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Author: Subject: Silver Nitrate Synthesis
Chemateur80
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[*] posted on 17-12-2017 at 11:41


I have also seen a video by Chemplayer on Youtube where they dissolve AgCl in aqueous ammonia, creating a water soluble silver complex.
This complex is then reduced using sodium dithionate (Na2S2O4).
They prepare the dithionite from sodium bisulfate and zink.
2NaHSO3 + Zn → Na2S2O4 + Zn(OH)2

Could this be the best way to go from AgCl, if I want to avoid precipitating silver with copper?

Using copper seems to be the easiest thing to do, but I'm concerned that copper particles will contaminate the precipitated silver. Most impurities could be washed from the silver with f ex dilute H2SO4/HCl and acetone, but not copper. How big is this problem?
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[*] posted on 18-12-2017 at 22:11


I've done it several times this way with great success, always obtaining a perfectly white sparkling shiny product:
http://forum.lambdasyn.org/index.php/topic,288.0.html
Freely translated:
0.46mol 99.99% silver nuggets bought OTC from a local goldsmith are dissolved in 0.56mol excess boiling pure aqueous HNO3* (some heating applied),
HNO3 is evaporated on hotplate until temperature reaches 200°C to remove excess HNO3, after cooling to room temperature the AgNO3 is crushed in a little abs. EtOH and then filtered .
Filtercake was washed with more cold EtOH to remove any small traces of acid and EtNO3 and product dried in a dessicator over techn. CaCl2 to obtain very pure snow white cristalline AgNO3 with a yield of more than 95%

(drying open by uncleaned undried air with lead to less pure greyish product, AgNO3 is extremly sensitive to dust and halide-ions, especially when exposed to sunlight)

If you're not rinsing with EtOH the product will smell slightly like EtNO3. If silver contains a little Cu product will become blueish over the time, as a Cu(NO3)2*2H2O will be formed

I recommend to use lab/pharma-grade OR freshly destilled EtOH or IPA instead of technical acetone for washing, no matter if you will loose 1-3% yield, as technical acetone is usually very dirty, causing side reactions (and grey product) when drying the AgNO3
EtOH also can be easily removed over CaCl2 in a dessiccator

*If you're using homemade fuming nitric acid (which does only react very slowly with Ag if water content <10%) you can mix Ag and HNO3 and then add up to 40mL destilled water in 10mL portions to get a very smooth reaction


[Edited on 19-12-2017 by EilOr]
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Chemateur80
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[*] posted on 11-1-2018 at 08:06


I decided to precipitate the Ag with Cu.
Cu-wire was cleaned with distilled water and acetone, and then added to two beakers with my AgNO3/Cu(NO3)2.
The pH in the beakers was around 2, so I guess there was HNO3 left.
In one beaker the solution was quite concentrated, and here all of the Ag precipitated quite fast. Some NO2 was produced.
Testing the solution with NaCl gave no precipitate, so I filtered off the Ag and washed it with dH2O, acetone and ethanol.
I dried the Ag-powder in an oven until the weight stabilized.

The solution in the other beaker was more dilute, and it was harder to precipitate the Ag. Testing with NaCl gave a precipitate of AgCl, even after a few days. I boiled the solution down a bit and added copper again, and more Ag formed.

After filtering and drying all the precipitated Ag I ended up with around 78g. This is more than the theoretical yield, since I dissolved around 76g in HNO3.
A bit weird, but I realized that my scale wasn't very accurate. That could explain the yeild.
Could the Ag be contaminated with Cu? The Cu-wire was quite corroded after the precipitation step. Maybe small copper particles are mixed in with the silver. They are not visible though.

What purity of Ag can you typically expect after this kind of reaction?

When precipitating Ag with Cu, what pH would be optimal? Should I adjust it if too much HNO3 is left?

How does the concentration of the solution affect f ex particle size and effectiveness of precipitation?
It would be bad if a lot of the Ag precipitates as very small particles that make it past the filter. On the other hand, I don't want to wait too long before precipitation is complete. Trial and error?

I'm thinking of converting the Ag to AgnO3, but the question is how pure this Ag is.
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[*] posted on 11-1-2018 at 17:39


If you redisolve your Ag in Nitric, it will be obvious if any Cu is present due to colour. If you cast your Ag into a solid block and then refine by electrolysis you will arrive at up to 5N Ag. then you can make your nitrate.



