[swansont]

!

Moderator Note

Let's not let this get off track, please. Keep it civil.

[John Cuthber]

I will stick a few numbers in the quote for easy reference.

Greg Boyles, on 13 December 2011 - 10:22 PM, said:

1)Perhaps your household ammonia is too old and has lost most of its strength or perhaps a small amount of heat would advance things.

2)I used ammonia to clean a corroded trailer plug with brass contacts, and I had to scrub them a little to dislodge some of the p[artially dissolved copper oxide/carbonate and get closer to the underlying metal. But no doubt if I left it for long enough and in fresher ammonia solution, or 0.88M ammonia which is easy enough to make, the carbonate/oxide would have dissolved without scrubbing.....eventually.


3)Perhaps standard household ammonia is generally to weak for use as a practical corrosion remover. But 880 ammonia is fairly easy to make or otherwise purchase.


4) Interesting huh John Cuthber?

5) Was reading and found that silver iodide wont dissolve in ammonia solution.

6) But I also found this that states that the solubility of silver iodide in water can be signficantly increased by heating the water.....

7) pretty standard chemistry.

8) OK.....so what if you were to put your tarnised silver ware in 880 ammonia, in sealed container and raised the temperature a little.

Might just manage to push the reaction equilibrium in the the right direction so that it more effectively removes mild tarnish from the silver.

(1) Or perhaps not. You have absolutely no basis for this breach of Occam's razor.
(2) I used kerosene to remove paint from something, but that doesn't mean it will remove tarnish from silver.
Brass really isn't the same as silver so the fact that ammonia cleans brass has nothing to do with the issue
(3) or (again) perhaps not. However the solubility and equilibrium data I gave earlier show quite clearly that ammonia doesn't dissolve silver sulphide and it (still) never will.
(4) no, not really.
(5) I know that, which is why I was able to write it earlier. Incidentally, do you know any examples of tarnished silver where the iodide is formed in any significan quantity? If not then you have to admit it's of questionable relevance to this issue. I introduced it to show that you were wrong about the idea that all silver salts would dissolve in ammonia.
(6) Have you looked how much the solubility changes? Your data suggest that, in hot water AgI is roughly 10 times more soluble. So, on a good day, it reaches a solubility of about 1 mole (about half a pound) in a million litres (that's a thousand tons) of water.
(7) it is indeed, and so is contemplating the effect of temperature on the ability of silver to form a complex with ammonia. One thing is certain- the complex is likely to dissociate when the solution is heated ( the entropy term in the Gibbs free energy will favour this).
So, ammonia will do a less good job of forming a complex with silver if you heat it.
As you say- pretty standard chemistry.

(8) I would possibly burst the bottle so I'm not going to try it (and I advise other not to). It's hardly practical even if it works.
You have not shown that it would work, and the thermodynamics suggests that it would not.

By the way, as I have said plenty of times before, if your theory doesn't tally with reality then it isn't because reality is wrong.
The silver wire remains tarnished.

Now, go and look up the meanings of the data I provided earlier and see what they tell you about this silly idea that silver sulphide will dissolve in household ammonia.

Sorry, I just realised I forgot about this bit.

"CHEMICAL CLEANING
The majority of silver objects recovered from archaeological contexts require only limited treatment.

1)In most instances, the various corrosion products can be removed with simple chemical solutions (Plenderleith and Werner 1971:227-229). Common tarnish caused by sulfur compounds can be eliminated easily with commercial silver cleaning solutions. Alternatively, a mild silver dip solution that consists of 5 percent thiourea and 1 percent non-ionic detergent in distilled water can be prepared. A solution of 15 percent ammonium thiosulfate in distilled water with a 1 percent non-ionic wetting agent is stronger than the silver dip and is effective for removing both tarnish and silver chloride.


2) For base silver with copper corrosion compounds, concentrated ammonia effectively cleans all copper compounds from the silver.

3)Care must be taken, however, because ammonia dissolves silver chloride and will substantially weaken badly corroded silver.

"

So, from (1) we see that these people don't suggest ammonia- which is cheap and easily available but prefer things like thiourea which is a bit more obscure and a suspect carcinogen. Perhaps that's because they know that ammonia doesn't really work.

