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

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.

About Bob Sandor

Bob began working as a chemist in 1987 and remains a science geek to this day. After his PhD he worked on the bench in materials and inorganic chemistry for 10 years. He then took on a love for marketing and sales. He combined his passion for science and business and took entrepreneur general management positions in large corporations like Hoecsht Celanese now Sanofi Aventis, Bel-Art and Smiths Detection. There he learned what it would take to run a business and finally Tovatech was co-founded in 2006. Bob’s hobbies include playing, listening and composing music, skiing, working out, the internet and all things science. Read More