The Purity and Purification of Solids Melting Points
The purpose of this experiment was to find the eutectic point for the mixture of naphthalene and biphenyl. This was done by measuring the melting point of both pure substances and five mixtures of different ratios. The purpose of the second section was to identify an unknown sample by measuring its melting point and mixing it with two known substances and comparing them. The results suggest that the eutectic point is closest to the weight % ratio of 10/90 naphthalene to biphenyl and the unknown sample is acetamide. Introduction:
One way to establish the purity of a substance is to measure its melting point. A pure substance will have a sharp melting range while an impure substance will have a more broad and depressed range. There is a point when a mixture of two substances will have a sharp melting range at a lower temperature than their respective pure melting points. This point is called the eutectic point. The purpose of this experiment is to find the eutectic point of a mixture of naphthalene and biphenyl and to identify an unknown sample by determining the melting point of a mixture with a known sample. Experimental Section:
For this experiment, a melt-temp apparatus was used to determine the mp of pure and mixed substances. To find the eutectic point of the naphthalene and biphenyl mixture, each person in the lab measured the mp of both pure biphenyl and pure naphthalene by warming them in the melt-temp apparatus at a rate of 2 °C/min and recording the temperature at which they begin melting and have completely melted. The class was then split in to equal groups to measure the mp of mixtures 10/90, 30/70, 50/50, 70/30, and 90/10. These were measured in the same way as the pure substances. The average mp was then recorded for each mixture and pure substance. The data was then plotted as a melting point diagram and used to determine the composition and temperature of the eutectic...
References: Karl Griesbaum, Arno Behr, Dieter Biedenkapp, Heinz-Werner Voges, Dorothea Garbe, Christian Paetz, Gerd Collin, Dieter Mayer, Hartmut Höke “Hydrocarbons” in Ullmann 's Encyclopedia of Industrial Chemistry 2002 Wiley-VCH, Weinheim.
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