FLOAT

Differences in density power this Lego dance. In the experiment, students place isopropyl alcohol (density = 0.79g/mL) and salt water (17% NaCl by mass, density = 1.12 g/mL) in a bottle along with a variety of Lego pieces. Some of the Legos were snapped together with others, some pieces were free. When shaken, the alcohol and saltwater form an emulsion with an intermediate density a little below 1 g/mL. But because the liquids are immiscible, they soon separate back into two distinct phases. Lego pieces, meanwhile, are made of acrylonitrile butadiene styrene (ABS), which has a density between 1.00 and 1.08 g/mL, so they float on salt water and sink in the alcohol and the emulsion. But snapping the Legos together traps enough air in between them to create units with a density of around 0.94 g/mL, meaning they will sink in isopropyl alcohol but float on the saltwater and the emulsion.

Details of and ways to modify this classroom experiment, called a density bottle, can be found in the paper linked below. This video/animation is sped up for file-size reasons.

Credit: J. Chem. Educ. 2015, DOI: 10.1021/ed500830w