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Chemistry Buchner Funnel Filtration

Filtration using a Buchner flask, suction pump, Buchner funnel

Filtration is a technique used either to remove impurities from an organic solution or to isolate an organic solid. The two types of filtration commonly used in organic chemistry laboratories are gravity filtration and vacuum or suction filtration.  This type of filtration is the suction method and is ideal for doing things quickly or for large quantities.

You need to use a heavy walled flask as when sealed on the top with a stopper or a Buchner funnel, the vacuum flask will hold a reduced pressure. These heavy walled flasks are designed to withstand pressure without imploding.  If you use a standard flask it will implode due to the pressure caused from the suction.

Set up of the equipment should look like this:
The flask is securely clamped; there is a rubber adaptor in the flask to form a seal with the funnel.

From the flask side arm the water suction is connected.  This tube needs to connect at the other end to a t-junction on the tap that the water passes through and creates the suction for the filtration.  The tubing from the flask to the connection needs to be thick-walled to with stand the pressure from the suction, normal tubing is likely to collapse.

Turn the suction on and ensure all is working before filtering anything.

Filter paper needs to be wet to ensure it is sealed to the filter and nothing goes under it etc.

Pour the solution into the filter; it should quickly pull the liquid through the funnel.

Turn the suction off and then remove the filter cake and place on a watch glass to dry.