What is Vacuum Filtration?
Vacuum filtration, also known as suction filtration is a laboratory technique that is widely used in chemistry labs to filter the given sample more precisely. This advanced form of filtration is not only more efficient but also faster than normal filtration since here both the air and solvent are forced down to filter paper, artificially.
Suction filtration is usually used to perform recrystallization, where a crystallized substance undergoes the crystallization process again, to become purer. However, vacuum filtration is not suitable for low boiling samples (having a solvent with a boiling point below 125°) since the reduced flask pressure may start boiling the filtrate.
How does Vacuum Filtration Work?
In normal filtration, we use a filter paper, place it at the mouth of the flask and let the sample pass through the paper, with the help of gravitational force. While doing so, the solid and bigger enough particles stay at this side of filter paper whereas the smaller particles pass through it along with other liquid content and fall to the flask.
In vacuum filtration, we don't rely completely upon the gravitational force and use a pressure gradient instead. This pressure gradient is attached to the flask that creates a suction within it. It, in turn, pulls the sample across the filter paper more strongly so not even a single drop of liquid is left to that side of the filter paper. You can change the intensity of the vacuum by adjusting the pump strength as per your needs.
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How to Perform Vacuum Filtration Step by Step?
For the vacuum filtration setup, you first need to gather the apparatus including the filter paper, Buchner funnel, rubber plug, rubber tubing, and the vacuum pump. On gathering all these things, you have to follow the given vacuum filtration setup steps.
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Step#1: Set the Filter Paper
Just as the first step of normal filtration, to experiment with a vacuum filter, you need to set the filter paper over the Buchner funnel. However, try your best to match the filter paper diameter accurately with that of the funnel. If the filter paper is too large, it won't be able to sustain the pressure and if it will be too small, it might be ripped off.
Cut the filter paper to the proper size and shape using scissors. Once cut to the accurate size, wet the filter paper a little with the same solvent your mixture-to-be-filtered contains. It will adhere the filter paper more firmly to the funnel and keep it from slipping inward.
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Step#2: Place Rubber Plug
Secondly, get the rubber plug and place it on the flask's mouth. In the center of the rubber plug, you'll notice a hole from where you need to pass a funnel. That's the very reason why we use rubber plugs so they can make the funnel fit into the vacuum flask chemistry apparatus safely and tightly. Also, it prevents the glass funnel from shaking or hitting the glass walls of the flask during filtration.
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Step#3: Connect Vacuum Pump with Vacuum Flask
Next, you have to put the filtration funnel to the rubber plug you fitted over the flask opening in the previous step. After this, connect the vacuum pump to the vacuum flask through the given side nozzle. To fix the vacuum pump tightly with the flask, you need rubber tubing.
Step#4: Pour Sample Mixture
Once you have set the vacuum filtration apparatus, you can experiment. Pour your sample mixture through the filter paper to the Buchner funnel and turn the vacuum pump on. In doing so, the solid will get extracted from the liquid content of the mixture under reduced pressure.
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