Chemical Forums
Chemistry Forums for Students => Inorganic Chemistry Forum => Topic started by: kailee33 on November 29, 2024, 05:56:39 AM
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Hi all, been searching the Internet for a while in creating K(AuCl4). The only real reference I could find was quite vague, 'Dissolve elemental gold in aqua regis in the presence of KCL. Looking for some input if possible?
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Okay so I found this which looks fairly straight forward, I guess my next question is to work out the percentage weight of each chemical required to produce the product without excess of either. (In reality I don't mind a small excess of potassium chloride, as long as its minimal).
As shown in Figures 8 and 6 and 7, the prior art provides a method of preparing potassium chloroaurate which is similar to the above-described prior art method for preparing sodium chloroaurate. The prior art method for preparing potassium chloroaurate is to treat the aqueous chloroauric acid solution with potassium chloride (KCl) or potassium carbonate (K 2 CO 3 ) at 100 ° C, and then evaporate, cool, crystallize and dry. The orange potassium chloroaurate crystal was obtained by treatment.
HAuCl 4 + KCl → KAuCl 4 + HCl (Formula 6)
2 HAuCl 4 +K 2 CO 3 →2 KAuCl 4 +H 2 O+CO 2 (Formula 7)
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I would choose KCl. If you use K2CO3 the solution could be at drag in to alcaline and gold oxide would precipitate. pH control is not easy and if you consumed all H+ then it's get dangerous to get to alcaline.
With KCl you can boil the solution and HCl evaporates.
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my next question is to work out the percentage weight of each chemical required to produce the product without excess of either
Not a good idea actually. Assuming just stoichiometric synthesis almost never works. In this case at best using stoichiometric amounts will make the dissolution slow at the end, but more likely there will be gaseous byproducts that will consume acids involved not letting them react with the gold itself.
You want excess of other reagents, to make sure you used and precipitated all gold, which is most expensive.
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I would choose KCl. If you use K2CO3 the solution could be at drag in to alcaline and gold oxide would precipitate. pH control is not easy and if you consumed all H+ then it's get dangerous to get to alcaline.
With KCl you can boil the solution and HCl evaporates.
Thanks Hunter, yeah, I had went ahead and ordered some HCL, really because I saw it used in the first aqua regia method. I believe this was an older method as you can produce the required HCL from the KCL to form Aqua Regia
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my next question is to work out the percentage weight of each chemical required to produce the product without excess of either
Not a good idea actually. Assuming just stoichiometric synthesis almost never works. In this case at best using stoichiometric amounts will make the dissolution slow at the end, but more likely there will be gaseous byproducts that will consume acids involved not letting them react with the gold itself.
You want excess of other reagents, to make sure you used and precipitated all gold, which is most expensive.
Any suggestions on a good starting point for weights? Also, would there be any way to precipitate out the KCL if I just go with a large excess?
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I believe this was an older method as you can produce the required HCL from the KCL to form Aqua Regia
I am starting to wonder if you should try this reaction, as it requires dealing with seriously dangerous reagents and apparently is way above your level of expertise.
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The dangerous part has already been done, the gold chloride has been made, I'm really just on the last step. I may not have the chemistry background but I do have a very technical background and research lots before anything practical. This particular step isn't very well documented hence the reason I have came here for some expert advice?
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So im now looking at solubility in diethyl ether, if im reading this correctly I can react the gold chloride with an excess of KCL. Then ether can be used to dissolve the KAuCl4 leaving the excess KCL as a solid which can be filtered off. Does this sound plausible?
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What is the solubility of KAuCl4 in Diethylether. Do you have a number.
But I don't think it's soluble. And if yes in water it would be more higher.
. .
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What is the solubility of KAuCl4 in Diethylether. Do you have a number.
But I don't think it's soluble. And if yes in water it would be more higher.
. .
I couldn't find specifics on how soluble but did find the following
Potassium gold chloride
Description
Yellow crystalline powder. Potassium gold cyanide is used in photography and paints for Porcelain and Glass.
Synonyms and Related Terms
potassium aurichloride; potassium chloroaurate; gold potassium chloride
Physical and Chemical Properties
Soluble in water, ethanol, ether.
Composition KAuCl4 - 2H2O
and KCL is described s practically insoluble in Diyethlether
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The same I also can find, but without ether.
And again it's high soluble in water. You never will get it transferred into ether.
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Even if I dry it? I have successfully dried AuCl4 to powder it using a vacuum chamber and low heat?
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There is no AuCl4. You have AuCl3 or better Au2Cl6. The other one is HAuCl4.This is existing as Trihydrate. HAuCl4 * 3 H2O. If you dry it decompose.
Drying and separation of two chemical is a different thing.
Check the solubilities of KCl and KAuCl4 and do fractional crystallisation in water.
PS For what you need the KAuCl4 by the way.
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Thank you very much for the help Hunter, I will read up on fractional crystallisation.
I use gold chloride on pottery. This is mixed with an organic binder & flux. But I find the shelf life is short, the gold seems to revert back to metallic Au after a couple of weeks. So I am looking at a more stable salt of gold for longer storage.
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I think for this purpose you don't need so pure compound. The removal of excess KCl is in my opinion not necessary.
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There is two routes I can take
The classic route in making a gold sulpho-resinate (Gold Salt + Sulphured resin)
Or the more modern route gold aryl mercaptide (Gold Salt + ethyl acetate + dimethylbenzenethiols + Polymer)
But I would prefer to work with more natural products
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I think for this purpose you don't need so pure compound. The removal of excess KCl is in my opinion not necessary.
