Sciencemadness Discussion Board - Silver Nitrate Synthesis

Silver Nitrate Synthesis

ElizabethGreene - 26-7-2013 at 05:35

Good Morning.

I'd like to prepare some Silver Nitrate for a pottery glaze. I believe the process to be as simple as dissolving silver in hot nitric acid under effective ventilation. The product is then recystallized and should yield colorless rhombic crystals with a max melting point of 212c. (CRC 57th Ed)

Theoretical Question: Why does this make Silver Nitrate and not Nitrite?

Practical Question: How can I neutralize the unreacted acid without introducing impurities? I don't mind coloring the potter's hands with AgNO₃ stains, but I would rather not give them acid burns.

Is it as simple as using excess silver and driving the reaction with heat until it won't go anymore?

Is it even simpler than that and heating (to dry the crystals)(assume 125-150c) will cook off the remaining acid?

Thanks in advance,
Elizabeth

Gooferking Science - 26-7-2013 at 05:54

Well, I don't see why you wouldn't be able to just boil off the remaining acid, but I am not completely sure. I don't want you to ruin your silver nitrate.

woelen - 26-7-2013 at 06:08

The reason that you don't get the nitrite is that nitrite is unstable at low pH. If any HNO2 is formed, then this decomposes to H2O, NO (whuich bubbles out of solution) and NO2, which reacts with water to HNO3 and NO (which also bubbles out of solution

).

You can boil most of the acid, but don't drive it too far, because you will decompose the AgNO3 as well (making a mix of Ag2O, Ag, AgNO3 in hot spots). I would put the material in a dark, dry and clean place, preferrably somewhat warm, and allow the liquid to evaporate slowly, while there is good ventilation. AgNO3 is not hygroscopic and so will become dry quite well. Just allow all of the liquid to evaporate. Be sure that no dust comes into the liquid. Each speck of dust introduces a little black spot in your AgNO3!

After you obtain crystalline material (which most likely is pale grey), then you can recrystallize from distilled water to obtain nice white crystals. You'll notice that it will be quite hard to get really white crystals, a very light grey colour always remains. I have commercially obtained AgNO3 and this was off-white, not white like snow or table salt.

annaandherdad - 26-7-2013 at 07:24

To get rid of the excess acid and to avoid dust contamination while drying the silver nitrate, you can use a desiccator bag with a tray of sodium hydroxide to absorb both the water and the excess nitric acid. Instead of a bag, I have used a plastic container (I think the brand is Rubber Maid (?), they're used for storing food in the kitchen, unfortunately not terribly cheap). I would store a beaker with silver nitrate/nitric acid solution in the container, along with a tray of cheap sodium hydroxide (drain cleaner). The container has a plastic lid that presses on and makes a seal. You have to change the sodium hydroxide dish when it gets soaked, and break up the silver nitrate crystals near the end, to expose the wet parts and get it all to evaporate. Use a glass rod or plastic spoon, not metal which will contaminate the silver nitrate.

I had a similar problem (getting rid of excess acid) while making zinc sulfate (from zinc plus sulfuric acid). Unlike nitric acid, sulfuric acid won't evaporate, so the same method wouldn't work. Instead, I made some zinc carbonate from a sample of the zinc sulfate, then used an excess of zinc carbonate to neutralize the left-over acid. Then filtering to remove the excess zinc carbonate left pure zinc sulfate.

annaandherdad - 28-7-2013 at 14:44

Also, I suspect the gray color woelen reports is due to silver, produced by the photo decomposition of silver nitrate.

DJF90 - 29-7-2013 at 09:03

Armarego and Perrin has this to say on the matter (taken from 6th Ed.):

Quote:

Recovery of silver residues as AgNO3 [use protective shield during the whole of this procedure]
can be achieved by washing with hot water and adding 16M HNO3 to dissolve the solid. Filter this through
glass wool and concentrate the filtrate on a steam bath until precipitation commences. Cool the solution in an
ice-bath and filter the precipitated AgNO3. Dry it at 120*C for 2hours, then cool it in a desiccator in a vacuum.
Store it over P2O5 in a vacuum in the dark. AVOID contact with hands due to formation of black stains.

bfesser - 29-7-2013 at 12:51

Quote: Originally posted by woelen

AgNO₃ is not hygroscopic and so will become dry quite well.
. . .
You'll notice that it will be quite hard to get really white crystals, a very light grey colour always remains. I have commercially obtained AgNO₃ and this was off-white, not white like snow or table salt.

