At the high school level, chemistry labs can be challenging for a variety of reasons. First, the typical high school class length is usually far too short for completing an entire lab experiment, and spreading a lab over multiple days may leave the concepts fragmented in students' minds. Second, the equipment and technique used in chemistry labs are unfamiliar to high school students, and misuse can lead to damaged equipment or shoddy data, subtracting from the laboratory experience. A video pre-lab assignment that demonstrates technique and procedural elements may be the ideal solution to remedy these challenges.
A chemistry lab is usually a foreign environment to high school students, often being the first time they've encountered the equipment or practiced specific techniques. For example, many students struggle with routine procedures like taring a balance before massing a sample even after being reminded to do so. Equipment and technique errors lead to incorrect data and waste valuable time when redoing trials or reteaching techniques. Online video pre-lab assignments have been found to improve the lab experience related to these issues. For instance, in 2000, an introductory undergraduate chemistry laboratory course used video pre-lab assignments to introduce the lab equipment and procedure. The instructor found that students had far fewer technique questions, which resulted in more time to work on the lab itself.1 In a 2004 study in a different undergraduate chemistry laboratory course, video pre-lab assignments led to a 12.7% reduction in the time required to complete the lab. Additionally, the researchers found that students used the equipment correctly, and they could take all measurements without any errors.2
What to Include in a Pre-Lab Assignment
I usually start pre-lab videos with background theory that focuses on a conceptual understanding of the lab topics. For example, in a lab that focuses on experimentally determining the density of pennies, I start the video with an exploration density using particle diagrams. Beginning the video with related theory usually activates some of the students' previous knowledge about the topic before getting into the lab procedure.
Image 1: Screenshot of a video clip explaining background theory related to density.
Demonstrate Proper Equipment Technique
Next, I demonstrate the lab procedure using the same equipment that they will use in the lab. Demonstrating the procedure is an excellent opportunity to demonstrate proper use of the equipment, like taring the balance and reading the bottom of the meniscus in a graduated cylinder.
Image 2: Screenshot of a video clip explaining how to read the meniscus in a graduated cylinder.
Finally, I provide a few example calculations so students can practice those in the lab. New calculations are often another area where students lose valuable time, so they will have more confidence after practicing them beforehand. For example, students often get confused about the difference between the actual and expected values in a percent error calculation. That said, they are far less likely to confuse them when they have performed one or two example calculations during the pre-lab.
Image 3: Screenshot of a video clip explaining calculations related to density.
Since starting to use virtual video pre-lab instruction this semester, my labs have run much more smoothly, and all have been completed within the regular instructional time. Additionally, my students think more deeply about the experiment since they don't have to worry about procedural items.
- McKelvy, G. M. (2000). Preparing for the chemistry laboratory: An internet presentation and assessment tool. University Chemistry Education, 4(2), 46-49.
- Burewicz, Andrzej, and Nikodem Miranowicz. "Effectiveness of multimedia laboratory instruction." Chemistry Education Research and Practice 7.1 (2006): 1-12.