Add your solution to be filtered and turn on the

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Unformatted text preview: -filter, your filtrate will not be contaminated. Place a collar on the top of the side-armed flask, and a Buchner funnel onto the collar. This collar is not intended to fit snuggly; it will be quite loose, but the vacuum, once applied, will draw it in tightly. Be sure that the vacuum works by turning it on and testing to see that a vacuum is created. Turn off the vacuum, and place a piece of filter paper into the Buchner funnel; the paper must not be larger than the funnel, but it must be large enough to cover all of the holes in the bottom of the Buchner funnel. Moisten the filter paper completely with a little distilled water. Add your solution to be filtered, and turn on the vacuum. If your crystals are to be washed, first, turn off and break the vacuum by lifting the Buchner funnel slightly. Add the wash liquid to the original container, and pour it onto the crystals in the Buchner funnel. Using a rubber policeman, VERY carefully stir the crystals to break them up and wash them thoroughly, but do NOT tear the filter paper. Re-apply the vacuum. This step is usually repeated three times. Decanting: Dakota State University Page 41 of 232 Basic Laboratory Procedures General Chemistry I and II Lab Manual There are times that you would like to separate a mixture, but it is not necessary to do so with extreme care. Decanting is a method in which one can separate liquids from solids in a mixture rapidly, but relatively sloppily. Typically, one begins by centrifuging the mixture; this forces all of the solid to the bottom of the test tube (although if you are decanting from a larger container, say, a beaker, this step is obviously impossible with standard laboratory equipment). Place a stirring rod across the top of the container, not to stop the solid from flowing out, but rather to help the liquid flow out more easily because it breaks the surface tension which can form without it. Slowly and carefully pour the liquid from the mixture into another container; stop when the solid is about ready to pour out as well. It must be kept in mind that this is not a good separation technique; it is designed to be fast and crude when this is all that is required. The solid will still have a considerable amount of liquid left on it, and the liquid will have some of the solid in it as well. Of course, do not use this as an excuse to be sloppy. It is really the analysts call as to when the separation is complete; if you try to get too precise with it, you lose the speed (which is the only real advantage), but if you are not precise enough, you may as well not be decanting at all. The only real hint I can give you is to pour slowly and try to avoid agitating the solution. Centrifuging: Centrifugation is a process which uses centrifugal force to separate mixtures by density; the more dense material will be on the bottom (typically solids) while the less dense will be on top (typically liquid, although a similar technique is used to separate proteins by biochemists). The most important th...
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