mixing STS yields dark precipitate?

Hey everyone. I'm playing around with reversal these days and I'm having trouble mixing my STS.

I used the following formula, gleaned from this post of Charles Scott's: https://www.icmag.com/ic/showpost.php?p=6997987&postcount=1 regarding the difference in weight of the anhydrous and pentahydrate forms of sodium thiosulfate. I have pentahydrate.

0.1M Sodium Thiosulfate solution = ~2.5g Na2S203 + 5 H20 in 100ml of distilled water.
0.1M Silver Nitrate solution = 1.7g AgNO3 in 100ml

mix 20ml (0.02M) Silver Nitrate solution + 80ml (0.08M) Sodium Thiosulfate solution.

Each solution is clear, but when they're mixed, an odd reaction occurs, giving me what appears to be Silver Sulfide (Ag2S, a grey/black precipitate) that eventually settles out. Initially I thought it was a problem of being exposed to light, but given the solid precipitate, I suspect there's some sort of imbalance in my ratios or contamination of some kind. I've washed the containers I've been using and rinsed them well with the same distilled water I use for the solution.

Unfortunately, ions were always my stumbling block with chemistry. I'll keep doing my own research, and post anything I learn here, but any thoughts about what might be going on would be greatly appreciated.

I thought I could help, but I have the anhydrous Sodium Thiosulfate...

gl man

Thanks anyway. I guess I should have paid a bit more attention when shopping. I assume your STS comes out clear?

FoothillsFarmer said:

I thought I could help, but I have the anhydrous Sodium Thiosulfate...

gl man

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My he ratios are different with hydrous and anhydrous , the convention is on a photo printing site come where I do have it lying around I'll try and find it

You can't just mix your two stock solutions. You have to add the Na-thio to the silver stock dropwise to the AgNO3 solution, while stirring. If you add the silver stock to the Na-Thio, the silver will crash out immediately; this is what you are seeing as precipitate.

Chimera said:

You can't just mix your two stock solutions. You have to add the Na-thio to the silver stock dropwise to the AgNO3 solution, while stirring. If you add the silver stock to the Na-Thio, the silver will crash out immediately; this is what you are seeing as precipitate.

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And it should take about five minutes to mix the whole lot if that , taking to long makes it worse . Ionic pull

30-45 seconds is plenty, each drop forms a small white cloud but dissipates immediately if the solution is being stirred.

Chimera said:

30-45 seconds is plenty, each drop forms a small white cloud but dissipates immediately if the solution is being stirred.

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Yes spot in I meant the whole procedure shouldn't take more tha. Give minutes measuring and so on

Got it. Thanks a lot Chimera and Ganja baba! I knew it had to be something simple.

FoothillsFarmer said:

I thought I could help, but I have the anhydrous Sodium Thiosulfate...

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Doesn't matter which form it is, cause the initial recipe is in mol .

Anyway: You should really try the slow addition while agitating like Chimera proposed. Should the problem persist, then your thiosulphate is likely too old. Silver nitrate if exposed to air will turn greyish and even black; hence, your correct that in this case the first solution would have to be coloured from the start.

Regarding Chimeras advice: I thought it was the other way round, add the silver nitrate to the sodium thiosulphate... Can't remember which way I tried but my thiosulphate was toast anyway.

I wondered about the thiosulfate. The silver nitrate is bright white, though clumpy and difficult to get out of the jar.

I tried going very slowly as chimera suggested, swirling the solution vigorously as I went. I did see the white STS precipitate and begin to dissolve, but invariably the solution turned orange and the silver fell out of solution.

I'm not sure if I have enough silver left for another try, but if I do, I'll try adding the silver to the thiosulfate. I guess if all else fails I can get 30ppm colloidal.

Thanks OO!

When I get home tomorrow I'll pm you with the real recipe and how to do , this whole process takes minutes and normally people mix it up the wrong way round as the Internet talks shit on this subject ,
Your silver n should be white with a grey tinge not hard or any other colour I would say may be your starting silver is not good , it has to be the proper stuff , I'll take some pics of my bottles for you buddy ,

Oh, that'd be great! thanks a lot, Ganja baba. I'd really like to get this figured out. I think it's entirely possible that both chems are old. I guess I shouldn't expect freshness from amazon. Next time i'll do some more research into sources.

photoformulary.com...yeehaw

Thanks, stoned-trout. I'll check it out. I figured photo supply would be the way to go.