Agreed, I would just like to minimise, hence why I was initially looking for approximate weights to use in the reaction, to keep excess potassium quite low
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So Stoichiometry calculation for 10g of KAuCl4 would require 8.99g of HAuCl4 + 1.97g of KCL so a ratio of 21.9% KCL.
To give minimal excess this could be 30%??
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Might as well tie the thread up with the complete formula, hopefully I've got it right :)
Au + 3HNO3 + 3HCl + KCl = KAuCl4 + 3NO2 + 3H2O
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Au + 3HNO3 + 3HCl + KCl = KAuCl4 + 3NO2 + 3H2O
Yes, this is correctly balanced, but slightly unrealistic. Reactions of the oxidation by concentrated nitric acid (which is not exactly a case here, but close) typically go through more than one pathway and produce more than one gaseous product. Details can depend on several others factor (like temperature, purity and concentration of the reagents used) - but the stoichiometry observed never exactly follows single reaction equation.
So yes, this is a good starting point, but what it really it tells is "if you use less reagents than this equation suggests you will fail". Finding correct excess is more or less guesswork and requires some trial and error experiments. I would start with something like 50%-100% excess of both acids. Plenty of chlorides in the solution (from HCl), so excess of KCl can be smaller - say 10% (doesn't mean it will be OK, that's just where I would start experimenting).
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I learned 40 years ago that Aqua Regia react in this way
3 HCl + HNO3 => NOCl + 2 H2O + 2 Cl* ( nasc)
Nitrosyl chloride NOCl and nascent Chlorine is developed.
There active chlorine radicals have the capability to dissolve the gold.
Au + 3 Cl* => AuCl3 => and this with more HCl gives H[AuCl4]
Also found on the german Wikipedia side
https://de.wikipedia.org/wiki/K%C3%B6nigswasser
The english one don't mentioned it???
https://en.wikipedia.org/wiki/Aqua_regia
Is there some new knowledge or the side is outdated?
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I learned 40 years ago that Aqua Regia react in this way
3 HCl + HNO3 => NOCl + 2 H2O + 2 Cl* ( nasc)
Nitrosyl chloride NOCl and nascent Chlorine is developed.
Definitely mechanism of Au dissolution by aqua regia, is not just a simple HNO3 oxidation. Feel free to develop an overall reaction from that. It won't change the situation - overall reaction only partially reflects the reality, nitrosyl chloride will most likely react further and decompose.
I didn't wrote
Reactions of the oxidation by concentrated nitric acid (which is not exactly a case here, but close)
without a reason.
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Au + 3HNO3 + 3HCl + KCl = KAuCl4 + 3NO2 + 3H2O
Yes, this is correctly balanced, but slightly unrealistic. Reactions of the oxidation by concentrated nitric acid (which is not exactly a case here, but close) typically go through more than one pathway and produce more than one gaseous product. Details can depend on several others factor (like temperature, purity and concentration of the reagents used) - but the stoichiometry observed never exactly follows single reaction equation.
So yes, this is a good starting point, but what it really it tells is "if you use less reagents than this equation suggests you will fail". Finding correct excess is more or less guesswork and requires some trial and error experiments. I would start with something like 50%-100% excess of both acids. Plenty of chlorides in the solution (from HCl), so excess of KCl can be smaller - say 10% (doesn't mean it will be OK, that's just where I would start experimenting).
Thank you Borek, the excess acid I'm used to, I have dissolved gold in aqua regia many times. Normally I start with excess HCL & calculated Nitric, when reaction slows/stops, add a little more nitric. Repeat until all gold has dissolved. Excess acid can easily be boiled off, then a few evaporation of water, leaving fairly pure HAuCl4
I just got a little worried about the quantity of KCl as I knew it wouldn't be as easy removing excess and wanted to keep the KAuCl4 of a fairly high purity. But I can do more practical experiments, keep notes on exact weights to find a good balance
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I learned 40 years ago that Aqua Regia react in this way
3 HCl + HNO3 => NOCl + 2 H2O + 2 Cl* ( nasc)
Nitrosyl chloride NOCl and nascent Chlorine is developed.
There active chlorine radicals have the capability to dissolve the gold.
Au + 3 Cl* => AuCl3 => and this with more HCl gives H[AuCl4]
Also found on the german Wikipedia side
https://de.wikipedia.org/wiki/K%C3%B6nigswasser
The english one don't mentioned it???
https://en.wikipedia.org/wiki/Aqua_regia
Is there some new knowledge or the side is outdated?
Thank you hunter, I will use this instead..
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I learned 40 years ago that Aqua Regia react in this way
3 HCl + HNO3 => NOCl + 2 H2O + 2 Cl* ( nasc)
Nitrosyl chloride NOCl and nascent Chlorine is developed.
Definitely mechanism of Au dissolution by aqua regia, is not just a simple HNO3 oxidation. Feel free to develop an overall reaction from that. It won't change the situation - overall reaction only partially reflects the reality, nitrosyl chloride will most likely react further and decompose.
I didn't wrote
Reactions of the oxidation by concentrated nitric acid (which is not exactly a case here, but close)
without a reason.
Agreed, for my purposes I am only really interested in one product since this is for more practical than theoretical purposes. But you have both been very kind in helping me understand the process in a deeper level, so thank you both. I have many more experiments ahead :)