Experiment Freezing Point Experiment

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The purpose of this experiment was to learn techniques to determine the freezing point of a pure benzophenone, a solvent. Furthermore, methods for determining the freezing point depression in relation to the solute, cyclohexanone, concentration were employed in addition to learning what molality is and how it related to the colligative properties being studied. These objectives were achieved by melting both pure benzophenone and benzophenone/cyclohexanone solutions (two solutions with different concentrations of the solvent, benzophenone) and recording the temperature as a function of time (intervals of 10 seconds) while each cooled. The times and temperatures were then plotted to generate freezing point curves for each solution, these graphs …show more content…
For the solution consisting of 7.57 grams of benzophenone + 0.5 mL of cyclohexanone, the experimental freezing point depression constant was calculated as 9.87 ˚C kg/mol, meaning that for a one molal solution the freezing point is depressed by 9.87˚C. These two Kf values were averaged, and the overall experimental freezing point depression constant, Kf, of the solution was determined to be 10.76˚C kg/mol. The accepted Kf of the solution is 8.7 ˚C kg/mol. When the accepted and experimental Kf values were compared, the experimental value resulted in an error of 23.68%. This error is fairly significant and is the result of a discrepancy in the experimental molality or freezing point depression —since both “Kf” and “i” are constant. The error in molality is due to the inaccuracy in measuring 5.0 grams of benzophenone at the beginning of the experiment; 0.507 grams were instead measured. This resulted in a smaller molality which produced greater Kf values since the values were determined by dividing the freezing point depression by the molality of solution. Additionally, there could have been an error in extrapolating the freezing point from the graph thus resulting in an inaccurate freezing point depression. A freezing point depression greater than the actual freezing point depression would result in a greater Kf value than the accepted value when divided by the molality of the

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