Finding the Optimal Mix

This day's activity culminates student's investigations with actual chemicals, and involves a simple yet elegant system for measuring and quantifying the gas that different ratios of baking soda and vinegar produce when they are measured and mixed. As seen in MOVIE 1, students use a ping-pong ball and plastic tube with a slightly larger inner diameter than the ball. Students put a pre-measured quantity of baking soda at the bottom of the tube. They then drop a ping-pong ball on top of the baking soda, and amount of vinegar (to which has been added 4 drops of liquid soap) so that the ingredients' mass totals 50 grams. Students then take timed measurements of the height that the ball is raised by the carbon dioxide bubbles every 30 seconds until the ball stops rising.

All students first establish a baseline by mixing a 25g/25g ratio of the two ingredients. They record their maximum height measurements on a class poster with the chemical ratio on the x-axis and the recorded height (in cm) on the y-axis. Teams then choose and test their own ratio of chemicals, staying within the weight constraint of 50 grams, while aiming for maximum gas production.