[mississippichem]

I agree with John Cuthber. An easy Ksp look up and two empirical observations are hard to argue with.

And the solubility of the tarnish salt or complex most certainly matters. In fact, it's about all that matters.

This is really a chemistry 101 question.

This post has been edited by mississippichem: 8 January 2012 - 10:25 PM

[Greg Boyles]

If you put tarnished silver in liquid ammonia then the solubility of Ag2S in water is totally irrelevant to whether or not the ammonia is capable of breaking the bonds in Ag2S. Assuming complex ions can form in non-aqueous solutions.......either way it should get across the point I am/was trying to make.

However I will concede that the solubility of Ag2S in water is probably not totally irrelevant for aqueous ammonia and that this statement of mine was an over statement.

Some interesting facts I have learned along the way.......

Silver can be tarnished through contact with organic sulfur containing compounds such as latex and perhaps sweat from hands, I guess these break down to release tiny amounts of H2S and over a long period......

Have also noticed a number of sources stating that pure silver is less prone to tarnishing than stirling silver, I guess because the copper is more reactive than the silver. That would mean that ammonia is more effective on stirling silver than it is on pure silver.

And chemistoftheelements, would you be in a position to repeat your experiments with stirling silver and pure silver and with warmed 0.88M ammonia in a sealed container?

I am interested to know if it would really make any noticeable difference to dissolving Ag2S tarnish. I don't have any silverware or silver wire on hand although I could make myself a small amount of 0.88M ammonia. Used to make it in my younger days for the purpose of making touch powder and I still have the flasks and stoppers etc.

This post has been edited by Greg Boyles: 9 January 2012 - 01:33 AM

[John Cuthber]

"If you put tarnished silver in liquid ammonia then the solubility of Ag2S in water is totally irrelevant to whether or not the ammonia is capable of breaking the bonds in Ag2S."
Except that, if ammonia broke those bonds, then it should still do so in the presence of water.

"I am interested to know if it would really make any noticeable difference to dissolving Ag2S tarnish. I don't have any silverware or silver wire on hand although I could make myself a small amount of 0.88M ammonia. Used to make it in my younger days for the purpose of making touch powder and I still have the flasks and stoppers etc. "
I bet you don't mean that.
The ammonia solution I used ( and found not to work, even on heating) was more than 0.88M.

[Greg Boyles]

John Cuthber, on 9 January 2012 - 07:00 AM, said:

"If you put tarnished silver in liquid ammonia then the solubility of Ag2S in water is totally irrelevant to whether or not the ammonia is capable of breaking the bonds in Ag2S."
Except that, if ammonia broke those bonds, then it should still do so in the presence of water.

Regardless the ability of ammonia to break those bonds, or not, is not determined by the solubility of Ag2S in water.

[hypervalent_iodine]

Greg, ammonia doesn't react to form a complex with silver sulphide (as I think John pointed out quite some posts ago), so your argument is still moot. It doesn't matter how many posts you spend arguing semantics, the fact remains that ammonia does not and will not remove silver sulphide from silverware.

[Greg Boyles]

hypervalent_iodine, on 9 January 2012 - 10:06 AM, said:

Greg, ammonia doesn't react to form a complex with silver sulphide (as I think John pointed out quite some posts ago), so your argument is still moot. It doesn't matter how many posts you spend arguing semantics, the fact remains that ammonia does not and will not remove silver sulphide from silverware.

You say water will not dissolve AgS. But you are talking absolutes which is not the case in chemistry. That is the same mistake I made at the beginning of this argument.

Ag2S is soluble in water albeit to an extremely small extent. And solubility in water will be increased by temperature, albeit still very low.

Therefore I still remain interested to what extent heat and high ammonia concentration would have on Ag2S in ammonia, albeit probably still low. If ammonia is a weaker ligand than water then you would have a point. But is it? I don't think it is. Water is not capable of dissolving copper hydroxide but ammonia is. That implies than ammonia is a stronger ligand than water.

But enough to make a noticeable difference to a thin film of tarnish on Ag (under the influence of heat and high concentration)?

This post has been edited by Greg Boyles: 9 January 2012 - 11:34 AM

[Chemistoftheelements]

"And chemistoftheelements, would you be in a position to repeat your experiments with stirling silver and pure silver and with warmed 0.88M ammonia in a sealed container?"

Hi Greg; after a bit of encouragement from 3 forum members, I've decided to stick around a bit. In answer to you question, not at the moment, but I may have access to a fume cupboard in the not- too distant future- hot ammonia is nasty stuff, so this is essential.

