edited by GEORGEL. GILBERT Denison University Granville. Ohio 43023
An Effective Demonstration of Some Properties of Real Vapors SUBM~TTED BY 0. Scott Metsger' Ohio State University Columbus. OH 43210 CHECKED BY:
Luther K. Brice Virginia Polytechnic Institute and State University Blacksburg. VA 24061
ideal gas to first year chemistry studkts. This versatile device is easv to use and several demonstrations can be done auicklv. . " The effects of pressure, volume, and temperature changes on a gas can be observed instantaneously. The following properties of a gas may be introduced or studied qualitatively: diffusion, pressure,
variahle densities, Charles' law (V = kT),and attractive forces hetween molecules. In addition, the following gas laws may be illustrated quantitatively: Buyle's law (PV = k ) , Gay-Lussac's law ( P = kT), and Dalton's law of partial pressures. Almost 40 years ago, a paper appeared in THIS JOURNAL that described an apparatus for demonstrating some properties of gases.2 The simpler apparatus presented here expands the number of properties that can be considered and uses hromine vanor. Students can see the vanor as it is manipulated, provided the demonstrations are done in front of a white background. CAUTION: Bromine is a powerful oxidizing a g e n t a n d should be handled carefully. A suitable cold bath must he available: dry ice in isopropyl alcohol is sufficient (-78"C), but liquid nitrogen (-196'C) enhances the demonstration. With slight modifications, one can also demonstrate that liquids and some solids (e.g., 12) exert measurable vapor pressures and that these vapor pressures are dependent upon temperature hut independent of atmospheric pressure. The heats of vaporization for several volatile liquids may also be calculated. The Apparatus T h e aonaratus consists of two bulbs ( A H with Teflon@ rudimentary knowledge of glassblowing is sufficientto assemble the apparatus, hut there must he no pinholes. Greaseless joints4 should be used throughout since bromine is soluble in stopcock grease. A few drops of mineral oil placed
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Current address: Miter Inc., 6550 Singletree Drive, Columbus, OH 43229. Martin, D., J. CHEM.EDUC., 21, 383 (1944). :Teflon stopcocks are available from: Kontes, Spruce St.. P O . Box 729, Vineland. NJ 08360 or Lab-Crest Scientific Division, Fischer & Porter Company, East County Line Rd.. Warminster, PA 18974. Solv-Sealo greaseless joints are available from Fischer & Porler.
Apparatus far demonstration of propenies of real gases. Dimensions are suggested for convenient use. See footnotes 3 and 4 for equipment sources.
on top of the mercury that is open to the system will retard the reaction between mercury and bromine. To quantitatively demonstrate Boyle's law, the volume of the manifold plus the volume of bulb B, and the volume of bulb A must be calibrated. This can be done when assemhline - ~-~ the apparatus by weighing the amount of water needed to fill the manifold and the bulbs. The volume of the manometer will be insignificant. ~~~
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Preparing the Apparatus for Classroom Use t1i111i ~ I I I I ~ and { J alt~cktm ( ' ~ t n t v tthr apparatus ,I pinIi&s wit11 ,, T C &
