Hey guys, I've got a little question. In a chem lab we synthed alum, and in figuring out moles or something we were told to factor in H2O, even though we had a dry powder from the vacuum filtration. I don't fully understand where the water comes from. Is alum so hygroscopic that it has some water even when it is completely dry?

I am a little drunk, so please forgive any vagueness in my questions and feel free to clarify anything...

http://en.wikipedia.org/wiki/Alum

It's a hydrated complex, thus the water is co-ordinated and not residual moisture. For every mole of aluminium, there are 12 moles of water.

Dunno about this one, but in certain hydrates you can remove the water of crystallisation by heating under vacuum.

charles bronson
the machanic.

Ok, now I'm really drunk after playing a few rounds of beer pong with one of my RAs, but I'll look at that in the morning, thanks. I guess I should have wiki'd it before making a thread though... g'night everyone!

Damn, Im good at typing when I'm drunk. It takes me a while though! :D