Externet Posted December 11, 2011 Posted December 11, 2011 Hi. A silverware cleaning method calls for a hot solution of sodium carbonate plus a 'pinch' of common table salt; or sodium bicarbonate, or sodium hexametaphosphate, and even plain table salt alone, all in an aluminium vessel. The reaction is supposed to be " 2Al(s) + 3Ag2S(s) + 6H2O -> 6Ag(s) + 2Al2(OH)3(s) + 3H2S(aq) " But with so many choices as above, I have to think it is more a product of guessy empirism than a fine tuned fact. Any solid suggestions and optimization please ?
Greg Boyles Posted December 11, 2011 Posted December 11, 2011 Hi. A silverware cleaning method calls for a hot solution of sodium carbonate plus a 'pinch' of common table salt; or sodium bicarbonate, or sodium hexametaphosphate, and even plain table salt alone, all in an aluminium vessel. The reaction is supposed to be " 2Al(s) + 3Ag2S(s) + 6H2O -> 6Ag(s) + 2Al2(OH)3(s) + 3H2S(aq) " But with so many choices as above, I have to think it is more a product of guessy empirism than a fine tuned fact. Any solid suggestions and optimization please ? 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. You can do the same thing with copper sulfate. Adding cloudy ammonia will initially in the copper ions precipitating out as pale blue copper hydroxide Cu(OH)2. But as you keep adding more ammonia, eventually it the pale blue precipitate starts dissolving as the mixture starts forming the complex ion Cu(NH3)4SO4 which is soluble in water and has a deep blue colour. So in other words ammonia is enough to remove the tarnish from both silver and copper based alloys.
John Cuthber Posted December 11, 2011 Posted December 11, 2011 I'm a long way from sure that the ammonia complex is strong enough to dissolve silver sulphide. It won't dissolve silver iodide and I think the sulphide is even less soluble than that. Anyway, it doesn't actually answer the original question. I have used the method given- I typically use a cup full of boiling water and a teaspoon full of baking soda (it fizzes when you dissolve it) then pour that into a glass bowl with the silver lying on a piece of aluminium foil. It works very well and I don't think the amounts of salt or whatever are that critical. I think you just need fairly alkaline conditions. It really is quite impressive the first time you see it.
Greg Boyles Posted December 11, 2011 Posted December 11, 2011 (edited) I'm a long way from sure that the ammonia complex is strong enough to dissolve silver sulphide. It won't dissolve silver iodide and I think the sulphide is even less soluble than that. Anyway, it doesn't actually answer the original question. I have used the method given- I typically use a cup full of boiling water and a teaspoon full of baking soda (it fizzes when you dissolve it) then pour that into a glass bowl with the silver lying on a piece of aluminium foil. It works very well and I don't think the amounts of salt or whatever are that critical. I think you just need fairly alkaline conditions. It really is quite impressive the first time you see it. As far as the formation of complex ions goes, it is irrelevant how soluble the simple salt is to begin with, whether it is silver sulphide or silver chloride. Copper hydroxide and copper oxide etc are, to all intents and purposes, completely insoluble in water. But if you add enough ammonia all of them will dissolve completely. Ammonia would work at least as well as aodium bicarbonate if not better. Silver carbonate is as insoluble as silver sulphide so I am dubious as to how effective it would be in removing tarnish anyway. With ammonia, the silver ammino sulphide that is formed is completely soluble in water and hence can be rinced away totally with fresh water. Might do a quicker job if you combined the ammonia with a mild abrasive such as toothpaste. Found this regarding the use if bicarbonate to clean silver. It apparently requires aluminium in the form of a saucpan or scrunched up foil. So there is more going on here that meets the eye. I am not familiar with complex ions involving silver and aluminium but this suggests to me that this is what is involved in the cleaning process here. I know that aluminium dissolves in alkaline solutions to form complex ions with hydroxide ions (generating H2 in the process). <H2>What you will need: Aluminium pan or stainless steel pan and aluminium foil; Bicarbonate soda; 4 cups of very hot water; Extra water; White vinegar; Rubber gloves; Wooden spoon; Draining board; Polishing clothHow to... </H2>1<H3 class=heading></H3> Place cutlery in an aluminium pan. Add 1/2 cup of bicarbonate soda (also known as baking soda) dissolved in 4 cups of very hot water. After a few minutes, wearing rubber gloves, remove the cutlery from the solution. If you need to use an implement, make sure it is wooden (do not use metal tongs). I'm a long way from sure that the ammonia complex is strong enough to dissolve silver sulphide. It won't dissolve silver iodide and I think the sulphide is even less soluble than that. Anyway, it doesn't actually answer the original question. I have used the method given- I typically use a cup full of boiling water and a teaspoon full of baking soda (it fizzes when you dissolve it) then pour that into a glass bowl with the silver lying on a piece of aluminium foil. It works very well and I don't think the amounts of salt or whatever are that critical. I think you just need fairly alkaline conditions. It really is quite impressive the first time you see it. As far as the formation of complex ions goes, it is irrelevant how soluble the simple salt is to begin with, whether it is silver sulphide or silver chloride. Copper hydroxide and copper oxide etc are, to all intents and purposes, completely insoluble in water. But if you add enough ammonia all of them will dissolve completely. Ammonia would work at least as well as