Tie-Dye Milk!

Soap!

Why do we need soap? How does it work? The reason we use soap is not only to smell good but also to remove the top layer of oil on our skin (which traps bacteria). In today’s lesson, students learned how soap is made and why it is useful for bathing and cleaning.

To make soap, you add a strong base to an oil or fat.  This breaks down the oil into small parts. Instructors used a method called hot process saponification to demonstrate how soap is made with the ingredients vegetable oil and lye (NaOH or sodium hydroxide).

We discussed two of soap’s special properties that allow it to clean-up greasy messes: it is amphiphilic (both hydrophilic “water-loving” and hydrophobic “water fearing”) and a surfactant (capable of lowering water’s surface tension.) Water and oil don’t mix together so we add soap in order to let the water penetrate the oil. This releases the dirt on our skin. During our activity, students saw how detergent acts as a surfactant and can disrupt the surface tension of many liquids. In one experiment, they added food coloring to a bowl of milk then dripped detergent over the top. Ask them what happened when they did this!