ARCHIVED—Building scientific concepts from the ground up
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- Why cleaning your room violates the laws of nature
- Concepts, rules and exceptions
- Communicating and understanding the results
Herzliah High School
Yofi Sadaka wants to send well-balanced students out into the world. Her aim is to prepare students to be independent learners who can apply theories and skills in real-world situations.
In science class, she believes this means teaching students how to "do science" rather than how to be scientists. She does not think high school students are ready to be scientists but she does think they are ready to learn how to think about basic concepts and to make inquiries. She teaches them that science involves being curious, not taking things for granted, and looking around at the world.
Recent changes in the Quebec science curriculum require teachers to use a constructivist approach (sometimes also called an investigative or building approach). Here Mrs. Sadaka tells us how she "turned her teaching methods upside down" to adopt the new approach. Instead of doing an experiment "to verify" what has been learned, with this approach the students are encouraged "to construct" their knowledge by doing their own investigation. Knowledge is "built" from the conclusion of an experiment or by trying to answer questions. Instead of passively assimilating facts, students are involved in finding solutions based on their previous knowledge.
Today, I teach science in almost exactly the opposite way from how I learned it. When I was in high school the teacher began by telling us about a scientific law. For example, we would be taught Boyle's Law (PV=constant) and that the value of the constant depends on the temperature and the amount of gas present. The teacher would then intone that when the pressure goes up, the volume goes down and vice versa.
Having learned the law, we then did an experiment that "proved" a hypothesis based on it.
The most dangerous thing about this approach is that it encourages students to rely on memorization exclusively. I use a more dynamic approach. I encourage the students to think about the relationship between concepts and facts: How can you explain that a tank of helium can fill hundreds of balloons? Why do SCUBA divers need to ascend slowly to avoid the bends? As the students look for answers they will eventually come to Boyle's law and when they understand the facts the conclusion can only be logical. There is no need for memorization.
Let me tell you how I approach the laws of thermodynamics with my classes today.
I start by making them curious, by making them wonder. One great way to do this is by bringing in a cold pack from a first aid kit. It looks like a plastic package with chemicals inside and has, although we cannot see it, a barrier that keeps a solid and a liquid apart. When we twist or bend the package, the barrier breaks and this starts a chemical reaction that makes the package very cold.
I like to pass one of these around the class. The students can feel it cooling off as it goes from hand to hand. Then, I ask them questions such as: What type of chemical reaction do we have? Does the dissolving of this chemical release heat or absorb heat? From where is this heat absorbed? Where is the heat going? What are the surroundings? When we place the cold pack on an injured part, how does this part feel in terms of temperature? From where does the chemical get the heat to dissolve? By asking these questions, I can introduce the terms related to energy transfers. I can then ask the students to design a lab to measure the heat transferred during this reaction. They can compare this value with the heat of other reactions. With this exercise, I am adapting the content of the course to the real world of the students. This shows them the relevance of what they are learning.
Chemistry teachers reading this will see that these basic questions lead to two other concepts, enthalpy and entropy. Rather than beginning with a lecture explaining the laws of thermodynamics that explain these, I make students curious about some related phenomena from their lives. One of my favourite ploys is to ask them, Have you ever considered why your shoelaces can come untied but that they never spontaneously tie themselves?
A little less seriously, I also ask them, Have you ever noticed that when you undress your natural tendency is to throw your clothes on the floor? What would happen if you just kept doing this and no one ever asked you to clean up your room?
When I ask students questions such as these, they quickly get an idea of where I am headed, but I do not spoon feed them the theory. I am leading them to phrase the conclusion. Eventually, we reach an understanding of the natural tendency of everything on earth to reach minimum energy and maximum disorder — in other words, things in nature tend to reach a state of minimum enthalpy and maximum entropy. Now the students understand why after all natural disasters, such as floods, volcanic eruptions or storms, things look messier and never neater. So by not cleaning their rooms, the students are simply aligning themselves with the laws of nature.
By coming up with such examples I can get the students to understand what drives chemical reactions, such as the one in the cold pack. We can then go a step further and talk about spontaneous and non-spontaneous reactions, and the effect of temperature on these reactions.
