Five standard chromium (VI) solutions were prepared through serial dilution technique with corresponding absorbance readings at 540 nm wavelength (as follows: Absorbance Concentration A1 = 0.650 C1 = 1.9 ppm A2 = 0.712 C2 = 4.0 ppm A3 = 1.370 C3 = 6.0 ppm A4 = 2.050 C4 = 8.0 ppm A5 = 3.423 C5 = 10.0 ppm The sample solution gives an average absorbance reading of 0.713. What is then the concentration of chromium (VI) ion in the sample?

Five standard chromium (VI) solutions were prepared through serial dilution technique with corresponding absorbance readings at 540 nm wavelength (as follows: Absorbance Concentration A1 = 0.650 C1 = 1.9 ppm A2 = 0.712 C2 = 4.0 ppm A3 = 1.370 C3 = 6.0 ppm A4 = 2.050 C4 = 8.0 ppm A5 = 3.423 C5 = 10.0 ppm The sample solution gives an average absorbance reading of 0.713. What is then the concentration of chromium (VI) ion in the sample?

Principles of Instrumental Analysis

7th Edition

ISBN:9781305577213

Author:Douglas A. Skoog, F. James Holler, Stanley R. Crouch

Publisher:Douglas A. Skoog, F. James Holler, Stanley R. Crouch

Chapter13: An Introduction To Ultraviolet-visible Molecular Absorption Spectrometry

Section: Chapter Questions

Problem 13.25QAP

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Five standard chromium (VI) solutions were prepared through serial dilution technique with corresponding absorbance readings at 540 nm wavelength as follows: Absorbance Concentration A1 = 0.650 C1 = 1.9 ppm A2 = 0.712 C2 = 4.0 ppm A3 = 1.370 C3 = 6.0 ppm A4 = 2.050 C4 = 8.0 ppm A5 = 3.423 C5 = 10.0 ppm The sample solution gives an average absorbance reading of 0.713. What is then the concentration of chromium (VI) ion in the sample? (Note: please provide necessary solutions)
Caffeine, C8H10O2N4 H2O (MW = 212.2 g/mol) has been shown to have an average absorbance of 0.644 for a concentration of 1.783 mg per 100 mL at 272 nm. A sample of 3.658 g of a soluble coffee product was mixed with water to a volume of 500 mL and a 25 mL aliquot was transferred to a flask containing 25 mL of 0.1 M H2SO4. This was subjected to the prescribed clarification treatment and made up to 500 mL. A portion of this treated solution showed an absorbance of 0.666 at 272 nm. Assumbe b = 1.0 cm. Calculate the % caffeine (w/w) in the sample.
A student prepared four standard solutions of (NH4)2Fe(SO4)2 and measured their absorbance at 505 nm. She created a calibration plot with the best-fit line of y = 9372 x + 0.0539. She measured the absorbance of her diluted unknown sample solution as (4.69x10^-1) nm. If she prepared her diluted sample solution by diluting 10.00 mL of the original solution to a total volume of 50.00 mL with deionized water, what is the concentration of Fe2+ in her original solution? Answer in units of M. Note: Your answer is assumed to be reduced to the highest power possible.
The standard curve was made by spectrophotographic analysis of equilibrated iron(III) thiocyanate solutions of known concentration. You are asked to analyze a Fe(SCN)2+Fe(SCN)2+ solution with an unknown concentration and an absorbance value of 0.4150.415 . The slope-intercept form of the equation of the line is ?=4558.4?+0.0147y=4558.4⁢x+0.0147 . The unknown was analyzed on the same instrument as the standard curve solutions at the same temperature. What is the Fe3+Fe3+ concentration of the unknown solution?
A 10.00 mL of natural water sample containing Ni2+ was pipetted into a volumetric flask and diluted to 50.00 mL with pure water. In the second 10.00 mL of natural water sample transferred into a volumetric flask, exactly 4.00 mL of a Ni2+ solution with a concentration of 5.99 mg/L was added and then diluted to 50.00 mL with pure water. The measured absorbance is A1= 0.436 and A2 = 0.663. What is the Ni2+ concentration in unit of mg/L in the natural water sample?
A 131.7 mg sample of powdered Carbamazepine tablets was boiled with ethanol, filtered and then made up to 100 mL with ethanol. 5 mL of this solution was then diluted to 250 mL with ethanol and the absorbance at 285 nm found to be 0.486 in a 1cm path length cell.Calculate the content (% m/m) of Carbamazepine in the powder, taking A(1%, 1 cm) as 490.(State your answer to 1 decimal place and include the units)
What is the molar absorptivity of a 2.50 x 10-4 M solution if its absorbance at 550 nm is 0.500? The sample is placed in the standard 1-cm quartz cuvette. 2.00 x 10-3 M-1cm-1 5.00 x 10-4 M-1cm-1 2.00 x 103 M-1cm-1 1.25 x 10-4 M-1cm-1
The absorbance of an iron(III) thiocyanate, Fe(SCN)3 (MM = 230.09 g/mol), solution containing 0.00181 mg/mL is reported as 0.833 at 540 nm. Calculate the specific absortivity of iron(III) thyocyanate with units cm-1 (mg/mL)-1 . A 0.77 cm sample cuvette is used. Report your answer to 3 significant figures.
A student prepared several solutions of an unknown molecule, each at a different concentration. The absorbance of each solution was measured at 630 nm with a path length of 0.760 cm. The student then plotted the absorbance of each sample vs. its concentration (in uM), and found a best-fit line of y = 0.00626x + 0.00732. Calculate the molar absorptivity of the unknown molecule (in M-1 cm-1).
A 5.00×10−4 M solution of analyte is placed in a sample cell that has a pathlength of 1.00 cm. At a wavelength of 490 nm, the solution’s absorbance is 0.338. What is the analyte’s molar absorptivity at this wavelength?
Calculate the molar absorptivity of benzene (FW = 78.11 g/mol) at 256 nm if a 25.80 mg of benzene per 250.0 mL solution using hexane (FW = 86.18 g/mol) as the solvent exhibited an absorbance of 0.2660 in a 10.00 cm cuvette. Pure hexane has negligible absorbance at this wavelength.
The nitrite in a series of standard solutions (mg/L, n = 5) are converted to azo dye and the slope of the calibration curve is 2.0 ppm1. A 10.00-mL mineral water sample is treated in the same way as standards and diluted to a final volume of 100.00-mL. It gives an absorbance of 0.80. The absorbance of blank solution under the same conditions is 0.10. Calculate ppm (mg/L) of NO2 (46 g/mol) and the molarity of NANO2 (69 g/mol) in the original sample