![]() ![]() Never fill the cone completely, since many precipitates tend to creep upward and may be par- tially lost.Try to keep the filter paper about 3/4 full of liquid during filtration to provide maximum filtra- tion speed.Utilize a rubber policeman on the end of a stirring rod to get the last grains of precipitate out of the beaker in a quantitative transfer.Employ a stream of solvent from a wash bottle to transfer the final portion of precipitate if quantitative transfer is required.Use a stirring rod to direct the flow of liquid into the funnel and prevent small amounts of liquid from running down the outside of the beaker when the transfer process is interrupted.The major transfer is done with the last wash. If the precipitate needs to be washed, the washing is most efficiently done while the solid is still in the beaker.Transfer the bulk of the solid during the last stages of the filtration process.This is done to prevent early accumulation of precipitate on the filter paper which would slow the filtration process. Then carefully decant (pour off liquid leaving solid in container) the supernatant liquid through the filter.Before filtering the mixture, allow the solid to settle to the bottom of the beaker.Transferring the mixture: If it is important to quantitatively (completely) transfer the solid to the filter paper, a beaker should be used as a transfer vessel rather than a flask.Place the tip of the funnel against the side of the vessel which receives the filtrate to eliminate spattering and to provide an unbroken stream of liquid from the undersurface of the paper to the bottom of the collection container.This method of folding and positioning the paper insures that most of the paper does not make direct contact with the funnel wall thereby permitting liquid to flow between paper and glass below an air tight seal.Moisten the paper with the solvent to be used in the filtration and press the top of the paper against the funnel all around its circumference to seal the space between the funnel wall and the paper.Tear off the corner of the paper to enable a closed seal to be made across the folded portion of the paper.Place the folded paper in the funnel so as to give a snug fit.The folding steps are illustrated in Figure PAGENUM. Much of this depends upon correct folding and positioning of the paper. Filter paper folding and positioning: Maximum advantage of capillary attraction must be taken to speed the passage of the filtrate through the paper.Sargent Welch S-32915, Whatman 1, and E-D 617 have appropriate pore size for work in this course. Filter paper porosity: Filtration operations in General Chemistry involve crystalline precipitates of relatively large crystal size so that coarse or medium porosity filter paper is used.Optimum filtration performance is achieved by the appropriate selection of filter paper porosity, by proper folding and positioning of the filter paper, and by following a few simple technique guidelines described below: It is convenient to support the filter funnel by a utility clamp. Gravity filtration usually utilizes the long stem funnel with normal quarter-folded 11 cm diameter filter paper (Figure PAGENUM), when the filtration is done at room temperature or below. ![]()
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