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Experiment 12 Colligative properties

Experiment 12 Colligative properties - Experiment 12...

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Experiment 12 – Colligative Properites Summer 2010 Name TD Khang Lab Section 409 Point Summary (See Blackboard for detailed grading rubric) Superior Excellent Satisfactory Fair Poor Omitted Introduction •Purpose of Report •Goals of Experiment Materials and Methods Results and Discussion •Description of data •Data Tables •Data Table Titles •Graphs •Figure Captions •Sample Calculations •Systematic Error •Random Error Discussion of discrepancies Other Lab Technique TOTAL POINTS TA Comments/Suggestions:
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C HEMISTRY 102L R EPORT T EMPLATE EXPT. Colligative Properties 12 12 Introduction The purpose of this report is to identify an unknown substance by determining its molar mass. The molar mass is determined by utilizing the Colligative Property Law and calculating the change in temperature through trials. Also, the purpose is to show how substances can affect the colligative properties of other substances through freezing point depression or boiling point elevation. The objective of the experiment was to first determine the average freezing point temperature of cyclohexane and compare it to a mixture of cyclohexane and an unknown substance to determine the overall change in freezing point. The average freezing point was determined by performing 4 trials of warming and cooling plots, determining the freezing point for each trial and taking an average. The change in freezing point was used to determine the molality and other given data was used to determine molar mass. Ultimately, the change in freezing point temperature was used to determine the identity of an unknown substance through the Colligative Property Law . Materials and Methods A cold aqueous salt solution was prepared by adding enough water to dissolve 35 g of solid NaCl in a 400-mL beaker. The salt water mixture was added to a 600-mL beaker filled 2/3 full. The cold aqueous salt solution was mixed with a stirring rod on top of a stir plate. A buret was used to transfer 25 mL of Cyclohexane into a 120-mL Erlenmeyer flask. The initial and final buret readings were recorded. A science workbench thermometer was inserted into a greased rubber stopper and then the stopper was placed onto the flask, making sure that the temperature sensor was touching the cyclohexane. The flask with cyclohexane was secured by a clamp and immersed in the ice bath. As soon as the flask filled with cyclohexane was immersed, the temperature was recorded every thirty seconds until it reached 3 o C. When this degree was reached, the flask was removed from the ice bath and held in the air by the clamp. The temperature was recorded again until it reached 12-15 o C. This process was repeated three more times for the pure cyclohexane solution. A total of four temperature trials were acquired.
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