What interests me most is that the results so far are strikingly different between fine silver and a high- silver alloy. Maybe it's Ag2S which forms on fine silver, and a mixture of copper compounds on sterling silver, with some silver compounds. As copper is higher up the reactivity series than silver, it may be that it preferentially corrodes and "protects" the silver, in the manner that the zinc in zinc plate on iron will do if this coat is scratched through to the iron.

On the solubility of Ag2S, it's always been my understanding that the solubility of a substance per say is not a barrier to forming soluble complexes, but if Ag2S- ammonia complex in water is insoluble, then the tarnish layer on fine silver, if it does consist of Ag2S, will not be removed. For example, TiO2 is extremely insoluble in water, yet is dissolved by hydrofluoric acid, because the complex formed is soluble. Hypervalent_iodine, what's your take on this? Thanks.

[Greg Boyles]

Chemistoftheelements, on 9 January 2012 - 01:04 PM, said:

Hi Greg; after a bit of encouragement from 3 forum members, I've decided to stick around a bit. In answer to you question, not at the moment, but I may have access to a fume cupboard in the not- too distant future- hot ammonia is nasty stuff, so this is essential.

Good! Cop it on the chin but return a right hook!

My understanding is that the issue is whether or not NH3 is a strong enough ligand to break the Ag2S bonds rather than whether or not (Ag(NH3)2)2S is soluble.

I would supect that the species in solution would be Ag(NH3)2OH rather than the former. I would also assume that the S would largely volatilise off as H2S. There are ammonium ions in ammonia solution and ammonium ions are a weak acid.

This post has been edited by Greg Boyles: 9 January 2012 - 01:27 PM

[hypervalent_iodine]

Greg Boyles, on 9 January 2012 - 11:33 AM, said:

You say water will not dissolve AgS. But you are talking absolutes which is not the case in chemistry. That is the same mistake I made at the beginning of this argument.

Ag2S is soluble in water albeit to an extremely small extent. And solubility in water will be increased by temperature, albeit still very low.

I'm not talking about water (and have never even mentioned it in any of my posts), I'm talking about ammonia. And no one is talking in absolutes, we're talking in chemistry, where negligible molar solubility is typically described as insoluble.

Quote

Therefore I still remain interested to what extent heat and high ammonia concentration would have on Ag2S in ammonia, albeit probably still low. If ammonia is a weaker ligand than water then you would have a point. But is it? I don't think it is. Water is not capable of dissolving copper hydroxide but ammonia is. That implies than ammonia is a stronger ligand than water.

That's because the ammonia reacts with the copper hydroxide, whereas the water does not. You're talking about two different compounds with very different reactivity profiles, so I quite honestly do not understand what point you are trying to drive here. Copper (II) is right on the borderline of being a hard and soft acid and will react accordingly with a hard base such as ammonia. Silver is a soft acid - i.e. it accepts electron pairs and will form complexes in which the predominating acid-base interaction is covalent in nature. Typically we say that soft acids will only react with soft bases and hard acids with hard bases; that being said, ammonia can, in some cases, donate its lone pair of electrons to form a covalent bond with a soft Lewis acid such as Ag⁺. This is why some silver halides react with it. Silver iodide does not react with ammonia though, as John noted. This is because the iodide ion is a soft base. Bromide and chloride ions are not. Sulfur is another soft base - do you see where I am going with this?

Chemistoftheelements, on 9 January 2012 - 01:04 PM, said:

On the solubility of Ag2S, it's always been my understanding that the solubility of a substance per say is not a barrier to forming soluble complexes, but if Ag2S- ammonia complex in water is insoluble, then the tarnish layer on fine silver, if it does consist of Ag2S, will not be removed. For example, TiO2 is extremely insoluble in water, yet is dissolved by hydrofluoric acid, because the complex formed is soluble. Hypervalent_iodine, what's your take on this? Thanks.

This is correct. Solubility should not be confused with the ability for something to dissolve. As noted, there are plenty of compounds that are insoluble in a given solvent, but will still dissolve due to various reactions that take place.

Greg Boyles, on 9 January 2012 - 01:23 PM, said:

Good! Cop it on the chin but return a right hook!

My understanding is that the issue is whether or not NH3 is a strong enough ligand to break the Ag2S bonds rather than whether or not (Ag(NH3)2)2S is soluble.

I would supect that the species in solution would be Ag(NH3)2OH rather than the former. I would also assume that the S would largely volatilise off as H2S. There are ammonium ions in ammonia solution and ammonium ions are a weak acid.

