Highlighting JChemEd: Student Observations of Dynamic Floating and Sinking of Plastics in Various Liquids

By Kim Duncan on September 27, 2017

AACT recently announced that in partnership with ACS Publications, members now have access to 25 articles a year from ACS Journals, including the Journal of Chemical Education. Each month, we will highlight one article that you may consider downloading using this new member benefit. This month, we are featuring an article from the Journal of Chemical Education titled The Dynamic Density Bottle: A Make-and-Take, Guided Inquiry Activity on Density by Thomas S. Kuntzleman.

The activity is introduced with students making observations about a density bottle that is composed of salt water, isopropyl alcohol, and different types of plastic pieces. As the activity begins, students see the density bottle unmixed, with the salt water (density ≈1.1 g/ml) settled in the bottom half of the bottle and the isopropyl alcohol (density ≈ 0.79 g/ml) in the top half. The plastic pieces (density between 0.92 and 1.07 g/ml) float between the two liquids. The instructor then shakes the bottle to completely mix the contents and students observe the position of all of the components of the mixture as time passes. After the initial observations, students complete guided inquiry activities to help them develop an understanding of their initial observations.

This activity can be adapted to fit the needs of a wide variety of learning abilities, ranging from middle school physical science students to advanced chemistry classes. As an introductory activity it includes the concepts of density and homogeneous and heterogeneous mixtures. Higher level classes can address the topics of miscibility and separation techniques, adding the concepts of interparticle forces and molecular polarity for even more advanced students.

The article includes information about using this activity to incorporate learning objectives from the Next Generation Science Standards (NGSS) and offers suggestions to modify the activity and the components of the density bottle.

Related AACT classroom resources have been compiled in the sidebar on the right-hand side above.