Rubenstein_Exp12 - Experiment 12 Colligative Properites...

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Experiment 12 – Colligative Properites Spring 2010 Name Alec Rubenstein Lab Section 438 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 explore colligative properties and to use them to determine the molar mass of a substance. The objective of the experiment was to use colligative properties to determine the molar mass of an unknown substance by recording the temperature of Cyclohexane as it freezes and melts and comparing this to the temperature of the substance with an unknown solute as it freezes and melts . The equations for boiling point elevation and freezing point depression will be used to calculate the unknown substance’s molar mass. Materials and Methods The procedure for this experiment was taken from the UNC Chemistry 102 Lab Manual Experiment 12 “Colligative Properties: Freezing Point Depression and Molar Mass.” First, the temperature sensor was calibrated through Data Studio. An ice/salt water bath was then prepared and 35.0 g of solid NaCl was placed in a 400 mL beaker and 100-200 mL of water was added to the solid NaCl to dissolve it. A 600mL beaker was then filled 2/3 full with water and salt water solution was added to it. A stir bar was placed in the base of the beaker and the beaker was put on top of the stir plate. The temperature sensor was then pushed through the hole in the rubber stopper using vacuum grease and 25 mL of Cyclohexane was transferred into a clean and dry 125 mL Erlenmeyer flask using a buret. The initial and final buret reading was recorded to measure the exact volume of Cyclohexane. The flask was then sealed with the rubber stopper, making sure the temperature sensor was submerged in the Cyclohexane. The flask was clamped in the salt ice-water bath and Data Studio was started and then stopped when the temperature sensor reached approximately 3 ˚ C. The flask was raised out of the bath and clamped to the ring stand. Next, data was collected in Data Studio until the temperature reached approximately 12~15 ˚ C. The flask was then placed back into the ice bath for three more trials. For the second part of the experiment, 0.7~0.8g of the unknown substance was measured using a balance to the nearest 0.001 g. The unknown was added to the 125 mL Erlenmeyer Flask with Cyclohexane. The flask was then swirled until all of the unknown solute was dissolved. A new ice bath was made by filling a 600 mL beaker 2/3 full of ice and 50 g of salt was dissolved on top of the ice. The ice bath was then filled with the ice/salt mixture and a stir bar until the mixture became slushy.
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Rubenstein_Exp12 - Experiment 12 Colligative Properites...

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