Lab Report Exp17

Lab Report Exp17 - Ryan Cohen 4/26/09 Colligative...

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Ryan Cohen 4/26/09 Colligative Properties: Freezing Point Depression The purpose of this lab was to explore the colligative properties of organic solutions; specifically the freezing point depression of a solution with respect to solute concentration. The first part of the lab interpreted graphical data of the cooling of pure Benzophenone in order to calculate the freezing point of the organic solvent. The lab then added varying amount of an organic solute, Cyclohexanone, again deriving the associated freezing points of each solution. Ultimately, the lab used the data to calculate the freezing point depression constant, K f , for a Benzophenone solvent. The first part of the lab determined the freezing point of pure Benzophenone by analyzing graphical trends in the cooling of Benzophenone over time. A sample of Benzophenone was heated past its melting point then set to cool, being vigorously mixed to speed the cooling process. The temperature of the sample was taken every 10 second, with the first sign of crystallization recorded. The temperatures were plotted as a function of time, as the boiling point was extrapolated from the lab data. Since at the freezing point relatively no change in temperature occurs, a relatively stable temperature reading following the formation of crystals suggested the freezing point of the sample. Crystals first appeared at 110sec with a temperature
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Lab Report Exp17 - Ryan Cohen 4/26/09 Colligative...

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