Wait a moment, <a href="http://en.wikipedia.org/wiki/Silver_nitrate" target="_ blank">AgNO3</a> <img src="../scipics/_wiki.png" /> isn't <a href="http://en.wikipedia.org/wiki/Hygroscopy" target="_blank">hygroscopic</a> <img src="../scipics/_wiki.png" />‽ Then why the heck am I wasting precious <a href="http://en.wikipedia.org/wiki/Dessicator" target="_blank">desiccator</a> <img src="../scipics/_wiki.png" /> space? I have a couple bottles of ACS Reagent grade AgNO3 from Sigma (if memory serves), and they say on the label to desiccate. The crystals are also perfectly colorless to white, no hint of grey. I wrap the caps with <a href="http://en.wikipedia.org/wiki/Parafilm" target="_blank">Parafilm</a> <img src="../scipics/_wiki.png" />, wrap the bottles in aluminum foil to keep out light, store them in a desiccator over <a href="http://en.wikipedia.org/wiki/Drierite" target="_blank">Drierite</a> <img src="../scipics/_wiki.png" />, and keep the desiccator in a dark cool closet.

Waffles SS - 29-7-2013 at 21:45

To get rid of the excess Nitric acid you can wash your AgNO3 with cold Acetone(silver nitrate is slightly soluble in Acetone)

Quote:

1000 grams Acetone dissolves 3.5 grams AgNO3 at 14°C (57°F)
1000 grams Acetone dissolves 4.4 grams AgNO3 at 18°C (64°F)
Solubility of Silver Nitrate

also you can add silver carbonate(Na2CO3+AgNO3) for neutralize excess acid.

[Edited on 30-7-2013 by Waffles SS]

Thanatops1s - 4-8-2013 at 16:48

Instead of starting a new thread, I figure I'll ask here. When making silver nitrate, could 50% nitric acid be used? If not, what is the minimum concentration necessary?

hyfalcon - 4-8-2013 at 17:06

It actually works better with dilute acid, not as many fumes that way.

[Edited on 5-8-2013 by hyfalcon]

ElizabethGreene - 4-8-2013 at 19:32

Seconding hyfalcon's response, I did a comparison of white fuming nitric acid (WFNA) vs. 60% acid for this synthesis and found that the reaction went painfully slow with the WFNA.

Inquiry: I can't make heads or tails of the requirements for shipping this stuff. Does anyone have experience shipping AgNO₃ or KNO₃?

Thanks,
Elizabeth

Oscilllator - 4-8-2013 at 23:40

Often very concentrated nitric acid forms passivation layers with metal e.g. with copper. Thats why the reaction goes slower with WFNA. If the WFNA was diluted with 10% water, then the reaction would probably proceed faster than with 60% acid

bfesser - 5-8-2013 at 09:57

Thanatops1s, you may wish to review <a href="viewthread.php?tid=25209&page=2#pid293680">Nitric Acid from Retort.</a> This exact topic was covered briefly in that thread.

[Edited on 25.11.13 by bfesser]

Chemateur80 - 17-3-2017 at 14:53

Hello.

There are a few threads about silver nitrate, and I chose to bump this one.

I'm doing a little project on converting some silver coins and jewlery into silver nitrate.
Most of the coins contain 40-50% silver, the rest being mostly copper.

I'm posting here to see if I can get some input regarding which methods to use.

The total weight of the silver was 75,86g.
The rest, mostly copper, weighed 106,83g

I used 65% nitric acid, diluted with dH₂O to around 40/50%, to dissolve the objects.
Since the acid was dilute I used the following formulas:

Copper:
3Cu + 8HNO₃ --> 3Cu(NO₃)₂ + 2NO + 4H₂O
106,83g Cu is 1,68moles
4,48moles of HNO₃ needed. This is 282g.
Since the acid is around 70%, 402g is needed. Around 400ml.

Silver:
3Ag + 4HNO₃ --> 3AgNO₃ + NO + H₂O
75,86g Ag is 0,7moles
0,931moles of HNO₃ needed. This is 58,7g.
Since the acid is around 70%, 84g is needed. Around 84ml.

Are my calculations correct?
I've seen on this and other forums that it takes 4,15ml 68% HNO₃/g Cu and 1,22ml 68% HNO₃/g Ag.
then I would need around 550ml HNO₃ to dissolve everything.

