Using an Analytical Balance in the Measure of Molar Mass of Condensed Vapor

An analytical balance is used to measure the weights of various equipment at different stages of the experiment

Determining the molar mass of condensable vapor may seem impossible if you don’t know how. This document explains the procedure in simple terms.  The process involves adding excess of the liquid that corresponds to the vapor to a weighed bulb.  This is then heated.  Once heated all the liquid in the bulb gets volatilized and the excess vapor is expelled.  Next the bulb is cooled and the weight of the bulb with the condensed vapor is measured. The condensed vapor’s mass is equal to the the vapor’s mass found in the flask at elevated temperature and the existing pressure.  This can then be used to calculate the moles present and the liquid’s molar mass from the “ideal gas law”.  Equipment used includes: ring stand, hot plate, analytical balance, beaker, flask, tap water, aluminum foil and 5 ml of an organic fluid that is volatile.

For further information visit www.kbcc.cuny.edu.