Crystallization

Materials:

• Sodium acetate trihydrate

• Flask

• Hot plate

• Water

Procedure:

• Put 160 grams of sodium acetate in a flask and add 30 mL of water.

• Put the flask on a hot plate, heat it gently and stir until the crystals of sodium acetate dissolve. Use a small amount of water to rinse down the inside of the flask.

• Remove the flask from the heat and let it cool slowly without disturbing it.

• Add one or two crystals (it only takes a single crystal) to the liquid in the flask. Don’t take your eyes off of the liquid as beautiful crystals begin to form inside the flask.

• Feel the flask… it’s warm

This experiment is an example of an exothermic reaction or the heat of crystallization. If you attempt to dissolve sugar in water, you reach a point where you cannot dissolve any more sugar. This is called a saturated solution. However, if you heat this solution, more sugar will dissolve. When the solution is cooled, the sugar will remain in solution. This is called a supersaturated solution, which is very unstable and will crystallize easily. The process of crystallization gives off heat and is said to be exothermic; that’s why it is used in hand warmers.