Pre-break demonstrations

As I mentioned in an earlier post, I was going to try to use more counterintuitive demonstrations to engage students. Ms. Hardy asked that I do one of these demonstrations on the 18th, their last day before the break. In my digging to find experiments of this nature, I discovered the Briggs-Rauscher oscillating reaction (see a video of it here). At this point, the students have seen reactions that cause precipitates to form, states of matter to change, and changes in color. However, once the reaction takes place, they're usually completed in a matter of seconds. The Briggs-Rauscher reaction is impressive, not only because three clear liquids are mixed to make a nice yellow solution, but because the solution then oscillates between yellow and blue for several minutes. It's a somewhat complex reaction (actually two simultaneous, competing reactions), but because it's right before the break, I didn't think explaining the details of the reaction wouldn't really be necessary, since they probably wouldn't have the attention span for something like that right before going on vacation anyhow. I was hoping it would be more like a treat for them to see and ask about when they get back.

Well, that didn't pan out because the necessary chemicals weren't available and Ms. Hardy told me that what they have is pretty much what they're stuck with, since the purchasing budget for the year has already been allocated. Perhaps I could order these chemicals for next semester with TF funds?

In lieu of that demonstration, I'll be doing two others: decomposition of hydrogen peroxide and triboluminescence. Both the chemistry and physical science classes have talked about energy that is consumed or released in reactions, and the physical science class has talked about types of reactions, so both of these demonstrations will have relevance in each class. The decomposition reaction HOOH-->2(H2O)+O2 is catalyzed by catalase, an enzyme found in many living organisms, including humans (it makes the hydrogen peroxide bubble when you put it on a cut) and baking yeast. The baking yeast can be added to consumer strength hydrogen peroxide to produce the decomposition. It produces a nice foam and the presence of O2 can be demonstrated by reigniting a wood splint that has just been blown out. Not only does this give a tangible example of a decomposition, it will also give me a chance to talk about how a catalyst affects the activation energy of a reaction.

Most of you have probably seen triboluminesence before. If you take a wintergreen Lifesaver and crack it with your teeth in the dark, you can see blue sparks. I think this is a neat demonstration of conservation of energy: the mechanical cracking imparts energy upon the electron, which transfers its energy to another atom, which vibrates and releases the energy mostly as UV light. Because wintergreen oil is fluorescent, the UV light causes blue sparks to appear.

I'll be presenting these tomorrow, so we'll see how it goes.