Hot Ice Is Real — And Easy To Make

Key Concepts:

• Sodium Acetate: A chemical compound that can be supercooled and rapidly crystallized.
• Supercooling: Cooling a liquid below its freezing point without it becoming solid.
• Nucleation Site: A point or surface where crystal growth can begin in a supercooled liquid.

Sodium Acetate and "Hot Ice" Experiment

The experiment demonstrates the rapid crystallization of supercooled sodium acetate, often referred to as "hot ice." The presenter recalls performing a similar experiment in third grade and aims to replicate it on a larger scale.

Preparation of Sodium Acetate

Sodium acetate can be created with adult supervision by mixing 1/4 cup of baking soda (sodium bicarbonate) with a liter of vinegar (acetic acid). This reaction produces carbon dioxide (CO2) gas and sodium acetate. The CO2 gas produced can be used to extinguish candles, as a bonus experiment. The resulting sodium acetate solution is then boiled for approximately one hour. After boiling, the solution is poured into a jar and allowed to cool, either at room temperature (covered) or in the refrigerator, until it is cool to the touch.

Supercooling and Crystallization

Sodium acetate has a freezing point of 58°C. Cooling the solution in the refrigerator results in supercooling, where the liquid is cooled below its freezing point without solidifying. Supercooling is possible because the liquid lacks a nucleation site, a place for crystal growth to begin. While supercooling water requires high purity, sodium acetate is a stable compound that can be supercooled easily. Introducing a nucleation site, such as a small amount of solid sodium acetate residue, triggers rapid crystallization. This crystallization process releases heat, making the resulting solid "hot ice" warm to the touch.

Conclusion

The experiment illustrates the principles of supercooling and nucleation using sodium acetate. The rapid crystallization of the supercooled solution, triggered by a nucleation site, demonstrates a phase transition and the release of energy in the form of heat.