Unformatted text preview: d initially, the reaction can become too vigorous for effective condensation of
vapors once the induction period is completed; a cooling bath must be prepared in
advance and be ready to be applied promptly to the reaction vessel. Remember that
viscous liquids transfer heat poorly and require special precautions.
Many reactions require some temperature control. Assemble your apparatus in such
a way that both heating and cooling can be controlled, that is, readily applied and
withdrawn. For example, when heating the contents of a test tube in a burner flame,
it is easy to overheat and cause the contents to boil up and out. To prevent this, hold
29 students short index 1/15/03 12:45 PM Page 30 the test tube with a test tube holder and heat it gently along the side, not at the bottom. Or, heat the contents of a test tube by placing it in a hot water bath. Never
point a heated test tube toward yourself or any other person. Oil and Sand Baths
When you use hot oil or sand for heating, take care to avoid hazardous splattering if
water or another organic liquid falls into the hot oil or sand.
Avoid overheating an oil bath. Watch for smoking of the oil; oil that is smoking is
too hot and may burst into flames at any moment. If an oil bath starts to produce
smoke, turn off the heat immediately and call your instructor. Do not leave an operating sand or oil bath unattended unless it is equipped with a high-temperature shutoff
and with a warning label (“Hot Oil” or “Hot Sand”).
Ensure that glassware that is to be used in an oil or sand bath is free of cracks and
other imperfections. Do not use a sand or oil bath unless it is equipped with a thermometer or other temperature-indicating device. In addition, an oil bath must be
labeled with the name of the oil and its maximum safe working temperature. Take
precautions to contain any spills of hot oil or hot sand caused by breakage or overturning of the baths.
Cooling Baths and Cold Traps
When ice water is not cool enough for use as a bath or cold trap, sal...
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This document was uploaded on 02/27/2014 for the course PHYS 1B at UCSD.
- Spring '07