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ElizabethGreene
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Silver Nitrate Synthesis
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
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Gooferking Science
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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.
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woelen
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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.
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annaandherdad
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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.
Any other SF Bay chemists?
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annaandherdad
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Also, I suspect the gray color woelen reports is due to silver, produced by the photo decomposition of silver nitrate.
Any other SF Bay chemists?
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DJF90
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Armarego and Perrin has this to say on the matter (taken from 6th Ed.):
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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.
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bfesser
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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">AgNO<sub>3</sub></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 AgNO<sub>3</sub> 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.
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Waffles SS
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To get rid of the excess Nitric acid you can wash your AgNO3 with cold Acetone(silver nitrate is slightly soluble in Acetone)
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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
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also you can add silver carbonate(Na2CO3+AgNO3) for neutralize excess acid.
[Edited on 30-7-2013 by Waffles SS]
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Thanatops1s
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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?
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hyfalcon
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It actually works better with dilute acid, not as many fumes that way.
[Edited on 5-8-2013 by hyfalcon]
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ElizabethGreene
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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
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Oscilllator
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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
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bfesser
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<strong>Thanatops1s</strong>, you may wish to review <strong><a href="viewthread.php?tid=25209&page=2#pid293680">Nitric
Acid from Retort.</a></strong> This exact topic was covered briefly in that thread.
[Edited on 25.11.13 by bfesser]
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Chemateur80
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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.
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Chemateur80
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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?
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Tsjerk
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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]
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AJKOER
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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]
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Chemateur80
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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?
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clearly_not_atara
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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.
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Chemateur80
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| 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.
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Melgar
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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 first step in the process of learning something is admitting that you don't know it already.
I'm givin' the spam shields max power at full warp, but they just dinna have the power! We're gonna have to evacuate to new forum software!
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Chemateur80
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| 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.
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Melgar
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| Quote: Originally posted by Chemateur80 | 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. |
What color is the precipitate? This is important, because silver metal particles are dark gray, and silver salts are white.
The first step in the process of learning something is admitting that you don't know it already.
I'm givin' the spam shields max power at full warp, but they just dinna have the power! We're gonna have to evacuate to new forum software!
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clearly_not_atara
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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
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Hot NaOH may convert some AgCl to Ag2O but I still wouldn't consider this preferable.
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Chemateur80
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| 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.
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