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…
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.
Complexometric 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…
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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_forwardThe 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 samplearrow_forwardSolutions 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_forward
- 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) Absorbancearrow_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_forwardAn unknown sample containing mixed alkali (NAOH, NaHCO3, or NazCO3) was analyzed using the double flask method. A 250 mg sample was dissolved in 250 mL CO, free water. A 20.0 mL aliquot of this sample required 11.3 mL of 0.009125 M HCI solution to reach the phenolphthalein end point. Another 29.0 mL aliquot of the sample was titrated to the bromocresol green endpoint using 311 mL of the standard acid. What is/are the component/s of the sample? O Cannot be determined O NAHCO3 only O NAOH and Na,CO3 O NazCO3 only O NAHCO, and Na2CO3arrow_forward
- An unknown sample containing mixed alkali (NAOH, NaHCO3, or NazCO3) was analyzed using the double flask method. A 250 mg sample was dissolved in 250 mL CO, free water. A 20.0 mL aliquot of this sample required 11.3 mL of 0.009125 M HCI solution to reach the phenolphthalein end point. Another 29.0 mL aliquot of the sample was titrated to the bromocresol green endpoint using 31.1 mL of the standard acid. What is/are the component/s of the sample? O NazCO3 only NaHCO3 only O NAHCO3 and Na>CO3 NaOH and NazCO3 O Cannot be determinedarrow_forwardA 370.00 mL solution of 0.00190 M AB5 is added to a 200.00 mL solution of 0.00165 M CD2. What is pQsp for AD5?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
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