Question about why this vacuum setup works.

[blackhole123]

So I'm degasing a solution in a glovebox. The way we did it is get a rubber septum that can cover the bottle opening. We stuck a needle through the top of it, as well as a glass tube with a porous end. We used the needle to create a vacuum in the bottle by hooking up it up to a pump. The glass tube is submerged in the solution, but is stuck through the rubber to be the only opening into the box. The argon from the glovebox then flows down the glass tube and out the frit at the bottom, degassing the solution.

 

I can't figure out why the gas would be sucked down the tube. Sure there is a vacuum in the bottle, but the tube opening is submerged. It doesn't know or care that there is a vacuum above it. The only part of the glass tube that experiences vacuum is the long tube part without any openings. So how is the vacuum sitting above the liquid making the gas flow into the tube which has it's end submerged?

 

Obviously it works for some reason, I just don't know why.

 

This has been bugging me, thanks.

Edited July 8, 2011 by blackhole123

[Marqq]

So I'm degasing a solution in a glovebox. The way we did it is get a rubber septum that can cover the bottle opening. We stuck a needle through the top of it, as well as a glass tube with a porous end. We used the needle to create a vacuum in the bottle by hooking up it up to a pump. The glass tube is submerged in the solution, but is stuck through the rubber to be the only opening into the box. The argon from the glovebox then flows down the glass tube and out the frit at the bottom, degassing the solution.

 

I can't figure out why the gas would be sucked down the tube. Sure there is a vacuum in the bottle, but the tube opening is submerged. It doesn't know or care that there is a vacuum above it. The only part of the glass tube that experiences vacuum is the long tube part without any openings. So how is the vacuum sitting above the liquid making the gas flow into the tube which has it's end submerged?

 

So, the argon is dissolved in the solution...and you're decreasing atmospheric pressure. I'm pretty sure I remember from high school chemistry that doing so would decrease the solubility of whatever is dissolved (along with moving the freezing/boiling point). Kinda like opening a can of pop-- air pressure inside the can is much higher than outside, and when you release that pressure (making a relative vacuum), the CO₂ .... I can't remember the word for un-dissolving--solve maybe?...but you get the point, and that's what you're doing to the argon. Do you also cool the solution while degassing? I think that also changes solubility, but that can also be a method for saturation, so idk how much difference it would make...

Edited July 11, 2011 by Marqq