Homework Help: chem

Posted by j on Monday, February 8, 2010 at 3:34pm.

.070g caffeine dissolved in 4 mL water. caffeine is extracted from aqueous solution 3 times with 2mL portions of methylene chloride. calculate total amount of caffeine that can be extracted into the 3 portions. caffeine has a distribution coefficient of 4.6 between methylene chloride and water

chem - DrBob222, Monday, February 8, 2010 at 4:32pm
There are two ways to do this.
1. K_o/a = concn organic/concn aq and do that three times, taking the answer from the previous extraction to use for the new extraction.
2. Or you can do all of it at one time with
f_n = [(1 + K_d*(V_o/V_a)]^-n where f_n = fraction solute REMAINING in the aqueous layer. o=organic layer; a = aqueous layer; concn can be in g/mL; V_o=Volume in organic layer; V_a = volume in aqueous layer.
Post your work if you get stuck. If you want the portion in the organic layer, just use the second method to find the fraction in the aq layer and subtract from 1 to find the fraction in the organic layer.

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