aodium bicarbonate if not better. Silver carbonate is as insoluble as silver sulphide so I am dubious as to how effective it would be in removing tarnish anyway. With ammonia, the silver ammino sulphide that is formed is completely soluble in water and hence can be rinced away totally with fresh water. Might do a quicker job if you combined the ammonia with a mild abrasive such as toothpaste. Found this regarding the use if bicarbonate to clean silver. It apparently requires aluminium in the form of a saucpan or scrunched up foil. So there is more going on here that meets the eye. I am not familiar with complex ions involving silver and aluminium but this suggests to me that this is what is involved in the cleaning process here.....assumung it does actually work. <H2>What you will need: Aluminium pan or stainless steel pan and aluminium foil; Bicarbonate soda; 4 cups of very hot water; Extra water; White vinegar; Rubber gloves; Wooden spoon; Draining board; Polishing clothHow to... </H2>1<H3 class=heading></H3> Place cutlery in an aluminium pan. Add 1/2 cup of bicarbonate soda (also known as baking soda) dissolved in 4 cups of very hot water. After a few minutes, wearing rubber gloves, remove the cutlery from the solution. If you need to use an implement, make sure it is wooden (do not use metal tongs). Also found this: I love this question! The usual tarnish on silver is the black sulfide. The cool thing about this is that you can instantly remove the tarnish from any silver item with commonly available household items, and I do mean fast! Aluminum is far above silver in the activity series for metals, and in a suitable solution will reduce the silver in the silver sulfide, reforming silver metal. The reaction is spontaneous and rapid in warm water: 2Al(s) + 3Ag2S(s) + 6H2O -> 6Ag(s) + 2Al2(OH)3(s) + 3H2S(aq) This might give some clues as to what is going on but it is impossible for this reaction to take place directly. For starters solid Al and insoluble Ag2S cannot chemically interact directly unless the Al was in the form of vapour. Secondly, in preparation of this home made solution, the Al is already disolved in the bicarbonate solution before it is applied to the silver. Thirdly Al does not form solid Al2(OH)3 in alkaline solutions. Rather it forms the following soluble complex ion: Al(H2O)2(OH)4]- (diaquatetrahydroxoaluminate). Hence the prepared cleaning solution would contain sodium diaquatetrahydroxoaluminate. If this solution works then there is clearly some sort of ion substitution occuring between the Ag2S and the Na[Al(H2O)2(OH)4] Edited December 11, 2011 by Greg Boyles
John Cuthber Posted December 11, 2011 Posted December 11, 2011 As far as the formation of complex ions goes, it is irrelevant how soluble the simple salt is to begin with, whether it is silver sulphide or silver chloride. Copper hydroxide and copper oxide etc are, to all intents and purposes, completely insoluble in water. But if you add enough ammonia all of them will dissolve completely. Ammonia would work at least as well as aodium bicarbonate if not better. Silver carbonate is as insoluble as silver sulphide so I am dubious as to how effective it would be in removing tarnish anyway. With ammonia, the silver ammino sulphide that is formed is completely soluble in water and hence can be rinced away totally with fresh water. Might do a quicker job if you combined the ammonia with a mild abrasive such as toothpaste. Found this regarding the use if bicarbonate to clean silver. It apparently requires aluminium in the form of a saucpan or scrunched up foil. So there is more going on here that meets the eye. I am not familiar with complex ions involving silver and aluminium but this suggests to me that this is what is involved in the cleaning process here. I know that aluminium dissolves in alkaline solutions to form complex ions with hydroxide ions (generating H2 in the process). <H2>What you will need: Aluminium pan or stainless steel pan and aluminium foil; Bicarbonate soda; 4 cups of very hot water; Extra water; White vinegar; Rubber gloves; Wooden spoon; Draining board; Polishing clothHow to... </H2>1<H3 class=heading></H3> Place cutlery in an aluminium pan. Add 1/2 cup of bicarbonate soda (also known as baking soda) dissolved in 4 cups of very hot water. After a few minutes, wearing rubber gloves, remove the cutlery from the solution. If you need to use an implement, make sure it is wooden (do not use metal tongs). As far as the formation of complex ions goes, it is irrelevant how soluble the simple salt is to begin with, whether it is silver sulphide or silver chloride. Copper hydroxide and copper oxide etc are, to all intents and purposes, completely insoluble in water. But if you add enough ammonia all of them will dissolve completely. Ammonia would work at least as well as aodium bicarbonate if not better. Silver carbonate is as insoluble as silver sulphide so I am dubious as to how effective it would be in removing tarnish anyway. With ammonia, the silver ammino sulphide that is formed is completely soluble in water and hence can be rinced away totally with fresh water. Might do a quicker job if you combined the ammonia with a mild abrasive such as toothpaste. Found this regarding the use if bicarbonate to clean silver. It apparently requires aluminium in the form of a saucpan or scrunched up foil. So there is more going on here that meets the eye. I am not familiar with complex ions involving silver and aluminium but this suggests to me that this is what is involved in the cleaning process here.....assumung it does actually work. <H2>What you will need: Aluminium pan or stainless steel pan and aluminium foil; Bicarbonate soda; 4 cups of very hot water; Extra water; White vinegar; Rubber gloves; Wooden spoon; Draining board; Polishing clothHow to... </H2>1<H3 class=heading></H3> Place cutlery in an aluminium