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…
10-mL aliquots of an environmental water sample were pipetted into five 50.00-mL volumetric flasks. Exactly 0.00, 5.00, 10.00, 15.00, and 20.00-mL of a standard solution containing 11.1 ppm Fe3+ were added to each, followed by an excess of thiocyanate ion to give the red complex Fe(SCN)2+. After dilution to volume, the instrumental response for each of the five solutions measured with a colorimeter was found to be 0.240, 0.437, 0.621, 0.809, 1.809, respectively.
Using Excel and the LINEST function, what was the concentration in the water sample (including error)? [HINT: consider the type of calibration scheme used.]
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
Chapter 15 Solutions
Principles of Instrumental Analysis
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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 absorbance value for the Standard was 0.625 and [FeSCN^ 2+ ] std is 2.00E 4M Calculate the [FeSCN^ 2+ ] in the equilibrium mixture, report the answer to the correct significant figures. The absorbance of the equilibrium solution was 0.451arrow_forwardA 50.0 mL of 3.1% (w/v, g/mL) NaOH solution is mixed with 40.00 mL of 1.2% (w/v, g/mL) Na2CO3 solution. What volume of 0.087 M HCl will be required to titrate the resultant solution to bromocresol green indicator end point (Bcg pH transition range 3.8-5.4, Fwt of NaOH=40 g/mol, Na2CO3= 105.99 g/mol).arrow_forward
- The determination of iron in wines was carried out by atomic absorption spectrophotometry, using the standard addition method. To do this, 10 mL of wine were placed in five 50 mL volumetric flasks; then 0, 5, 10, 15 and 20 mL of a 10 ppm iron standard solution were added to each of them. Next, they were gauged with distilled water and the absorbance was measured, obtaining the values of 0.040, 0.062, 0.081, 0.102 and 0.125 respectively. Calculate the regression parameters and obtain the iron concentration in the wine, in µg / mL.arrow_forwardA 0.3045 g of CaCO3 primary standard was dissolved using concentrated HCl, evaporated to incipient dryness, and quantitatively transferred to a 250 mL volumetric flask and diluted to mark. A 10 mL of aliquot was then transferred to an Erlenmeyer flask, together with 5mL buffer and 5 drops of EBT indicator, and was used to standardize the EDTA titrant. The solution turned blue after the addition of 24.10 mL of EDTA. A blank correction was made and was determined to be 0.4 mL. [Analysis] A 30 mL unknown water sample was treated with 37.6 mL of EDTA. A blank correction was made and was determined to be 0.4 mL. What is the concentration of Ca2+ (40.0780 g/mol) in ppm?arrow_forwardA 0.3045 g of CaCO3 primary standard was dissolved using concentrated HCl, evaporated to incipient dryness and quantitatively transferred to a 250 mL volumetric flask, and diluted to mark. A 10 mL of aliquot was then transferred to an Erlenmeyer flask, together with 5mL buffer and 5 drops of EBT indicator, and was used to standardize the EDTA titrant. The solution turned blue after the addition of 24.10 mL of EDTA. A blank correction was performed and was determined to be 0.4 mL. What is the concentration of EDTA obtained (MW CaCO3 = 100.0869 g/mol)?arrow_forward
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- A 20 ml aliquot of drinking water containing Fe(II) and Fe (III) is treated with hydroquinone to reduce all dissolved iron to Fe(II),0- phenanthroline is added and the aliquot is diluted to 50 ml and the absorbance in a 2.00 cm cell is 0.085 at 510 nm. Calculate the iron content of the water as ppm? ε = 1.11 x 104 L/mol cmarrow_forwardThe chromium in an aqueous sample was determined by pipetting 10.0 ml. of the unknown into each of five 50.0-mL volumetric flasks. Various volumes of a standard containing 12.2 ppm Cr were added to the flasks, following which the solutions were diluted to volume. Unknown,mLStandard, mLAbsorbancc 10.00.00.201 10.010.0 0.292 10.020.0 0.378 10.030.0 0.467 10.040.0 0.554 (a) Plot the data using a spreadsheet. (b) Determine an equation for the relationship between absorbance and volume of standard. (c) Calculate the statistics for the least-squares relationship in (b). (d) I)ctcrmine the conccnt ration oÍCr in ppm in the sample. (e) Find the standard deviation of the result in (d).arrow_forwardCommercial Vanadyl Sulfate (VOSO4) is contaminated with H2SO4 and H2O. A solution was prepared dissolving 0.2447 g of impure VOSO4 in 50.00 mL of water. A spectrophotometric analysis indicated that the The concentration of vanadyl ions, VO2+ (blue) was 0.0243 M. A 5.00 mL sample was passed through a column filled with a cation exchange resin in H+ form, to retain the vanadyl ion and the eluent necessary for its titration 13.03 mL of NaOH 0.02274 M. Calculate the percentage by weight of each component (VOSO4, H2SO4, and H2O) in commercial vanadyl sulfate. (Pm VOSO4, 162.96; H2SO4, 97.94)arrow_forward
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