Sciencemadness Discussion Board

Silver nitrate solutions revisted...

Chemist514 - 8-10-2006 at 06:04

Hello,

I was givin a solution of silver in nitric acid, but its a: blue, like VERY blue and b) odd white dust settles to the botton on standing. I can smell the nitric acid and see pieces that look like they were probably pieces of jewlery along with some erm, junk.. it seems to be very heavy for 500 ml of nitric acid.

My guesses.... Theres alot of copper nitrate that got formed along with silver nitrate when they kept dumping garbage silver in the acid hence the blue.
The dust is either silver dropping out of the solution as temps go up and down? or silver oxide? Its not shiny like silver, more like a white to grey..

Its a mess, id like to recover something from it though if possible and figured id post my problem before making MORE of a mess of it.

12AX7 - 8-10-2006 at 08:32

Chloride precipitates silver no matter the pH (except around ammonia and other soluble silver complexes).

If you add a bunch more chloride, you could precipitate all the silver as AgCl, wash then neutralize it to get Ag2O, then dissolve in pure HNO3 to get pure AgNO3 solution. If you want to avoid Hg and Pb, you can dissolve the AgCl in NH3 solution, then add a reducing agent to precipitate Ag metal (or does that deposit a mirror, I forget).

Tim

[Edited on 10-8-2006 by 12AX7]

not_important - 8-10-2006 at 09:38

Yeah, diluting it a bit, adding salt solution to precipitate all the silver as the chloride, washing that (water plus a few drops of HNO3), then reducing the chloride to the metal is one way.

If there is only a very small amount of solids you could ignore them, distill off most of the acid, evaporate the last bit to dryness, heat the mixed nitrates to roughly 250 to 300 C - the silver nitrate melts, copper nitrate decomposes, coll, dissolve in water and filter off from copper oxides and any silver chloride. That gives you nitrate without having to redissolve the silver as above.

Chemist514 - 8-10-2006 at 10:46

Hi,

Replies noted!

12AX7 : (I wonder how many people know your a vacuum tube... lol)
So the white percipitate IS already silver chloride you suspect? which will fall out of solution as more of some chloride is added. good to know. thanks.

I have silver nitrate so either silver chloride or silver oxide are new compounds to add to the collection. I suspect theres ALOT of silver in this volume of solution, prolly as much as there can be.

not important : I cant ignore them, theres alot of crap in there, i think they tossed in some really lowend jewlery with plastic supports in it etc, ill tell you what ive done so far...
Thanks for input muchly though.

I decanted some of the clear blue liquid into a small 80 ml beaker and added 31.45% hcl, about 20mls... ALOT of white powder went to the bottom... Its much different then the grey sludge about 1 inch deep in the original bottle, something just came to mind, this was an original bottle for fisher nitric acid... lol, wish theyd sell to me.
I guess ill try to clean it to so theres no original sludge then take silver chloride out as a pure chem, ill try to add more nitric acid to the sludge... this crap is staining everything brown.

observation on grey sludge...

Chemist514 - 8-10-2006 at 11:34

I decanted all the clear blue liquid off and added 200 mls of 15% nitric acid to the sludge, it does not disolve... gotta be pretty inert stuff as im killing the heat at a rolling boil. cackle.

chemoleo - 8-10-2006 at 15:13

What would you like to recover from it? Pure silver, or just remove impurities, and make a specific Ag-salt solution?
In all cases, best is probably if you filter and wash, dry your AgCl precipitate thoroughly. Avoid light exposure. Then redissolve with ammonia, forming the complex salt. Then you can get the silver out of it with reducing agents (inc. sugars etc), and this can be redissolved in HNO3 if you wish.

Swany - 8-10-2006 at 15:41

Chances are it is a solution of sterling silver, which would contain about 7.5% copper, and thus explains the blue solution and such.

Chemist514 - 8-10-2006 at 15:54

I've been going through silver chloride filtering all afternoon so I suppose thats it for now, much filter paper and distilled water used, erm... how bad IS the light exposure thing exactly here? I kept it out of the sun and had a small light on with a normal bulb... I turned off the halogen.

