FR expt 1 dumas method - Mapa Institute of Technology 170L...

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M170L – A31 info: ary, 2011 [email protected] r-density, Dumas method, molar mass, orifice, volatile Mapúa Institute of Technology School of Chemical Engineering, Chemistry, Biological Engineering and Materials Science Engineering Determination of Molar Mass of a Volatile  Liquid by Vapor-Density Method Austria, Meynard 1 Baniqued, Paul Dominick E. 2 1 Professor, School of Chemical Engineering, Chemistry, Biological Engineering and Materials Science Engineering, Mapua Institute of Technology; 2 Student, CHM170/A31 Physical Chemistry Laboratory 1, Biological Engineering and Chemistry, Mapua Institute of Technology ABSTRACT The molecular weight of a certain volatile compound can be determined by its vapor density. This can be calculated by deriving the ideal gas equation. In this experiment, a set-up of a pre- weighed Erlenmeyer flask covered in aluminum foil and tightly secured by a copper wire is made. The excess foil beneath the copper wire was cut off to minimize errors. A sample of liquid is then injected to the flask by making a tiny orifice at the foil. The sample is then completely vaporized in a water bath then cooled down to room temperature. The mass of the condensed liquid is then determined and the molecular weight of the compound is calculated. Possible sources of error were the assumption of the vaporized sample as an ideal gas where intermolecular forces and the volume of the gas particles were negligible. High percent differences were obtained as a result but the values when compared with the three samples were significant since the chemical properties of the compounds vary. INTRODUCTION One of the early methods for the determination of the molar mass of volatile substances was through the measurement of the density of the vapor of the substance. The method is reliable and convenient and is still employed in some situations. Molar mass of a volatile liquid can be determined through Dumas method which is pioneered by the French Chemist Jean Baptiste Dumas in 1820’s. A volatile liquid is generally defined as the liquid that readily evaporates at temperature less than 100˚C when heated. Molecular weights of gases can be determined easily using simple ideal gas principles. From the ideal gas law, PV = nRT = (g/MW) RT eqn. 1 By rearranging the equation above, molecular weight the molecular weight is given by the equation, MW = gRT/PV eqn. 2 M = (wt/V) (RT/p) eqn. 3 Eqn 3 is sometimes called the vapor density form of the combined gas law. This measurement is performed at low pressure because at medium to high pressure, the equation is not obeyed since this equation is only applicable to ideal gas. From the relationship stated above, assuming
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This note was uploaded on 04/27/2011 for the course CHM 170 taught by Professor Ng during the Spring '11 term at Mapúa Institute of Technology.

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FR expt 1 dumas method - Mapa Institute of Technology 170L...

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