What Kind of Filter Paper is Used for Buchner Funnel?

Overview of filter paper

As a ceramic instrument in the laboratory, the Buchner funnel is made of plastic and used to filter by vacuum or negative pressure suction. It is generally believed that the inventor was Edward Buchner, the winner of the Nobel Prize in Chemistry in 1907. In fact, the Buchner funnel was invented by the chemist Ernst Büchner.

The Buchner funnel has many small holes on the bottom of the cylinder with a flat shape. There is a long and narrow cylindrical outlet underneath. When in use, the filter paper disc is generally placed on the bottom of the cylinder, the funnel is inserted into the upper opening of the Buchner flask and the interface is sealed (for example, with a rubber ring).

The side port of the Brinell beaker is connected with a suction system. Then the solid and liquid mixture to be separated is poured into the upper part, the liquid component is drawn into the beaker under the action of negative pressure, and the solid remains on the upper part. The application in organic chemistry experiments to extract crystals is frequently used.

After the filtration, in this case, is completed, to wash away impurities on the crystal surface, a small amount of pure solvent can also be used. Both the Buchner funnel and the suction filter bottle are used to separate the precipitate and the solution. Use a water pump or a vacuum pump to reduce the pressure in the suction filter bottle to accelerate the filtration.
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Use of filter paper in Buchner funnel

Operators will usually use the filter paper together with the filter funnels and Buchner funnels in experiments. Before the experiment, the operators will fold the filtration filter paper into a certain shape to make it suitable for the experience. The flower-like shape filter paper is frequently used. With the higher folding degree, the filter paper will provide a larger surface area and get a better filtering effect. But, please note that the folded filter paper should be not easy to break. It’s suggested to place a drained glass rod on the multi-layer filter paper evenly to prevent damage.

Before use, you need to prepare suction filtration equipment, such as vacuum pump, suction filter bottle, Buchner funnel holder (sealing ring), the vacuum tube (rubber tube), filter paper, Buchner funnel, etc. Wet the filter paper with water first, and pump it so that the filter paper is close to the bottom of the funnel to prevent the things to be filtered from leaking. Pour in the filtrate, turn on the machine to pump, stir a little, to make only the filtered material left.

It is not possible to directly use an ordinary funnel, paste the filter paper, and connect to the suction pump for suction filtration (replace the Buchner funnel). Because the four walls of the funnel are close to the filter paper, negative pressure suction filtration does not work on it. The top corner of the funnel produces a pressure difference. Because the mouth is large and there is only one mouth, it is easy to break(The wet filter paper is not strong).

Summary of filter paper

The filter paper should not be cut too large, otherwise, it will leak easily, and it is better to just cover the hole. It needs to be wetted before suction filtration. If fast hot suction filtration is required, make sure that both the Buchner funnel and the suction filter bottle are heated. Turn on the suction pump first when filtering, pull out the pipe when it is finished, and turn off the power to restore normal pressure to prevent back suction. Choose the right size Buchner funnel and suction flask.