Narration : 13. Vacuum Filtration
- Vacuum filtration is suitable for separation of light and fine precipitate, since gravity filtration is time consuming. An aspirator reduces the pressure to make the filtration fast.
- Organic precipitates in synthetic experiments are usually collected by this method.
- Connect a filtration chamber and an aspirator with thick wall rubber tubing through a three-way stopcock.
- Attach a rubber adapter to a Büchner funnel and set it at the top of the filtration chamber.
- Put a beaker in the filtration chamber. If the beaker is too far from the tip of the funnel, place a rubber board underneath.
- Wet the contact between the bottom rim of the filtration chamber and the coaster glass plate. Slightly rub ground glass to make a good contact.
- Put a filter paper slightly smaller than the inside of the Büchner funnel and add a small amount of a solvent to wet it.
- Turn on the aspirator and open the three-way stopcock to fit the filter paper to the funnel.
- Stir the sample and pour it into the funnel with vacuuming.
- The remaining precipitate in the container is completely transferred into the funnel as follows. Release the vacuum in the filtration chamber via the three-way stopcock. Transfer the filtrate back to the original container. Pour the mixture onto the filter paper again while applying vacuum.
- Next, wash the precipitate 2 or 3 times as follows. Release the vacuum in the filtration chamber via the three-way stopcock. Pour a suitable solvent to the funnel to soak the precipitate on the filter paper.
- Suck the liquid thoroughly under vacuum by gently pressing the precipitate on the filter paper with the bottom of a small beaker. Continue sucking for an additional few minutes.
- Release the vacuum in the filtration chamber via the three-way stopcock.
- And, release the vacuum in the aspirator.
- Finally turn off the aspirator.
- If the aspirator is turned off first, the water backflushes into the filtration chamber.