Subject: CD Burner Demonstration
A CD appears to erupt in flames and burn for about a minute.
- combustion reactions
- exothermic reactions
- oxidation of an alkane
Elmer's rubber cement (contains n-hexane)
lighter or matches
I begin this demonstration by asking my students who has their own computer. Of those students who have their hand up, I ask which also have a CD burner with their computer. The responses vary from one class to another, of course. I then ask which students wish they had a CD burner with their computer. I always get at least a few students who raise their hands. At this point I tell them that they can make their own CD burner for very little money. While telling them about my new "discovery" I open up the jar of rubber cement and liberally cover about half of the CD with it. After closing the rubber cement cover, I light the CD while holding it with the crucible tongs. At this point the students realize the joke and let out a few groans. I discuss the reaction while allowing it to burn itself out (about 1 minute) before setting it down to cool. (I usually add a joke about making sure not to place the CD in the CD drawer while it is "burning" or it might interrupt the file creation process; more groans.)
After the demo has finished I point out to the students the structure of n-heptane and we discuss what products were made during this reaction then balance the chemical equation. It makes for a good demo-a-day and allows for an introduction to or review of combustion reactions, or could be used to demonstrate the oxidation of alkanes in organic chemistry.
In this reaction the n-heptane (the solvent for the cement) burns off of the CD without causing the CD to burn (the CD will begin to melt).
A balanced equation for the reaction is: C7H16 + 11 O2 ---> 7 CO2 + 8 H2O
This activity has potential hazards which need to be evaluated. The reaction can produce smoke, and the burning rubber cement does pop and sputter. Perform this demo over a flame proof substance such as sheet metal or sand. As with all demonstrations, never perform a demonstration for the first time in front of students. Practice it first. Moreover, when performing this or any demo, use common sense and wear protective safety gear!
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Michael Geyer (firstname.lastname@example.org)
Deer Park High School, Cincinnati, OH<