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Vacuum filtration separates solids from liquids using a filter and vacuum pump. It is commonly used to collect recrystallized solids and separate solids from unsaturated solutions. The amount of solid collected depends on the filter paper’s pore size.
Vacuum filtration is a separation method used to remove a solid from a liquid. Generally the solid is dissolved in a solution. The solution can be unsaturated, saturated or supersaturated, the difference being the concentration of the solid in the liquid. A filter is used to separate the solid from the liquid and a vacuum pump is used to force the liquid through the filter.
In most cases, vacuum filtration is used to collect recrystallized solids. These are particles that have been dissolved in water or some other solvent and then recovered, or recrystallized, by heating. The liquid is evaporated in the process.
After most of the liquid has evaporated, the contents of the beaker or flask are deposited on a filter paper, which is placed inside a Buchner funnel. The funnel is connected to a filter flask, which has a side opening through which air will be drawn through a rubber tube connected to a vacuum.
The rubber hose is first connected to the vacuum source and tested. If there is suction at the other end of the tube, it is then attached to the side arm of the filter flask. Once attached, the top of the filter flask should have suction.
As the sample is poured onto the filter paper, the vacuum pulls the solvent through the paper and deposits it into the filter flask. The vacuum will remove as much solvent as possible from the solid crystals. The solid residue on the filter paper is then collected and weighed.
Vacuum filtration is also used to separate solids from liquid solutions. Unsaturated solutions are solutions that can dissolve multiple solids. It is generally clear and has no suspended particles. Saturated solutions cannot dissolve any additional solids, but are usually clear as well. Supersaturated solutions are generally unclear and have suspended or sinking particles.
Solutions with suspended particles can be separated by vacuum filtration. Solutions in which the solid is dissolved, such as unsaturated solutions, generally require some form of chemical treatment or heating before vacuum filtration can be effective. Generally, saturated solutions cannot be separated by vacuum filtration, but some particles can be collected if the filter paper has an adequate pore size.
The amount of solid collected through vacuum filtration generally depends on the pore size of the filter paper. A smaller pore size will produce more material, while a larger pore size will produce less material. Generally, the pore size of a filter paper is less than a micrometer in diameter.
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