Firstly, your initial sentence in this post is rather unnecessary. This isn't fight club, it's a discussion board. I understand there has been a deal of hostility, but there's no reason to try and encourage more.

Secondly, the only person who has talked about the existence (Ag(NH₃)₂)₂S is you. Ignoring the fact that you have written it chemically incorrect, I am incredibly skeptical that such a compound would exist; talking about whether or not it's soluble in ammonia is therefore a pointless endeavor. Ag₂S won't react with ammonia, nor is it soluble in it. John and I have tried saying this to you a number of times in a number of ways already.

This post has been edited by hypervalent_iodine: 9 January 2012 - 05:42 PM

[mississippichem]

I also highly doubt the existence of the naked sulphide ligand as written by Greg Boyles. The charges and orbitals don't work.

[hypervalent_iodine]

My assumption was that the two silver atoms were still bound to the central sulphur the same way as in Ag₂S. Either way, it doesn't make chemical sense (and is also not bond breaking, as mentioned in Greg's post).

[mississippichem]

hypervalent_iodine, on 9 January 2012 - 05:38 PM, said:

My assumption was that the two silver atoms were still bound to the central sulphur the same way as in Ag₂S. Either way, it doesn't make chemical sense (and is also not bond breaking, as mentioned in Greg's post).

Oh...I missed the 2 subscript. Still I don't think that geometry is allowed for Ag(I), if you consider the amino ligands. Also, I've never seen a bimetallic complex of that type without stronger electron withdrawing terminal ligands.

I won't say the complex is impossible, just unlikely.

[John Cuthber]

OK, we have a bit of data to play with. Lets see what happens when we look at the numbers.
I'm in a bit of a rush so I hope I get this right.

The solubility of silver sulphide in water is about 10^-16 molar.
Adding 1M ammonia will complex all but 1 in 10 million of the ammonia so the solubility should rise roughly 10^7 fold.
So the solubility in 1M ammonia is about 10^-9 Molar
Using conc ammonia (about 10 molar) should increase the solubility about a hundredfold.
That takes us to about 10^-7 M

It's not clear if the effect of temperature even goes in the right direction but, just for the sake of having a number, lets assume the effect is that same as the effect of solubility on silver iodide (since Greg gave us some numbers for that).
That gives us roughly another 10 fold improvement.
That takes the estimated solubility of silver sulphide in hot conc ammonia (under dangerously high pressure) to something like 10^6 molar. I think that's rather less than one part in a million w/w.

So Greg, now do you believe me when I say it won't work?

[Chemistoftheelements]

hypervalent_iodine, on 9 January 2012 - 04:49 PM, said:

This is correct. Solubility should not be confused with the ability for something to dissolve. As noted, there are plenty of compounds that are insoluble in a given solvent, but will still dissolve due to various reactions that take place.

Thanks. Briefly, withought trying to break out into another thread, could you recommend something which would help me understand why some complexes dissolve and others don't ( e.g. Cu2+ ammonia complexes versus Ni2+ ammonia complexes), in water under standard conditions? Many thanks.

This post has been edited by Chemistoftheelements: 9 January 2012 - 09:20 PM

[John Cuthber]

I think it would be better to start another thread for that. It hasn't anything to do with this topic.

[Greg Boyles]

hypervalent_iodine, on 9 January 2012 - 04:49 PM, said:

I'm not talking about water (and have never even mentioned it in any of my posts), I'm talking about ammonia. And no one is talking in absolutes, we're talking in chemistry, where negligible molar solubility is typically described as insoluble.



That's because the ammonia reacts with the copper hydroxide, whereas the water does not. You're talking about two different compounds with very different reactivity profiles, so I quite honestly do not understand what point you are trying to drive here. Copper (II) is right on the borderline of being a hard and soft acid and will react accordingly with a hard base such as ammonia. Silver is a soft acid - i.e. it accepts electron pairs and will form complexes in which the predominating acid-base interaction is covalent in nature. Typically we say that soft acids will only react with soft bases and hard acids with hard bases; that being said, ammonia can, in some cases, donate its lone pair of electrons to form a covalent bond with a soft Lewis acid such as Ag⁺. This is why some silver halides react with it. Silver iodide does not react with ammonia though, as John noted. This is because the iodide ion is a soft base. Bromide and chloride ions are not. Sulfur is another soft base - do you see where I am going with this?



This is correct. Solubility should not be confused with the ability for something to dissolve. As noted, there are plenty of compounds that are insoluble in a given solvent, but will still dissolve due to various reactions that take place.



