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Principles of Solution Thermodynamics: Demonstration of Nonideal Behavior of Henry's Law. An Undergraduate Laboratory Experiment

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Luke Chandler Short and Thorsten Benter

Bergische Universität Wuppertal, Fachbereich C – Naturwissenschaften und Mathematik, , D-42119 Wuppertal, Germany

J. Chem. Educ., 2006, 83 (8), p 1233

DOI: 10.1021/ed083p1233

Publication Date (Web): August 1, 2006

Section:

History, Education, and Documentation

Abstract

Quantitative analysis of formaldehyde, HCHO, using the Nash reaction has seen a wide application in both the fields of environmental chemistry and medicine. Our group uses portable Nash systems both to monitor trace levels of HCHO (ppbV, 1/10⁹) present in urban air, as well as measure HCHO in urine, an indicator of bladder cancer. Although several techniques are available for the measurement of HCHO, the rugged nature and reliability of modern, off-the-shelf wet chemical monitoring systems places them ahead of other techniques for several applications. Insightful and practical experiments in physical chemistry for the advanced undergraduate laboratory course are possible with this system. Here we discuss a technique to sample both the gas and the liquid phases of a solution of HCHO(aq), permitting the quick and direct determination of the partition coefficient for a nonideal, solute–solvent mixture. Two scenarios are presented to demonstrate factors that influence this thermodynamic ratio: (i) concentration effects and (ii) temperature effects. The goal of this laboratory exercise is to introduce a commonly used type of HCHO analyzer, and then to apply this knowledge to demonstrate nonideal, biphase thermodynamic equilibrium.