How To Filter A Solution

Filtration

Filtration is a technique used either to remove solid impurities from an organic solution or to isolate an organic solid. The two types of filtration commonly used in organic chemistry laboratories are gravity filtration and vacuum or suction filtration.

Gravity Filtration

Gravity filtration is the method of choice to remove solid impurities from an organic liquid. The impurity can be a drying agent or an undesired side production or leftover reactant. Gravity filtration can be used to collect solid product, although generally vacuum filtration is used for this purpose because it is faster.

A filtration procedure called "hot gravity filtration" is used to separate insoluble impurities from a hot solution. Hot filtrations require fluted filter paper and careful attention to the procedure to keep the apparatus warm but covered so that solvent does not evaporate. Hot gravity filtrations are no longer included in the routine procedures for the experiments in the organic chemistry teaching labs. If you demand to do such a filtration, read the procedure in the Handbook and consult your TA.

To perform a standard gravity filtration, first select the size of filter paper that, when folded, volition be a few millimeters below the rim of your stemmed funnel. Fold the paper into a cone by start folding it in one-half, and and so in half once again, as shown.

Next, support the glass funnel in a ring or identify it in the neck of an Erlenmeyer flask. Wet the filter paper with a few milliliters of the solvent to be used in the post-obit process. Wetting the paper holds information technology in place confronting the glass funnel. Cascade the mixture to be filtered through the funnel, in portions if necessary.

Fluted filter paper is often better for gravity filtration with organic solvents. A diagram of how to fold fluted filter paper is shown below.

Vacuum Filtration

Vacuum filtration is used primarily to collect a desired solid, for case, the drove of crystals in a recrystallization procedure. Vacuum filtration uses a Buchner funnel and a side-arm flask. Vacuum filtration is faster than gravity filtration, considering the solvent or solution and air is forced through the filter newspaper by the application of reduced pressure. Do not apply vacuum filtration to filter a solid from a liquid if it is the liquid that y'all want, and if the liquid is low boiling. Whatever solvent which boils at about 125 degrees or lower volition boil off under the reduced pressure in the vacuum flask.

	To perform a vacuum filtration, clamp the flask deeply to a ring stand up.
	Add a Buchner funnel with a condom funnel adaptor.
	Obtain a piece of filter paper in the funnel that is pocket-size enough to remain flat but large enough to embrace all of the holes in the filter. If necessary, you can cutting a larger piece of filter newspaper downwardly to size.
	Place the paper in the funnel.
	Connect the side arm flask to a vacuum source. Always use thick-walled tubing, since Tygon tubing will collapse under reduced pressure.
	Moisture the paper with a small amount of the solvent to exist used in the filtration. This causes the paper to attach to the plate and keeps materials from passing under the paper during filtration. Turn on the vacuum source. Make sure that the paper is secure on the filter, that air is existence drawn through the newspaper, and that all of your apparatus is securely clamped. If you are using a Neoprene filter adaptor, you might demand to press on the funnel to engage the seal and thus the vacuum.
	Pour the mixture to exist filtered onto the filter paper. The vacuum should rapidly pull the liquid through the funnel. Watch that particulates practise non creep nether the edges of the paper. If this happens, start over and advisedly pour portions of the solution onto the very center of the newspaper.
	Rinse the cake with a pocket-sized amount of fresh, cold solvent to assistance remove impurities that were dissolved in the filtrate.
	Carefully disconnect the rubber tubing.
	Remove the filter paper and the collected solid that is on information technology.
	Usually you will need to fix the product on a watch glass and let it air dry out for a while.