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teaching chemistry
Janice Crowley (Courtesy College Board)

Anyone who has watched a few “CSI” episodes knows that “rigor mortis” refers to the rigidity or stiffening of muscles that occurs after a person dies. Rigor, in this case, means inflexibility. As a student, I had teachers who were “rigorous” – that is, inflexible in their demands for more critical thinking. Now, as a high school chemistry teacher, I make similar demands of my students. At first such rigor makes students uncomfortable, especially if they are in the habit of memorizing and then regurgitating facts on tests.

Critical thinking – the heart of a rigorous education – happens best in a nurturing classroom, where students feel free to ask and answer questions without ridicule. Students work hard for teachers they respect and with whom they feel connected. A master teacher inspires students to take personal responsibility for their own learning. For students to achieve continuous intellectual growth, teachers need to supply meaningful content and engaging activities.

The trick for the teacher is to channel a child’s inner Goldilocks: to discover the sweet spot where learning something new is neither too easy nor too hard but rather “just right.” In a classroom of 20 or 30 students – most of whom have disparate interests and learn at different paces – this is rarely easy and never accidental. A teacher must work hard, each lesson and every day, to find the sweet spot. Its location can vary by student, class, time of day, day of the week and even by the weather or season.

In my chemistry lessons, I challenge students to think beyond mere definitions. One of the best ways to foster critical thinking is by conducting Socratic-style discussions where the teacher asks questions regarding concepts and stretches the students to develop their own thought-processes. The teacher who is fanatical about asking “Why?” doesn’t settle for half-baked answers from students. Moreover, a healthy obsession with “Why?” on the teacher’s part can stimulate a similar curiosity in students: Why does the world work the way it does? What physical laws govern it? How do we know what we know? How confident are we in that knowledge? Is our level of confidence justified?

Take, for example, a discussion I have every year with students about atmospheric pressure. Beginning from the premise that “atmospheric pressure” is pressure pushing down on them, I ask whether that pressure is the same in our home state of Kansas as in the Rocky Mountains. Students consistently say the pressure is greater in Kansas.

“But why?” I ask.

In my class, students learn to articulate not just what they know but how they know it. I continue with questions: Will you be able to cook pasta faster in Kansas or the Rockies? Students are split roughly 50-50. Some argue that the boiling point of water will be lower in the Rockies, and they’ve read on the packaging that the pasta can be added once the water boils, so they conclude the pasta will cook more quickly at a higher altitude. That this is incorrect doesn’t matter at the moment; I say nothing and instead ask another question: If you are baking two cakes in two ovens, one at 300°F and one at 400°F, which cake will be finished baking first? Invariably they say – correctly, this time – the cake in the 400-degree oven.

We establish, then, that higher temperatures cook food faster. And at this point students are ready to revisit the example of cooking pasta in the Rockies. Thinking more deeply about the situation, students slowly realize that cooking pasta will take longer in the Rockies than in Kansas because the boiling point in the Rockies is lower and because ultimately it’s the temperature that determines how quickly food is cooked.

Let’s now look more concretely at how I might teach a four-day unit on solutions in my 10th-grade chemistry class. My ultimate objectives are twofold: for students to demonstrate a deep and abiding understanding of major concepts (e.g., solute, solvent, saturation, supersaturation, colligative properties, boiling-point elevation) and for students to apply these new understandings in a real-world experiment.

To make terms more than mere definitions and to foster long-term memory, I provide students with vivid examples to which they can relate. When we discuss a saturated solution, for instance, we think about the tea-drinking habits of those sad souls who frequent dimly lit diners across the country. Relentlessly, they add sugar to their tea until a miniature mountain of it forms at the bottom of their cup. But why do people do this? Because, it appears, they don’t understand the concept of saturation.

My students, on the other hand, know that the tea in this example is saturated – as sweet as it can get – and that the evidence of this is the fact that additional sugar accumulates at the bottom because it can no longer be absorbed in the liquid. Now, when my students see customers in restaurants thoughtlessly adding sugar to their already saturated tea, they get angry! “Don’t these people understand,” my students ask, “that their tea cannot get any sweeter?”

