The content of manganese (Mn) in steel was determined spectrophotometrically and with the use of the standard addition method. An unknown sample of Mn from a digested steel sample gave an absorbance of 0.185 when analyzed spectrophotometrically. When 5.00 mL of solution containing 95.5 ppm Mn was added to 50.0 mL of the unknown steel solution (digested sample), the absorbance was 0.248. Calculate the concentration, in parts-per-million (ppm), of Mn in the digested steel sample solution. NOTE: When a problem does not state diluted to a given volume, then you consider the sum of the volumes for Vf. A. 9.55 B. 20.2 C. 5.68

The content of manganese (Mn) in steel was determined spectrophotometrically and with the use of the standard addition method. An unknown sample of Mn from a digested steel sample gave an absorbance of 0.185 when analyzed spectrophotometrically. When 5.00 mL of solution containing 95.5 ppm Mn was added to 50.0 mL of the unknown steel solution (digested sample), the absorbance was 0.248. Calculate the concentration, in parts-per-million (ppm), of Mn in the digested steel sample solution. NOTE: When a problem does not state diluted to a given volume, then you consider the sum of the volumes for Vf. A. 9.55 B. 20.2 C. 5.68

Chemistry

10th Edition

ISBN:9781305957404

Author:Steven S. Zumdahl, Susan A. Zumdahl, Donald J. DeCoste

Publisher:Steven S. Zumdahl, Susan A. Zumdahl, Donald J. DeCoste

Chapter1: Chemical Foundations

Section: Chapter Questions

Problem 1RQ: Define and explain the differences between the following terms. a. law and theory b. theory and...