It's not the thiosulfate, or the nitrate. There are several silver thiosulfate complexes - the first being insoluble and unstable in water, converting to sulfide in seconds to minutes as you have seen. I know this because I tried it when this thread was first posted and the same thing happened to me and I'm supposed to be a chemist. Did the google while the thiosulfate was recrystallizing and it all makes perfect sense now.

It's possible that one STS complex is better than another for us for some reason, but the original work on Cannabis used a 1:8 by weight mixture. This 1:4 recipe that Sigma-Aldrich has on their site - that goes back to at least 1996 - might be unwisely dilute, at least the thiosulfate part. There's no good reason to make both stock solutions the same molarity or that dilute.

It looks like the more concentrated the thiosulfate, the better, and the faster the silver is added to that the better, as long as the mixing is very good. A 1:6 version of STS is now in my refrigerator, with only the slightest straw color.

Bump & Sub

Use distilled water. You have Calcium and Copper carbonates as well as free Chlorine and chlorides in your tap. Both drop Silver precipitate. Excess NO3 in the AgNO3 could cause problems by oxidizing your sulfate to sulfite/sulfur which drop AgS as black nano particles. If you can, test the pH of the AgNO solution if its in distilled (should be no lower than 6). If you ever get AgCl, its white in its nano form. I don't know why there would be a point to mixing differently than 2 mol of Ag to 1 mol of thiosulfate ratio.

AgNO3 or nano silver will also drop anthers, just not as well.

I formulate for 50ppm Ag. Get full male flowers if sprayed well. No burning or growth stunting. They seem to stretch more actually. Not sure why people are reporting unhealthy plants after. Maybe they are over doing it. I did this on top of root rot. Nothing different but the anthers popping really.

I've seen red/orange come out before. Looks like some nanoGold precips I've done in the past. Was a mixture. This happens because of the size of the particles being precipitated. Its probably a very specific size and shape in this case because Silver almost always looks black in its nano forms.

Mixing is irrelevant. I pay no mind. Its mostly about which chem is worse to splash. I pour the sulfate into the nitrate only because the nitrate is a pour bottle and the sulfate is a squeeze bottle (that is no real reason to insist on that sequence though), never thought it would change the reaction to do the other way. I have little concern for AgNO3 as its applied to open wounds for bacteria/fungi kills on occasion. Just put em together and have a stable solution for weeks at room temp. Also, like Calcium nitrate, Silver thiosulfate is not incompatible with everything. You can mix some solutions with stable results.

There is no complex unless you have impurities in your water. The compound resulting in this solution will be Ag2O3S2 + NaNO3 + either excess NO3 or excess NaS2O3

Ag is oxidized to -1 most of the time and exists in that state as AgNO3
S2O3 (thiosulfate) exists as oxidation state -2. If your thiosulfate is disrupted to -1, you will see Silver precip.

I do not have precip problems using distilled or highly filtered near 0 ppm water.

Both AgNO3 and NaS2O3 last a long time stored dry. AgNO3 will precip in UV light but is fairly stable in the dark in solution. The NaS2O3 will degrade to sulfite and sulfur in acidic water. That will drop Silver sulfide which is black when the sulfite or sulfur contact AgNO3.

djimb said:

Hey everyone. I'm playing around with reversal these days and I'm having trouble mixing my STS.

I used the following formula, gleaned from this post of Charles Scott's: https://www.icmag.com/ic/showpost.php?p=6997987&postcount=1 regarding the difference in weight of the anhydrous and pentahydrate forms of sodium thiosulfate. I have pentahydrate.

0.1M Sodium Thiosulfate solution = ~2.5g Na2S203 + 5 H20 in 100ml of distilled water.
0.1M Silver Nitrate solution = 1.7g AgNO3 in 100ml

mix 20ml (0.02M) Silver Nitrate solution + 80ml (0.08M) Sodium Thiosulfate solution.

Each solution is clear, but when they're mixed, an odd reaction occurs, giving me what appears to be Silver Sulfide (Ag2S, a grey/black precipitate) that eventually settles out. Initially I thought it was a problem of being exposed to light, but given the solid precipitate, I suspect there's some sort of imbalance in my ratios or contamination of some kind. I've washed the containers I've been using and rinsed them well with the same distilled water I use for the solution.

Unfortunately, ions were always my stumbling block with chemistry. I'll keep doing my own research, and post anything I learn here, but any thoughts about what might be going on would be greatly appreciated.

Click to expand...