Analytical Chem istry - DePauw University

Chapter 10 Spectroscopic Methods649(c) The concentrations of Cu 2+ , Co 2+ , and Ni 2+ in a sample that hasan absorbance of 0.423 at a wavelength of 732.0 nm, 0.184 at awavelength of 462.9 nm, and 0.291 at a wavelength of 378.7 nm.The pathlength, b, is 1.00 cm for all measurements.15. The concentration of phenol in a water sample is determined by separatingthe phenol from non-volatile impurities by steam distillation,followed by reacting with 4-aminoantipyrine and K 3 Fe(CN) 6 at pH7.9 to form a colored antipyrine dye. A phenol standard with a concentrationof 4.00 ppm has an absorbance of 0.424 at a wavelengthof 460 nm using a 1.00 cm cell. A water sample is steam distilled anda 50.00-mL aliquot of the distillate is placed in a 100-mL volumetricflask and diluted to volume with distilled water. The absorbance of thissolution is found to be 0.394. What is the concentration of phenol (inparts per million) in the water sample?16. Saito describes a quantitative spectrophotometric procedure for ironbased on a solid-phase extraction using bathophenanthroline in apoly(vinyl chloride) membrane. 22 In the absence of Fe 2+ the membraneis colorless, but when immersed in a solution of Fe 2+ and I – , themembrane develops a red color as a result of the formation of an Fe 2+ –bathophenanthroline complex. A calibration curve determined usinga set of external standards with known concentrations of Fe 2+ gave astandardization relationship ofA = (. 860× 10 3 M− 1 ) × [ Fe2+]What is the concentration of iron, in mg Fe/L, for a sample with anabsorbance of 0.100?17. In the DPD colorimetric method for the free chlorine residual, which isreported as mg Cl 2 /L, the oxidizing power of free chlorine converts thecolorless amine N,N-diethyl-p-phenylenediamine to a colored dye thatabsorbs strongly over the wavelength range of 440–580 nm. Analysis ofa set of calibration standards gave the following results.mg Cl 2 /L absorbance0.00 0.0000.50 0.2701.00 0.5431.50 0.8132.00 1.08422 Saito, T. Anal. Chim. Acta 1992, 268, 351–355.