Analytical Chem istry - DePauw University

348 Analytical Chemistry 2.0organic phase(I 2 ) orgK D(I 2 ) aq + I – K fI – 3Figure 7.32 Extraction scheme forProblem 7.30.(ML 2 ) orgaqueous phaseorganic phaseK Dβ 2(ML 2 ) aq M 2+ + 2L –aqueous phaseFigure 7.33 Extraction scheme forProblem 7.31.30. The relevant equilibria for the extraction of I 2 from an aqueous solutionof KI into an organic phase are shown in Figure 7.32. (a) Is the extractionefficiency for I 2 better at higher or at lower concentrations of I – ?(b) Derive an expression for the distribution ratio for this extraction.31. The relevant equilibria for extracting the metal-ligand complex ML 2from an aqueous solution into an organic phase are shown in Figure7.31. (a) Derive an expression for the distribution ratio for this extraction.(b) Calculate the extraction efficiency when a 50.0-mL aqueoussample that is 0.15 mM in M 2+ and 0.12 M in L – is extracted with 25.0mL of the organic phase. Assume that K D is 10.3 and that b 2 is 560.32. Derive equation 7.32.33. The following information is available for the extraction of Cu 2+ byCCl 4 and dithizone: K D,c = 7× 10 4 ; b 2 = 5 × 10 22 ; K a,HL = 2 × 10 –5 ;K D,HL = 1.01 × 10 4 ; and n = 2. What is the extraction efficiency if a100-mL sample of an aqueous solution that is 1.0 × 10 –7 M Cu 2+ and1 M in HCl is extracted with 10 mL of CCl 4 containing 4.0 × 10 –4 Mdithizone (HL)?34. Cupferron is a ligand whose strong affinity for metal ions makes it usefulas a chelating agent in liquid–liquid extractions. The following tableprovides pH-dependent distribution ratios for the extraction of Hg 2+ ,Pb 2+ , and Zn 2+ from an aqueous solution to an organic solvent.Distribution Ratio forpH Hg 2+ Pb 2+ Zn 2+1 3.3 0.0 0.02 10.0 0.43 0.03 32.3 999 0.04 32.3 9999 0.05 19.0 9999 0.186 4.0 9999 0.337 1.0 9999 0.828 0.54 9999 1.509 0.15 9999 2.5710 0.05 9999 2.57(a) Suppose you have a 50.0-mL sample of an aqueous solution containingHg 2+ , Pb 2+ , and Zn 2+ . Describe how you can effect a separationof these metal ions. (b) Under the conditions of your extractionfor Hg 2+ , what percent of the Hg 2+ remains in the aqueous phase afterthree 50.0-mL extractions with the organic solvent? (c) Under the conditionsof your extraction for Pb 2+ , what is the minimum volume of