Question

The partition coefficient for aniline between 1-octanol and water is 0.90. 2.00 g of aniline is dissolved in 100 mL of 1-octanol, then is extracted with 100 mL of water. What is the mass in grams of aniline in the aqueous layer after equilibration?

Answer 1

The octanol-water partition coefficient is defined as

Pow = Coctanol/C Cwater

where Coctanol is the molar concentration of the organic compound in the octanol phase and Cwater is the molar concentration of the organic compound in water when the system is at equilibrium. The units are usually dropped and Pow is generally reported as a unitless ratio.

Pow = 0.90

We can either take molar concentrations or simply mass of aniline in both phases.

Thus

0.90 = 2.00 g/ a

Whra a = mass of aniline in aqueous phase.

a = (2.00/0.9) g = 2.22 g