When you pour salad dressing on your lettuce, flavor is probably all that you’re concerned with.
But there’s a lot at play in that dressing; there’s chemistry. Amanda Olson’s fifth-grade science students can tell you all about it. They first learned about matter, from atoms to molecules to substances to mixtures.
Then Ms. Olson took things to the next level and introduced some building blocks of chemistry. They started learning about the attraction of molecules and what causes certain substances to stay together.
That’s where the salad dressing came in. They observed that oil and water do not mix and deduced that oil and vinegar also do not mix (because water and vinegar have similar properties). But are there additives that might make them emulsify? Is there a substance that will result in no sediment in the salad dressing?
“We don’t want it to separate; we want it to stay all together,” Ms. Olson said.
That’s where the “stability test” experiment came in: The students worked with lecithin, flour and corn starch to test which substance might cause vinegar and oil to stay together (but they used water).
“When we do this experiment,” Ms. Olson said to the class, “timing is extremely, extremely crucial.”
The students each were assigned either a task of timing the experiments or a substance to mix into water in a plastic tube. They shook the mixtures at different intervals and observed and noted any layers that emerged.
“I see some layers here,” a student said, holding the tube up to her eyes. “Mine isn’t the right one.”
Which substance was the “right” one? (Drum roll.) Lecithin, which, according to Merriam-Webster, is “any of several waxy hygroscopic phospholipids that are widely distributed in animals and plants, form colloidal solutions in water, and have emulsifying, wetting, and antioxidant properties.”