Soap bubbles burst when their walls thin because of evaporation or the effects of gravity. Glycerin is thought to increase the lifetime of bubbles because it is hygroscopic and very viscous. Since it is hygroscopic, it helps to prevent evaporation of the water. Its high viscosity increases the time that it takes for downward flow of the material in the bubble. Other substances such as corn syrup, liquid fruit pectin, and sugar appear to work similarly. When added to soap solution, rubbing alcohol results in short-lived bubbles, possibly because it greatly increases the solution's evaporation rate. In this activity, students first create a standard solution by mixing water with liquid dishwashing detergent. They then add glycerin, rubbing alcohol, and one or more additional substances (corn syrup, liquid fruit pectin [Certo], or sugar) to samples of the detergent solution. The solutions are compared to see which produces the longest-lasting bubbles.
Bubbles are a fun way to introduce the concepts of surface tension, intermolecular forces, and the use of surfactants. They also fit into a discussion of organic molecules such as soaps and detergents, and the concept of how a molecule can be both hydrophilic and hydrophobic. Additional investigations could compare the bubble lifetime and cost of commercial and homemade bubble solutions or could systematically vary solution composition (including type or amount of detergent or soap and amounts of additives) to produce the longest-lasting bubbles possible.
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Citation
JCE Editorial Staff, . J. Chem. Educ.2001 78 40A.
Keywords
Inquiry-Based / Discovery Method; Intermolecular Forces; Introductory / High School Chemistry; Surface Science; Teaching / Learning Aids
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