On 09/11/13 17:17, Stefan Trethan wrote:
> Do you have access to higher concentration H2O2?
> If so you can leave the SG low, and let it build during regular etching.
I've got a bottle of 35% on hand.
I also noticed that my etch tank isn't 1 litre -- it's 2.25l. Which
means I don't have 750ml of etchant -- I have TWO LITRES.
So the acid concentration calculations look even worse now. To get the
acid concentration to 2.75 Molar, I'd have to drain off around 400ml of
solution and neutralise it, then add roughly the same amount of 35% HCl...
My current plan of action looks something like this:
∗ Drain off 400ml etchant. Neutralise and dispose of -- per
<
http://chemistry.stackexchange.com/questions/872/copper-chloride-neutralizing-and-disposal>:
∗ Add Aluminium foil - result: AlCl_3 in solution, Cu metal
(also see <
https://www.flinnsci.com/media/622135/95000.pdf>)
∗∗∗ VERY exothermic reaction ∗∗∗
∗ Add sodium carbonate - CuCO_3 in water or precipitated
∗ Add sodium hydroxide - CuOH?
∗ Add HCl to increase the acid level
∗ Add copper metal (wire)
It looks like my best bet might be to fix the acid concentration
(increase to at least 1.0 Molar, maybe 1.5 Molar) then throw in some
copper, leave it in the etch tank with air on and readjust s.g. and HCl
concentration after the copper is gone.
Which leaves one remaining question -- how much copper do I need to add?
> If you don't have concentrated H2O2 you may want to increase the SG
> and put the oxygen in from the air.
>
> You'll notice a lack of HCl when adding H2O2 does not help, and the
> surface of the copper turns blue.
I don't think there's a problem with the oxidation state of the copper
chloride -- that is to say, based on solution colour, I definitely have
Cu(II)Cl (cupric chloride, green/blue) not Cu(I)Cl (cuprous chloride,
olive green).
Although to be absolutely honest the solution seems to be edging towards
blue -- going by the photos on Wikipedia
(<
http://en.wikipedia.org/wiki/Cupric_chloride>, under "properties and
reactions"), that might suggest that the acid level is indeed quite low.
It certainly turns blue when diluted (e.g. when washing out the glassware).
--
Phil.
ygroups@...http://www.philpem.me.uk/