Aluminum Properties: Why Does It Not React with H2 and Plate Silver?

[kq6up]

I find it strange that Aluminum is high on the activity series but does not react with evolution of hydrogen with many strong acids. I actually tried this when I was a kid. I had access to any acid or salt I wanted. I tried dissolving Al in H2SO4, HNO3, and HCl with no H2 bubbles. Aqua regia absolutely destroyed it. Is this due to the oxide coating on the Al?

Moreover, I have read that it is inert to single replacement of Ag in spent photographic fixer, and that it is recommended to use as an electrode to plate Silver out of spent fixer. I have it in old photographic fixer now, and it does not seem to be involved in any replacement reaction.

Cu would not work as it would be replaced by the Ag out of the fixer, and it would just cause the Ag to precipitate instead of plating out.

Any hints as to what is going on hear would be appreciated.

Thanks,
Chris Maness

 

[Alkim]

Al is indeed very reactive. However, usually it is covered by a thin and compact oxide layer. If you remove that layer and assure it is not formed immediately (e.g. rubbing the surface of the metal with mercury or mercury nitrate), the metal behaves more or less like magnesium, reacting vigorously with air, water and acids. Also, aluminum powder with no previous treatment burns like magnesium when thrown into a flame.

 

[Borek]

http://en.wikipedia.org/wiki/Passivation_(chemistry)

 

[kq6up]

It is working. There is grey Ag on the bottom with a Ag colloid hovering above it. The Al electrodes was inert in this process. They look exactly the same.

I think I would rather plate it out than gather a precipitate. Al would be an ideal substrate because it does not dissolve in HNO3 readily. However treating the surface might change that.

My desire is to convert all of this to AgNO3 to experiment with wet plate or tin type photography. I have five gallons of very heavily used fixer. It probably contains well over an ounce per gallon.

Thanks,
Chris Maness