A Extraction of Caffeine

In this experiment, 0.070 g of caffeine is dissolved in 4.0 mL of water. The caffeine is extracted from the aqueous solution three times with 2.0-mL portions of methylene chloride. Calculate the total amount of caffeine that can be extracted into the three portions of methylene chloride (see Technique 12, Section 12.2). Caffeine has a distribution coefficient of 4.6, between methylene chloride and water. 

NOTE To obtain good results, you should make all weighings as aoourately as possible, preferably on a balance that Is aoourate to within 0.001 g. 

Before beginning this experiment, check your screw-cap centrifuge tube for leaks. Add exactly 0.070 g of caffeine to the centrifuge tube. Then add 4.0 mL of water to the tube. Cap the tube and shake it vigorously for several minutes until the caffeine dissolves completely. It may be necessary to heat the mixture slightly to dissolve all the caffeine. 

After shaking, place the tube in a test tube rack or beaker and let it stand until the layers separate completely. It may be necessary to tap the sides of the tube to force all the methylene chloride layer to the bottom of the vial. Occasionally, a drop of water will get stuck in the very bottom part of the tube, below the methylene chloride layer. If this happens, depress the bulb slightly and try to draw the water drop into a Pasteur pipette. Transfer this drop to the upper layer. 

Repeat this extraction two more times using 2 mL of fresh methylene chloride each time. Combine the organic layer from each of these extractions with the methylene chloride solution from the first extraction. 

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