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The mixture of liquid and solid is poured into a Buchner funnel which has been inserted to a flask with a side-arm (Buchner flask) connected by a hose to a vacuum source. The liquid is sucked into the flask, and the solid remains in the funnel.
More important detail about the apparatus and the procedure:
A rubber fitting is inserted between the funnel and the flask so that a vacuum can be achieved.
This is in black in the photograph and orange-red in the diagram.
What about the filter paper?
As shown in the diagrams, the Buchner funnel has a flat bed to increase the surface area over which the solid is spread and enhance removal of the solvent from the solid. The solvent goes through holes in the flat bed.
The solid collects on top of filter paper that covers the holes in the flat bed of the funnel. The diameter of filter paper used should be just less than the inside diameter of the funnel so that the filter paper lies flat.
To ensure maximum separation of solid and liquid when the slurry is poured into the funnel, the filter paper is first sucked onto the flat bed of the funnel. Thus after putting the filter paper into the funnel, it is moisten with a small amount of liquid. Then the vacuum is turned on.
To ensure maximum separation of solid and liquid when the slurry is poured into the funnel, the filter paper is first sucked onto the flat bed of the funnel. Thus after putting the filter paper into the funnel, it is moisten with a small amount of liquid. Then the vacuum is turned on.
Swirl the mixture and then pourthe resulting slurry into the funnel. Depending on how quickly the filtration occurs, you may have to do this more than once. If solid remains in the flask, use a spatula with one end bent (or a glass with a flat end) to guide the solid out of the flask onto the bed of the funnel.
The solid should be distributed over the bed of the funnel in an even layer. Any lumps should be crushed by applying gentle pressure using a glass rod or spatula.
Once there is a uniform layer of solid, leave the vacuum on, pulling air through the solid for several minutes.
How are traces of soluble impurities removed?
This can be done by pouring a small amount of a cold appropriate solvent solid through the solid on the bed of the funnel.