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4. The %Mn in steel can also be determined spectrophotometrically by oxidizing the manganese to the intensely colored permanganate, MnO4-. Standard solutions of permanganate gave the following absorbances (in a 1 cm cell): ABSORBANCE CONC. OF MnO4 (g/mL) 0.210 1.05 x 10-5 0.315 1.61 x 10-5 0.429 2.21 x 10-5 0.599 2.98 x 10-5 0.801 4.04 x 10-5 The following samples of steel were thoroughly reacted to convert the manganese into permanganate and then diluted to 500.00 mL. WT. OF STEEL (g) ABSORBANCE 0.5886 0.611 0.3498 0.359 0.4555 0.482 Again using Excel, plot the calibration data and calculate the %Mn in the steel.
A spectrophotometric method for the analysis of iron has a linear calibration curve for standards of 0.00, 5.00, 10.00, 15.00, and 20.00 ppm. An iron ore sample with an expected iron content of 40–60% w/w is to be analyzed by this method. An approximately 0.5-g sample is taken, dissolved in a minimum of concentrated HCl, and diluted to 1 L in a volumetric flask using distilled water. A 5.00-mL aliquot is removed with a pipet. To what volume (10, 25, 50, 100, 250, 500, or 1000 mL) should it be diluted to minimize the uncertainty in the analysis? Explain.
Commercial 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)
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 0.392. The slope-intercept form of the equation of the line is y = 4538.1x +0.0077. The unknown was analyzed on the same instrument as the standard curve solutions at the same temperature. What is the Fe³+ concentration of the unknown solution? [Fe³+] = mol/L Absorbance Iron(III) thiocynate standard curve 1.0 V 0.5 0.0001 Fe³+ concentration (M) 0 0.0002
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.
A sample of steel was dissolved and the manganese present was converted to MnO4– (aq). Water was then added to give a final solution volume of 100.00 mL. A sample of this solution was examined and was found to have an absorbance at 525 nm of 0.600 (pathlength = exactly 1 cm). What is the concentration of MnO4– in the solution? (The molar absorptivity is 3.62 × 103 L/(mol cm).)
Fe+3 (aq) + SCN – (aq) FeSCN +2 (aq) She mixes 4.00 mL of 2.00 mM SCN– and 5.00 mL of 2.00 mM Fe+3 ions, then diluting with 1.00mL of water to give a total volume of 10.00mL. She measures the absorbance of the solution asbeing 0.210. If she has previously calculated the molar absorbtivity constant (ε) of the product tobe 2583 cm–1 M–1, what is her best estimate for the K value for this reaction?
Five white, 500-mg uncoated ascorbic acid (AA) tablets with an average weight of 0.6100-g were pulverized in a mortar. A sample of the powdered ascorbic acid weighing 0.4610-g was placed in an iodine flask and was dissolved in 50-mL H2SO4 then 5-g of KBr was added to the resulting solution. The solution was titrated with 46.73-mL of 0.0152 M STD. KBrO3 to reach a faint yellow endpoint then 3-g KI and 5-mL Starch TS. The blue color solution is then titrated with 2.78-mL of 0.1047 M STD. Na2S2O3 to reach the disappearance of the blue iodostarch complex. MW: KBrO3 = 167.0 ; KIO3 = 214.0 ; Na2S2O3 = 158.11 ; C6H8O6 = 176.12 Compute the milligrams of pure AA per tablet from the assay. None of the choices 349.7 mg 264.3 mg 462.7 mg
A standard iron solution was prepared by dissolving 0.0140 g of pure iron in acid then transferring to a 50.00 mL volumetric flask with orthophenanthroline as a complexing agent. At a wavelength of 540 nm, the absorbance of the standard was 0.214 in a 1.00 cm cuvette. A 0.128 g sample of an iron ore was crushed and digested in 5 mL of concentrated acid. The digested sample was then transferred to a 10.00 mL volumetric flask and diluted to the mark with water. A 1.00 mL aliquot of the sample was transferred to a 25.00 mL volumetric flask, and diluted to the mark with water. A portion of the diluted sample was then transferred to a 1.00 cm cuvette and measured at a wavelength of 540 nm. The resulting absorbance was 0.216. Determine the % w/w of Fe in the iron ore.
(Standard addition) Tooth enamel consists mainly of the mineral calcium hydroxyapatite, Ca10(PO4)6(OH)2. Trace elements in teeth of archeological specimen provide anthropologists with clues about diet and diseases of ancient people. Student at Dankook University measured the trace element strontium (Sr) in enamel from extracted wisdom teeth by atomic absorption spectroscopy. Solutions were prepared with a constant total volume of 10 mL containing 0.750 mg dissolved tooth enamel plus variable concentrations of added standard Sr. Added Standard Sr (ng/mL=ppb) 0 2.50 5.00 7.50 10.00 Emission Signal 28.0 34.3 42.8 51.5 58.6 (a) Make a graph showing the experimental data and the calculated straight line. (b) Find the concentration of Sr in the tooth ennamel in parts per million = μg/mL.
A water sample was analyzed for Fe content using the iron- phenanthroline method. The following data were obtained from the analysis: Reagent Blank Absorbance Absorbance (au) Reagent Blank Absorbance 0.003 Concentration of Stock Solution: 10 ppm Volume of Stock Solution (mL) Total Volume of Standard Solution Concentration of Standard Solution (ppm) Absorbance (au) (mL) 0.50 10.00 0.012 1.00 10.00 0.132 2.00 10.00 0.267 3.00 10.00 0.349 4.00 10.00 0.428 5.00 10.00 0.560 Volume of Unknown Solution Total Volume of Unknown Solution Trial Absorbance (au) (mL) (mL) 1 5.00 10.00 0.289 2 5.00 10.00 0.296 3 5.00 10.00 0.281 Determine the value of the slope (m), y-intercept (b), and the coefficient of determination (r²) A m = 0.1128; b = -4.0 x 10-5; r2 = 0.9880 B m = 0.1128; b = -4.0 x 10-5; r² = 0.9762 C) m = 0.1128; b = -3.0 x 10-³; r² = 0.9880 D m = 0.1128; b = -3.0 x 10-³; r² = 0.9762
A chemist obtained the following data for percent lindane in the triplicate analysis of an insecticide preparation: 7.23, 6.95, and 7.53%. Calculate the 90% confidence interval for the mean of the the three data, assuming that (a) the only information about the precision of the method is the precision for the three data. (b) on the basis of long experience with the method, it is believed that s---->σ lindane. (c) If s=0.28 is good estimate of σ, how many replicate measurement should be made in order for the mean for the analysis of sample to be within 0.2% of the true mean 90% of the time.