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[*] posted on 12-1-2018 at 08:42


Quote: Originally posted by diddi  
If you redisolve your Ag in Nitric, it will be obvious if any Cu is present due to colour. If you cast your Ag into a solid block and then refine by electrolysis you will arrive at up to 5N Ag. then you can make your nitrate.


I was planning to dissolve a small sample of my Ag in HNO3 to see if any blue colour is visible.
However, I don't know how much Cu-contamination is required to actually see it. If no colour can be seen, is the Ag then 99% pure? Or 99,9? Etc.
Good enough for making quite pure AgNO3?
I'd like to avoid electrolysis and just use chemistry.


[Edited on 12-1-2018 by Chemateur80]
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[*] posted on 12-1-2018 at 08:46


How about washing the silver with a mix of HCl and H2O2?
Will it help to get rid of copper without affecting the silver powder at all?
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[*] posted on 12-1-2018 at 11:15


Hydrogen peroxide will oxidize both silver and HCl. Probably not a good plan. AgCl is also soluble in hydrochloric acid.

Ferric sulfate might work, if I'm interpreting the standard electrode potentials right.




[Edited on 04-20-1969 by clearly_not_atara]
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[*] posted on 15-1-2018 at 08:30


Quote: Originally posted by clearly_not_atara  
Hydrogen peroxide will oxidize both silver and HCl. Probably not a good plan. AgCl is also soluble in hydrochloric acid.

Ferric sulfate might work, if I'm interpreting the standard electrode potentials right.


I thought that the reaction of H2O2 with HCl was rather slow. The mixture is used for etching for example.
If copper is present, wouldn't it be attacked before the silver?
And if the peroxide/acid mix is diluted, does it still attack silver?

How would ferric sulfate work?
Something like this? https://chemistry.stackexchange.com/questions/21685/does-iro...
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[*] posted on 15-1-2018 at 15:57


I do not know the specifics of the HCl/H2O2 rxn. I know it is much slower than the reaction with HBr, and I know silver is more easily oxidized in the presence of chloride.

Ferric sulfate solution may oxidize copper to soluble copper sulfate but sulfate is a poor ligand for silver. Again I don't know the specifics but the half cell for Ag+/Ag > Fe3+/Fe2+ > Cu2+/Cu which is promising imo.

Edit: looks like you need FeCl3, I'd go with that.

[Edited on 15-1-2018 by clearly_not_atara]




[Edited on 04-20-1969 by clearly_not_atara]
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[*] posted on 16-1-2018 at 06:43


Quote: Originally posted by clearly_not_atara  
I do not know the specifics of the HCl/H2O2 rxn. I know it is much slower than the reaction with HBr, and I know silver is more easily oxidized in the presence of chloride.

Ferric sulfate solution may oxidize copper to soluble copper sulfate but sulfate is a poor ligand for silver. Again I don't know the specifics but the half cell for Ag+/Ag > Fe3+/Fe2+ > Cu2+/Cu which is promising imo.

Edit: looks like you need FeCl3, I'd go with that.

[Edited on 15-1-2018 by clearly_not_atara]


Interesting. I've never seen the FeCl3-method before in silver refining. Are there any references?
I don't want to contaminate my silver with even more metals if I can avoid it.

Anyway, I dissolved about 0,1g of Ag-powder in a few drops of HNO3 and dH2O in a test tube. It dissolved quite fast and crystals of AgNO3 started to precipitate out. When all the silver had dissolved I added a few drops of water and the AgNO3 dissolved. A clear solution was obtained. No visible blue colour from copper salts.
This, of course, only tells me that there is not enough copper to actually see it.
Is my silver actually quite pure? Pure enough for making good AgNO3?

Even if there is some copper left, maybe I can get rid of it when crystallizing AgNO3? I've searched for solubility of Cu(NO3)2 in different solvents, but haven't found much.
Does anyone know of a good solvent to separate the two?
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[*] posted on 16-1-2018 at 21:21


I might be able to answer you if you can express why you think that copper contamination would be a problem? If you simply recrystallize AgNO3 it should be clean enough for "most" practical purposes, but if you're trying to do something where you need absolutely copper-free silver nitrate then you might need to use a different technique.

