Vapor Density - Victor Meyer experiment

VAPOR DENSITY

This experiment illustrates a practical method for determining the molecular weight of a volatile material. It provides excellent practice in the use of simple physical-chemical apparatus.

Theory.

The density of a vapor is more easily determined than the density of a gas because the substance may be weighed accurately when condensed to a liquid at room temperature. Very accurate vapordensity results have been obtained in this way.When only moderate accuracy is required, however, of the various methods available that of Victor Meyer is the simplest and the one most frequently used.

A known weight of liquid is vaporized in a chamber maintained at an appropriate and constant high temperature. The air displaced from the chamber is cooled to room temperature and its volume carefully measured. Substitution of air for the actual vapor thus provides a means of determining the volume the known weight of vapor would have occupied at room temperature if it could be cooled without condensation. It should be noted that it is not necessary that the temperature of the vaporization chamber be known, but it must be constant.

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