Exp7 - Discussion In this experiment the concepts of...

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Discussion: In this experiment the concepts of colligative properties, more specifically freezing point depression, were used to determine the molar mass of an unknown liquid. The freezing point of water was experimentally determined first by preparing an ice bath with water, ice and salt. A test tube of distilled water was placed in the bath to and its temperature recorded every fifteen seconds. To determine the freezing point of the unknown liquid, the same process was repeated twice and the results recorded. Once the data had been collected from all three runs of the experiment, the data was graphed and analyzed. The freezing point of the liquids was given by the temperature indicated in the graphs were the temperature was fairly constant across time. Using the formula for freezing point depression to find molality, and form there calculating number of moles along with the mass of the liquid, the molecular weight was calculated. The molar weight for the two trials was averaged and then the identity of the unknown liquid was determined from the molecular weight. For this experiment, it was important to completely dissolve all the solute in the solvent before measuring the freezing point depression of the experiment. Failure to do so would lead to a higher freezing point and a smaller T because the rate of the transfer of molecules from liquid to vapor would not slow down enough to reach the true, lower freezing point. Since this value is used to calculate the molar mass, the resulting molar mass would be greater because the smaller T causes the molality to be smaller as well which causes a smaller number of moles which increases the molecular weight. It is important to notice that molality was used for this experiment as opposed to molarity. This is due to the fact that molarity depends on the volume of
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This note was uploaded on 03/08/2010 for the course CHEMISTRY 1310 taught by Professor Williams during the Spring '10 term at Georgia Tech.

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Exp7 - Discussion In this experiment the concepts of...

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