Crystallization of Supersaturated Sodium Acetate and the Temperature Dependence of the Autoionization Constant of Water

Joseph A. Pergler , Ronald O. Ragsdale and Thomas G. Richmond
University of Utah, Salt Lake City, UT 84112
J. Chem. Educ., 1995, 72 (11), p 1027
DOI: 10.1021/ed072p1027
Publication Date: November 1995

Abstract

The temperature rise caused by the exothermic crystallization of a supersaturated solution of sodium acetate is visualized by performing the crystallization in the presence of phenolphthalein. As the solution warms to near 50 oC, a distinct pink color appears. Heating the solution to 90 oC affords a brilliant pink color. Quantitative spectroscopic measurements at 554 nm as a function of temperature shows that the absorbance obeys a van't Hoff relationship. The color change is ascribed to the variation of Kw (and thus the derived hydrolysis constant Kb for acetate ion) with temperature.

Keywords (Audience):

First-Year Undergraduate / General

Keywords (Domain):

Inorganic Chemistry

Keywords (Feature):

Filtrates and Residues

Keywords (Pedagogy):

Hands-On Learning / Manipulatives

Keywords (Subject):

Crystals / Crystallography
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  • Received: August 03, 2009

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