pan. Add 1/2 cup of bicarbonate soda (also known as baking soda) dissolved in 4 cups of very hot water. After a few minutes, wearing rubber gloves, remove the cutlery from the solution. If you need to use an implement, make sure it is wooden (do not use metal tongs). You don't seem to know what you are talking about. The solubility of the original salt has a lot to do with whether or not the salt- say the sulphide- will dissolve in a complexing agent like ammonia. As I said, silver iodide isn't soluble in aqueous ammonia, but silver chloride is. The complex formed is the same in both cases. The difference is that silver iodide is a lot less soluble. The reaction does not make silver carbonate so the solubility of that salt is irrelevant. There was no reason for you to bring it up. This bit of your post "Found this regarding the use if bicarbonate to clean silver. It apparently requires aluminium in the form of a saucpan or scrunched up foil. So there is more going on here that meets the eye. I am not familiar with complex ions involving silver and aluminium but this suggests to me that this is what is involved in the cleaning process here. I know that aluminium dissolves in alkaline solutions to form complex ions with hydroxide ions (generating H2 in the process)." shows that you have entirely missed the point of the reaction. The silver sulphide is reduced to metallic silver. You say ammonia " Might do a quicker job if you combined the ammonia with a mild abrasive such as toothpaste.". Did you watch the video? It's not like the reaction is slow.
Greg Boyles Posted December 11, 2011 Posted December 11, 2011 (edited) You don't seem to know what you are talking about. The solubility of the original salt has a lot to do with whether or not the salt- say the sulphide- will dissolve in a complexing agent like ammonia. As I said, silver iodide isn't soluble in aqueous ammonia, but silver chloride is. The complex formed is the same in both cases. The difference is that silver iodide is a lot less soluble. The reaction does not make silver carbonate so the solubility of that salt is irrelevant. There was no reason for you to bring it up. This bit of your post "Found this regarding the use if bicarbonate to clean silver. It apparently requires aluminium in the form of a saucpan or scrunched up foil. So there is more going on here that meets the eye. I am not familiar with complex ions involving silver and aluminium but this suggests to me that this is what is involved in the cleaning process here. I know that aluminium dissolves in alkaline solutions to form complex ions with hydroxide ions (generating H2 in the process)." shows that you have entirely missed the point of the reaction. The silver sulphide is reduced to metallic silver. You say ammonia " Might do a quicker job if you combined the ammonia with a mild abrasive such as toothpaste.". Did you watch the video? It's not like the reaction is slow. Silver halides, except for silver fluoride, are extremely insoluble in water. As far as I have ever known and according to this from Wikipedia there is NO distinguishing between the relative solubilities of silver halides - they are all regarded as insoluble period. John it is utterly impossible for the aluminium foil or the aluminium saucpan to reduce the silver sulphide to silver metal. The only way that can happen is if the reductant (aluminium) is in solution. When the aluminium is dissolved in the alkaline bicarbonate solution the aluminium is already oxidized and has no further available electrons to dontate to the silver ions in the silver sulphide.....in order to reduce it to silver metal in a redox reaction. So reduction of silver sulphide is CLEARLY not the mechanism here. It might work that way if you made the silver item the cathode is an electrolytic cell. with an appropriate solution. Most tarnish removal involves removal of the silver sulpide, by means of an abrassive or via chemical means, to expose the underlying untarnished silver metal. Sorry buddy but your chemistry is some what 'rusty'. Edited December 11, 2011 by Greg Boyles
John Cuthber Posted December 11, 2011 Posted December 11, 2011 (edited) As far as I have ever known and according to this from Wikipedia there is NO distinguishing between the relative solubilities of silver halides - they are all regarded as insoluble period. Thank you for confirming the extent of your ignorance. You may find this helpful. http://chemed.chem.purdue.edu/genchem/topicreview/bp/ch18/ksp.php Incidentally wiki does know that the solubilities of the chloride and bromide differ. http://en.wikipedia.org/wiki/Solubility_table#S Perhaps the most important observation is that a simple experiment with some tarnished silver wire and a solution of ammonia has confirmed that you are wrong, the sulphide does not dissolve in ammonia. I could post a picture if it would help. This "John it is utterly impossible for the aluminium foil or the aluminium saucpan to reduce the silver sulphide to silver metal. The only way that can happen is if the reductant (aluminium) is in solution." is obvious nonsense too. If I put a nail in some copper sulphate solution the iron reduces the Cu++ ions to Cu metal. If I do the same with a solution of silver nitrate I get metallic silver. I can use Al instead of iron but, unless I remove the oxide film from the Al, it won't work very well. One way to remove that oxide is to dissolve it in an alkali like hot sodium carbonate solution. Edited December 11, 2011 by John Cuthber
