Aurum - 16-7-2014 at 00:34
I was etching a PCB today using Ammonium Persulphate and after it had finished I assumed I had mainly Copper Sulphate but before throwing it down the
drain I added Sodium Bicarb to precipitate copper carbonate. There was lots of fizzing and the solution went a very nice blue/purple colour. Anyone
any idea what was produced?
Mike.
woelen - 16-7-2014 at 03:39
By adding the sodium bicarbonate (which is slightly alkaline), you apparently released sufficient ammonia from the ammonium ions in the solution to
allow formation of the tetrammine complex of copper. This ion, [Cu(NH3)4](2+) has a beautiful deep blue color with an indigo tinge.
The fizzing is due to formation of CO2 from the bicarbonate.