- I am uncomfortable with Sharon Geyer's article entitled "Phasing out the demo" (Chem 13 News, May 2014). Yes, it's fun and engaging for a student to make the thermite reaction come alive by smashing a rusty iron sphere against an aluminum foil-covered sphere — the sparks certainly fly. But let’s not throw the baby out with the bath water. Without an initial teacher demonstration, accompanied by explanation and guiding questions, the exercise is reduced to entertainment. To learn something as complicated as chemistry, students need effective instruction. This is why the teacher demonstration, accompanied by commentary, anecdotes and questions, is a staple of effective chemistry teaching. Students need explanation. (I'm not a fan of edu-babble, but I believe this is called "guided inquiry".) We don't teach someone to drive simply by tossing him or her the car keys. I get it — people need to practice driving, but only after instruction and with plenty of guidance. Who cares about the "oohs" and "aahs" that come from a student doing an untutored activity? The real “oohs” and “aahs” come with real learning, not with the sparks that accompany the activity.
Michael P Jansen
Crescent School, Toronto ON
- I am sure you will get many letters on this, but lycopodium is not a pine, as stated on the cover of the May 2014 issue, but a clubmoss. They do look like little pine trees and the common name for some species does include the word "pine", e.g., ground pine or princess pine. To make it even more complicated, clubmosses are related to ferns, not mosses.
Boston Latin Academy, Boston MA
- The photograph of the lycopodium “explosion” brought back a memory — one of my lab courses in my early days (1981 +) at Mohawk College used the "oleic acid drop on lycopodium- covered water" experiment.
Basically a very dilute solution of oleic acid in an alcohol is dropped onto water covered in lycopodium powder. The alcohol dissolves in the water, and the oleic acid spreads out on the surface of the water, pushing out the powder. If it is assumed that the oleic acid layer is one molecule thick, from the area of the spread and the volume of the oleic acid, it is possible to make an estimate of the size of the oleic acid molecule.
In theory, the experiment makes the size of a molecule "real". The course I was teaching was introductory chemistry for physiotherapy students — a class of high achievers. The experiment is suitable for sophisticated senior secondary school students, or college or university students. They need good math skills and the ability to visualize abstract concepts.
We ran out of lycopodium powder at Mohawk College, were unable to find a supplier (pre-web, eh) and had to abandon the experiment after trying unsuccessfully to use chalk dust or talcum powder instead of lycopodium.
Visit the websites below for numerous ways to do this lab.
- Science Curriculum by Aaron Keller
- Mrs. Koepl's Webpage
- David A. Katz’s website Chymist.com (PDF)
- Teachers Resources for ChemCom®.
David Cash (retired)
Mohawk College, Hamilton ON