Buchner Flask Setup: Separating Liquids Made Easier

buchner flask

The Buchner flask’s principal function is that of removing unwanted solids from liquids. It does so by making the mixture of liquid and solid pass through a filter, which itself has a paper-made filter in the funnel.

This way, it blocks the solid particles so that the remains can be passed into the flask, thereby collecting them at the end.


Buchner Flask – The Setup

Buchner funnels are made in different materials. The most commonly-used for funnels are porcelain as well as plastic or glass. In general, porcelain is used more than all the others.

A Buchner flask made of glass must be placed on a flat table. On top of this flask, there is another container having a modest hole at the bottom. You have to gently place this container on top of the flask made of glass.


The hole has to face downward. Here, the most important part is the piece of paper acting as a filter. You have to place it inside the funnel because it can segregate the solids from the fluid. At the side hole, there is another vacuum sucking out the air present in the flask.

It is very important that the funnels are placed on a flat surface because vacuum filtration is only properly done in this way.

Another important rule that you must follow is to check that the filter task and a vacuum trap (hole) are securely fastened.

When you pour the mixture into the top container of the Buchner flask, the solid particles will adhere to the filter paper. Liquids will flow freely through the filter paper, directly inside the flask placed below. The funnel is mainly used to collect recrystallized compounds. It does so by drying the wet crystal with vacuum suction, leaving dry crystal compounds behind.


Removing Unwanted Solids 

For proper removal of the unwanted solids from the fluids, there are some basic norms you should follow all throughout the process while using a Buchner flask:

1. You have to moisten the filter paper with a solvent before using it, so that it may prevent leakages;

2. The pouring fluid that has to be filtered into another receptacle is forced through suction of vacuum;

3. The general norm is that the solvent shouldn’t exceed the necessary conditions, otherwise the extra will also get sucked into the vacuum suction.

4. Always cut the filter paper with scissors if it is too big for the funnel;

5. You have to thoroughly check the equipment used. The filter flask made of glass has to be flawless, without any cracks.

6. Vacuum filtration is usually not suitable for those solvents having a low boiling point, such as diethyl ether or in general solvents that boil easily. If a solvent boils, it evaporates in a vacuum. This means the solids that were previously dissolved fall inside the filter paper, therefore clogging up its pores.



Being one of the most important and widely used tools in chemistry, Büchner funnels are easily found in chemistry laboratories. It is the essential equipment you can use to speed up the chemical processes, making your experiments easier.

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