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Name: Cathy
Status: educator assistant
Grade: 9-12
Location: MN
Date: March 2008


Question:
I am the CHO/Science Assistant for our 9-12 grade high school. We are doing fractional distillation of alcohol in General Chemistry using 50 ml of an isopropyl alcohol solution, hot plates, flasks, and condenser tubes, etc. with Vernier temperature probes. We have tried a 10% and a 30% isopropyl solution but the graphing results are rather vague. With 70% rubbing alcohol, the graphs are easy for the students to understand. Are we safe in using this strength? No open flames, supply bottles capped...



Replies:
most are not. A steam bath would be a better source of heat. If "nothing goes wrong" you may have no problem, but if a boiling flask breaks you could have 70% isopropanol vapor coming into contact with the circuitry inside the hot plates. A fire could result. In planning an experimental procedure the rule is to run through the procedure step-by-step and ask the question, "What can happen here that would be bad, and if it happens, what will I do?" Always apply Murphy's Law.

Vince Calder



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