The first three days of this unit are composed of lectures and Socratic-style discussion of new terms, but it’s not your usual lecture with students madly scribbling notes.

Rather, there is a constant give-and-take between teacher and student. I field tons of questions. Students know there’s nothing worse than remaining confused, and so they ask clarifying questions that help everyone reach new understandings. A student who thought he understood everything perfectly will realize, through a classmate’s question and our subsequent discussion, that he actually had everything backwards. He’ll then follow up with a question of his own.

On the fourth day of class, students undertake a laboratory experiment in which they make candy. Students add sugar and corn syrup to water in their pans. The sugar partially dissolves. Students have little difficulty correctly identifying the result as “a saturated mixture.” Next, students heat the mixture and notice that by the time it reaches 125°C, the mixture clears. Most have no idea why.

We talk through what happened – how, when heated to 125°C, all of the sugar and corn syrup dissolve. As the mixture cools, they have a solution that solidifies because it is unstable.

But if water boils around 100°C at 1 atmospheric pressure, I ask, how and why did the mixture reach a temperature of 125°C? Students debate what they’ve just witnessed; they know they’re looking for something other than a quick, simple solution. Using their new knowledge of “colligative” properties, students are able to articulate the answer: that the sugar and corn syrup, when added to water, raise the boiling point. Density has increased, making it harder for water molecules to escape as a gas, and therefore a higher temperature must be applied. This is how candy is made. Sugar is dissolved in water to the point of saturation, and then the mixture is heated up so that more sugar can be added as the temperature rises further; the end result is supersaturation and, when the mixture cools, an intensely sweet solid we know as candy.

It is perhaps helpful to view what students are asked to do in this unit through the lens of Bloom’s Taxonomy. At the most basic level, they learn new knowledge (facts, definitions), after which they have to apply that knowledge to a new problem (making candy in the experiment). Analysis, synthesis and evaluation – skills at the top of Bloom’s hierarchy – follow in our debriefing and their eventual write-up of the lab experiment.

Our animated conversations after such labs serve as evidence to me that students have moved well beyond the more basic cognitive skills of recollection and comprehension. We arrive in that rarer territory where application, analysis and synthesis reign supreme. Students’ curiosity is piqued. “Does that help explain why some people get the bends ( when they surface after scuba diving?” one student asks.

And off in new but related directions we go. Yes! Gases dissolve better when there is more pressure, according to Henry’s Law. If you come up too quickly from scuba diving, the inert gases in your body (and your spinal fluid) dissolve and expand so rapidly that nerve endings are affected. Severe cases of the bends can result in death.

Another student asks, “Why do people tap on the top of a Coke can before opening it?” Classmates offer various theories, some more plausible than others. We explore them all and arrive, eventually, at the best explanation: so the gas comes to the top, ensuring a release of pressure (without spillage) when the can is actually opened.

The questions and discussions could continue forever. Why do we get fevers when we’re sick? (Because white blood cells come out and try to fight the infection; this increased bodily activity causes the body temperature to rise.) Once students see that chemistry is all around them – just like math, physics, biology, music, art – they want to understand the phenomena we too often take for granted. They become, in short, “Why?” fanatics.

It is rigor and compassion together that allow me to set the bar so high with all my students. Rigor without compassion is rigor mortis – that is, inhumane. Compassion without rigor is the soft bigotry of low expectations.

– As told to Justin Snider

Janice Crowley is the chemistry and science department chair at Wichita Collegiate High School in Wichita, Kansas. In 1997 she was one of four teachers in Kansas to be recognized with a Milken National Educator Award, and in 2009 she was named the Siemens National AP Teacher of the Year.

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  1. I attended an institute for AP chemistry teachers taught by Ms. Crowley as part of the Massachusetts Math and Science Initiative. I can tell you she is nurturing even to us older folks when teaching us. Developing a rapport with students leads to improved performance in the classroom. This nurturing effect stimulates student interest and motivates them to work harder even in subhect areas where they may have little interest initially. Ms. Crowley’s style is a good example of this nurturing attitude. Her results are comparable to those of the best teachers at the national level. The nation needs more educators like Ms. Crowley.

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