Actually I should have realized this earlier but you can't actually "wash" copper out of silver in its metallic state, because any "etchant" that you use will not penetrate the metal. So trying to dissolve only copper and not silver is a dead end.

As a simple test for Cu2+ you can take advantage of the fact that AgF is soluble in water while CuF2 is not (0.075 g / 100 mL), so adding a few drops of your nitrate solution to a solution of fluoride salts will precipitate copper fluoride if there is significant copper contamination. Fluoride is IIRC the only anion with this property, and this method will only exclude copper to about 1% or so.

To completely get rid of copper I guess you can precipitate AgCl, reduce to the metal and re-dissolve as silver nitrate -- kind of annoying, but it might be worth it depending on your requirements.




[Edited on 04-20-1969 by clearly_not_atara]
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[*] posted on 18-1-2018 at 07:30


Quote: Originally posted by clearly_not_atara  
I might be able to answer you if you can express why you think that copper contamination would be a problem? If you simply recrystallize AgNO3 it should be clean enough for "most" practical purposes, but if you're trying to do something where you need absolutely copper-free silver nitrate then you might need to use a different technique.

Actually I should have realized this earlier but you can't actually "wash" copper out of silver in its metallic state, because any "etchant" that you use will not penetrate the metal. So trying to dissolve only copper and not silver is a dead end.

As a simple test for Cu2+ you can take advantage of the fact that AgF is soluble in water while CuF2 is not (0.075 g / 100 mL), so adding a few drops of your nitrate solution to a solution of fluoride salts will precipitate copper fluoride if there is significant copper contamination. Fluoride is IIRC the only anion with this property, and this method will only exclude copper to about 1% or so.

To completely get rid of copper I guess you can precipitate AgCl, reduce to the metal and re-dissolve as silver nitrate -- kind of annoying, but it might be worth it depending on your requirements.


I really appreciate the help, and I suppose I just like the idea of getting the Ag/AgNO3 as pure as possible, within reason.
Of course I could buy pure silver and dissolve in nitric acid, but I wanted to convert coins/jewelry into pure silver nitrate as efficiently as possible using just chemistry.
Since there are a few different methods I'd like to find the most efficient one.
If I have any contamination I guess it would be mostly copper, since I used that to precipitate the silver. I suppose there could be other metals as well, such as zinc and aluminium from the coins.
However, these metals should not precipitate out with the silver when copper is added.

I do have NaF, so I could add a small amount of that to a small amount of an AgNO3 solution.

I thought about the AgCl-method, but of course, it's more work, and maybe I'll lose more silver using that.

Copper nitrate and silver nitrate are both very soluble in water, so how efficient would a recrystallization be? How would I do that?
How about adding a solvent that makes the silver nitrate crash out, while any copper nitrate left stays in solution? I haven't found any good solvent for that though.


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[*] posted on 18-1-2018 at 07:43


Yesterday I dissolved 1g of my silver nitrate in a small amount of HNO3/dH2O. Still no sign of blue colour.
The solution has a faint yellowish colour to it, and there are quite a lot of small particles floating around.
The yellow colour could be dissolved NO2, but what about the particles?
I used clean glassware, pure HNO3 and dH2O.

My guess is that the particles could be from when I filtered the silver metal. I used paper filters and maybe some fibers and other pieces of paper came off.
These could stain my AgNO3 black when they get oxidized.

After making the AgNO3-solution, could I get rid of them by filtering the solution through a fritted glassfilter, or should I even use very fine silicon dioxide? SiO2 shouldn't react with AgNO3 or HNO3.
Any other ideas?
I really want to avoid having those particles in the dry silver nitrate.

[Edited on 18-1-2018 by Chemateur80]
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[*] posted on 18-1-2018 at 08:58


It's possible the particles you observed are elemental silver, as AgNO<sub>3</sub> decomposes on exposure to light. Try adding a drop of nitric acid and see if they dissolve.

