Don’t hold the
pickles: Theatrics animate chemistry classes
BY DAWN LEVY
 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.
Photo:
Bananas, beware! Chemistry professor Richard Zare
prepares to torture fruit with liquid nitrogen, just one
of the many theatrical demonstrations he uses to
captivate students’ interest.
Photo by
L.A. Cicero
Zare, the Marguerite Blake
Wilbur Professor in Natural Science, 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 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.
SR
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