Update: It’s important for kids to understand the purpose of Experiment 5.1. No, the purpose is NOT busy work. The purpose is to understand the relationships among the volume and mass of a drop of dish soap and mass, moles, and molecules. Because the dish soap is so diluted, the density of the drop is 1.0 g/mL; the volume of a drop equals its mass. The mass of one drop is between 0.6-0.2 g of dish soap. Only 0.0125% of dish soap is sodium stearate; the sodium stearate molecules are spread in the circle of pepper. Once you calculate the mass of sodium stearate, convert the mass into moles, then into molecules. Divide the area of the circle by the number of molecules to determine the area of a single molecule of sodium stearate. The square root of the area is the width of a molecule. None of these calculations or relationships are intuitive.
My kids are working through Experiment 5.1. I’m scheduling extra Zoom chats to explain the lab and work through the math. After the kids work through the math, they go back and summarize their calculations on one sheet of paper, largely to help the kids see how we arrived at the width of a molecule. Below is a lab photo and a set of summary calculations. Yes, all of this work on behalf of the students and me is worth it.
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