Working for a client on a Tollens Reagent based very fast silvering solution I had 50 ml of a silver nitrate/ammonia/sodium hydroxide solution explode
in the night in a lab storage cupboard.
Here’s the post-explosion 100 ml HDPE bottle which contained it:
The recipe was about 1.5 M AgNO3, 0.5 M NaOH and 5 M NH3 and was taken, with minor adaptations, from a spray-on silvering solution’s MSDS by a
Company called Spectrachrome.
The solution was about 2 days old when it spontaneously detonated. Obviously the high concentrations of silver and ammonia had favoured the formation
of Ag<sub>3</sub>N. The sodium hydroxide may have exacerbated things, I don’t know.
The physical damage done was negligible but it did create the mother of all messes, with a difficult clean-up due to particles of unreacted
Ag<sub>3</sub>N still clinging to everything.
Things could have been much, much worse of course. Don’t mess with concentrated ammoniacal silver solutions, they are inherently dangerous. Brain&Force - 19-8-2014 at 08:45
Are you alright? At least it was an HDPE, not a glass bottle. I think you're right about the hydroxide influencing nitride formation, as acidification
is the procedure for disposing of Tollen's reagent.blogfast25 - 19-8-2014 at 09:16
I wasn't there when it happened, so I'm fine, thanks.
Acidification turns ammonia into ammonium from which the nitride cannot form. Excess NaOH of course drives the NH3 + H2O < === > NH4(+) + OH(-)
even more to the left, maybe that promotes nitride formation even more.Bert - 19-8-2014 at 09:48
Thanks for the post and picture- Every new generation of mirror makers requires a reminder!
This is one of the CLASSIC lab/industrial hazardous mixture events.
Silvering mirrors? Mix the ammount of chemicals required as needed, use same day and DISPOSE OF LEFTOVERS before leaving the work area at end of day.
Storage, even just overnight... Is a bad practice.
It's been written about repeatedly, for well over 150 years now, and safety departments at schools or businesses handling the chemicals involved frequently try to educate about the
danger. blogfast25 - 19-8-2014 at 10:40
What also amazes me is that the MSDS sheet I used for information on a commercial (Spectrachrome) silvering solution (of strong silver nitrate in
strong NH3) did not mention this hazard. It's unlikely they sell this as a premixed solution though...
[Edited on 19-8-2014 by blogfast25]BromicAcid - 19-8-2014 at 13:35
I'm sure you've seen MSDS sheets intentionally vauge. There is the potential there was a proprietary stabilizer that is in the commercial preparation
that is not included in the MSDS sheet.blogfast25 - 20-8-2014 at 04:45
I'm sure you've seen MSDS sheets intentionally vauge. There is the potential there was a proprietary stabilizer that is in the commercial preparation
that is not included in the MSDS sheet.
It's entirely possible (which stabiliser though?)
It's also possible they supply the silvering solution as a two component system: silver nitrate solution and ammonia/NaOH solution, to be mixed on the
day of use and neutralised or otherwise discarded after use.Morgan - 21-8-2014 at 07:16
One time long ago I made some silver nitrate with a silver dollar and some nitric acid and decided to try to mirror a flask having read a very short
account of how to make it by using ammonium hydroxide. And so I did without any real knowledge of what I was doing, before the Internet. After the
effect I poured the solution out of the mirrored flask onto a large, perfectly round flat stepping stone whereupon it completely mirrored the surface
which was rather unexpected. It was just a stone in an out-of-the-way spot in the yard, not part of a walk or anything.
And so I thought that was that and went off in my car to do something. I was living at home and when I returned my father was in a very bad mood.
Apparently the thin layer of mirroring solution exploded and a few pebbles had struck his forehead somehow leaving a few tiny red marks.
I think he may have been raking near the stone at the time.
The mysterious part was that initially I had no idea what he was talking about, insisting I didn't put anything in the yard that would explode and I
was confounded. In some way it was funny that he thought I would do something like that which I would never even consider and secondly that although
it was potentially very hazardous, it turned out OK. He satirically remarked he was afraid to go out in his own backyard.
So when it says to discard the solution after use I guess it means more than to just pour it out on a rock. It's strange to think how thin of a layer
it was and how it must have really startled him.
[Edited on 22-8-2014 by Morgan]blogfast25 - 21-8-2014 at 08:25
