8th grade is in the middle of their chemistry unit. They have been learning about the periodic table and different properties of these elements. This week, the 8th grade was looking at boiling and freezing points. It’s hard to imagine a liquid oxygen molecule or a solid gas since we are used to living at a comfortable climate. So to understand this, students investigated dry ice or frozen carbon dioxide. At a cool -109 degrees F (approximately) and the classroom at a temperature of 68 degrees F, this drastic temperature change creates a sublimation state change for the dry ice; it changes straight from a solid to a gaseous form.
Students began to understand how the quick change creates a dense gas or fog coming off the dry ice. This dense air sank and created a bubble of air the students could use to float the block on top of the counter. They pushed pennies into the block to see how matter responds at that temperature and how solid gases react to warmer solids colliding into them. By adding water to the block, they saw the water bubble (boil) with white gas filled bubbles and then freeze the water they had once put over the dry ice.
They then related their understanding of what was happening in our solar system. As frozen gases orbit through space, when they come close to stars, they melt, much like our dry ice was doing on the table, and produce a gaseous tail. We recognize these orbiting frozen gas balls as comets.