Lab Experiment 4

Lab Experiment 4 - 10 Make sure the thermometer is not...

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Tanisha Billups Experiment 4 February 20, 2008 Colligative Properties: Freezing-Point Depression and Molar Mass Purpose: The purpose of this lab is to apply the colligative property of freezing-point depression and to use it to determine the molar mass of an unknown substance. Procedure A: Cooling Curve for Pure Naphthalene 1. Weight a large test tube to the nearest .01g 2. Add 15 to 20g of naphthalene 3. Weigh the test tube again 4. Insert a thermometer into a 2-hole stopper 5. Loop a wire loosely around the thermometer and extend the straight part of the wire out of the second hole in the stopper (to stir the solution) 6. Make a water bath using a 600-mL beaker that has been placed on a tripod or o-ring (use wire gauze) 7. Fill the 600mL beaker nearly full of water and heat it to 85°C 8. Place the test tube containing naphthalene into the water bath to melt the solid 9. When most of the naphthalene has melted, insert the thermometer and stirrer into the test tube
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Unformatted text preview: 10. Make sure the thermometer is not resting on the bottom or touching the sides of the test tube 11. When all the naphthalene has melted, stop heating 12. Remove the tube with the stopper assembly in place 13. Put it into a large beaker that has a paper towel in it 14. Record T readings every 30 sec until it resolidifies 15. Stir constantly OMIT PROCEDURE B (Sulfur) Procedure C: Determination of the Molar Mass of an Unknown 1. Replace test tube of naphthalene into water bath 2. Heat until melted 3. Using weighing paper weigh about 2g of an unknown 4. Remove the stopper form the test tube 5. Do not lose any of the naphthalene 6. Add the unknown to test tube 7. Replace the stopper and stir gently until all the unknown has dissolved 8. Remove from water bath 9. Dry the test tube 10. Place the test tube a large beaker that has a paper towel in it 11. Record T readings as before until the sample solidifies (stir constantly)...
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This note was uploaded on 05/01/2011 for the course CHEM 112 taught by Professor Hibbard during the Spring '08 term at Spelman.

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Lab Experiment 4 - 10 Make sure the thermometer is not...

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