Filtration

Filtration is a technique used to separate a solid from a liquid and is used in many labs. Though filtration can be done simply with gravity, more often vacuum filtration is employed because it is much faster. Several points are worth remembering. First, be sure to clamp your filter flask down. These flasks are easily upended. Place a water trap between your filter flask and the aspirator. Also, be sure to use thick-walled vacuum tubing and not the thin walled tubing used for water lines. You should also turn the water on full blast to achieve the maximum vacuum.

The Water Trap



1) Turn water on full blast when filtering. Otherwise please turn water off as we have found that after prolonged used the cup sinks will leak into the lab drawers, onto the floor, and through the ceiling of the basement labs!

2) Close pinch clamp to filter. Open clamp to release vacuum.

3) Clamp should be used to keep trap from tipping.

Also notice that thick-walled tubing is used.

Please keep the water trap assembled on the benchtop at all times. Do not dissassemble the water trap in an attempt to clean up after an experiment. You may dissassemble, clean, and reassemble the water trap as necessary, but it should be left assembled and ready for use all the times.
You will need to find a filtration flask (Erlenmeyer with side arm), vacuum adaptor, Buchner funnel, filter paper (5.5 cm diameter), thick-walled rubber tubing, and a spatula.
 Supplies
Typical Apparatus Setup



1) Thick-walled rubber tubing is used.

2) Pinch clamp should be closed during filtration..

3) Clamp filter flask securely.

Once your setup is complete, place a piece of filter paper on the filter and wet it with the solvent that you will be pouring through filter. A mixture of a solid and a liquid can be separated by simply pouring through the filter. Solid that remains in your flask can be further transferred with the aid of a spatula or with a little more solvent.

After filtration, the solid or crystals that you collect can be washed with a small amount of a solvent in which they have a low solubility. Often, a solvent cooled in an ice bath is a good choice. After washing, the apparatus can be dissasembled by breaking the vacuum. You may either open the pinch clamp or remove the vacuum tubing from the filter flask. If you turn off the water before releasing the vacuum, you will likely draw water into the water trap (if you remembered to use the trap!) or into your filter flask, which is undesirable.