CHM 2201 Fall 2007 Organic Chemistry Lab I Department of Chemistry Villanova University Extraction Determination of a Distribution Coefficient From Bell, Clark and Taber, pgs. 41, 42 Apparatus required: 2 50 mL burettes (use one for benzoic acid solution and the other for NaOH solution) 1 250 mL Volumetric flask 2 250 mL Erlenmeyer flasks 10 mL Graduated cylinder 125 mL separatory funnel 1 Ring Clamp Hot plate 1 50 mL Beaker A. Preparation of the Standard Benzoic Acid Solution 1. Weigh out 0.61 g of benzoic acid onto some weighing paper. 2. Place this benzoic acid in a 250 mL Erlenmeyer flask and add 150 mL of water 3. Heat the resulting mixture on a hot plate with occasional swirling until the benzoic acid is dissolved to give a clear solution. 4. Carefully pour the resulting solution into a 250 mL volumetric flask. Rinse the Erlenmeyer flask several times with water and put the washes into the 250 mL volumetric flask. These washes ensure a quantitative transfer of all benzoic acid from the Erlenmeyer flask to the volumetric flask. 5. Cool the solution in the volumetric flask to room temperature and then add water to the flask to adjust the total volume to exactly 250 mL. This provides a standard 0.02 M benzoic acid solution. NOTE: CARRY OUT EXTRACTIONS IN YOUR HOOD B. Single Extraction and Distribution Coefficient Determination 1. Using a burette, place 50 mL of the standard 0.02 M benzoic acid solution into a 125 mL separatory funnel. MAKE SURE THAT THE FUNNEL STOPCOCK IS CLOSED BEFORE THE ADDITION. 2. Then, using a 10 mL graduated cylinder, add exactly 10 mL of methylene chloride to the separatory funnel. 3. Stopper the funnel and, holding the stopper securely in place, shake vigorously for 30 seconds. Vent the funnel and then place it in its supporting ring in the hood. 4. Remove the stopper and allow the layers to separate. 5. Carefully drain off the lower methylene chloride layer into a beaker. 6. Gently, swirl the separatory funnel for 5 – 10 seconds and then, after allowing the funnel to stand for several minutes, drain off a small amount of lower layer that may have accumulated after the swirling process. 7. Pour the aqueous layer remaining in the funnel into a 250 mL Erlenmeyer flask. 8. Rinse the separatory funnel twice with a few mLs of water and put the washes into the Erlenmeyer along with the main aqueous layer. (Continued on other side) 1CHM 2201 Fall 2007 Organic Chemistry Lab I Department of Chemistry Villanova University 2 9. Add two drops of phenolphthalein solution to the aqueous solution in the Erlenmeyer and carefully titrate with 0.02 M sodium hydroxide to a pink endpoint. You may want to place a white sheet of paper underneath the Erlenmeyer to better visualize the pink endpoint. 10. Calculate the number of grams of benzoic acid remaining in the water according to the Calculation Worksheet (Section B.1., 2.) accompanying this handout. 11. By difference, calculate the number of grams of benzoic acid in the methylene chloride layer. See Calculation Worksheet (Section B.3.). 12. Calculate Kd using the above values and volumes. See Calculation Worksheet (Section B.4.) for details. C. Multiple Extractions 1. Place another 50 mL of the standard benzoic acid solution into the separatory funnel. 2. Add 5 mL of methylene chloride to the separatory funnel. 3. Stopper and shake the funnel vigorously for 30 seconds. Vent the funnel and then place it in its supporting ring in the hood. 4. Remove the stopper and allow the layers to separate. 5. Carefully drain off the lower methylene chloride layer into a beaker. 6. Gently, swirl the separatory funnel for 5 – 10 seconds and then, after allowing the funnel to stand for several minutes, drain off a small amount of lower layer that may have accumulated after the swirling process. 7. Add another 5 mL portion of methylene chloride to the separatory funnel containing the aqueous layer. 8. Stopper and shake the funnel vigorously for 30 seconds. Vent the funnel and then place it in its supporting ring in the hood. 9. Remove the stopper and allow the layers to separate. 10. Carefully drain off the lower methylene chloride layer into a beaker. 11. Gently, swirl the separatory funnel for 5 – 10 seconds and then, after allowing the funnel to stand for several minutes, drain off a small amount of lower layer that may have accumulated after the swirling process. 12. Pour the aqueous layer remaining in the funnel into a 250 mL Erlenmeyer flask. 13. Rinse the funnel twice with a few mLs of water and put the washes into the Erlenmeyer along with the main aqueous layer. 14. Add two drops of phenolphthalein solution to the aqueous solution in the Erlenmeyer and carefully titrate with 0.02 M sodium hydroxide to a pink endpoint. You may want to place a white sheet of paper underneath the Erlenmeyer to better visualize the pink endpoint. 15. Calculate the amount of benzoic acid removed from the aqueous layer with the two 5 mL extractions and compare with that number with the amount removed with the single 10 mL extraction. (See Calculation Worksheet, Section C.1., 2., 3.). What results did you expect?; what results did you observe? 16. Using the Kd value you determined above in Part B12, calculate the theoretical amount of acid that should be removed by two 5 mL extractions (See Calculation Worksheet, Section C.4) and compare it with the amount that you found experimentally with the two 5 mL extractions. How do the experimental and theoretical values compare? TMB
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