A 2.50-mL aliquot of a solution that contains 3.8 ppm iron(III) is treated with an appropriate excess of KSCN and diluted to 50.0 mL. What is the absorbance of the resulting solution at 580 nm in a 2.50-cm cell? See Problem 14-21 for absorptivity data. See Problem 14-21 for absorptivity data: A solution with a "true" absorbance [A = log(P0 / P)] of 2.10 was placed in a spectrophotometer with a stray light level (Ps/P0 ) of 0.75% What absorbance A’ would be measured? What percentage error would result

A 2.50-mL aliquot of a solution that contains 3.8 ppm iron(III) is treated with an appropriate excess of KSCN and diluted to 50.0 mL. What is the absorbance of the resulting solution at 580 nm in a 2.50-cm cell? See Problem 14-21 for absorptivity data. See Problem 14-21 for absorptivity data: A solution with a "true" absorbance [A = log(P0 / P)] of 2.10 was placed in a spectrophotometer with a stray light level (Ps/P0 ) of 0.75% What absorbance A’ would be measured? What percentage error would result

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 13.24QAP

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The acid-base indicator HIn undergoes the following reaction in dilute aqueous solution: HIncolor1H++Incolor2 The following absorbance data were obtained for a 5.00 I0-4 M solution of HIn in 0.1 M NaOH and 0.1 M HC1. Measurements were made at wavelengths of 485 nm and 625 nm with 1.00-cm cells. 0.1 M NaOH A485 = 0.075 A625 = 0.904 0.1 M HC1 A485 = 0.487 A625 = 0.181 In the NaOH solution, essentially all of the indicator is present as In-; in the acidic solution, it is essentially all in the form of HIn. (a) Calculate molar absorptivities for In- and HIn at 485 and 625 nm. (b) Calculate the acid dissociation constant for the indicator ¡fa pH 5.00 buffer containing a small amount of the indicator exhibits an absorbance of 0.567 at 485 nm and 0.395 at 625 nm (1.00-cm cells). (c) What is the pH of a solution containing a small amount of the indicator that exhibits an absorbance of0.492 at 485 nm and 0.245 at 635 nm (1.00-cm cells)? (d) A 25.00-mL aliquot of a solution of purified weak organic acid HX required exactly 24.20 mL of a standard solution of a strong base to reach a phenolphthalein end point. When exactly 12.10 mL of the base was added to a second 25.00-mL aliquot of the acid, which contained a small amount of the Indicator under consideration, the absorbance was found to be 0.333 at 485 nm and 0.655 at 625 nm (1.00-cmcells). Calculate the pH of the solution and Ka for the weak acid. (e) What would be the absorbance of a solution at 485 and 625 nm (1.50-cm cells) that was 2.00 10-4 M in the indicator and was buffered to a pH of 6.000?
At 21 °C, a solution of 12 mL each of 0.00200 M Fe3+ and 0.001000 M SCN- was mixed and brought to 25.0 mL with 0.1 M HNO3. The absorbance at 450 nm was measured to be 0.350 (A450 = 0.350). This solution was then heated to 45 °C and the absorbance at 450 nm was measured to be 0.142 (A450= 0.142). Is the reaction: Fe3+(aq) + SCN -(aq) → FeSCN2+(aq) exothermic or endothermic? Explain.
11. [15'] the molar absorptivity (extinction coefficient) of benzene (C6H6) equals 100 M-¹ cm¹ at 260 nm. (Assume that this number is independent of solvent or other effects) a) What concentration would give an absorbance of 1.0 in a 1 cm cell at 260 nm? b) If the density of pure, liquid benzene is 0.8 g cm²³, what 'thickness' of pure benzene would also give an absorbance of 1.0 at 260nm?
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 solution containing a mixture of the compounds X and Y had an absorbance of 0.584 at 443 nm and an absorbance of 0.501 at 520 nm when measured with a 1.00 cm cell. The molar absorptivities (E) of X and Y at each wavelength are shown in the table. What are the concentrations of X and Y in this mixture? Wavelengt h (1, nm) Molar Absorptivity (E, M-cm-1) X 443 15790 3725 520 3841 6.180x103
A solution containing 4.48 ppm KMnO4 exhibits 85.9 %T in a 1.00-cm cell at 520 nm. Calculate the molar absorptivity of KMnO4 at this wavelength.
A green solution containing Ni+2 ions absorbs 580 nm light. Undiluted, a sample of this solution sampled in a 1.00 cm diameter cuvette has an absorbance of 0.9765 a.u.. If the molar absorptivity coefficient for Ni+2 is 6.3 x 104 M -1 cm -1 at 580 nm, how much of the original stock Ni+2 solution (in mL) needs to be added to water to create a total dilute solution volume of 10.00 mL that measures an absorbance of 0.146 a.u. at 580 nm? Report your answer to 3 significant figures. Do not include the "mL' unit label in your response
A solution containing 4.48 ppm KMnO, had a % transmittance of 30.9% in a 1.00 cm cell at 520 nm. Calculate the molar absorptivity of KMnO, at 520 nm.
What is the molar absorptivity, in M-1cm-1, for a 4.00×10-5 M solution placed in a 2.00 cm cuvette that is measured to have an absorbance of 0.263?
tion 13 of 24 > 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+ solution with an unknown concentration and an absorbance value of 0.179. The slope-intercept form of the equation of the line is y = 4536.6x + 0.0392. The unknown was analyzed on the same %3D instrument as the standard curve solutions at the same temperature. What is the Fe3+ concentration of the unknown solution? Iron(III) thiocynate standard curve 1.0 - Fe*] = mol/L 0.5- 0.0001 0.0002 Fe+ concentration (M) Absorbance
* 14-10 The acid-base indicator HIn undergoes the following reaction in dilute aqueous solution: HIn color 1 H* + In color 2 The following absorbance data were obtained for a 5.00 X 10¬4M solution of HIn in 0.1 M NaOH and 0.1 M HCl. Measurements were made at wavelengths of 485 nm and 625 nm with 1.00-cm cells. 0.1 M NaOH A 485 0.075 A625 = 0.904 0.1 М HСІ A 485 0.487 A625 = 0.181 In the NaOH solution, essentially all of the indicator is present as In ; in the acidic solution, it is essentially all in the form of HIn. (a) Calculate molar absorptivities for In and HIn at 485 and 625 nm. (b) Calculate the acid dissociation constant for the indicator if a pH 5.00 buffer containing a small amount of the indicator exhibits an absorbance of 0.567 at 485 nm and 0.395 at 625 nm (1.00-cm cells). (c) What is the pH of a solution containing a small amount of the indicator that exhibits an absorbance of 0.492 at 485 nm and 0.245 at 635 nm (1.00-cm cells)? (d) A 25.00-mL aliquot of a solution of…
A 2.50 mL aliquot of a solution that contains 3.85 ppm Fe(III) is treated with an appropriate excess of KSCN and diluted to 100.0 mL. What is the absorbance of the resulting solution at 580 nm in a 0.50 cm cell? (Molar absorptivity of Fe (SCN)2+is 7.0 x 105L mol-1cm-1).