Exploring and proving gas laws

In the Gases and the Atmosphere unit of gr.11 chemistry, the gas laws (Boyle’s, Charles, and Gay-Lussac) are often taught in a sequential and systematic manner. The first formula of Boyle’s law is introduced, followed by the formula (pv = pv), and then a bunch of busy work practice questions and on to the next law. I remember teaching this during my practicum, and as a new teacher, I followed the curriculum order to the tee. But how does teaching the gas laws, and having students complete series and series of questions beneficial to their conceptual understanding of the content. The students may have discovered the quickest way of completing the busy work, but when provided a conceptual question relating the pressure and volume, how do they measure up? Lin et al (2000) discovered that many students who have done the mathematical calculations of the laws failed to understand many conceptual real life situations. Gr.11 chemistry students were presented a series of real life conceptual questions where students who supposedly completed the gases unit still did not understand the relationship of pressure, volume and temperature. (fig.1)

To combat and encourage conceptual understanding, I exposed the 3 gas laws by introducing the 3 variables in a series of demonstrations, and examples. Simple demonstrations such as looking at the relationship of the size of a balloon in a cool vs hot environment suggests a direct correlation between the variables. Another example is using a closed off syringe to illustrate the inverse relationship between the volume and pressure. After the students have visually seen the relationships, and example calculations, a summary of the 3 laws with their mathematical relationships is provided. Then their task is to design an experiment to prove one of the 3 gas laws quantitatively. I have found that the most challenging task for a high school student in science classes is to prove something with supported data. Their experiments can vary, and can explore different ideas. I have seen failing experiments, to ones with Ward’s data hub with data hooked up inside a vacuum to collect data of pressure. The important aspect here is not to have students design a flawless experiment, but to have them design, experiment, and revise their experimental design to encourage critical thinking and teamwork.

At the end of the “experimental week”, the students were provided with conceptual questions to see their conceptual understanding of various gas law topics. I was amazed to see their depth and reasoning in applying their knowledge to the questions.

References

Lin, H., Cheng, H., & Lawrenz, F. (2000). The Assessment of Students and Teachers Understanding of Gas Laws. Journal of Chemical Education, 77(2), 235