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An Inexpensive Microscale Method for Measuring Vapor Pressure, Associated Thermodynamic Variables, and Molecular Weight

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Jason C. DeMuro , Hovanes Margarian , Artavan Mkhikian , Kwang Hi No and Andrew R. Peterson

U. S. Grant High School, 13000 Oxnard Street, Van Nuys, CA 91401

J. Chem. Educ., 1999, 76 (8), p 1113

DOI: 10.1021/ed076p1113

Publication Date (Web): August 1, 1999

Section:

History, Education, and Documentation

Abstract

Existing methods for measuring vapor pressure are too expensive or not quantitative enough for chemistry classes in secondary schools. Our method measures the vapor pressure inside a bubble trapped in a graduated microtube made from a disposable 1-mL glass pipet. Vapor pressures of water, methanol, and ethanol are measured over temperature ranges of 4-90 °C. The enthalpy and entropy of vaporization and boiling points, calculated using the Clausius-Clapeyron equation, agree well with published values. The vapor pressures of aqueous solutions of ethanol and methanol plotted against mole fractions of water give positive deviations from Raoult's law, but concentrations were identified from which molecular weights of the alcohols could be calculated. These molecular weights are not significantly different from published values. Sources of error in the method are analyzed. A procedure for use in secondary schools is outlined.

Keywords (Audience):

High School / Introductory Chemistry

Keywords (Domain):

Laboratory Instruction

Keywords (Feature):

The Microscale Laboratory

Keywords (Pedagogy):

Hands-On Learning / Manipulatives

Keywords (Subject):

Aqueous Solution Chemistry

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This article has been cited by 1 ACS Journal articles (1 most recent appear below).

Enthalpy of Vaporization and Vapor Pressures: An Inexpensive Apparatus
Rubin Battino , David A. Dolson and Michael R. Hall , Trevor M. Letcher
Journal of Chemical Education2007 84 (5), 822
- Enthalpy of Vaporization and Vapor Pressures: An Inexpensive Apparatus
  Rubin Battino , David A. Dolson and Michael R. Hall , Trevor M. Letcher
  Journal of Chemical Education2007 84 (5), 822
  An inexpensive apparatus is described for the determination of the vapor pressure of a liquid as a function of temperature for the purpose of calculating enthalpy changes of vaporization. The solid-state pressure transducer is linear above 100 torr, is ...
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