Crystallization of Sodium Acetate

One of the most fascinating demonstrations I encountered as a student dealt with crystallization. The demonstration has now become a favorite of my students.

Sodium acetate is extremely soluble in hot water and much less at room temperature. Careful preparation and cooling of a hot, saturate solution can give a supersaturated solutio@oom temperature. When the sodium acetate crystallizes as a hydrate, the crystals rapidly form a solid matrix sufficient to support the mixture in a tall column.

The following procedure for preparation of the supersatu­rated solution generally works smoothly. Place about 50 g of sodium acetate trihydrate in a 125-ml Erlenmeyer flask, add about 5 ml of water, and heat gently over a low flame from a Meker burner using a wire gauze between the burner and the flask. Wear gloves and use tongs to hold and swirl the flask until the crystals dissolve. If any crystals remain an the sides in the flask, quickly wash down the sides with a small amount of water. Remove the flask from the heat, cover it tightly with a clean piece of foil, and allow it to cool. The solution and flask must be free of all traces of crystals. If too much water is added, a watery matrix result, but the excess water can be boiled off.

To crystallize, place a few sodium acetate crystals on the bench and slowly and steadily pour the solution an them. Crystallization will begin immediately and continued pouring will give a tall column of crystals. If a seed crystal is added to the solution remaining in the flask, crystals will grow rapidly in all directions from the seed.

The sample can be dissolved and used again, but a hot filtration of a somewhat diluted solution may be necessary to remove debris that promotes premature crystallization. Excess water should be boiled off.

lit Literatur und Bearbeitung
Autor (Text):	Gene A. Hiegel; California State University, Fullerton;  Fullerton, CA 92634:  Journal of Chemical Education Vol 57, Number 2, February 1980
Bearbeitung (WWW):	Klaus-G. Häusler
Literatur:	For other crystallization demonstrations see Bacon, E. K., J. CHEM. EDUC., 25,251 (1948), Barelli, N. and Leite, C. R., J. CHEM. EDUC., 53, 508 (1976), and Engels, C. J., Amer. J. Phys., 41, 744 (1973). A considerable amount of heat is released during the crystallization. This can be felt by touching the crystals.

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