Greg Boyles Posted December 11, 2011 Posted December 11, 2011 (edited) Thank you for confirming the extent of your ignorance. You may find this helpful. http://chemed.chem.p...bp/ch18/ksp.php Incidentally wiki does know that the solubilities of the chloride and bromide differ. http://en.wikipedia....ubility_table#S Perhaps the most important observation is that a simple experiment with some tarnished silver wire and a solution of ammonia has confirmed that you are wrong, the sulphide does not dissolve in ammonia. I could post a picture if it would help. Well I did read something about semi covalent bonding between silver and sulphide ions in silver sulphide so you may actually be right in saying that the regular household ammonia is not strong enough to break that bond and dissolve the silver sulphide. But perhaps 0.88M ammonia might be up to the task, but I don't know for sure. I did read that strong acids were capable of breaking the bond between Ag and S, although they do not form complex ions with Ag. But clearly bicarbonate is not a strong acid. Please post a valid chemical equation that explains how the aluminium reduces the silver ions, taking into consideration that in the afore mentioned cleaning solution: 1) That it is impossible for the Al atoms in the Al foil and the Ag ions in the tarnish to interact directly and that the Ag ions can only interact with Al ions once the Al foil has dissolved. 2) That you can't form Al(OH)3 in aqueous solution - it always forms sodium etc aluminate Bayer process From Wikipedia, the free encyclopediaJump to: navigation, search The Bayer process is the principal industrial means of refining bauxite to produce alumina (aluminium oxide). Bauxite, the most important ore of aluminium, contains only 30–54% alumina, Al2O3, the rest being a mixture of silica, various iron oxides, and titanium dioxide.[1] The alumina must be purified before it can be refined to aluminium metal. In the Bayer process, bauxite is digested by washing with a hot solution of sodium hydroxide, NaOH, at 175 °C. This converts the alumina to aluminium hydroxide, Al(OH)3, which dissolves in the hydroxide solution according to the chemical equation: Al2O3 + 2 OH− + 3 H2O → 2 [Al(OH)4]− 2Al(s) + 3Ag2S(s) + 6H2O -> 6Ag(s) + 2Al2(OH)3(s) + 3H2S(aq) " This is not a valid equation since the solid Al foil and solid tarnish are never in direct contact. The only way that could happen is if the Al is in the form of vapour at extremely high temperatures, no doubt enough to melt the silver. And by the way John......as far as dipping your silver wire in ammonia....... Coke and ammonia removes the tarnish from 1c and 2c pieces, but you usually have to leave them in it over night to notice any difference. Thank you for confirming the extent of your ignorance. You may find this helpful. http://chemed.chem.p...bp/ch18/ksp.php Incidentally wiki does know that the solubilities of the chloride and bromide differ. http://en.wikipedia....ubility_table#S Perhaps the most important observation is that a simple experiment with some tarnished silver wire and a solution of ammonia has confirmed that you are wrong, the sulphide does not dissolve in ammonia. I could post a picture if it would help. This "John it is utterly impossible for the aluminium foil or the aluminium saucpan to reduce the silver sulphide to silver metal. The only way that can happen is if the reductant (aluminium) is in solution." is obvious nonsense too. If I put a nail in some copper sulphate solution the iron reduces the Cu++ ions to Cu metal. If I do the same with a solution of silver nitrate I get metallic silver. I can use Al instead of iron but, unless I remove the oxide film from the Al, it won't work very well. One way to remove that oxide is to dissolve it in an alkali like hot sodium carbonate solution. I might have to stand corrected here. Further reading about this bicarbonate/Al method reveals that the silver and the aluminium have to touch. So it appears that this process is meant to be electrolytic rather than purely chemical, as I have assumed from what I previously read about it. So I was on the right track when I said reducing silver sulphide to silver metal would work if you made the silver item the cathode in an electrolytic cell. In which case the afore mentioned reaction that I said was invalid could be appropriately split into the two seperate components (one at the cathode and one at the anode) such that it makes sense practically. The seperate reactions would be something like this: 4Al(s) + 6H2O -> 6Ag(s) + 2Al2(OH)3(s) + 3H2 + 12e 6Ag2S(s) + 12Na-(aq) + 12e -> 12Ag(s) + 12Na2S(aq) " This is usually the correct way of representing electrolytic chemcial reactions. Edited December 11, 2011 by Greg Boyles
John Cuthber Posted December 11, 2011 Posted December 11, 2011 "Well I did read something about semi covalent bonding between silver and sulphide ions in silver sulphide so you may actually be right in saying that the regular household ammonia is not strong enough to break that bond and dissolve the silver sulphide." I'm right; not because you read something, but because I'm right. The reason I know it's right is that I tried it. "And by the way John......as far as dipping your silver wire in ammonia....... Coke and ammonia removes the tarnish from 1c and 2c pieces, but you usually have to leave them in it over night to notice any difference." Are these coins silver or is your point irrelevant? If you watch the vid (or any of loads like it) you will see that this "2Al(s) + 3Ag2S(s) + 6H2O -> 6Ag(s) + 2Al2(OH)3(s) + 3H2S(aq) " is a perfectly valid equation (apart from the messed up formula). I have news for you. Both silver and aluminium are electrical conductors, so the transfer of electrons from Al to Ag+ ions can take place just fine. Anyway there are a series of reactions, but the overall result might as well be 3Ag2S +Al --> Al2S3 +3 Ag and Al2S3 +3 H2O --> Al2O3 + 3 H2S Al2O3 +2 OH- +H2O -->2 Al(OH)4 - H2S + Na2CO3 ---> CO2 + H2O + Na2S but that reaction isn't anything like complete- the reaction mixture smells of H2S when you do this experiment. Now, perhaps you could explain why it was that you started to argue without actually finding out what the facts were?
