Oil and Water: Washing Up with Surfactants
In a very hands-on activity, students observe and feel the differences between two cleaning methods, with and without hand soap, using coffee grounds to represent "dirt." Most of the dirt and bacteria on our hands is encased in a thin layer of oil, so because of the properties of oil and water, cleaning your hands with water alone has little effect when trying to remove the dirt. This activity demonstrates the importance of using a surfactant, such as hand soap, when washing your hands.
During this activity, students experiment to see how a surfactant helps clean dirty hands covered with cooking oil and coffee grounds. Artificial surfactants are chemically engineered for an uncountable number and variety of household and industrial uses, such as maintaining this clean room for preparing samples for a space experiment.Copyright (left) 2010 Samuel DuPont and Ryan Cates. STARS – University of South Florida, (right) NASA http://www.sti.nasa.gov/tto/spinoff2001/langley.html
Soaps and detergents are commonly used in industrial processes. In order for a process to be reproducible, the materials and/or objects involved in the process must be free from any contamination, such as dirt and oil. Surfactant-based soaps and detergents are commonly used to ensure all components of a process are clean so that the process results in a product of consistent quality every time it is made.
After this activity, students should be able to:
- Identify the purpose of soap when washing your hands and/or other objects and surfaces.
- Identify that washing hands with water alone is not sufficient to remove the oily grime that contains bacteria.