2/16/00

Dawn Levy, News Service (650) 725-1944; e-mail dawnlevy@stanford.edu

Chemistry teacher captivates young minds with lab theatrics

There's no classroom demonstration so riveting as one in which the teacher may die.

­ Jearl Walker, former Scientific American columnist, often referred to as "the G. Gordon Liddy of physics"

 

For the ultimate classroom demonstration, Walker used to tread on white-hot coals to illustrate the sizzle, or Leidenfrost, effect, in which the firewalker is so scared that sweat insulates his feet from getting burned. (He gave it up after getting badly burned because he became so nonchalant that his feet did not get damp enough.)

Chemistry Professor Richard Zare says he would not go to Walker's extremes, but his lecture demonstrations are nonetheless dramatic. Pickles get electrocuted. Bananas get submerged in liquid nitrogen and shattered. Brave is the student who sits in the front row.

Zare, the Marguerite Blake Wilbur Professor in Natural Science at Stanford, uses theatrics for a reason. "They make a very lasting effect," he told an audience during a Feb. 3 lecture on the value of the laboratory experience in the sciences. "While lectures are forgotten, there are certain moments that are captured, brought away, and they really work."

The lecture was part of the "Award-Winning Teachers on Teaching" series sponsored by the Center for Teaching and Learning. Zare is winner of a 1987 School of Humanities and Sciences Dean's Award for Distinguished Teaching, a 1996 Bing Fellowship in recognition of excellence in teaching and a 1997 Allen V. Cox Medal for Faculty Excellence Fostering Undergraduate Research.

Having hands-on laboratory experience makes "a huge difference," Zare said. "I talked to people about why they go into various fields of science. My experience has been not because there was a great homework problem that they solved. The thrill that is lasting is when you can do something with your own hands and think about what it means and interpret it."

While laboratories mirror the methodology of science, they can foster slavish intimidation rather than innovation. They are costly and time-consuming. Some critics have even suggested doing away with labs altogether, replacing them with computer simulations. Doctors, for instance, could learn gross anatomy not by dissecting cadavers, but by using special gloves, goggles and computer equipment to carve up virtual corpses.

But is computer training alone sufficient? "That's not the doctor I want to see, who's been trained only that way," said Zare, who thinks that computers are valuable tools but that nothing replaces real experience. "And real experience is at best a comedy of errors. Progress in experimental science consists of going from one failure to another with undiminished enthusiasm. Too often our labs are arranged to perfectly work and show something, when in life, it isn't that way."

With a National Medal of Science and about 600 publications to his credit, Zare, a pioneer in laser chemistry research, has been about as successful as a scientist can be. But, ironically, a key to his success is learning from failure.

"It's important then to design the lab and not overdesign it, to let there be ways that things can go wrong and do go wrong and take advantage of it," Zare said. "Some of the best lecture demonstrations that I have done are those that in some sense are failed." He cited an honors freshman chemistry course in which he was decomposing water into its constituents, hydrogen and oxygen. "They all knew the formula for water ahead of time ­ H2O ­ and they knew there was going to be twice as much hydrogen as there was oxygen. And we looked at the buret, and it didn't come out that way. People who had AP credit in chemistry wondered was it that the formula for water, now that they've come now to Stanford, was no longer H2O?" The anomalous result spawned a discussion of different solubilities of hydrogen and oxygen in water.

Zare urged science teachers to use more laboratories and lecture demonstrations to encourage students as early as grade school to continue their science studies.

Zare did his part when his eldest daughter's teacher invited him to speak to her first-grade class. "I had never prepared for such a group," he recalled. "It was in many ways eye-opening and disappointing." He had given the children paper cups filled with sodium bicarbonate and vinegar. He was going to have them pour the two together and watch them foam, as in various baking reactions. "Before I could tell them what to do, not one but several students had eaten them," he said. "They were foaming and belching. I'm glad I didn't bring copper sulfate."

Zare is more at home with the college crowd, where his antics seduce even the science-shy. "We turn to the matter of the glowing gherkin," he announced, plugging electrical leads into the ends of a pickle. "We're now going to pass current through this pickle." Someone dimmed the lights. One end of the pickle began to glow a translucent yellow. It began to steam. "If you go from 110 to 220, you can read by this," Zare joked.

Creating a pickle lamp was only the beginning of the lesson. Like Socrates, he questioned: Why is only one side of the pickle yellow? What could you learn from this? Why does it matter?

"What we know about the stars, for example, is only what we see," he said. "We see at various radiations ­ one of them is the visible ­ and we analyze them into colors. And then we make wonderful statements about what goes on, assuming that whatever takes place on Earth is transferable to far out there where we haven't been. What would we conclude about a pickle far away? We would conclude that it was a raging sodium inferno, right? But really, it has about 16 percent sodium. You'd be missing a lot. It's the same way of looking at a candle flame and not understanding all the processes that are going on."

Zare went on to use his overhead projector, a laser pointer, colored solutions and other common classroom items to dramatically illustrate properties of light, such as diffraction.

Nonscience majors in his Chem 1 class like his hands-on approach to teaching. Zare designed experiments students could conduct in their dormitories. After showing a movie about powers of 10, he had his students serially dilute salt water to see at what point it quit tasting salty. Similarly, he asked them to dilute ammonia to find out at what point its odor was undetectable. Then he asked them to dilute blue food coloring until the dye was no longer visible.

"Your eye is much more sensitive ­ that had the parts per million type level," Zare said. "The others were parts per thousand. And this allowed us to talk about the terrors of parts per trillion in our environment, what it meant, and why we care and when we care. . . . I want them to learn powers of 10 and what they're like and what numbers are like, because otherwise how can I ever teach what Avogadro's number is?"

Students complained that they got different answers. "So-and-so could still see it as being blue when so-and-so could not. What's the right answer? That's an important question. And that led to the idea of reference standards and instrumentation."

Other experiments of chemical kinetics ­ the speed at which chemical reactions progress ­ used Alka-Seltzer tablets. Students raced Alka-Seltzer tablets to see if they'd dissolve faster in hot or cold water (hot), in a glass with a tablet already dissolved in it versus a glass of unpolluted water (the same), half a tablet versus a whole (the same), powdered versus whole tablets (powdered), etc. The exercise allowed students to make a prediction. Then they ran experiments to observe the actual behavior and formulated explanations of what they had observed. "My wife had a great time checking out these hundreds of Alka-Seltzer tablets. I remember her going to a local store here and having the girl at the checkout counter look up at her and say, 'It must have been quite a party.'"

Behind all the fun, laboratories are helping students develop their capacity for independent research. "They teach students to focus on observation, to deal with uncertainty, to distinguish between fact and interpretation ­ really key matters in science," Zare said. "When done well, positive lab experiences are some of the best-remembered teaching experiences you can produce, and they can be most decisive in choosing a career in the sciences."

 

Thursday, Feb. 10, the Center for Teaching and Learning presents the next Award-Winning Teachers on Teaching lecture. Lynn Orr, dean of the School of Earth Sciences, speaks on "Soap Bubbles, Thermodynamics and Engineering Science: Teaching the Ideas Behind All the Mathematics," from noon to 1 p.m. in the Hartley Conference Center of the Mitchell Earth Sciences Building.

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By Dawn Levy