Principles of Instrumental Analysis
7th Edition
ISBN: 9781305577213
Author: Douglas A. Skoog, F. James Holler, Stanley R. Crouch
Publisher: Cengage Learning
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Chapter 15, Problem 15.10QAP
Interpretation Introduction
Interpretation:
The percentage of quinine in the tablet should be determined.
Concept introduction:
The expression of percentage of quinine in the sample of
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0 The acid-base indicator HIn undergoes the following reaction in dilute aqueous solution:HIn color1 m H1 1 In2color2The following absorbance data were obtained for a 5.00 3 1024M solution of HIn in 0.1 M NaOH and0.1 M HCl. Measurements were made at wavelengths of 485 nm and 625 nm with 1.00-cm cells.0.1 M NaOH A485 5 0.075 A625 5 0.9040.1 M HCl A485 5 0.487 A625 5 0.181In the NaOH solution, essentially all of the indicator is present as In2; in the acidic solution, it is essentiallyall in the form of HIn.(a) Calculate molar absorptivities for In2 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 amountof 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…
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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?arrow_forwardtion 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) Absorbancearrow_forwardComplexometric titrations are generally conducted to determine divalent cations. The most important applications are the titration of calcium and magnesium with EDTA. (a) A supplement tablet containing about 300.00 mg of calcium ion was dissolved, filtered, and diluted to 100.00 ml volume. Several 2.00 ml samples of the total solution were titrated with 0.0100 M EDTA solution. The mean corrected titration volume was 13.65 mL. Calculate the calcium content of the supplement tablet in mg units. (b) A sample of Epsom Salt of mass 0.7567 g was dissolved uniformly in distilled water in a 250.00 mL volumetric flask. Portions of the magnesium ion solution of volume 10.00 mL were titrated using a 0.01000 M solution of EDTA. The mean corrected titration volume was 12.25 ml. Calculate the percentage by mass (% w / w) of the magnesium in the Epsom Salt sample. (c) A 100.00 mL sample of tap water was titrated with 0.0100 M EDTA solution. The mean corrected titration volume was 14.80 mL. Determine…arrow_forward
- Solutions of cobalt (II) ions have a magenta color with a molar absorptivity constant (e) value at 511 nm of 5.87 M-1cm-1. A 0.500 mL sample is transferred from a 50.0 mL stock solution of Co(NO3)2 and diluted with water to a final volume of 7.50 mL. The dilution had an absorbance value at 511 nm in a standard cuvette (1.00 cm light path) of 0.382. Calculate the mass of Co(NO3)2 contained in the original 50.0 mL stock solution.arrow_forwardQuinine in a 1.664 g antimalarial tablet was dissolved in sufficient 0.10 M HCl to give 500 mL of solution. A 15.00 mL aliquot was then diluted to 100.0 mL with the acid. The fluorescense intensity for the diluted sample at 347.5 nm provided a reading of 288 on an arbitrary scale. A standard 100 ppm quinine solution registered 180 when measured under conditions identical to those for the diluted sample. Calculate the mass in milligrams of quinine in the tablet.arrow_forwardThe molar absorptivities of an indicator HIn (Ka = 4.6 × 10-5) and its conjugate base In− at 630 nm were determined as εHIn = 821 and εIn- = 375, respectively. Calculate the absorbance A (b = 1.00 cm) for the buffered indicator solution with a total HIn concentration of 6.32 × 10-4 M at pH = 4.00arrow_forward
- Calculate the hardness in terms of parts per million calcium carbonate (100.0869 g/mol) in a 50.00 mL aliquot of milk sample. The sample was treated with a small amount of ammonia buffer to bring the pH to 10 followed by the addition of 10 drops EBT indicator. The milk sample required 10.00 mL of 8.000 x 10-3 M EDTA for titration. 160 ppm 4 80 320arrow_forwardA second calibration standard solution of an iron(III) salicylate complex was prepared in two steps. First, 10.0 mL of a 0.100 M stock solution was added to 90.0 mL of solvent to make 100.0 mL of the first calibration standard solution and, secondly, 80 mL of that first calibration solution plus 20.0 mL of solvent were mixed to make the second calibration standard. What is the concentration of the second calibration standard solution?arrow_forwardIn a Complexometric Titration Experiment, the preparation of the EDTA solution is as follows: In a 250 mL beaker, weigh 0.10 g MgCl2*6H2O and 1.0 g NaOH. Add approximately 200 mL distilled water and stir to dissolve. Add about 2.0 g of EDTA and transfer the solution quantitatively to a 1-L volumetric flask. Dilute to the mark with distilled water. What is the purpose of adding MgCl2*6H2O? Please show COMPLETE solution.arrow_forward
- A 865.6 gram sample of bacon was pureed in a blender with 100 mL water. The suspension was filtered and the clear solution containing dissolved sodium nitrite was adjusted to pH 2. This solution was treated with 15.00 mL of KMnO 4 solution (1 mL » 212.4 mg H 2C2O4 × 2H 2O) and was back titrated with 12.73 mL of FeSO4 solution (1 mL » 87.5 mg K 2Cr2O7). Calculate the amount of nitrite (NO2–1) in ppm. H2C2O4 × 2H 2O (126) K2Cr2O7 (294.2) a. 370 b. 1480 c. 740 d. 1110arrow_forwardIf the absorbance for the solution was 0.342, calculate the equilibrium constant, Keq, with zero places after the decimal.arrow_forward* 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…arrow_forward
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