I have about 150g of silver contacts trimmed with a little copper left. I mixed about 300ml ~12% HCL and 100ml 3% H2O2 and added maybe 10g of the copper I trimmed from the contacts, just to try and get the solution going but it wasn't going green so I added all the contacts(non-magnetic) and it started turning green. Came back maybe 20 minutes later and there was a black haze/cloud around the contacts at the bottom of the solution. What could this be? I believe I have added far too much HCL and H2O2 for the amount of contacts present, is it possible it is silver chloride? I gave the glass a swirl and it disappeared.
Black cloud in AP
- Thread starter brockles
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Probably saturated Copper Chloride.
So can I just keep on adding HCL until all the solid copper has dissolved and the black cloud no longer precipitates? I had read that copper would precipicate out white?
Thanks
Martijn
Well-known member
Add an air bubbler. Only add HCl when you get white precipitate on the bottom or when the solution turns darker.
Martijn
Well-known member
Copper 1 chloride.
The brown is not a precipitate, it is concentrated so adding either Oxygen or fresh HCl will fix it.
Are you using an air bubbler?
It may be faster, since all reactions are faster in the heat.
It will also evaporate faster, so one needs to keep an eye on it so it do not dry out.
Martijn
Well-known member
This is a picture from one of our members.
Golddigger76
Well-known member
I don't believe that your solution could have been saturated in 20 minutes .
Golddigger76
Well-known member
Sorry but I got distracted and couldn't finish what I wanted to say and ask, but was there any solder on the contracts or was some of them coated with black soot from arching- failure ?
If you reread the post, you will see it formed under stagnant conditions, and disappeared when stirred.
Some of them were silver soldered to the little fingers. Some may have contained remnants of arcing but would that just be oxides of metals the contacts contain?
Over the past couple of days I have been adding bits of HCL and today I noticed some of the copper remains of the fingers(I did clip them as close to the contacts as possible) were a grey colour, similar to the colour of the silver contacts after being in the solution for a while but when rubbed, the grey material would wipe off/come off in flakes, exposing the copper underneath. Is this silver chloride precipitated out onto the copper?
Most likely Tin
Would this be metallic tin or tin chloride? If metallic, can it just be removed with NaOH or HCL? If tin chloride, removed with water?
When it dissolves in HCl it becomes Tin Chloride.
It is probably Tin metal that cements out on the fingers.
In thery it should not happen, but in the real world it does sometimes.