The idea is to begin each topic with materials and processes known to the student, but not necessarily understood, scientifically speaking. It is a rather long journey from a cold pack to the laws of thermodynamics. A simpler concept, such as the effect of heat on the solubility of solids and gases, will give a better idea of the whole process. Most Grade 8 students know that sugar will dissolve faster in hot tea than in ice water. From there they might simply conclude that everything dissolves faster with heat. Follow this principle and you will be right most of the time, but there are exceptions.
I follow up the discussion about temperatures and solubility by asking students to write a hypothesis about what happens to the molecules that makes them dissolve faster as the temperature increases. Then I ask if this principle would apply to gases. A few years ago, during a hot summer, thousands of fish were found dead on the shores of Long Island. Can the previous hypothesis explain this observation? What are the solvent and the solute here?
I then ask, If heat makes things dissolve faster, why was there less oxygen dissolved in the water when it got really hot? Heat has the same effect on gas molecules as it does on solids, so what explains the different results? Once again, questioning, observing and analysing will bring us to the conclusion that, unlike for solids, the solubility of gases decreases with temperature.
From this discussion I get the students to come up with a hypothesis on this subject that they can test in a lab. We then move on to read solubility graphs and solve related problems.
I don't want to give the impression that my students always figure out the solution to the questions I pose about matters such as the fish kill or shoelaces that don't tie themselves. As a teacher I must engage the students in this inquiry-based learning, which is time-consuming, particularly at the beginning. To do so, one should:
- start the topic with examples to which the student can relate or with hands-on activities, rather than a lecture
- ask thought-provoking questions: a good question should prompt the students to fully participate in the class discussion by sharing ideas
- sequence the questions logically
- adapt the questioning to the grade level
- get feedback on the students' previous knowledge by the responses they give
- give the students projects they can relate to.
To come back to the case of Boyle's Law for a moment… When I teach it using this new method my students' first reaction is to ask why Boyle gets the credit for thinking of something so obvious. Of course it wasn't obvious to anyone before Boyle figured it out but what is important is that it is obvious to someone who understands the concepts.
Communicating results is another important step. You don't understand something until you can explain it clearly to someone else.
One of the tricks I teach students is to pass their written labs along to a fellow student who didn't do the lab. I tell them that if their classmate can't figure out what is going on from the write-up, they have not written it well enough. The students must present the hypothesis, procedure, data (tables and graphs) and conclusion clearly and neatly.
As with generations of teachers before me, I make the students do problems to see if they have the concepts down, but I discourage them from simply plugging numbers into equations. Often I will ask them simply in what direction the numbers will go. If they have the concept they will always be able to say if the result will be larger or smaller. If they are obviously just guessing, then they haven't got it yet. The same is true for units: I ask them to do a unit analysis before giving me a number answer.
Another way to reinforce a concept is by using technology. I am a great believer in "wet" labs. I think that if you haven't spilled acid, broken a beaker or stained a bench, you haven't done chemistry. Because of this I always begin with real labs. Once that stage is finished, however, I think that computerized labs are a great way to make sure students understand the concepts.
These electronic labs differ from the real kind in that there is no experimental error nor clean up. That makes it possible to try a whole set of situations very quickly. I can manipulate variables I can't access in the "real" lab. Before entering the variables into the program I ask students to anticipate what will happen. Again it is easy to see when they understand and when they do not.
One last point that I would like to make is the importance of encouraging students to participate in science fairs, essay competitions and special projects. The important thing to remember is that, in the end, the only people who fail are those who do not try. There is much to gain from these events in terms of preparing and presenting your work, sharing ideas with other people in the field and making contacts. If I hadn't encouraged my students to send a proposal for the Canadian Space Agency's Canadian Protein Crystalization Experiment, we would have missed the excitement of witnessing the launch of the space shuttle Atlantis with our experiment on board.
The old scientific method meant to formulate a hypothesis, do extensive experimentation and accumulate data. The new scientific method means to formulate a hypothesis, patent it and raise $10 million. I consider this reality when preparing my students. When they leave my classes, they will be faced with a barrage of scientific claims from such diverse groups as advertisers hawking new kinds of shampoo to environmental groups looking for money. Even if the students haven't memorized the science related to these claims, they will use their critical thinking and problem-solving skills to begin evaluating the claims' relative merits and make their own judgement.
From facts and understanding comes knowledge. It is important to equip the students with the skills necessary to evaluate what goes on around them and to show them the relevance of what they are learning to their lives.