Sciencemadness Discussion Board

Need help to purify silver nitrate

vibbzlab - 28-2-2020 at 21:13

I had an old silver jewelry with me ,which was around 30years old or so. I thought I could make some silver nitrate with that and I allowed to react that with nitric acid. The reaction immediately started and lot of nitrogen dioxide fumes were formed and the solution turned green. I am pretty sure that jewelry has copper contamination in it. Is there any way to remove the copper salt from it and get the silver nitrate?

IMG_20200229_104128.jpg - 3.4MB

Sulaiman - 28-2-2020 at 21:44

Solid copper should replace the silver in silver nitrate via a simple replacement reaction,
to produce more copper nitrate - and solid silver with MUCH lower copper contamination.

you could purify further by re-crystalisation, or better, by electrolysis.

Loads of texts online and plenty of YouTube videos.

vibbzlab - 28-2-2020 at 22:33

Yes I just did it and already made a lot of silver

IMG_20200229_114230.jpg - 4.9MB

Sulaiman - 29-2-2020 at 00:12

If you thoroughly wash the silver,
then dissolve in nitric acid,
you get an idea of how much copper is left in the silver from the colour.
I found it difficult to completely remove all visible traces of copper.
Very slow evaporation gives pretty, almost pure silver nitrate crystals.

vibbzlab - 29-2-2020 at 00:18

Yup I will do it today. Btw how slow should the cooling be. Should I use water bath?

Heptylene - 29-2-2020 at 02:26

To cool slowly you can use a large hot water bath and but your beaker of AgNO3 solution in the bath. Cooling can occur over a day with this method. If you have some insulating foam or styrofoam box you can also use that.

Sulaiman - 1-3-2020 at 22:51

Nice video, a few suggestions/comments ;
. when using nitric acid to dissolve silver and/or copper (or aqua regia for gold, platinum etc.)
try to use the minimum quantity of nitric acid required to dissolve the metal,
because the next step usually involves reduction to the the pure metal,
and any excess nitric acid will re-dissolve the metal requiring excessive quantities of your reductant.
In this case you used solid copper to replace the silver in the silver nitrate,
the excess nitric acid causes more copper than necessary to enter solution as nitrate.

. use a solid piece of copper (e.g. a length of copper tube/pipe) rather than turnings/shavings/powder that may not be easy to remove from the silver powder.

Judging by the colour of your final silver nitrate solution,
I guess that your silver still has at least 0.1% copper.
Quote: Originally posted by vibbzlab  
Yup I will do it today. Btw how slow should the cooling be. Should I use water bath?

Due to its very high solubility and tendency to super-saturate,
silver nitrate is (I believe) best crystalised slowly ... days rather than hours or minutes.
Here is a photo of my most satisfying recrystalisation of silver nitrate, about 1/3 down the page https://www.sciencemadness.org/whisper/viewthread.php?tid=27...

P.S. recrystalisation is a good technique for purification,
but for it to work you must not be 'greedy'
... collect much less than 1/2 of the weight of crystals expected = leave more than half of your product in solution
and immediately use absorbent material to remove as much adhering solution as possible.
If you don't mind recycling a little more material then wash the crystals in ice cold distilled water,
(silver nitrate is very soluble in even ice cold water ... 122g/100ml)
Your best bet for high yield purification is probably electrolysis.
... don't use copper in your electrolysis cell :P

[Edited on 2-3-2020 by Sulaiman]

Herr Haber - 2-3-2020 at 05:13

Quote: Originally posted by Sulaiman  
Nice video, a few suggestions/comments ;
. when using nitric acid to dissolve silver and/or copper (or aqua regia for gold, platinum etc.)
try to use the minimum quantity of nitric acid required to dissolve the metal,
because the next step usually involves reduction to the the pure metal,
and any excess nitric acid will re-dissolve the metal requiring excessive quantities of your reductant.
In this case you used solid copper to replace the silver in the silver nitrate,
the excess nitric acid causes more copper than necessary to enter solution as nitrate.

. use a solid piece of copper (e.g. a length of copper tube/pipe) rather than turnings/shavings/powder that may not be easy to remove from the silver powder.

[Edited on 2-3-2020 by Sulaiman]


That is true. If bubbles form on your copper then you have some acid left. Silver powder has a bigger surface area than your copper bar so you'll have a back and forth reaction.
BUT, it'll clean your bar of oxides. And that is good.

Do not ever use copper powder it's really counterproductive.