# Determining the Molar Mass of an Unidentified Volatile Liquid

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• Published : December 8, 2012

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Determining the Molar Mass of an Unidentified Volatile Liquid Abstract
Molar mass helps to determine how much of a substance is present in a sample. Volatile liquids change from liquid to gas at relatively low temperatures and atmospheric pressures. In this investigation an unknown volatile liquid is vaporized so that the ideal gas law can be used to determine its molar mass. This study will apply the ideal gas law in tandem with the concept of volatile liquids and basic molar mass related stoichiometry to identify the molar mass of an unknown liquid. A small sample of the unknown liquid was but into Erlenmeyer flask and vaporized in a water bath. Measurements of mass, pressure, temperature and volume were taken in order to calculate a molar mass of 78.09 gmol-1 . Calculated results from other groups who followed the same procedure included 78.61 gmol-1 and 91.06 gmol-1. A large variety of systematic and random errors in conjunction with confounding variables may have caused inaccuracies in the results therefore they are rejected as invalid. Further studies might investigate the how to determine the molar mass of volatile solids or may investigate other ways of applying the ideal gas law. Introduction

When considering the amount of substance weight and volume are methods of measurement that cannot be trusted. Different substances can have very different densities, which greatly affect how much space they can occupy and how heavy they are. To avoid confusion the mole (mol) unit of measurement was introduced and with it the concept of molar mass. One mole of a substance has 6.022 x 1023 particles of the substance and has a mass equal to its molar mass given in grams per mol. Every element has a unique molar mass, which when added together can create the molar mass of different compounds. When presented with an unknown substance molar mass can also help to identify it. (Neus, 2007) A volatile liquid is one that is easily vaporized, that is to say to change from liquid phase to gas phase. Therefore volatile liquids have low boiling points, some of which can even evaporate into the air at room temperature, a potentially hazardous trait. For example Chloromethane (CH3Cl) is a volatile liquid that vaporizes at 20oC, room temperature, and can cause symptoms similar to drug intoxication when inhaled. In this investigation an unknown volatile liquid is vaporized so that the ideal gas law can be used to determine its molar mass. (Beychok, 2012) The ideal gas law relates the idea of ideal gases, whose particles move randomly and do not interact, to the temperature and pressure settings that achieve this state. Most real gasses at standard temperature and pressure resemble ideal gasses. Gasses tend to behave more like ideal gasses at lower pressure and higher temperature. The ideal gas law is a combination of Charle’s and Boyle’s laws of gasses which state that volume and temperature at standard pressure are related and that pressure and volume are inversely proportional at standard temperature, respectively. Five variables are considered in this law; pressure, volume, temperature, number of moles of the substance and the universal gas constant. The gas constant relates then energy scale in physics to the standard temperature scale; it is equal to 8.314 JK-1mol-1. (Clark, 2010) This study will apply the ideal gas law in tandem with the concept of volatile liquids and basic molar mass related stoichiometry to identify the molar mass of an unknown liquid. A realistic situation where a similar procedure may be required would be when observing the properties of a newly formed liquid compound. It is expected that molar mass will be determined but may deviate from the actual molar mass of the liquid, which is unknown. Materials and Methods

Materials