The Law of Conservation of Mass states that the mass of a system must remain constant over time, as system mass cannot change quantity if it is not added or removed.
In a professional development class with Georgia Tech’s Center for the Enhancement of Teaching and Learning, I had the opportunity to design and implement a mock lesson plan for a group of my peers. In my lesson, I completed a simple demonstration of the Law of Conservation of Mass (LCM) by weighing a cookie, subjecting that cookie to physical change (crumbling), and then taking a final mass after the “reaction”. Students followed along using the handout provided, which allowed them to model the experimental process, or scientific method. Though every detail of the lesson was considered – including statewide education standards, learning objectives, background notes, materials and a complete procedure – not every detail of the lesson went according to plan.
During the lecture portion of my presentation, I introduced the topic by defining relevant terms and explaining how to properly balance a chemical equation. I then walked the class through a few examples on the board. As I spoke, I noticed that several students appeared disengaged, and I knew that the lesson was not being received that way I’d hoped. I decided later that if I were to offer this lesson again, I would call volunteers to the board to practice balancing equations with me.
I’ve learned that the best way to keep students connected mentally is to have them contribute actively.
It has since been a technique that I practice in my chemistry recitations as a teaching assistant, as well as in my one-on-one tutoring sessions.
Confusion About the Lesson
After completing my lesson and grading the formal post-assessment, I found that students seemed to grasp the concepts well, but were somewhat confused by the cookie demonstration. My assessment had two parts: one about the definition of the LCM and balancing chemical equations and another part about the activity, which only asked students to give a hypothesis, record data and discuss results. While everyone was able to describe the LCM and balance equations, a number of students rejected their hypotheses because the mass of the cookie was not exactly the same before and after crumbling. I determined that this is an issue with the effectiveness of the activity, as some of the crumbs were lost or brushed off in the crumbling process and, therefore, not included in the final mass.
This experience helped me realize that, in order to successfully get the point across, an instructor must be prepared to show or explain things in a variety of ways, as one example is never enough.
To improve this particular experiment, for example, next time I would first do the demonstration with a piece of paper or something that is easier to weigh once it has been fractioned. After that, I could try breaking the cookie into halves, then fourths, and eventually crumbling it, recording the weight after each physical change. By moving the class through different examples, I can divide the learning into multiple levels of understanding – moving from beginner to a higher level.
Overall, this exercise not only helped me improve my teaching practices, but also taught me that as a teacher, it is important to be willing to learn from your mistakes. Reflection and self-assessment are lessons that I will carry with me on the journey to becoming a masterful educator.