Experiment 15 - Experiment 15- Freezing Point: A...

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Experiment 15 - Freezing Point: A Colligative Property of Solutions Jonathan Brate 2/9/09 Monday 2:00-5:00 Group 1 TA: Carolina Garcia
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Introduction: There were multiple objectives laid out for Experiment 15. One objective was to determine the freezing points of several liquids, which was done by recording temperature of the liquids as they were being cooled. When the temperature of the liquids had a slight increase but then began cooling again, the freezing point of the liquid was indicated. The jump in temperature indicated that the liquid had left its super cooling phase and froze. The increase in temperature was due to the liquids heat of fusion. Another objective for the experiment was to combine our data with other students in our lab. This was done by having everyone enter their data into the laboratory computer, and then printing off a plot of the combined data. A third objective of the experiment was to prepare a solution of an unknown solute and measure its freezing point. This was accomplished by using the same technique that was used to determine the freezing points of the known liquids. The last objective of the experiment was to determine the molar mass of the unknown solute using its freezing point. This was done by using the class’s combined data plot to determine the unknown solute’s concentration. Once the concentration was known, the number of moles of the solute could be calculated. By dividing the concentration by the number of moles, the molar mass of the unknown solute was able to be determined. One topic covered in the experiment that relates to Chemistry 102 lecture is the heat of fusion of a liquid, which is the heat released by a liquid when a it freezes. Another topic examined in Experiment 15 that was covered in lecture is the idea of a substance experiencing super cooling. This happens when the liquid doesn’t freeze right at its freezing point, but still continues to cool. When the liquid does begin to freeze, however, the released heat of fusion causes the temperature of the substance to return to its true freezing point. A laboratory technique used in this experiment was the use of cooling curves to
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This note was uploaded on 10/20/2011 for the course ENGIN 200 taught by Professor Miller during the Spring '11 term at University of Cincinnati.

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Experiment 15 - Experiment 15- Freezing Point: A...

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