safety-in-academic-chemistry-laboratories-students

Dispense and handle these substances in a laboratory

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Unformatted text preview: Do not work with such substances on a laboratory bench. Dispense and handle these substances in a laboratory hood. See “Laboratory Hoods” on page 27. 6 students short index 1/15/03 12:45 PM Page 7 Distillations Distillation is a common method of separation and purification used in laboratory and industrial operations. Potential dangers arise from pressure buildup, the use of flammable materials, initiation of an exothermic chain (runaway) reaction, and the necessity to use heat to vaporize the chemicals involved. Various apparatus designs are used to accomplish distillations at atmospheric pressure, under inert atmospheres, at reduced pressure (vacuum distillation), or by the addition of steam to the distillation mixture (steam distillation). Careful design and construction of the distillation system are required to accomplish effective separation and to avoid leaks that can lead to fires or contamination of the work area. It is desirable to ensure smooth boiling during a distillation and to avoid bumping, which can knock the distillation apparatus apart or cause other damage. Stirring the distillation mixture (e.g., with a magnetic stirrer) is one way to prevent bumping. Alternatively, boiling stones can be effective for distillations performed at atmospheric pressure. Use fresh boiling stones to boil a liquid without stirring. Do not add boiling stones or any other solid material to a liquid that is near or at its boiling point, because the addition is likely to cause the hot liquid to suddenly erupt and boil over. Instead of boiling stones, use a short glass tube that has one end closed. Before starting the distillation, place the tube in the liquid to be heated in an approximately vertical orientation, open-end down. If the distillation is stopped and it is necessary later to reinitiate the distillation, you will need a second glass tube, or you can remove the original glass tube, drain out its contents, and then put it back into the liquid for use again. The source of heat is an important...
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This document was uploaded on 02/27/2014 for the course PHYS 1B at UCSD.

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