Greg Boyles Posted December 11, 2011 Posted December 11, 2011 "Well I did read something about semi covalent bonding between silver and sulphide ions in silver sulphide so you may actually be right in saying that the regular household ammonia is not strong enough to break that bond and dissolve the silver sulphide." I'm right; not because you read something, but because I'm right. The reason I know it's right is that I tried it. "And by the way John......as far as dipping your silver wire in ammonia....... Coke and ammonia removes the tarnish from 1c and 2c pieces, but you usually have to leave them in it over night to notice any difference." Are these coins silver or is your point irrelevant? The point is that your silver wire test, that you presumably conducted in response to my post, may be inadequate to draw the conclusion that it does not work. Household ammonia works only very slowly on copper coins, as it would on tarnished silver, and you would need more than 5 minutes treatment to see if it really works or not on silver. Might also work better and a little faster if you heated the cloudy ammonia a little. As for the Al foil bicarbonate treatment, I was not familiar with the process until it was brought up in here. I can only go on what people have written about it online and clearly many of them are not properly educated chemists and don't really understand how the process works. Hence their documentation of the method is inadequate and does not credibly explain how it works to some one like me who is educated to some extent in chemistry. That last website I found, where the silver and Al must touch, was the only one they gave me the clue that the process is electrolytic rather than chemical. And as an basically educated chemist that reaction involving reduction of silver sulfide to silver metal does not make sense in terms of the way that the method is described on most websites I looked at. It only makes sense in terms of an electrolytic process which that chemical reaction gives no clue about. Electrolytic chemical reactions are usually represented by the seperate half reactions at each electrode and not by a combined chemical reaction. As far as I can see the H2S would not be generated directly by the process anyway. Al would cause H2 to be released from the water as it dissolves and the sulphide ions would combine with the sodium ions in the bicarbonate. Sulphide ion is a weak base and a proportion would draw off H ions from water molecules to generates a small amount of H2S and leave behind more hydroxide ions. The silver item forms the cathode and only one chemical reaction can occur at each electrode at a time. At the cathode it is reduction of silver ions. Generation of H2S at the cathode represents a seperate reaction that would require the combining of sulfide ions with hydrogen ions, however the electrolyte in this case is alkaline and contains hydroxide ions rather than hydrogen ions. I know this because I used to make rotten egg gass bombs at high school - dust steel wool with sulfur dust and then set fire to it, this creates iron sulfide, then you soak this in a little dilute acid and small amounts of H2S are generated. So even if the silver reduction part of that equation is valid in terms of an electrolytic process, the direct generation of H2S is not valid given that the electrolyte is alkaline.
John Cuthber Posted December 12, 2011 Posted December 12, 2011 The following statements in your posts are factually incorrect 1 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. 2 So in other words ammonia is enough to remove the tarnish from both silver and copper based alloys. 3 As far as the formation of complex ions goes, it is irrelevant how soluble the simple salt is to begin with, whether it is silver sulphide or silver chloride. 4 Ammonia would work at least as well as aodium bicarbonate if not better. 5 Silver carbonate is as insoluble as silver sulphide so I am dubious as to how effective it would be in removing tarnish anyway. 6 With ammonia, the silver ammino sulphide that is formed is completely soluble in water 7 For starters solid Al and insoluble Ag2S cannot chemically interact directly unless the Al was in the form of vapour. 8 Secondly, in preparation of this home made solution, the Al is already disolved in the bicarbonate solution before it is applied to the silver. 9 If this solution works then there is clearly some sort of ion substitution occuring between the Ag2S and the Na[Al(H2O)2(OH)4] 10 As far as I have ever known and according to this from Wikipedia there is NO distinguishing between the relative solubilities of silver halides - they are all regarded as insoluble period. 11 John it is utterly impossible for the aluminium foil or the aluminium saucpan to reduce the silver sulphide to silver metal. 12 The only way that can happen is if the reductant (aluminium) is in solution. 13 So reduction of silver sulphide is CLEARLY not the mechanism here. 14 The only way that could happen is if the Al is in the form of vapour at extremely high temperatures, no doubt enough to melt the silver. 15 As far as I can see the H2S would not be generated directly by the process anyway. 16 So even if the silver reduction part of that equation is valid in terms of an electrolytic process, the direct generation of H2S is not valid given that the electrolyte is alkaline. Since, as you said " I was not familiar with the process until it was brought up in here." perhaps you should have learned more and typed less. And, btw, I'm sure that anyone who reads this will come to their own conclusion about to whom the phrase " Sorry buddy but your chemistry is some what 'rusty'. applies."
