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Sublimination of Iodine at Various Pressures: Mutlipurpose Experiments in Inorganic and Physical Chemistry

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Ilya A. Leenson

Department of Chemistry, Moscow State University, Moscow 119899, Russia

J. Chem. Educ., 2005, 82 (2), p 241

DOI: 10.1021/ed082p241

Publication Date (Web): February 1, 2005

Section:

History, Education, and Documentation

Abstract

The aim of this article is to elucidate some interesting phenomena, which can be observed in the process of heating solid iodine in closed vessels at various pressures. The experiments provide useful possibilities for discussing the following items: vaporization and melting of iodine crystals at atmospheric pressure; long storage of iodine crystals in air and in vacuum; temperature at which iodine vapors above crystals in a closed vessel becomes visible; the rate of iodine sublimation in high vacuum; “jumping” of heated iodine crystal in vacuum and “jet force” which emerges at different temperatures; diffusion of iodine vapors and “random walk” of iodine molecules; experimental determination of mean free path and collision frequency; mean free path in real life; calculation of the number of iodine atoms in equilibrium with molecular iodine at boiling point; and safety considerations (strength of glass ampules of different diameters against internal and external pressure). The article and questions therein may be used in classroom discussion with students of the general, inorganic, and physical chemistry (molecular-kinetic theory).