Vacuum Filtration

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Vacuum Filtration
Step 1: Pour filtrate into Buchner funnel with correct size* filter paper already in place. The filter paper is wetted with the vacuum on. To get as much solid as possible, swirl before pouring.

*smallest size - D=4.25 cm - from Service Center Counter

•Avoid the most common mistakes: the use of thin-walled hose (it collapses under vacuum), forgetting the neoprene vacuum adapter (without it there is no vacuum), and connecting to natural gas instead of vacuum (!!).

•Check out with the vacuum tap before connecting to it and determine by the sound which position gives maximum vacuum - the taps do vary a little.

•Clamping is recommended.

REMINDER: Vacuum filtration is the method of choice for collection of a solid product. Typically, to remove solid impurities from a desired solution, gravity filtration is used instead.  In both processes the solution passing through the filter is called the "filtrate."

Step 2:

©2001,2002 Daniel A. Straus

Wash the filter cake (collected solid) with a couple of small portions of cold solvent (The photo shows that the wash solvent can do double duty by using it to rinse some of the solid left behind onto the filter):

•Turn vacuum off.

•Pour in cold wash solvent to cover solid.

•Turn vacuum on.

•Repeat.

•Air-dry: suck air through the filter cake for a few minutes to remove much of the solvent.

(A drying procedure is often the next step, to purify the product of solvent traces.)

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