Firstly, your initial sentence in this post is rather unnecessary. This isn't fight club, it's a discussion board. I understand there has been a deal of hostility, but there's no reason to try and encourage more.

Secondly, the only person who has talked about the existence (Ag(NH₃)₂)₂S is you. Ignoring the fact that you have written it chemically incorrect, I am incredibly skeptical that such a compound would exist; talking about whether or not it's soluble in ammonia is therefore a pointless endeavor. Ag₂S won't react with ammonia, nor is it soluble in it. John and I have tried saying this to you a number of times in a number of ways already.

Quote

Solubility is the property of a solid, liquid, or gaseous chemical substance called solute to dissolve in a solid, liquid, or gaseous solvent to form a homogeneous ...

Solubility is ability to dissolve in a solvent. There is no difference between a coordination complex involving water molecules (which many or most salts form when they dissolve in water) and a coordinaion complex involving both ammonia and water molecules.

So I have not the faintest idea what you mean by this statement iodine:

Quote

Solubility should not be confused with the ability for something to dissolve

And Cuthber specifically refered to solubility of Ag2S as determining whether or not ammonia could break the chemical bonds.

And I have never once indicated that I believed that the chemical species in ammonia solution would be (Ag(NH₃)₂)₂S

This post has been edited by Greg Boyles: 10 January 2012 - 08:23 AM

[hypervalent_iodine]

Greg Boyles, on 10 January 2012 - 07:54 AM, said:

What the %^&* are you on about Cuthber???

Might want to check who actually wrote that post. Hint: it was me.

Quote

Solubility is ability to dissolve in a solvent. There is no difference between a coordination complex involving water molecules (which many or most salts form when they dissolve in water) and a coordinaion complex involving both ammonia and water molecules.

You can dissolve something without it being soluble in the solvent you are putting it in. This, however, is completely aside from the OP. If you would like to discuss it further, please start a thread about it.

Quote

And I have never once indicated that I believed that the chemical species in ammonia solution would be (Ag(NH₃)₂)₂S

In fact:

Greg Boyles said:

Silver forms complex ions with ammonia. For example, silver chloride and silver sulphide salts are both insoluble in water, but if you add enough ammonia (as in cloudy ammonia) these insoluble salts will dissolve to form Ag2(NH3)4S and Ag(NH3)2Cl.

Greg, you appear to be going in confusing circles with whatever it is you are trying to say. At this point in the argument your only reproach is to argue semantics for purposes I fail to understand. Do you still have an argument to make in light of what everyone has said here and if so, would you be so kind as to summarize it for us so that we might get back on topic?

[Greg Boyles]

hypervalent_iodine, on 10 January 2012 - 08:18 AM, said:

Might want to check who actually wrote that post. Hint: it was me.



You can dissolve something without it being soluble in the solvent you are putting it in. This, however, is completely aside from the OP. If you would like to discuss it further, please start a thread about it.



In fact:



Greg, you appear to be going in confusing circles with whatever it is you are trying to say. At this point in the argument your only reproach is to argue semantics for purposes I fail to understand. Do you still have an argument to make in light of what everyone has said here and if so, would you be so kind as to summarize it for us so that we might get back on topic?

Oops.......reflex action.....will rephrase the post as a non-Cuthber reply

[hypervalent_iodine]

Greg Boyles, on 10 January 2012 - 07:54 AM, said:

Solubility is ability to dissolve in a solvent. There is no difference between a coordination complex involving water molecules (which many or most salts form when they dissolve in water) and a coordinaion complex involving both ammonia and water molecules.

My post is still factually correct. It does not need to be soluble to dissolve in some cases. This is not true for all or even most compounds, but it is nonetheless true. If you read the entirety post #29, I did go to some effort to explain that, which you appear to have ignored.

The rest of post #37 still stands with all your editing, so feel free to reply to it.

[John Cuthber]

"And Cuthber specifically refered to solubility of Ag2S as determining whether or not ammonia could break the chemical bonds."

Yet another simply untrue statement from Greg.
The exchange was

""If you put tarnished silver in liquid ammonia then the solubility of Ag2S in water is totally irrelevant to whether or not the ammonia is capable of breaking the bonds in Ag2S."
Except that, if ammonia broke those bonds, then it should still do so in the presence of water."



So, I said that it's the ability of the ammonia to break the bands that determines the solubility, not the other way round.


Anyway, the stuff doesn't dissolve: it never did and it never will.

I'm thinking of starting a book on how long it takes Greg to accept that he was wrong from the very start.