Van der Waals equation (VdW), (P+n 2a/V 2) (V-nb) = nRT is used to correct the volume and the pressure of the samples. Figure 1 shows the plot of the temperature versus pressure for the volatile liquids used in this experiment. The volatile liquids did not emulate the ideal gas law and correction has been made to the vapor pressure. Except for acetone, the other liquids have strong hydrogen bonding, higher vapor pressure and are polar substances. The selected liquids have boiling points between 56-83☌ and a density of about 0.79 g/mL, possessing rapid evaporation characteristics at room temperature.
Another problem that is avoided by volume measurement is the mass of the air in the flask before the volatile liquid was added. Measuring the volumes of the condensed liquids instead of the mass avoids problems associated with the unwanted weight droplets of water that could attach to the gas container and covering of the flask. The volatile liquid was evaporated to fill the container, the vapor was cooled to condensation and the volume of the liquid was measured to calculate the gram-molecular weight. To determine the Gram-molecular Weight (GMW) of the samples the Ideal Gas law equation was manipulated to give the following derived equation: GMW = mRT/PV where m is the mass of the condensed liquid, T is the temperature in kelvin, P is the pressure in atmospheres, V is the volume of the kettle, and R is the gas constant. The procedure described below can be performed in residential kitchens and the materials are available at low cost in the local markets.
In this report, a simplified version of a tea kettle apparatus was used to measure the properties of several volatile liquids at water boiling temperature. The tea kettle experiment is very useful to teach simple experiments as well as organic, analytical, and physical chemistry investigations in undergraduate laboratories. Everyday use of volatile liquids in aerosol spray, paint thinners, and nail polish removers make these molecules worthwhile to study. The accepted and accurate method of determining the molecular weight of liquids is mass spectroscope, but the cost and maintenance of the instruments make it unpractical for undergraduate education. The Dumas bulb method has been employed in many different laboratory experiments to measure the gram-molecular weight and other properties of various volatile liquids at higher temperatures.
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