When do we use Vacuum Filtration?When 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 techniques– gravity filtrationgravity filtration– suction filtrationsuction filtration

• In this course, we will use suction filtrationsuction filtration primarily when our objective is to further process the solid phasesolid phase.– We will normally discard the solution that is captured in

the process

• Gravity filtrationGravity filtration is normally used when the liquid phase is the one in which we are interested. A separate presentation deals with gravity filtration.

The The ApparatusApparatus

aspirator

ring stand

Thick walled rubber tubing

filter paper

Buchner

funnel

filter flask

clampclamp holder

wash bottle

Rubber stopper

Locate a water tap equipped

with an aspirator.

Clean and rinse a filter flask with distilled water

Clean 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 arm of the aspirator using

thick walled rubber tubingassemble it

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

Transfer liquid from the beaker containing desired precipitate using stirring rod

When there is no more liquid, use a stirring rod with rubber policeman to scrape remaining solid into funnel.

Keep Aspirator On

Use stirring rod to direct stream to center of filter

paper

Wash collected precipitate with small

amount of solvent. Then dry by sucking air

through precipitate

With aspirator still flowing -- remove top part of Buchner

funnel to break vacuum. Then turn off aspirator.

Keep Aspirator On

Using 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.

Check that the filtrate (liquid) in the suction flask is clear.

If it isis, the filtration has successfully

recovered the solid.

If it is notis not, consider repeating the

filtration.