Question

Calculate the partition coefficient of caffeine in water/methylene
chloride from the following data: 10.3 g/100 mL for methylene
chloride and 2.04 g/100 mL for water.
Using the same data a student follows our procedure and extracts the caffeine using 3 extractions of 7 mL of methylene chloride. How much caffeine is in the combined 21 mL of methylene chloride? How much remained in the water?

Answer 1

You don't say but I assume these numbers you give are the solubility of caffeine in the two solvents.
Ko/a = 10.3/2.04 = 5.049


fn = [(1+K(Vo/Va)^-n
fn is the fraction of the solute REMAINING in the aq phase after n extractions.
NOTE: I don't see any number for the volume used for the aq phase. I see the 7 mL for organic phase but nothing for the aq phase. I've show you how to do if assuming you just didn't type that information in.