Organic 2 Review Problem 28

Organic 2 Review Problem 28 - for filtering hot solutions....

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12 PRACTICAL ORGANIC CHEMISTRY filter it in the usual way through a Buchner funnel. The dis- advantage of this method is that the heavy porcelain funnel may so chill the solution that crystallisation occurs before filtration is complete and the funnel may become choked with crystals, both above the filter and below in the stem. The disadvantage may be often overcome by boiling a quantity of the pure solvent (particu- larly if the latter is water) and, immediately before filtration of the solution, placing the filter-papers in the funnel and filtering a moderate quantity of the pure boiling solvent through the funnel into the flask. The solvent is then poured out, and the hot solution at once filtered through the hot apparatus. This pre- heating of both funnel and flask will often enable a hot solution to be filtered and the clear filtrate transferred into a beaker before any separation of solid matter occurs. A "hot-water funnel" is a slower and less efficient apparatus
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Unformatted text preview: for filtering hot solutions. A satisfactory form of the apparatus is shown in Fig. 6, in which the double-walled funnel is heated by blowing steam through the apparatus as shown. A glass filter funnel of the usual type fits snugly into the hot-water funnel. This type has the advantage that, during the fil-tration of a hot inflammable liquid, the steam generator (and therefore the heating appar-atus) can be removed to a safe distance. It should be noted that the inner glass funnel should have a stem so short that it projects only just below the outer metal funnel. If the stem is longer it serves merely to cool the filtered solution, which may then crystallise and com-pletely stop the filtration. For the filtration of small quantities of dilute solution, it is often possible to dispense with the outer heater, and use the ordinary glass funnel which has been heated above a flame immediately before use. Steam FIG. 6....
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This note was uploaded on 09/19/2011 for the course CHM 2211 taught by Professor Castalleano during the Fall '06 term at University of Florida.

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