Question

At a pH of 4, the Cu-neocuproine complex formed in the liquid-liquid extraction experiment has a partition coefficient of about 6.3 when equilibrated between the acid aqueous solution and chloroform. Calculate the concentration of Cu in the chloroform phase if 37.0 mL of a 0.24 M aqueous Cu solution buffered to pH 4 is equilibrated with 20.0 mL of chloroform.

Answer 1

Extraction with 20.0 mL of chloroform: Fraction of solute present in water = q = [V_aq/K_D V_org + V_aq) ^n where n = number of extractions = 1 q = fraction of solute present in aqueous phase V_aq = Volume of the aqueous phase = 37.0 mL V_org = Volume of the chloroform (organic phase) = 20.0 mL K_D = partition coefficient or distribution coefficient = 6.3 q = (V_aq/K_D V_org + V_aq) ^n q = (37/(6.3 times 20) + 37) ^1 q = (37/163) q = 0.226994 Concentration of Cu remaining in aqueous phase = 0.226994 times 0.24 M = 0.054479 M Concentration of Cu remaining in chloroform = 0.24 M - 0.054479 M = 0.185521 M Concentration of Cu remaining in chloroform phase = 0.186 M