2When do we use Vacuum Filtration? Filtration is the separation method of choice when the phases to be separated are a solid (precipitate) and a liquid (solution).There are two major filtration techniquesgravity filtrationsuction filtrationIn this course, we will use suction filtration primarily when our objective is to further process the solid phase.We will normally discard the solution that is captured in the processGravity filtration is normally used when the liquid phase is the one in which we are interested. A separate presentation deals with gravity filtration.
3The Apparatus ring stand aspirator filter flask wash bottle Buchner funnelRubber stopperfilter paperclampclamp holderThick walled rubber tubing
4Locate a water tap equipped Clean and rinse a filter flask with with an aspirator.Clean and rinse a filter flask withdistilled water
5Clean the parts of a Buchner funnel, rinse with distilled water and Secure filter flask on a ring stand with clamp and connect the flask to the side armof the aspirator using thick walled rubber tubingassemble it
6Place Buchner funnel assembly in the top of suction flask Place Buchner funnel assembly in the top of suction flask. Start water flow in aspirator and check that vacuum is produced when you hold your hand over the mouth of the funnel.Insert filter paper in Buchner funnel. Wet the filter paper with small portion of distilled water from wash bottle.Keep Aspirator On
7Use stirring rod to direct stream to center of filter paper Transfer liquid from the beaker containing desired precipitate using stirring rodWhen there is no more liquid, use a stirring rod with rubber policeman to scrape remaining solid into funnel.Use stirring rod to direct stream to center of filter paperKeep Aspirator On
8Then turn off aspirator. Wash collected precipitate with small amount of solvent. Then dry by sucking air through precipitateWith aspirator still flowing -- remove top part of Buchner funnel to break vacuum.Then turn off aspirator.Keep Aspirator On
9Using a spatula, loosen the filter paper from the funnel and transfer it to a watch glass The precipitate cannot ordinarily be separated from the filter paper until both are dry.
10Check that the filtrate (liquid) in the suction flask is clear. If it is, the filtration has successfully recovered the solid.If it is not, consider repeating the filtration.