Greg Boyles Posted December 12, 2011 Posted December 12, 2011 The following statements in your posts are factually incorrect 1 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. 2 So in other words ammonia is enough to remove the tarnish from both silver and copper based alloys. 3 As far as the formation of complex ions goes, it is irrelevant how soluble the simple salt is to begin with, whether it is silver sulphide or silver chloride. 4 Ammonia would work at least as well as aodium bicarbonate if not better. 5 Silver carbonate is as insoluble as silver sulphide so I am dubious as to how effective it would be in removing tarnish anyway. 6 With ammonia, the silver ammino sulphide that is formed is completely soluble in water 7 For starters solid Al and insoluble Ag2S cannot chemically interact directly unless the Al was in the form of vapour. 8 Secondly, in preparation of this home made solution, the Al is already disolved in the bicarbonate solution before it is applied to the silver. 9 If this solution works then there is clearly some sort of ion substitution occuring between the Ag2S and the Na[Al(H2O)2(OH)4] 10 As far as I have ever known and according to this from Wikipedia there is NO distinguishing between the relative solubilities of silver halides - they are all regarded as insoluble period. 11 John it is utterly impossible for the aluminium foil or the aluminium saucpan to reduce the silver sulphide to silver metal. 12 The only way that can happen is if the reductant (aluminium) is in solution. 13 So reduction of silver sulphide is CLEARLY not the mechanism here. 14 The only way that could happen is if the Al is in the form of vapour at extremely high temperatures, no doubt enough to melt the silver. 15 As far as I can see the H2S would not be generated directly by the process anyway. 16 So even if the silver reduction part of that equation is valid in terms of an electrolytic process, the direct generation of H2S is not valid given that the electrolyte is alkaline. Since, as you said " I was not familiar with the process until it was brought up in here." perhaps you should have learned more and typed less. And, btw, I'm sure that anyone who reads this will come to their own conclusion about to whom the phrase " Sorry buddy but your chemistry is some what 'rusty'. applies." OK John, will you be gracious enough to concede that some of your assertions about ammonia were also factually incorrect. http://www.silversmithing.com/care.htm <A href="http://www.silversmithing.com/index.htm">Silver Care Salt Shaker Corrosion Those crusty corrosion marks on and in your salt shaker can be a real annoyance. One way to avoid this problem from the very start is to empty the shaker after a dinner party and thoroughly wash it; this way the salt doesn't have time to do its damage. Heavily gold plating the interior is the only other way to preserve the finish because gold is impervious to the effects of salt. It is still wise to clean out the shaker at least twice a year and inspect the plate to make sure it has not been abraded by the salt. There is a simple way to remove the corrosion yourself. Do this in a well-ventilated area and with nitrile gloves since you will be using ammonia. (Silver dips will not perform as well as ammonia.) If you are removing corrosion from a salt shaker, pour ammonia into a container, place the shaker inside, and cover the container. Let the shaker sit for ten minutes, then remove from the container and inspect. If the black corrosion spots remain, place the shaker back in and let stand for another ten minutes and inspect again. If the corrosion is not gone after 30 minutes, have the shaker professionaly refinished.
Externet Posted December 13, 2011 Author Posted December 13, 2011 Thanks, gentlemen. Perhaps I should re-touch the original post; my curiosity is around which of the proposed chemicals -sodium carbonate -sodium bicarbonate, -sodium hexametaphosphate, -sodium chloride, -a combination of which, -or another simple compound does a better job in cleaning silver tarnish by sulphide, not by table salt and/or optimal proportions of them to set aside what seems more empirical than science. The original (and similar video) that triggered the use of this method maaany years ago is from Haley's hints : ----> http://www.youtube.com/watch?v=Fg9skPKr5xc And now, visiting my family overseas, water softener (sodium hexametaphosphate ?) is not available locally. So trying to do it with other compounds that could produce as good results as possible, reading other articles in the same subject there is opinions of other chemicals performing equally? well. Even found someone saying that ClNa alone also works ; and being the aluminium and heat the important items for the performance that transfers the tarnish from the silver to the aluminium. Of course understanding the principle of the reaction is also interesting. Thanks again.
