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4. Things Every Chem 201/202/212 Student Should Know
4.1 Self-Protection in the Lab
Fume Hoods: Virtually all of the experiments in Chem 201/202 involve volatile organic compounds and must be performed in a fume hood. Use the fume hood closest to your lab drawer to minimize foot traffic or collisions in the lab.
4.2 Avoiding Accidents
The experimental procedures in Chem 201/202/212 tend to be more complicated than those in Chem 101/102. Most accidents can be prevented by following instructions and by paying attention to the hazardous properties of each substance and procedure.
Pay particular attention to procedures that require heating or generate their own heat (exothermic reactions). These procedures are the ones that might lead to a sudden and dangerous splash, fire, or explosion.
It's on TV: The Most Toxic Substance… There is a great deal of attention given to synthetic toxins introduced into
the environment. However, it might be interesting to compare these to natural toxins (concentration
and quantity aside). Dioxin, more properly, 2,3,7,8-tetrachlorodibenzo[1,4]dioxin (TCDD), has
a reported LD50 of 0.045 mg of dioxin/kg of body mass for rats. LD50 is the concentration expected
to kill half a given population. The toxicity of plutonium is harder to compare as it is expressed
in units of radioactivity rather than mass, though a very conservative LD50 is given at about
0.015 mg of plutonium/kg of body mass. |
Never Create an Open Flame: Open flames can set off fires, and even explosions, when they come into contact with the vapors from volatile organic compounds (fuel). Most of these vapors are heavier than air, so they tend to stay close to bench tops and travel large distances horizontally.
Never Heat a Closed System: Heated gases expand rapidly and can “explode” a closed system. Before heating any apparatus (especially reflux and distillation apparatus), make sure you have checked it to make sure there is an opening for expanding gases to escape.
Use Boiling Chips or a Stirrer: Liquids do not boil smoothly unless a source of nuclei is present on which the bubbles of vapor may readily form. Otherwise, a liquid will become superheated and vaporize suddenly with almost explosive force (“bump”). Most bumping problems can be overcome by very good stirring or by adding one or two boiling chips to a solution before it is heated.
Exothermic, Out of Control Reactions: You can control most exothermic reactions by either conducting the reaction at reduced temperature (use a cooling bath), combining reagents more slowly, or working on smaller scales. Some additional tips:
- Keep additional ice (or an ice bath) on hand to cool a reaction that might become uncontrolled
- Never use your heat source to support your reaction flask. Instead, put your heat source on top of a “lab jack” and clamp your reaction flask to a metal support rod so that the clamp+rod supports your flask. Then, if the reaction starts to go out of control, you can lower (or remove) the lab jack and quickly separate your heat source from your reaction flask.
If a reaction does go out of control, close the fume hood entirely, remove all external sources of energy (example: lower and unplug a ceramic heater or hot plate). Finally, notify your lab instructor.
4.3 What Should You Read Next?
Chem 201/202/212 students can stop reading this manual at this point and may sign the safety statement. After doing that, students should consult their lab course manual for additional safety instructions. We also encourage students to quickly scan Chapters 6 and 7 in this manual just to get acquainted with the rest of this manual’s contents.
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