EDTA forms colored complexes with a variety of metal ions that may serve as the basis for a quantitative spectrophotometric method of analysis. The molar absorptivities of the EDTA complexes of Cu2+ and Co2+ at two wavelengths are summarized in the following table (all values of f are in M-1 cm-1). metal absorptivity at 732 nm absorptivity at 462.9 nm Co2+ 2.11 15.8 Cu2+ 95.2 2.32 In one solution, it has an absorbance of 0.453 at a wavelength of 732.0 nm and 0.107 at a wavelength of 462.9 nm. Determine the concentrations of each metals ions. (Note this is a simultaneous equation) 1. [ Select ] 2. [ Select ]

EDTA forms colored complexes with a variety of metal ions that may serve as the basis for a quantitative spectrophotometric method of analysis. The molar absorptivities of the EDTA complexes of Cu2+ and Co2+ at two wavelengths are summarized in the following table (all values of f are in M-1 cm-1). metal absorptivity at 732 nm absorptivity at 462.9 nm Co2+ 2.11 15.8 Cu2+ 95.2 2.32 In one solution, it has an absorbance of 0.453 at a wavelength of 732.0 nm and 0.107 at a wavelength of 462.9 nm. Determine the concentrations of each metals ions. (Note this is a simultaneous equation) 1. [ Select ] 2. [ Select ]

Fundamentals Of Analytical Chemistry

9th Edition

ISBN:9781285640686

Author:Skoog

Publisher:Skoog

Chapter26: Molecular Absorption Spectrometry

Section: Chapter Questions

Problem 26.17QAP

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A dual beam UV-visible spectroscopy was used to determine the levels of Fe(II) in the run-off water of a local mine using the ferrozine assay (i) During a check of the instrument a step-like feature at 360 nm was observed in spectrum of the standard. Suggest what may give rise to this with reference to the instrument configuration and comment on how it may be remedied. (ii) The molar absorptivity of the [Fe(Ferrozine)3]2+ complex is 27900 cm−1 M−1 at 562 nm in aqueous solution (pH 5.5). If the EU maximum contaminant level for Fe is 200 ug /L and the contract required detection limit is 100 ug/L, comment on the suitability of the assay for the detection of iron. (iii) Determine the sample range, in terms of concentration and ppm, of Fe(II) that can be confidently analysed by UV-visible spectroscopy using a 1 cm cuvette. Explain with reference to an appropriate equation and solution phenomena, the origin of the limitations that define this range
b. Given that the cuvette path length was 1.17 cm, use the slope of this line to calculate the molar absorptivity of the cobalt complex at this wavelength. (Assume Beer’s law is obeyed.) c. An unknown cobalt sample was treated as follows: 40.8 mg of the unknown was dissolved in solvent to prepare 50.00 mL of solution in a volumetric flask. 4.00 mL of this solution was treated with thiocyanate, and diluted to a final volume of 50.00 mL. A sample of this final solution was placed in the same cuvette as the standards, and showed an absorbance of 0.38 at 625 nm. Determine the percentage of cobalt in the original unknown, given that the atomic mass of cobalt is 58.933 g/mol.
The molar absorptivity for cobalt and nickel complexes with 2,3-quinoxalinedithiol are 3.64x104L/M-cm for Co at 510nm, 5.52x103L/M-cm and 1.24x103L/M-cm for Co at 656nm and 1.75x104L/M-cm for Ni. A 250mg soil sample that was collected near an industrial metal-processing plant is dissolved, and masking agent is added to avoid interference from other metals present. Color is developed by adding the complexing agent and the sample is diluted to 100.00ml. The absorbance at 510nm is 0.517 and at 656nm it is 0.405 in a 1.00cm cell. Calculate the weight percent of Co and Ni in the soil.
Describe the principle and operation of anodic stripping voltammetry (ASV). How does it differ from adsorptive stripping voltammetry? What is the quantitative signal?
A calibration curve for the colorimetric determination of phosphorous in urine is prepared by reacting standard solutions of phosphate with molybdenum(VI) and reducing phosphomolybdic acid complex to produce the characteristic blue color. The absorbance (A) is plotted against the concentration of phosphorous. From the following data, determine the linear least-squares straight line and calculate the concentration of phosphorous in the urine sample. Phosphorous (ppm) 1.00 2.00 3.00 4.00 Unknown urine sample Fluorescence intensity 0.205 0.410 0.615 0.820 0.625
21. (What exactly is meant by potentiometric methods? What are they even?)
Graphite furnace atomizers are renowned in Atomic Absorption Spectrometry for their exceptionally low detection limits (10-12 g and lower for many elements). Why are detectabilities so much better with graphite furnaces than with flame atom cells in AAS?
An aqueous solution of sodium hexaiodoplatinate(IV) isblack. What conclusions can be drawn about the absorption spectrum of the [PtI6]2- complex ion?
A standard solution was put through appropriate dilutions to give the concentrations of iron shown in the table that follows. The iron(II)-1,10-phenanthroline complex was then formed in 25.0-mL aliquots of these solutions, following which each was diluted to 50.0 mL. The following absorbances (1.00-cm cells) were recorded at 510 nm: Calculate the concentration, in ppm, of a sample with an abosrbance of 0.829. Fe(II) concentration (ppm) A510 4.00 0.160 10.0 0.390 16.0 0.630 24.0 0.950 32.0 1.260 40.0 1.580
(i) You have been provided with a sample collected from a water pool beside a slag heap at the iron ore mine. 35 uL of the sample is added to 1165 uL of buffered ferrozine (excess). If the %T recorded at 562 nm in a 2 mm cuvette is found to be 25%, calculate the concentration of Fe(II) in the sample in mol L−1 and ppm. Comment on the contamination level. (ii) Comment on a possible contaminant that could interfere with the assay and suggest an approach that could be used to account for its presence.
The molar absorptivity (ε) of the FeSCN2+ complex ion is 4700 M-1 · cm-1 at a wavelength of 450 nm. Using a 1-cm sample tube, you measure the absorbance as (2.0x10-1). What is the concentration of FeSCN2+?
A solution of Tryptophan has an absorbance at 280 nm of 0.54 in a 0.5 cm length cuvette. Given the absorbance coefficient of trp is 6.4 x 103 Lmol-1cm-1. What is the concentration of solution?