Although many students have been exposed to the concept of density before reaching my Chemistry class, I always start the year with this POGIL-like activity.
One day during class I presented the disappearing rainbow demonstration and explained the chemistry behind it. After doing so, I had a student ask me if a particular bartending trick called “rainbow shots” was done in a manner similar to the way the disappearing rainbow demonstration is performed.
A paper square rubbed with graphite on one side is placed at the interface between two immiscible liquids, hexane and water.
A cast iron bomb is completely filled with ice water, then placed into a dry-ice/acetone slush and covered with a wooden box. When the water in the bomb freezes, the cast iron bomb explodes, breaking into several pieces, and destroying the box in which it was placed.
A normal ice cube is less dense than liquid water, but a deuterium oxide ice cube is more dense than liquid water.
An H2O ice cube is less dense than liquid water, but a D2O ice cube is more dense than liquid water.