[ccrome]

Hi there,
   Tonight I was etching a PCB with an HCl + H2O2 (3%) mixture, in about 1:2 ratio. 

I happened to have a soda can nearby, so i wanted to see what happened when I dipped the can into the etchant.  The reaction is MUCH faster than with the Copper PCB.  I let it etch away a couple square inches of the aluminum can.

The mixture got quite hot, and I was getting scared, so I decided it's time to neutralize the evil stuff.  It was a coppery/green color, clear solution at this point. 

I started pouring in baking soda to neutralize the acid.  After some vigorous bubbling, the whole mixture turned color from green to blue, and turned into a gel!

What did I make?

Thanks,
  -Caleb

[unsu]

What is PCB ?

[ccrome]

What is PCB ?

A printed circuit board: http://en.m.wikipedia.org/wiki/Printed_circuit_board

[Tittywahah]

My best guess? is that you got first an aluminium carbonate, But, this is not stable and would decompose to aluminium hydroxide which is insoluble, But very deliquescent, and that gel might be the hydroxide of aluminium promoted by the bicarbonate you added due to the extra H⁺ ions added. The blue however is indicative of copper, and you could have also copper hydroxide mixed in with the aluminium hydroxide. When you added the bicarbonate you displaced the copper chloride green with copper carbonate dominating with the blue as well probably, which I might add does not exist except in the hydrated form as azurite and malachite. The malachite is green and the azurite blue, but it is impossible to get this azurite under these conditions except that here you might have a combination of the two hydroxides mixed - all in all Pretty much a real headache of a mixture.  These are my first thoughts, probably someone might have a simpler explanation though. Basically a load of precipitated hydroxides.

[ccrome]

My best guess?

Ha!  So, maybe not so simple :-) 

Thanks for the guess.

-Caleb