Question

Solute S has a partition coefficient of 5.9 between water (phase 1) and hexane (phase 2).

(a) Calculate the concentration of S in hexane if [Swater] is 0.015 M.



(b) If the volume of water is 85.0 mL and the volume of hexane is 18.0 mL, find the quotient (mol S in hexane/mol S in water).

Answer 1

(a) 0.0885 M

(b) 1.25

Explanation:

Solute S has a partition coefficient of 5.9 between water (phase 1) and hexane (phase 2).

i.e Partition coefficient Kd = [S(hexane]/[S(water) = 5.9

to calculate the concentration of S in hexane; we have;

[S(hexane]/0.015 = 5.9

[S(hexane)] = 5.9 x 0.015

= 0.0885 M

Question B say ,

If the volume of water is 85.0 mL

and the volume of hexane is 18.0 mL,

to find the quotient (mol S in hexane/mol S in water), we will multiply the

Partition coefficient Kd with volume of hexane divided by volume of water

i.e Partition coefficient Kd = (moles/volume of S in hexane)/(moles/volume of S in water)

∴

(moles of S in hexane/moles of S in water) = Kd x (volume of hexane/volume of water)

= 5.9 x 18.0/85.0

= 1.25