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Author: Subject: Silver nitrate - green !!?? help
mario840
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sad.gif posted on 8-7-2011 at 09:41
Silver nitrate - green !!?? help


Helo, i made some silver nitrate from jewellery 92,5% Ag, the whole solution was green , i evaporate , pracipatates out silver nitrate impure with copper nitrate, i filtrated this , grren powder sometimes white , and made aqueous solution and add some copper plates to make pure silver, i must washed too little my silver but next reacting with 40% HNO3 gave much lighter green solution, this wet powder i want to dry more quickly in heating mantle but when i start heat my dish with "wet" AgNO3 it started to turn strong green colour, what's wrong with this chemical ? i must dry this in dessicant or one more make silver , wash more carefully and than make "white" powder AgNO3 ?
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not_important
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[*] posted on 8-7-2011 at 10:31


Green generally is from copper. Take the crude AgNO3, dry, then fuse in a ceramic container at 250 to 350 C, with stirring. Copper nitrate decomposes at that temperature, AgNO3 does not until 440 C or thereabouts. Cool, dissolve in distilled/deionised water, filter to remove CuO. Repeat if the solution has a blue tint.

Alternative is to ppt the silver as AgCl, wash with dilute HCl, reduce the AgCl with one of a number of reductants.

Use the search engine as this topic has been covered a number of times before.
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cyanureeves
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[*] posted on 8-7-2011 at 11:15


i think you should've melted the the silver you got when you added the copper plates. the blue color you got probably would've burned up. i'm surprised the silver wasnt pure enough, i always add table salt to the nitrated sterling when its all dissolved and watch it turn white then add hcl acid and drop zinc from a penny in the mix. the black sponge will also have traces of green color when dried but will burn up before the silver sponge melts. but i believe the method you used should yield cleaner silver.i think you just had a little copper nitrate in your silver fibers and wouldnt have survived a torch because it was not in a metallic state.
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Fleaker
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[*] posted on 15-7-2011 at 16:43


If you started from sterling, you can boil it with sodium formate to give you 99,99 fine silver.

Or precipitate copper as cement, rinse the silver crystal well, and redissolve it, then precipitate with base and add sugar.




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mario840
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[*] posted on 19-7-2011 at 03:14


After 2 times "getting" out silver from solution AgNO3 with copper plates , and once recrystallization from water and drying over P2O5 (NOT AIR IT TOOk FOREVER In MY CASE) i got pure product, thanks for any advice
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spotlightman1234
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[*] posted on 20-7-2011 at 00:40


Quote: Originally posted by not_important  
Green generally is from copper. Take the crude AgNO3, dry, then fuse in a ceramic container at 250 to 350 C, with stirring. Copper nitrate decomposes at that temperature, AgNO3 does not until 440 C or thereabouts. Cool, dissolve in distilled/deionised water, filter to remove CuO. Repeat if the solution has a blue tint.

Alternative is to ppt the silver as AgCl, wash with dilute HCl, reduce the AgCl with one of a number of reductants.

Use the search engine as this topic has been covered a number of times before.
Wouldn't the silver nitrate also decompose to silver metal, nitrogen dioxide, and oxygen? EDIT: oops the decomp temperature of AgNO3 is 444C. Never mind.

[Edited on 20-7-2011 by spotlightman1234]
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Melgar
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[*] posted on 21-7-2011 at 08:25


Just a thought, but if you're using jewelry and getting a green color, it's probably from nickel, since that's a common jewelry alloying agent. If copper was the contaminant, you'd be getting more of a blue color:

Copper nitrate vs. Nickel nitrate

Of course, there's a good chance you have both and your salt is a blue-green color.

[Edited on 7/21/11 by Melgar]
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mario840
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[*] posted on 9-8-2011 at 08:53


I tried many methods purify , over and over i waste about 4-5 g silver but now i know that best route is

silver/some crap (copper,nickel etc.) + HNO3 ----> silver nitrate (and crap) ------->filter and dissolve in water + NaCl(aq) -------> silver chloride + NaOH + glucose --------> pure silver

from that silver , silver nitrate is white "snow", very pure, no waste of copper, high yield, to all who want silver refining this is for me best method, tested over 3 times
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annaandherdad
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[*] posted on 11-10-2011 at 11:03
Purifying sterling silver


Quote: Originally posted by mario840  
I tried many methods purify , over and over i waste about 4-5 g silver but now i know that best route is

silver/some crap (copper,nickel etc.) + HNO3 ----> silver nitrate (and crap) ------->filter and dissolve in water + NaCl(aq) -------> silver chloride + NaOH + glucose --------> pure silver

from that silver , silver nitrate is white "snow", very pure, no waste of copper, high yield, to all who want silver refining this is for me best method, tested over 3 times


I agree, I've been experimenting with purifying sterling silver for several months, only recently learned about the existence of this forum. To make a long story short, I agree that this is the best method.

One method I tried was to dissolve the sterling in HNO3, getting a blue solution of presumably AgNO3 and Cu(NO3)2, then reducing the AgNO3 with Cu metal (I used household wire), making sure that the wire didn't completely dissolve to avoid small pieces of copper in the mix. Then filter and wash the (beautiful) collection of silver crystals that result.

Unfortunately, when I dissolved this a second time in HNO3, it turned out green. Very glad for the suggestions here that that may be nickel, I was wondering because copper would have been blue. Whatever it is, it is some contaminant that came out of the solution when the copper wire was added. Not sure how this could come about, can copper reduce nickel ions? Or could it have been contamination from the copper wire itself? Anyway, this method failed to purify the silver.

Best approach is, dissolve sterling in HNO3, precipitate AgCl, and reduce with dextrose + NaOH.
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Retard-3000
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[*] posted on 11-10-2011 at 11:12


Couldn't the last step (reducing with dextrose + NaOH) be omitted as AgCl photochemically decomposes into chlorine and silver metal?
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ScienceHideout
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[*] posted on 11-10-2011 at 12:02


I did the same thing... Here's what to do-

Turn the green crystals into a blue, aqueous solution. Now add copper wire. The silver will precip. out. Dissolve the precipitated silver in nitric acid. Presto! :D




hey, if you are reading this, I can't U2U, but you are always welcome to send me an email!


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annaandherdad
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[*] posted on 19-10-2011 at 11:49


Quote: Originally posted by Retard-3000  
Couldn't the last step (reducing with dextrose + NaOH) be omitted as AgCl photochemically decomposes into chlorine and silver metal?


Yes, but it's slow and it won't work unless the light can get to all the AgCl particles, so you'd have to stir it in the light. Even with AgBr or AgI I think it's easier to use the dextrose reduction method.

Involves heating and stirring for 15 minutes at 70-80C in a solution of NaOH and dextrose. I have a recipe I got from a research article, will look for the details.

After doing this I dissolved again in HNO3, no green color this time, then dried out and found the silver nitrate crystals that resulted to be fine for silvering mirrors.




Any other SF Bay chemists?
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nezza
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[*] posted on 19-10-2011 at 23:53


Quote: Originally posted by not_important  
Green generally is from copper. Take the crude AgNO3, dry, then fuse in a ceramic container at 250 to 350 C, with stirring. Copper nitrate decomposes at that temperature, AgNO3 does not until 440 C or thereabouts. Cool, dissolve in distilled/deionised water, filter to remove CuO. Repeat if the solution has a blue tint.


I have used this method before and it works fine. The difference in decomp temperature is enough to completely decompose the copper nitrate before affecting the silver nitrate. All you need to do then is dissolve in water and filter off the CuO.
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