Mass of benzoic acid in water (mg) Volume of water (ml) Distribution coefficient

Question

Mass of benzoic acid in water (mg) Volume of water (ml) Distribution coefficient, K 0.0655 3 Part B -Extraction of Caffeine watey+ 1. Check your centrifuge cap for leaks (see step 1 of Part A above). Weigh out 65-70 mg of tubat tube along with 4.0 mL of water. Record the mass-tcakfe 18, 923 caffeine and place in the centrifuge accurate to the nearest 1 mg. Cap and shake vigorously until the caffeine is totally di (it may be necessary to warm the mixture to get all of the caffeine dissolved). 2. Add 2.0 mL of dichloromethane (methylene chloride) to the centrifuge tube and mix 9 thoroughly for 1-2 min. Remember to period inside and outside pressures can equilibrate. Remember not to shake too vigorously which could lead to formation of an emulsion and a difficult separation. Set the centri aside and allow the layers time to completely separate. Using a glass pipette and rubber bulb, draw off the dichloromethane layer and place it in a stoppered test tube. This is the first extract. Continue with the centrifuge tube containing the top layer (water). Repeat steps 2-3 with the water layer in the centrifuge tube. The bottom layer is the second extract. It should be combined with the first extract in the stoppered test tube. Continue with the centrifuge tube containing the water layer. ically "vent" - remove the cap briefly so that the fuge tube 3. 4. 27

Explanation / Answer

The answer is yes, we need to use the volumes pf the two immiscible solvents in order to calculate K(Partition Coefficient). 'K' is the ratio of concentration of solute in 2 immiscible solvents.. Since here the volumes of the 2 immiscible solvents are different (4mL water and 2mL DCM), we require the volumes to calculate K since they''ll not cancel up in the ratio.  

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