Greg Boyles Posted December 13, 2011 Posted December 13, 2011 Thanks, gentlemen. Perhaps I should re-touch the original post; my curiosity is around which of the proposed chemicals -sodium carbonate -sodium bicarbonate, -sodium hexametaphosphate, -sodium chloride, -a combination of which, -or another simple compound does a better job in cleaning silver tarnish by sulphide, not by table salt and/or optimal proportions of them to set aside what seems more empirical than science. The original (and similar video) that triggered the use of this method maaany years ago is from Haley's hints : ----> http://www.youtube.c...h?v=Fg9skPKr5xc And now, visiting my family overseas, water softener (sodium hexametaphosphate ?) is not available locally. So trying to do it with other compounds that could produce as good results as possible, reading other articles in the same subject there is opinions of other chemicals performing equally? well. Even found someone saying that ClNa alone also works ; and being the aluminium and heat the important items for the performance that transfers the tarnish from the silver to the aluminium. Of course understanding the principle of the reaction is also interesting. Thanks again. If you read that web page it states clearly that ammonia takes care of both forms of silver corrosion, the crsuted form caused by sodium chloride and the black form consisting of silver sulfide.
John Cuthber Posted December 13, 2011 Posted December 13, 2011 I concede that it "takes care" of silver suphide by saying that it doesn't really work "If the black corrosion spots remain, place the shaker back in and let stand for another ten minutes and inspect again. If the corrosion is not gone after 30 minutes, have the shaker professionaly refinished."
Greg Boyles Posted December 13, 2011 Posted December 13, 2011 (edited) I concede that it "takes care" of silver suphide by saying that it doesn't really work "If the black corrosion spots remain, place the shaker back in and let stand for another ten minutes and inspect again. If the corrosion is not gone after 30 minutes, have the shaker professionaly refinished." Well the experts seem to think that ammonia does take care all but severe sulfide based silver corrosion. That makes all your relative solubility of silver halides and silver sulfide effecting whether or not the silver can form complex silver ammino ions with ammonia a load of nonsense. Which makes you as stubborn as I concede I can be! If the sulfide corrosion is severe enough for ammonia not work then it is highly likely that the bicarbonate aluminium method will not remove it either and you would still have to get it done professionally. Edited December 13, 2011 by Greg Boyles
John Cuthber Posted December 13, 2011 Posted December 13, 2011 (edited) Ho Hum. I have two choices here. I can believe the evidence of my own observation. The tarnished bit of silver wire is still sitting in the ammonia, and it's just as tarnished as it ever was. Or I can believe the website you quoted as being "expert". Call me cynical but since I see that what they are saying seems not to be true, I wonder why they are saying it. Well, lets analyse what they are saying, and who they are. The site is silversmithing.com. It's the association of silversmiths. What they say is "if your silver needs cleaning then we suggest you try soaking it in snake oil,and, if that doesn't work, sending it to use so we can charge you for the privilege of cleaning it." Do you have any idea how long I agonised over deciding what to believe. So, "That makes all your relative solubility of silver halides and silver sulfide effecting whether or not the silver can form complex silver ammino ions with ammonia a load of nonsense." or it makes them mistaken (or worse), and the bit of wire shows which interpretation is correct. "Well the experts seem to think that ammonia does take care all but severe sulfide based silver corrosion." they are plainly not experts, if they were then I would have a nice shiny bit of wire by now. So this "If the sulfide corrosion is severe enough for ammonia not work then it is highly likely that the bicarbonate aluminium method will not remove it either and you would still have to get it done professionally. " is also plainly hogwash, because it doesn't work with fairly mild tarnishing. Incidentally, if you knew enough chemistry to comment usefully on this topic you would have looked up a few bits of data. Solubility product: Ksp(Ag2S, 25 °C)= 6.69x10−50. and What is the Equilibrium constant of Ag (NH3) 2+? Ag(NH3)2+ 1.67 x 10+ 7.223 stability constant I will leave it to you to work out how those data (and a few sensible assumptions) explain why silver sulphide does not, and never will, dissolve in household ammonia. Being stubborn is only good if you are right. Edited December 13, 2011 by John Cuthber
Greg Boyles Posted December 13, 2011 Posted December 13, 2011 (edited) Ho Hum. I have two choices here. I can believe the evidence of my own observation. The tarnished bit of silver wire is still sitting in the ammonia, and it's just as tarnished as it ever was. Or I can believe the website you quoted as being "expert". Call me cynical but since I see that what they are saying seems not to be true, I wonder why they are saying it. Well, lets analyse what they are saying, and who they are. The site is silversmithing.com. It's the association of silversmiths. What they say is "if your silver needs cleaning then we suggest you try soaking it in snake oil,and, if that doesn't work, sending it to use so we can charge you for the privilege of cleaning it." Do you have any idea how long I agonised over deciding what to believe. So, "That makes all your relative solubility of silver halides and silver