Twospoons
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Queries on the silver mirror process
I have a couple of questions regarding glass silvering by reduction of ammoniacal silver nitrate, as in the thread on electroforming
I really don't want to waste $10 worth of fine silver, which I've converted to silver nitrate so -
1. Can I store the ammoniacal silver nitrate solution, or will it decompose, or form something nasty like silver fulminate?
2. Can I use NaOH in place of KOH, or is there something special about KOH?
3. Does anyone have a method of making silver nitrate from silver metal, that doesn't involve the clouds of NO2 you get by dissolving it in
conc. nitric acid?
( I'd rather not repeat that ...)
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neutrino
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1. Actually, fulminating silver (different but still quite explosive). I don't see what's wrong with just storing a solution of silver
nitrate.
2. K<sup>+</sup> is a spectator ion, so there shouldn't be anything special about it. If anyone knows any better, please correct me.
3. There isn't really a better way. You need a strong oxidizer to get Ag to Ag<sup>+</sup> and exclude most anions at the same time
(to prevent creating an insoluble coating). That's why aqua regia won't dissolve silver: the chloride ions.
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BromicAcid
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There is some worry to storing an ammonical silver nitrate solution, from memory there is an explosive compound that could be formed, fulminating
silver (AgN3) different from silver fulminate. This is normally produced by the action of ammonia on silver oxide but it can be produced in these
solutions if left, I think I have read some warnings on this and that is one of the reasons these solutions are usually made just before use, there is
incidently a thread on this forum on fulminating silver.
Edit: Hummm... I guess it could be silver nitride (that is the thread on this forum) from just some casual searching around there seems to be a bit
of a nomenclature issue on what can be formed in this solution. None the less it appears as though some explosive compound could be formed.
[Edited on 7/18/2005 by BromicAcid]
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The_Davster
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For clarification as there is a lot of confusion on the explosive product produced when silver salts react with ammonia, the explosive formed is
fulminating silver(silver nitride); Ag3N, not silver fulminate; AgONC. Usually it is a bit more complicated than just being Ag3N with other explosive
compounds such as Ag2NH or AgNH2, but in relativly minor ammounts.
EDIT: BTW Bromic the formula you posted is for silver azide.
[Edited on 18-7-2005 by rogue chemist]
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12AX7
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Oh, and on the subject, how is fulminate not cyanate (also -O-C=N AFAIK)?
Tim
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The_Davster
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Fulminate vs cyanate
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Lambda
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Twospoons, Ag3N is indeed formd. This compound amoungst the silver diamine complex crystalise out, and ..."bang" goes your solution. They
can spontainouesly explode on standing, just by mere stress induced by crystalisation. Ag3N behaves similair to nitrogen iodide during filtration, and
is well known to explode within the solution. Please check out "Brauer". Keeping these solutions for prolonged periodes of time is a big
"No No". They are very unpredictable as to when they will detonate. Please allso read "Bretherick" on the great amount of
accidents that this stuff has caused (I had uploaded this book). I have many books on this stuff, and it has a very nasty history and regretfully to
say, future ahead.
[Edited on 18-7-2005 by Lambda]
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12AX7
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| Quote: | Originally posted by rogue chemist
Fulminate vs cyanate |
Oh, okay. So it's a quadruple bond, but since that doesn't work (esp. with N = 3+), it's expressed as a charge, and since the oxygen
is also positive, the cation could be bonded to either end, no? Though I'd think it would prefer the O+ since O is stronger than C.
Tim
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Tacho
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I have made silver nitrate by electrolisys of a silver anode in a nitrate (sodium IIRC) electrolyte. A paper dipped in this electrolyte would turn
dark upon exposure to sunlight. Of course, the resulting solution is far from a pure nitrate.
I wonder what would happen If you used ammonium nitrate solution as eletrolyte. Maybe you could skip the ammonium hydroxide mixing step on the mirror
making process. Or maybe fulminate would form instantly and explode on your face...
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12AX7
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Electrolysis would work if you use a diaphragm between anode and cathode, otherwise the AgNO3 finds NaOH and Ag2O drops out.
Tim
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Cyrus
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I did a lot of research on these electroless silver baths a while ago, and the general opinion was that these explosive compounds wouldn't form
unless the solution was allowed to dry or get nearly dry. I'm not certain that this is correct, though.
Cyrus
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Twospoons
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Thanks for all the replies, and correcting my nomenclature regarding 'fulminating' vs 'fulminate'. I must admit I couldn't
quite see how silver fulminate could form, as my memory of the procedure for mercury fulminate required some things which aren't present in the
silver mirror process.
I think I'll store the silver nitrate as pure solution and add the ammonia as needed.
The procedure I have warns that the fulminating silver forms if the KOH solution is added too rapidly, and suggests dropwise addition ( and safety
goggles).
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