a huge fart.
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A fart consists more of CH3SH and C2H5SH (mercaptans) which contribute mainly to the foul smell rather than H2S.
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psychokinetic
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Ah, so either way, you're going to have a mess, and no longer your finest silver cutlery!
“If Edison had a needle to find in a haystack, he would proceed at once with the diligence of the bee to examine straw after straw until he found
the object of his search.
I was a sorry witness of such doings, knowing that a little theory and calculation would have saved him ninety per cent of his labor.”
-Tesla
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