Bassam Z. Shakhashiri was demonstrating how to conduct a lab demonstration. His audience was a ballroom-full of high school chemistry teachers, who were attending the American Chemical Society’s (A.C.S.) High School Chemistry Day.
Standing behind a large table strewn with the accoutrements of the chemistry lab, the University of Wisconsin chemist picked up a large beaker containing a colorless liquid.
“What do I have here?” he asked. “A beaker, right, a beaker. How large is the beaker? 1000 mls? 600 mls? Right. How did you know? You read the numbers. Reading the numbers is a perfectly good observational method.”
He added another colorless liquid, dropped in several pellets of a solid, poured in another liquid, and stirred the mixture, all the while talking to his audience.
After the second liquid had been added, smoke began to pour from the beaker, and the liquid changed color dramatically from pink to blue. “What’s the most obvious change?” Mr. Shakhashiri asked his audience. “Smoke.” offered one teacher. “Color change,” suggested another.
“The increase in volume,” Mr. Shakhashiri said, looking slightly smug. Then he flashed an equation on the overhead projector.
“I could have done that to begin with, but I maintain that you would miss, and the students would miss many of the other changes taking place here,” Mr. Shakhashiri told the teachers. “The overall change is represented by the equation, but the intermediate changes are also characteristic of the reaction.”
Mr. Shakhashiri was one of several champions of the chemistry-lab demonstration whose presentations were part of A.C.S.'S High School Chemistry Day, held in conjunction with the society’s recent annual meeting in New York City.
The session was called “What the High School Student Can Learn From Demonstrations,” but the real message was for teachers: Don’t be afraid to use one of the most powerful teaching tools available.
‘The few teachers know the “secret” of demonstrations, said Roger R. Festa, a Norwalk, Conn., educator who presided over the session. Mr. Festa said that the meeting’s planners chose to focus on demonstrations because many chemistry teachers do not make effective use of them, because they either don’t know how or are afraid that the demonstration will not work and that they will lose face with students as a result.
The secret is, speakers said, that with practice any chemistry teacher can use demonstrations as more than just a technique for rousing somnolent students-although, as Enid S. Lipeles, a chemistry teacher from Masuk High School in Monroe, Conn., noted, demonstrations make excellent diversions for students weary of learning how to balance equations.
Ms. Lipeles was scheduled to show her colleagues at the conference several “pyrochemical demonstrations,” but the New York City Fire Marshal doused the plan. “I’ve only had one ceiling go up,” Ms. Lipeles commented, “but that’s a long story.”
Mr. Shakhashiri, however, emphasized that demonstrations go far beyond provoking astonishment. “A chemical demonstration should be a process, not an event.
“I don’t believe in doing chemical magic tricks. I believe the teacher should be prepared to explain the principles behind the reaction.”