What is your ultimate goal with this project? Silver nitrate for other experiments? Silver metal for sale? I get the feeling you're going a little overboard on purity concerns for an amateur setting. But that depends on your ultimate end product and it's planned use.
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[*] posted on 18-1-2018 at 09:54


Quote: Originally posted by MrHomeScientist  
It's possible the particles you observed are elemental silver, as AgNO<sub>3</sub> decomposes on exposure to light. Try adding a drop of nitric acid and see if they dissolve.

What is your ultimate goal with this project? Silver nitrate for other experiments? Silver metal for sale? I get the feeling you're going a little overboard on purity concerns for an amateur setting. But that depends on your ultimate end product and it's planned use.


The solution hasn't been exposed to any daylight, but maybe you're right. So even silver nitrate in solution is reduced to elemental silver? Not just the dry powder?
I'll add some drops of nitric acid to see if anything dissolves.
The particles look more like dust though, and they're not heavy and sinking to the bottom immediately as silver metal would.
I definitely want to filter the silver nitrate solution somehow, without using filter papers.

Maybe I'm a bit overboard, but I like the idea of getting it reasonably pure :)
I enjoyed the method of precipitating silver with copper though. Beautiful silver crystals forming in the deep blue solution. It would have been even better if there would have been less nitric acid left. A lot of the silver turned cementlike because of that.
I've seen your videos with the silver tree and silver melting. Very nice.
It would be fun to melt some of the silver, but I don't think I have the equipment for that.

The goal with this project is to try and find the most efficient way to make pure silver nitrate from impure silver.
I guess I just like the feeling of having a whole bunch of pure silver nitrate that I've made myself. Kind of like element collectors that want really pure samples.
I do plan to use the silver nitrate for experiments, and maybe it doesn't need to be superpure for those.
Things like silver mirror, making other silver salts and maybe a little silver acetylide.
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[*] posted on 18-1-2018 at 10:52


From your description it sounds like the best plan is to precipitate the silver as the bromide, dissolve in ammonia and reduce with glucose. If you want very high purity, you'll always sacrifice some yield to get it. Chloride/acetate will also precipitate silver but slightly less efficiently.



[Edited on 04-20-1969 by clearly_not_atara]
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[*] posted on 18-1-2018 at 11:17


Thanks! Glad you liked the videos. It's a very beautiful experiment.

Regarding silver particles, you said you dissolved some silver nitrate in water then observed particulate. I assumed decomposition while you were storing it as a solid. Supposedly it's near-impossible to get pristine white silver salts, I've heard.

Although interestingly I did just find this reference:
https://www.chemicalbook.com/ChemicalProductProperty_EN_CB22...
Quote:
Pure silver nitrate crystal is stable to light and is easily to be reduced to black metallic silver in the presence of organic matter. Wet silver nitrate and silver nitrate solution can be easily subject to decomposition upon light.
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[*] posted on 9-4-2018 at 05:39


Quote: Originally posted by MrHomeScientist  
Thanks! Glad you liked the videos. It's a very beautiful experiment.

Regarding silver particles, you said you dissolved some silver nitrate in water then observed particulate. I assumed decomposition while you were storing it as a solid. Supposedly it's near-impossible to get pristine white silver salts, I've heard.

Although interestingly I did just find this reference:
https://www.chemicalbook.com/ChemicalProductProperty_EN_CB22...
Quote:
Pure silver nitrate crystal is stable to light and is easily to be reduced to black metallic silver in the presence of organic matter. Wet silver nitrate and silver nitrate solution can be easily subject to decomposition upon light.


Ah, sorry. I meant I dissolved 1g of silver metal in a small amount of nitric acid.

No blue colour, so I suppose that there isn't much copper there.
I also took a small amount of the silver nitrate solution and added a little NaF. No visible precipitate of CuF2.
Thanks for the tip clearly_not_atara.

I then played around a little and added NaHCO3. A yellow precipitate of Ag2CO3 formed.
I dissolved this again with some nitric acid and added a little NaCl. White AgCl formed, and to this I added some NaOH-solution. No reaction.
I suppose Ag2O only forms if the mix is heated.

So, maybe my silver metal is quite pure. However, I do see small, brown particles in the solution of AgNO3. They are not that heavy, but sink to the bottom if the solution is allowed to stand.
I'm guessing that the particles come from the filter paper.
They should be easy to filter off with a fritted glass filter when I decide to make some more AgNO3.
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