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Unformatted text preview: shielding. If you use vacuum
pumps, place a cold trap between the apparatus and the vacuum pump so that
volatiles from a reaction or distillation neither get into the pump oil nor out into the
31 students short index 1/15/03 12:45 PM Page 32 atmosphere of the laboratory. When possible, vent exhausts from pumps to a laboratory hood. Vacuum pumps with belt drives must be equipped with belt guards.
Water aspirators for reduced pressure are used for filtration purposes and for some
rotary evaporations. Use only equipment that is approved for these purposes. For
example, use only a heavy-walled filter flask designed for the purpose; never apply
reduced pressure to other flat-bottomed flasks. When you use a water aspirator for
reduced pressure, place a trap and a check valve between the aspirator and the apparatus so that water cannot be sucked back into the system if the water pressure should
fall unexpectedly while filtering.
Superheating and consequent bumping (sudden boiling) frequently occur when you
use reduced pressure for distilling. Therefore, it is important that the assembled apparatus is secure and that heat is distributed more evenly than is possible with a flame.
Use a heating mantle whenever possible. See the “Distillations” section on page 7.
Evacuate the assembly gradually to minimize the possibility of bumping. Stirring or
using a nitrogen or other inert gas (never use air) bleed tube often can provide good
vaporization while preventing bumping or overheating and decomposition. Use standing shields to surround the apparatus for protection in the event of an implosion.
After you finish a reduced-pressure distillation, allow the system to cool before slowly
bleeding in air; the oxygen in air that is introduced into a still-hot apparatus may
induce an explosion in the hot system. Pure nitrogen or other inert gas is preferable
to air during distillation and for cooling the system. 32 students short index 1/15/03 12:45 PM Page 33 4. Safety Equipment and Emergency Procedures
Chemistry laboratories are equipped with one or more eyewash fountains and safety
showers. Each person who uses...
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This document was uploaded on 02/27/2014 for the course PHYS 1B at UCSD.
- Spring '07