OCHEM question

Question

The partition coefficient for compound A between hexanes and water is 12. Assume 10 grams of A is dissolved in 100mL of water . This aqueous solution is extracted with 100 mL of hexanes. How much A will the first hexanes fraction contain? How about a second extraction with another 100 mL of hexanes?

Answer 1

12:1 is 12 parts in hexane and 1 part in H2O for a total of 13 parts.

12/13 = 0.92 which is the fraction that goes into hexane.

Since equal volumes of hexane and water are used, they can be ignored.

First extraction:  10 g x 0.92 = 9.2 g in hexane extract

This leaves 0.8 g left in the water.

Seconde extraction:  0.8 g x 0.92 = 0.74 g in hexane extract