sulfide effecting whether or not the silver can form complex silver ammino ions with ammonia a load of nonsense." or it makes them mistaken (or worse), and the bit of wire shows which interpretation is correct. "Well the experts seem to think that ammonia does take care all but severe sulfide based silver corrosion." they are plainly not experts, if they were then I would have a nice shiny bit of wire by now. So this "If the sulfide corrosion is severe enough for ammonia not work then it is highly likely that the bicarbonate aluminium method will not remove it either and you would still have to get it done professionally. " is also plainly hogwash, because it doesn't work with fairly mild tarnishing. Incidentally, if you knew enough chemistry to comment usefully on this topic you would have looked up a few bits of data. Solubility product: Ksp(Ag2S, 25 °C)= 6.69x10−50. and What is the Equilibrium constant of Ag (NH3) 2+? Ag(NH3)2+ 1.67 x 10+ 7.223 stability constant I will leave it to you to work out how those data (and a few sensible assumptions) explain why silver sulphide does not, and never will, dissolve in household ammonia. Being stubborn is only good if you are right. Perhaps your household ammonia is too old and has lost most of its strength or perhaps a small amount of heat would advance things. 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. CHEMICAL CLEANINGThe majority of silver objects recovered from archaeological contexts require only limited treatment. 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. For base silver with copper corrosion compounds, concentrated ammonia effectively cleans all copper compounds from the silver. Care must be taken, however, because ammonia dissolves silver chloride and will substantially weaken badly corroded silver. A solution of 5-30 percent formic acid in de-ionized water is effective for dissolving copper compounds without affecting silver chlorides. Formic acid can also be used to brighten silver that has already been cleaned with another chemical or technique. Metallic copper films can be removed with a silver nitrate solution. In general, however, simple washing in soapy water or rubbing the silver object with a mild polishing abrasive is usually sufficient. First of all, ammonia added to your silver polish will remove some of the spotting far better than just using silver polish. I found this tip in a book of old formulas and it does work! 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. Apparatus and chemicals Eye protection for the teacher Round- or flat-bottomed flask, 1 dm3 (see note 1) Rubber stopper, to fit flask Beaker (250 cm3) Measuring cylinders (25, 100 and 250 cm3) Dropping pipette Glass rod Access to a fume cupboard (for handling '880' ammonia solution) The quantities listed below are sufficient for three demonstrations: Silver nitrate (Corrosive, Dangerous for the Environment), 8.5 g Potassium hydroxide (Corrosive), 11.2 g Glucose (dextrose), (Low hazard), 2.2 g '880' Ammonia solution (35% w/v) (Corrosive, Dangerous for the Environment), 30 cm3 Concentrated nitric acid (Oxidising, Corrosive), 100 cm3 Purified (distilled or deionised) water, 800 cm3 Technical notes Silver nitrate (Corrosive, Dangerous for the Environment) Refer to CLEAPSS Hazcard 87 Potassium hydroxide (Corrosive) Refer to CLEAPSS Hazcard 91 Ammonia solution (‘880’ or 35% w/v) (Corrosive, Dangerous for the Environment) Refer to CLEAPSS Hazcard 6 Concentrated nitric acid (Oxidising, Corrosive) Refer to CLEAPSS Hazcard 67 Interesting huh John Cuthber? Was reading and found that silver iodide wont dissolve in ammonia solution. But I also found this that states that the solubility of silver iodide in water can be signficantly increased by heating the water.....pretty standard chemistry. 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. Best Answer - Chosen by Voters _____Solubility and temperature Ksp AgI at 25C = 8.3 x 10-17 = [Ag+][i-] = x^2 moles/liter SOLVE for x moles AgI = 1E-4 g AgI / MW AgI g/mole = ?? liter more water = [moles AgI / x moles/liter] - 1.0 liter = ?? ln (Ksp) = -dG/RT SOLVE for dG Ksp @ higher T = K2 = (0.001g AgI/MW AgI g/mole)^2 ln(K2/K1) = -- dG/R (1/T2 - 1/T1) SOLVE for T2 Basic mathematics is a prerequisite to chemistry – I just try to help you with the methodology of solving the problem. Source(s): HBC&P 66th : Solubility AgI = 2.8 x !0-7.27 @ cold water Solubility AgI = 2.5 x 10-6.6 @ hot water Edited December 13, 2011 by Greg Boyles
John Cuthber Posted December 14, 2011 Posted December 14, 2011 The longer you spend trying to defend this silly idea the sillier you will look.
Greg Boyles Posted December 14, 2011 Posted December 14, 2011 The longer you spend trying to defend this silly idea the sillier you will look. There are rather a lot of industry professionals who also seem to think that ammonia is able to clean the tarnish from silver John. So perhaps you need to take a look at yourself and how silly you might seem.
swansont Posted December 14, 2011 Posted December 14, 2011 ! Moderator Note Let's not let this get off track, please. Keep it civil.
John Cuthber Posted December 14, 2011 Posted December 14, 2011 (edited) I will stick a few numbers in the quote for easy reference. 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. Edited December 15, 2011 by John Cuthber
Chemistoftheelements Posted December 26, 2011 Posted December 26, 2011 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 Posted December 27, 2011 Posted December 27, 2011 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? -3
swansont Posted December 30, 2011 Posted December 30, 2011 ! Moderator Note Since the pettiness and sniping has not stopped, I am closing this
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