Buchner funnels are a piece of laboratory equipment used in filtration.
It is traditionally made of porcelain, but glass and plastic funnels are also available. On top of the funnel-shaped part there is a cylinder with a fritted glass disc/perforated plate separating it from the funnel.
A funnel with a fritted glass disc can be used immediately. For a funnel with a perforated plate, filtration material in the form of filter paper is placed on the plate, and the filter paper is moistened with a liquid to prevent initial leakage. The liquid to be filtered is poured into the cylinder and drawn through the perforated plate/fritted glass disc by vacuum suction.
The main advantage in using this type of filtration is that it proceeds much more quickly than simply allowing the liquid to drain through the filter medium via the force of gravity. It is essential that the amount of liquid being used is limited to less than what would overflow the flask; otherwise, the liquid will be drawn into the vacuum equipment.
Uses of Buchner funnel
- It is used in organic chemistry labs to assist in collecting recrystallized compounds. The suction allows the wet recrystallized compound to dry out such that the pure dried crystal compound is left remaining. However, it is often the case that further drying is required, by an oven or other means, in order to remove as much residual liquid as possible.
- It is often used in combination with a Buchner flask, Buchner ring and sinter seals. A vacuum tight seal and stability of the Buchner flask and filter are essential during the filtration process. A Buchner ring can be used with Buchner funnels, flasks, glass crucibles and Gooch crucibles. The wide flange and large surface contact create an excellent vacuum tight seal whilst the rings are easy to remove and offer excellent support to even the largest funnels.