I decided to add the acid in smaller portions, and see how much I would need.

I've done the following so far:
Dissolved the objects by adding dilute acid in portions. The reaction was not very violent, and I had to heat
everything to get the last pieces of metal to dissolve.
Some NO₂ was formed. I did this outside, so I only got a few really small whiffs of the gases. Awful smell.
When everything had dissolved I was left with a dark blue solution.
Around 440ml of 68% HNO₃ was needed.
I filtered the solution using two filter papers in a buchner funnel, and a vacuum pump.
Some black/grey particles got stuck in the filter.

The blue solution has now been standing for a few weeks in dark bottles.
I've noticed that some precipitate has formed at the bottom. Could this be silver that has formed somehow? Or unreacted silver particles that passed through the filter paper?

I would like some advice on how to proceed. I've seen a few different methods on converting impure silver nitrate into
silver and then into silver nitrate again.
Of course I would like to get the purest silver nitrate possible with the smallest loss of silver in the process.
I will not use electrolysis.

This is what I plan to do:
Dilute the blue solution a bit and then add copper to precipitate the silver.
Formula: Cu + 2AgNO₃ --> Cu(NO₃)₂ + 2Ag
0,7moles Ag require 0,35moles Cu. This is 22,2g Cu, but it will be added in excess.

When no more silver precipitates out, a solution of NaCl will be used to make sure that there is no silver left in solution.

The silver will be filtered and washed with dilute Hcl and acetone to remove impurities.
What about copper impurities? Could this precipitation method lead to copper particles being mixed with the silver? They would
be hard to remove since they don't react with f ex HCl.

The washed silver powder is then reacted with dilute HNO₃.
The silver nitrate will then be allowed to crystallize out slowly, maybe in two batches. The first batch would be more pure than the second one.
Remaining silver nitrate in solution could be precipitated as silver oxide, using NaOH.

Sorry about the wall of text. I would greatly appreciate any advice on this little project.

Chemateur80 - 17-3-2017 at 15:18

And here are a few questions.

How long should I let the copper react with the silver nitrate solution?
Is it important to dilute the solution?
I plan to stir the solution occasionally to remove the precipitated silver from the copper wire. Could this cause copper particles to detach from the wire, contaminating the silver? Can I avoid this?

How about the leftover nitric acid from the reaction? I don't think it's very much left, since I added it in small portions in excess.
Could it cause problems, besides consuming the copper?

Any ideas on what filter paper to use when filtering the precipitated silver powder? I don't want to lose silver because it passes through the filter paper.

Any ideas about the best way to purify the silver nitrate after reacting the silver with HNO₃ again? Recrystallization?
Maybe a good idea to let as much as possible crystallize out slowly, filter the crystalls and then convert the remaining silver nitrate in solution to AgCl or Ag₂O so I don't lose any silver, but still get quite pure AgNO₃.

I've seen other methods than precipitating silver with copper.
Could they be better for this experiment?

I could react the silver nitrate with NaCl to form AgCl, react the AgCl with NaOH to form Ag₂O, and then reduce this to silver with some sort of sugar.

I could also convert the silver/copper nitrate directly to silver/copper oxide using NaOH, and heat this to decompose the silver oxide to silver.
The copper oxide could then be removed with HCl or H₂SO₄, leaving pure silver.

Would these methods give a purer product with less loss than the copper-method I'm planning to use? They seem to be more work, but is it worth it?

Other methods?

Tsjerk - 17-3-2017 at 17:37

I don't know to much about this kind of chemistry, but I think that the precipitated silver you see after filtration is because of pieces reducing filter paper. They dis-attach from the filter and over time reduce silver too the metal. This is the same phenomenon as Woelen describes with dust.

Maybe you can get something like this for cheap?
http://www.sigmaaldrich.com/catalog/product/sigma/n9145?lang... Or else cut up a women's nylon tights to filter the nitrate. I guess for the metal, paper filters are fine.

Edit: Tights, not panties....

