On 3/25/2012 11:03 PM, Drew Melby posted to the ChemEd-L discussion list
“I’ve never felt the need to ‘entertain’ students by making things ‘memorable’. Chemistry is a serious business, not a magic show”
I got interested in Chemistry in high school because of the magic. not necessarily specific demos, but the different labs (probably using very dangerous chemicals at the time) and intimate participation in the magic. Chemistry (and science) is magic and a mystery. We don’t truly know why anything does anything, but trying to find that answer (and thousands of “smaller” answers along the way) is a great journey for any scientist.
I think the distinction between entertainment, demonstration, and experimentation is important.
A pyrotechnics show that is not connected to anything the students are currently learning serves only to entertain. Entertainment can serve a useful purpose, but anything that is purely entertainment is time not spent on the things you’ve actually decided that you want your students to learn. In my opinion, if you find yourself wanting to do a lot of demos that don’t have an obvious connection to the curriculum, you should seriously consider starting a chemistry club. Kids can come to your room after school and play with the magic of chemistry to their heart’s content without costing you any class time.
A demonstration can be entertaining, but it needs to be connected in a tangible way to something the students are currently studying. I do a lot of small demos. I use concentrated HCl and baking soda to demonstrate a spontaneous but endothermic reaction. I demo the aluminum and copper (II) chloride reaction in chemistry I to introduce chemical reactions, and I do the same demo with measured quantities to demonstrate stoichiometry and limiting reactant. I use an ice cube to boil water in a sealed flask to demonstrate the connection between temperature, pressure, and phase diagrams. I do a spectacular demo to show how forming bonds releases energy. (See for a write-up with pictures.) [Discussion on the ChemEd-L list suggests that my explanation has some inaccuracies, but I think it does a great job of making the point in a memorable way that forming bonds releases energy, thereby undoing the damage caused by their biology
teachers.]
When I do demos, my students always demand to know why they work. For demos that appear to have an element of danger, quite a few students visibly express concern for my safety until I explain exactly how I make the demo inherently safe while still giving the illusion of risk that’s not really there. I would never do a dangerous-looking demo without including this discussion. Besides allaying the concerns of some of the more sensitive students, it teaches students valuable lessons about experimental design (adjusting conditions to ensure safety while still giving a spectacular result) and lab safety (risk assessment and elimination). It also allows me to reiterate the message that I would never do a demo unless I was confident that I could do it safely and I understood the science behind it.
Lab experiments serve yet another purpose. They give students an opportunity to connect what they learned in the classroom with something they can manipulate themselves. They also teach and/or reinforce lab techniques that will be useful in later experiments, as their knowledge of the connections between theory and experiment continues to grow. I believe that the best experiments have an inquiry component with clear connections to the curriculum. Because labs are part of how my students acquire their working knowledge of chemistry, the students’ understanding may be still be weak when they do the lab. For this reason, these experiments are usually a lot less complex than the demos.
Flame tests can work as a demo or as a lab. Like many chem teachers, I have my students do the experiment when they’re studying electron configuration, and I insist that their lab reports discuss the energy transitions that produce the colors. I find it unfortunate that some teachers save the flame test lab to use when students’ interest in chemistry is flagging, almost as if to say, “The stuff we’re studying right now is boring and not relevant to anything you might find useful, so we’re going to take a break from the drudgery.”
As for the procedure, I put a little of each powder in a separate test tube. Each lab station has the test tube of chemical, Bunsen burner, some cotton swabs, a mini Erlenmeyer flask full of water to wet the swabs (so they hold more powder), and a 250 mL beaker with water in it for disposing of the used cotton swabs. The only problem is that some of the powder inevitably gets spilled into the Bunsen burners. (A colleague uses candles instead of Bunsen burners, in order to avoid contaminating the burners. I’ll try that next time I do the lab.) The powders produce colors that are just as spectacular as the ones I got the one time I did the experiment with alcohol. (This was in my second year of teaching. One student lit his arm on fire when he poured alcohol on a flame that he wasn’t able to see. His lab partners smothered the fire right away and no one was hurt, but when that happened, I swore I’d find a way to do the lab without the risk of using alcohols.)
Originally posted to the ChemEd-L discussion list.