All the best!

12AX7 - 8-10-2006 at 18:54

Not much of a problem for the chloride IIRC. Bromide and iodide are the good photosensitive ones. (I wonder how fast astatide would photolyse.. I mean, besides all the gamma ray photons the stuff would be casting off just sitting there for a few microseconds!) If it's turning dark, you may want to cover it.

I forget what the reaction is...reduction? That would leave metal. If it's just dissociation, it'd have to be the oxide, which is even easier to deal with.

Tim

Rosco Bodine - 8-10-2006 at 22:25

I am pretty sure that you can selectively , separately precipitate the oxides of silver and copper from a hot
solution of their mixed nitrates . The nitrate of copper
in solution is colored , but the nitrate of silver in solution
is colorless . IIRC you can perform a gradual addition of
NaOH solution to the stirred hot solution and at the
point where the color disappears suddenly , all of the
copper will have been precipitated as the oxide .
Filter out the copper oxide , and continue the basification
of the filtered colorless solution of silver nitrate to
get your silver oxide . Filter and dry the silver oxide and fire it in a crucible to melting and you get relatively pure 99+% silver .

not_important - 8-10-2006 at 22:29

Quote:
Originally posted by Chemist514
Hi,

Replies noted!

12AX7 : (I wonder how many people know your a vacuum tube... lol)
So the white percipitate IS already silver chloride you suspect? which will fall out of solution as more of some chloride is added. good to know. thanks.


Chloride contamination is common. If it was old jewlery then salt from sweat, in a lab or metal workshop not uncommon to have HCl fumes.
Quote:

I have silver nitrate so either silver chloride or silver oxide are new compounds to add to the collection. I suspect theres ALOT of silver in this volume of solution, prolly as much as there can be.
Personally I think the nitrate is much more useful, the chloride just sits around slowly darkening from light and organic vapours; not much use for it unless prepared in the proper way for photo emulsion.
Quote:

not important : I cant ignore them, theres alot of crap in there, i think they tossed in some really lowend jewlery with plastic supports in it etc, ill tell you what ive done so far...
Thanks for input muchly though.

In that case you would want to filter them off, and wash them to remove the last of the AgNO3. Couldn't leave organic stuff in if you were to evaporate - nitrating organics and heating isn't always smart - and if you fused the AgNO3 for removing copper any organics would react with the AgNO3, reducing it.

If it was just a little AgCl then you could ignore it, just evaporate.

If they tossed any old stuff in it might be worth working up the solid gunk, could have some silver and even other precious meals in it. Fuse it with Na2CO3 and NaNO3, adding the gunk to the fusion mix in small amounts, to oxidise organics and base metals. Pour the fusion mix onto a cold slab of stone or steel/iron plate, unless there wasn't much gunk so the fusion mix is small in volume in which case just rotate the crucible while cooling down so the melt forms a thin layer on the sides. When it's cold dissolve the melt in hot water, filter, treat the solids with dilute acetic acid to dissolve carbonates. Whatever is left as a solid is either precious metals or oxides of metals Al/In/rare earths/W/No/Ta/Hf/Zr.
Quote:

I decanted some of the clear blue liquid into a small 80 ml beaker and added 31.45% hcl, about 20mls... ALOT of white powder went to the bottom... Its much different then the grey sludge about 1 inch deep in the original bottle, something just came to mind, this was an original bottle for fisher nitric acid... lol, wish theyd sell to me.
I guess ill try to clean it to so theres no original sludge then take silver chloride out as a pure chem, ill try to add more nitric acid to the sludge... this crap is staining everything brown.


As silver chloride is more soluble in HCl solutions than in pure water, it is better to use common salt to precipitate from just slightly acidic solution, and to do the first washings of the AgCl with dilute NaCl solution.

Thanks for the help! Many thanks all!

Chemist514 - 9-10-2006 at 17:33

Hello!

Well, we're done... I'll dry it out of the desicator in a couple days.

Filled a small 125ml nalgene bottle up nice.

Next time ill use the "soluble chloride" method as thats what all of you seemed to recommend.

Thanks again.