Concept explainers
The 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,mL Standard, mL Absorbancc
10.0 0.0 0.201
10.0 10.0 0.292
10.0 20.0 0.378
10.0 30.0 0.467
10.0 40.0 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).
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Chapter 9 Solutions
Principles of Instrumental Analysis
- 2+ as (6) A sample of an ore was analyzed for Cu* follows. A 1.25 g sample of the ore was dissolved in acid and diluted to volume in a 250 mL volumetric flask. A 20 mL portion of the resulting solution was transferred by pipet to a 50 ml volumetric flask and diluted to volume. An analysis showed that the concentration of 2+ Cu* in the final solution was 4.62 ppm. What is the weight percent of Cu in the original ore?arrow_forwardAn EDTA solution prepared from its disodium salt was standardized using 0.250-g primary standard CaCO3 (MW=100.087) and consumed 28.50 mL of the solution. The standard solution was used to determine the hardness of a 2.0 L sample of mineral water, which required 35.57 mL EDTA solution. Express the analysis in terms of ppm CaCO3arrow_forwardSilver nitrate can be standardized using primary standard KCl. A dried sample of analytical grade KCl of mass 0.918 g was dissolved and diluted to 250.0 mL. Repeat 10.00-mL aliquots of the potassium chloride solution were titrated with the silver nitrated solution. The mean corrected titration volume was 8.98 mL Calculate the molarity (M) of the silver nitrate solution.arrow_forward
- The 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_forward4arrow_forwardThe mass percent of Fe in an unknown salt sample was determined using both volumetric and gra vimetric titration. Ten determinations using both methods were performed. Volumetric(% of Fe): 24.22, 23.86, 24.07, 24.49, 24.69, 23.71, 24.28, 24.11, 24.26, 24.10 Gravimetric (% of Fe): 24.35, 24.26, 24.10,24.19, 24.18, 24.32, 24.11, 24.33, 24.17, 24.12 a. Do the two methods give similar standard deviations? b. Do the two methods give similar results for the mass percent of Fe at the 95% confidence level?arrow_forward
- A 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_forwardTitration of Ca²+ and Mg²+ in a 50.00-mL hard water sample required 23.65 mL of 0.01205 M EDTA. A second 50.00-mL aliquot was made strongly basic with NaOH to precipitate Mg²+ as Mg(OH)2(s). The supernatant liquid was titrated with 14.53 mL of the EDTA solution. Calculate the total hardness of the water sample, expressed as ppm CaCO3.arrow_forwardThe concentration of ammonia in a cleaning product was determined by back titration.Firstly, 10.00 cm3 of the cleaning product was pipetted into a large conical flask,containing 250.00cm3 of 0.50 mol/l HCl to give Solution A.Following a period of reaction and shaking, 50.00cm3 of Solution A was removed anddiluted to 250 cm3 with water in a volumetric flask to give Solution B.20 cm3 samples of Solution B were titrated against 0.05 mol/l Na2CO3 solution, givingan average titre of 12.45 cm3. i) Write equations for the reactions that have taken place.ii) Determine the concentration of NH3 in the original cleaning product in mol/l,g/l, ppm, and % w/v.arrow_forward
- 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 = 0.9762arrow_forward45.0 mL of an unknown FeCl3 solution is diluted to a total volume of 230.0 mL. The diluted FeCl3 solution measured an absorbance of 0.223. Calculate the molarity of the undiluted unknown FeCl3 solution if the molar extinction coefficient is 230.0 M-1⋅cm-1 and a path length of 1.00 cm.arrow_forwardStandardization of EDTA was done using MgSO4 standard wherein a 50-mL aliquot of solution obtained from 0.480 g MgSO4 in 500 mL needed 39.4 mL of the EDTA solution to reach the endpoint. Determine how many milligrams of CaCO3 will react per mL of this EDTA solution.arrow_forward