What remains after H2O evaporates from H2SO4?

[maker]

Hi,

I have a 5 gallon container that was 1/2 filled with an H2SO4 solution (15% by volume). The solution also had 6051 aluminum rod that was sitting inside.

After sitting for several months, all of the water has evaporated (or reacted?) and a portion of the aluminum tubing has corroded away. What is left is white crystal powder attached to the remaining aluminum.

Can someone tell me what this substance is? I'm guessing it is salt crystals attached to aluminum rod, but I'm no chemist! Assuming this is something other than salt, what is the best method of disposal (i.e. Bring it to hazardous waste disposal, dilute and flush, poor it in my garden :) , pour it in my neighbors garden :D)?

My Ph meter is broken, so I can't even check the Ph at the moment.

Thanks,
M

 

[Charles Link]

It's likely that it produced aluminum sulfate. You can google it. It is sometimes used to lower the pH of soil and apparently is also sometimes used to melt ice and snow on sidewalks.

 

[hilbert2]

Water doesn't evaporate from a $H_2 SO_4$ solution of that strength, because the sulfuric acid is hygroscopic. Instead, it absorbs water vapor from the air and becomes more dilute. $H_2 SO_4$ reacts with aluminum to produce hydrogen gas and aluminum sulfate/bisulfate or complexes of those salts with $H_2 O$ and $OH^-$ species (except maybe if the acid is so concentrated that it acts as an oxidizer and produces a protective film on the metal). If you put aluminum and $H_2 SO_4$ in a sealed container, it is likely to explode because of the pressure of the hydrogen gas - don't do that. You probably had an open or loosely closed container in this case ?

 

[nikkkom]

Can someone tell me what this substance is?

It's Al2(SO4)3, AlH(SO4)2 and similar.

what is the best method of disposal (i.e. Bring it to hazardous waste disposal, dilute and flush, poor it in my garden :) , pour it in my neighbors garden :D)?

Neither aluminum nor SO4 ions are hazardous, or we wouldn't routinely use aluminium spoons and gypsum.

 

[snorkack]

Water doesn't evaporate from a $H_2 SO_4$ solution of that strength, because the sulfuric acid is hygroscopic. Instead, it absorbs water vapor from the air and becomes more dilute.

No. Data of sulphuric acid humidity:
http://bio.groups.et.byu.net/Equilibrium_Humidity_of_Sulfuric_Solutions.phtml

 

[Nik_2213]

Per original question, if you 'dehydrate' an H2SO4 solution, you'll finish with SO3. It's hard energetically, as both SO3 and the increasingly concentrated H2SO4 are very, very hygroscopic.

FWIW, I used to work in an Analytical lab, remember noticing a 'serious stupid' in progress; "Hey ! Acid to water, not--"
Click !
The Pyrex litre measuring cylinder had cracked at the interface between the 900 mls of 'Conc Sulf' and the slosh of water. The crack spiralled down the cylinder's length. For a cartoon-instant, the mortally wounded cylinder just stood there. Then, it twisted open, emptying its contents over the bench. The operator jumped back. I jumped *sideways*, went for the acid-spill kit...
{Shudder...}

 

[hilbert2]

No. Data of sulphuric acid humidity:
http://bio.groups.et.byu.net/Equilibrium_Humidity_of_Sulfuric_Solutions.phtml

Thanks for the correction. What's the temperature where this data has been measured, and what are the corresponding equilibrium partial pressures of gas-phase sulfuric species (if the $H_2 SO_4$ evaporates to any extent) ?