[Edited on 18-3-2017 by Tsjerk]

AJKOER - 18-3-2017 at 12:50

I have previously prepared tetraamine silver nitrate from tetraamine Silver hydroxide, [Ag(NH3)2(H2O)4]OH. The latter was prepared by dissolving silver metal in dilute ammonia water with 3% hydrogen peroxide and adding a touch of potassium nitrate as an electrolyte. Jump start the reaction in a microwave, and replenish the H2O2 periodically. To this I added magnesium nitrate, until a cloud of white magnesium hydroxide is no longer visible. Reaction:

2 [Ag(NH3)2(H2O)4]OH + Mg(NO3)2 ---> 2 [Ag(NH3)2(H2O)4]NO3 + Mg(OH)2 (s)

Let the Mg(OH)2 settle out and decant to obtain the final product of silver nitrate by allowing the tetraamine silver nitrate simply to evaporate in a large shallow vessel in the dark. Caution: a small amount of silver nitride, a powerful and shock sensitive explosive (even when wet), could possibly also be formed upon the evaporation assuming the presence of unreacted tetraamine silver hydroxide, and its subsequent decomposition on standing.

Mg(NO3)2 can be prepared from ammonium sulfate and potassium nitrate upon freezing out the potassium sulfate as I have previously detailed on SM. I created my ammonium sulfate by adding ammonia water to Epsom salt, MgSO4, and allowing the magnesium hydroxide to settle (or filter out with vacuum suction).

The main advantage of this preparation for silver nitrate (with likely magnesium and potassium impurities) is that it avoids employing nitric acid and the creation of possible toxic NOx gases utilizing widely available and inexpensive chemicals including potassium nitrate commonly sold as a stump remover.
-----------------------------------------
A possible alternate path is from thermal decomposition of magnesium nitrate:

2 Mg(NO3)2 → 2 MgO + 4 NO2 + O2

Reference: see https://en.wikipedia.org/wiki/Magnesium_nitrate

This is followed by passing NO2 over heated Ag2O (Silver oxide is formed by the action of NaOH on Silver acetate prepared by reacting Ag, H2O2, vinegar and a touch of KNO3 after jump starting in a microwave). Possible reaction based on reference for Ag2O/NO (see https://www.researchgate.net/publication/244522410_Reaction_... ) is:

Ag2O + NO2 ---> AgNO3 + Ag

as: " Ag2O + NO → Ag[NO2]+ Ag "

[Edited on 18-3-2017 by AJKOER]

Chemateur80 - 14-12-2017 at 07:20

Hello again.
I was planning on finishing my silver nitrate project during Christmas.
Not very much feedback on my last post, so here I go again

What I have now is a solution of mainly copper nitrate and silver nitrate, but since I reacted coins and jewelry with nitric acid there could also be traces of zinc, aluminum and other metals.
The solution has been standing since March, and I can see a small amount of a precipitate at the bottom. What could this be?
Maybe silver metal from silver nitrate that got reduced somehow?
Maybe silver chloride from small amounts of chloride ions present? Distilled water was used for the reaction.

I'm considering two methods to get pure AgNO₃:
1. Precipitate silver metal with copper wire and react this silver metal with HNO₃
2. Precipitate AgCl with NaCl, convert the AgCl into Ag₂O with Na/KOH, and then react the oxide with HNO₃

Which method would give me the purest silver nitrate with the least loss of silver?

Questions about method 1:
Could copper particles contaminate the precipitated silver nitrate? How should I deal with this?

Could copper and other metal ions get stuck in the precipitated silver?

Questions about method 2:
When precipitating the AgCl, could other metal ions get stuck in the precipitate? Any ways to minimize this problem?

Any suggestions on what kind of filter to use for the chloride/oxide? I don't know how small the particles will be or if some filters will react with them.

I'm planning to use an excess of NaCl and Na/KOH. If too much excess is used, could water soluble silver complexes form?

Does it matter if I use NaOH or KOH? Could it affect f ex particle size of the Ag₂O formed?

OK, those were my thoughts on the project.
Ideas and suggestions?

clearly_not_atara - 14-12-2017 at 17:59

You can't convert AgCl to Ag2O with NaOH, at least not the last time I checked. The reaction goes the other way: 2 NaCl + Ag2O + H2O >> 2 NaOH + 2 AgCl. This is a simple synthesis of NaOH which works because of silver's very high affinity for chlorine.

Instead, you could precipitate silver as silver sulfate, and then add this to sodium hydroxide. Silver sulfate is more soluble (0.5% w/w) than silver oxide (0.003% w/w), so the oxide will be preferentially formed. Most other sulfates are soluble, except calcium, but there shouldn't be any calcium in your flask.