(2) shows that they can tell the difference between copper compounds (which dissolve in ammonia solution) and silver which doesn't.

3 might be important if the silver has been lying under the sea or something, but otherwise I can't explain where the chlorine came from. Can you?
It's true enough that silver chloride is soluble in ammonia- I think I may have pointed that out already- but it's not the black stuff you find on tarnished silver.
There's a relatively simple way to distinguish the black sulphide from the white chloride- only one of them dissolves in ammonia. Have you learned which yet?

Incidentally, if Greg comes back and still insist that he's right I think we should transfer this to the "religion" part of the forum since he is insisting on the truth of something, even after the published solubility data and experiment proved it to be false.

This post has been edited by John Cuthber: 15 December 2011 - 07:11 PM

[Chemistoftheelements]

The Al foil in sodium hydrogen carbonate/NaCl solution method works because there is an appreciable difference in electronegativity between silver and aluminium, and when you place them in contact in a solution containing an electrolite, aluminium will function as an anode and corrode; meanwhile, hydrogen is building up on the cathode, which in this case is silver, which, probably being in its nascent form, reduces the AgS to Ag, and H2S is produced.

As for the ammonia method, I don’t think this can be completely written off, as from an experiment I just did using 99.99% pure silver and 9% ammonia solution, there may be some sort of reaction, as the tarnished silver seemed to become became untarnished in places, although I should have taken pictures before and after to be sure, and until I can find some more decently tarnished silver I reserve judgement. HOWEVER, I just treated some very tarnished sterling silver with 9% ammonia solution for just a few seconds, and this proved a very effective means of removing tarnish.

As for the influence of solubility of a substance on it’s ability to form a soluble complex, there are some extremely insoluble substances which form soluble complexes very easily- just dunk some titanium, zirconium or hafnium dioxides in HF to confirm this, or indeed the pure metals. The solubility of the substance you were trying to dissolve would, however, certainly influence the RATE of dissolution. HOWEVER, a while ago I tried dissolving some CuO as formed on a copper wire by heating in said ammonia solution, and the result was no detectable dissolution, while I know that Cu2+ while in solution, when neutralised with ammonia remains in solution as a soluble complex. Just some observations to throw into the discussion!

[Greg Boyles]

Chemist of the elements, on 26 December 2011 - 09:34 PM, said:

The Al foil in sodium hydrogen carbonate/NaCl solution method works because there is an appreciable difference in electronegativity between silver and aluminium, and when you place them in contact in a solution containing an electrolite, aluminium will function as an anode and corrode; meanwhile, hydrogen is building up on the cathode, which in this case is silver, which, probably being in its nascent form, reduces the AgS to Ag, and H2S is produced.

As for the ammonia method, I don't think this can be completely written off, as from an experiment I just did using 99.99% pure silver and 9% ammonia solution, there may be some sort of reaction, as the tarnished silver seemed to become became untarnished in places, although I should have taken pictures before and after to be sure, and until I can find some more decently tarnished silver I reserve judgement. HOWEVER, I just treated some very tarnished sterling silver with 9% ammonia solution for just a few seconds, and this proved a very effective means of removing tarnish.

As for the influence of solubility of a substance on it's ability to form a soluble complex, there are some extremely insoluble substances which form soluble complexes very easily- just dunk some titanium, zirconium or hafnium dioxides in HF to confirm this, or indeed the pure metals. The solubility of the substance you were trying to dissolve would, however, certainly influence the RATE of dissolution. HOWEVER, a while ago I tried dissolving some CuO as formed on a copper wire by heating in said ammonia solution, and the result was no detectable dissolution, while I know that Cu2+ while in solution, when neutralised with ammonia remains in solution as a soluble complex. Just some observations to throw into the discussion!

Are you paying attention Cuthber!

Hence my suggestion to up the ammonia concentration and increase the heat!

For interest's sake....are you a qualified chemist John Cuthber?

[swansont]

!

Moderator Note

Since the pettiness and sniping has not stopped, I am closing this