Q: How do you spell vaccume?
A: Vacuum.

Q: When do you use vacuum filtration?
A: Generally when you want to isolate a solid. It is rapid (in most cases) so the slurry being filtered will remain cold - an advantage in cases where the solid is partly soluble in the solvent being used. (By contrast, gravity filtration is advantageous when removing minor amounts of solid impurities from a solution. It can be done on a hot solution whereas vacuum filtration may not.)

Q: My filtrate appears cloudy - how would product be passing through the filter paper?
A: If you don't wet the filter paper with solvent being used in the filtration first, some solid may get under it when the slurry is poured in.

Q: What could cause my filtration to be slow?
A: The most common error is to leave out the neoprene adapter - without it you can't maintain a vacuum in the sidearm flask. Another common mistake is to use thin-walled tubing, which collapses under vacuum. Most of the filtrations we are doing in this lab should be reasonably fast.

Q: Why turn off the vacuum when adding wash solvent?
A: So the solvent comes in contact with all of the solid - use just enough wash to cover the solid, the turn the vacuum on.

Q: Is it necessary to stir the solid on the funnel during washing?
A: Not really, and you run the risk of tearing the filter paper. Lehman recommends this, but I don't.

Q: Will we be using a trap on the vacuum line as shown in the text?
A: No. We are using house vacuum directly (yellow taps). The trap is intended to accompany a water aspirator, which we will not be using. (The trap would keep water from the aspirator from backing up into our sidearm flask).

©2001,2002 Daniel A. Straus