Chemateur80 - 15-12-2017 at 08:53

Quote: Originally posted by clearly_not_atara

You can't convert AgCl to Ag2O with NaOH, at least not the last time I checked. The reaction goes the other way: 2 NaCl + Ag2O + H2O >> 2 NaOH + 2 AgCl. This is a simple synthesis of NaOH which works because of silver's very high affinity for chlorine.

Instead, you could precipitate silver as silver sulfate, and then add this to sodium hydroxide. Silver sulfate is more soluble (0.5% w/w) than silver oxide (0.003% w/w), so the oxide will be preferentially formed. Most other sulfates are soluble, except calcium, but there shouldn't be any calcium in your flask.

That seems strange. I have seen several videos on silver refining where NaOH is added to damp AgCl, and the white chloride precipitate immediately turns grey/black. This should be Ag₂O.
Isn't the oxide less soluble than the chloride under strongly basic conditions?

Here's a thread on the subject:
http://www.chemicalforums.com/index.php?topic=32471.0

According to this thread it seems that aluminum could pose a problem because it might precipitate out, and since I've dissolved coins I could very well have aluminum in soulution.

Melgar - 15-12-2017 at 10:12

Is your solution covered or exposed to air?

Traces of halide ions can slowly cause precipitation from silver nitrate solutions, if they're exposed to light. Light will gradually split AgX into Ag metal and halogen radicals. Halogen radicals can react a number of ways, most of which result in more AgX salts. Since AgX salts are slightly soluble in water, and silver metal is totally insoluble in water, this reaction will gradually occur over time, driven by solubility and the energy from ambient light.

Chemateur80 - 15-12-2017 at 10:44

Quote: Originally posted by Melgar

Is your solution covered or exposed to air?

Traces of halide ions can slowly cause precipitation from silver nitrate solutions, if they're exposed to light. Light will gradually split AgX into Ag metal and halogen radicals. Halogen radicals can react a number of ways, most of which result in more AgX salts. Since AgX salts are slightly soluble in water, and silver metal is totally insoluble in water, this reaction will gradually occur over time, driven by solubility and the energy from ambient light.

The solution is in an amber bottle with a teflon lined screwcap and the bottle is stored in a dark place. I,ve used pure 70% HNO₃ and distilled water.
Traces of chloride ions could come from the coins/jewelry or the glassware used.

Melgar - 15-12-2017 at 14:10

Quote: Originally posted by Chemateur80

What color is the precipitate? This is important, because silver metal particles are dark gray, and silver salts are white.

clearly_not_atara - 15-12-2017 at 22:36

Chemateur: from your link:

Quote:

Silver chloride should be avoided simply because it is very difficult to manipulate--making Ag2O from it is exceptionally troublesome

Hot NaOH may convert some AgCl to Ag2O but I still wouldn't consider this preferable.

Chemateur80 - 16-12-2017 at 06:26

Quote: Originally posted by clearly_not_atara

Chemateur: from your link:

Quote:

Silver chloride should be avoided simply because it is very difficult to manipulate--making Ag2O from it is exceptionally troublesome

Hot NaOH may convert some AgCl to Ag2O but I still wouldn't consider this preferable.

According to the post in the thread it's troublesome if the AgCl is allowed to dry. What about directly converting the damp AgCl to Ag₂O?
Since this is pretty common among amateurs who refine silver it seems strange that there should be any problems. Losses would make people use other methods.
However, I'm not doing this to earn money, just for fun to get as pure AgNO₃ as possible with the least loss of silver.
Maybe the AgCl method is not the best for this.

Quote: Originally posted by Melgar

What color is the precipitate? This is important, because silver metal particles are dark gray, and silver salts are white.

It's hard to see what color it is since it's in an amber bottle with a dark blue solution. It looks more white than grey/black, so I'm guessing AgCl.

Chemateur80 - 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?

EilOr - 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]

Chemateur80 - 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.

diddi - 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.

Chemateur80 - 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]

Chemateur80 - 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?

clearly_not_atara - 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.

Chemateur80 - 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...

clearly_not_atara - 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]

Chemateur80 - 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?

clearly_not_atara - 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.

Chemateur80 - 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.

Chemateur80 - 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]

MrHomeScientist - 18-1-2018 at 08:58

It's possible the particles you observed are elemental silver, as AgNO3 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.

Chemateur80 - 18-1-2018 at 09:54

Quote: Originally posted by MrHomeScientist

It's possible the particles you observed are elemental silver, as AgNO3 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.

clearly_not_atara - 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.

MrHomeScientist - 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.

Chemateur80 - 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:

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.