Sciencemadness Discussion Board

Silver Tarnish Cleaning

MagicJigPipe - 30-10-2010 at 18:49

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]

not_important - 30-10-2010 at 19:00

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.

madscientist - 30-10-2010 at 19:10

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" :D 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]

MagicJigPipe - 30-10-2010 at 19:54

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.

Random - 31-10-2010 at 00:47

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.

psychokinetic - 31-10-2010 at 14:35

I put mine in the oven. Roasted silver = clean silver :)

MagicJigPipe - 31-10-2010 at 20:46

Thanks Random, I didn't even think of that.

Will heating the silver decompose Ag2S? Is that what you mean psychokinetic?

psychokinetic - 31-10-2010 at 21:55

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]

argyrium - 1-11-2010 at 11:38

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.



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.

not_important - 1-11-2010 at 13:22

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.

psychokinetic - 1-11-2010 at 14:58

Ok, makes sense. Any idea then what a favourable temperature for decomposition but not melting of Ag2S would be then?

not_important - 1-11-2010 at 15:15

Quote: Originally posted by psychokinetic  
Ok, makes sense. Any idea then what a favourable temperature for decomposition but not melting of Ag2S would be then?


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.

psychokinetic - 1-11-2010 at 15:53

If the mp of Ag2S is higher than that of silver, I'm guessing the silver metal will melt as it is formed, right?

not_important - 2-11-2010 at 15:33

MP of Ag2S is lower than that of siliver, its decomp temp in an inert atmospere is higher (I think)

metalresearcher - 2-11-2010 at 17:50

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" :D but more along the lines of skunk, natural gas, or a huge fart.


A fart consists more of CH3SH and C2H5SH (mercaptans) which contribute mainly to the foul smell rather than H2S.

psychokinetic - 2-11-2010 at 19:01

Ah, so either way, you're going to have a mess, and no longer your finest silver cutlery!