Cobalt is often added to steel in order to increase its hardness. The cobalt content of 5 different steel samples was measured by titration and by spectroscopy (Table 2). Table 2: Cobalt content (in mg L1) in 5 different steel samples. Sample Titration Spectroscopy 1 134 135 2 144 156 3 126 137 4 125 137 137 136

Cobalt is often added to steel in order to increase its hardness. The cobalt content of 5 different steel samples was measured by titration and by spectroscopy (Table 2). Table 2: Cobalt content (in mg L1) in 5 different steel samples. Sample Titration Spectroscopy 1 134 135 2 144 156 3 126 137 4 125 137 137 136

Fundamentals Of Analytical Chemistry

9th Edition

ISBN:9781285640686

Author:Skoog

Publisher:Skoog

Chapter17: Complexation And Precipitation Reactions And Titrations

Section: Chapter Questions

Problem 17.31QAP

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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.
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.
Which of the following salts does NOT cause permanent hardness? A FeCl, B CaCl, © Ca(HCO,), (НСО ,), D MgSO 4
Gold can be determined in solutions containing high concentrations of diverse ions by ICP. Aliquots of 50.0 mL of the sample solution were transferred to each of four 100.0 mL volumetric flasks. A solution was prepared containing 10.0 mg/L Au in 20% H2SO4, and quantities of this solutions were added to the sample solution to give 0, 2.5, 5 and 10 mg/L added Au in each of the flask. The solutions were made up to a total volume of 100.0 mL, mixed and analyzed by ICP. The resulting data are presented in the following table: Added Au (mg/L) Emission Intensity (Counts) 0.0 12568 2.5 19324 5.0 26622 10.0 40021 a) Attach an excel graph for the determination showing the X intercept. b) Calculate the concentration of gold in the sample, report with its uncertainty. c) The known concentration of gold in the sample is 8.51 mg/L. Test the hypothesis that your result is equal to this value at the 95% confidence level. l
A mined alloy sample weighing 2.0840 g is dissolved in minimal amounts of concentrated HNO3 before diluted to 50 mL. Ten mL of this diluted sample was titrated using 0.091 M KSCN and required 14.20 mL to reach the endpoint. Calculate the concentration of silver (%w/w) in the mined alloy. (Hint: A dilution factor (DF) is needed in the formula.) Titration reaction: Agt + SCN- → A9SC'N(s) FW: Ag = 107.87 %3D
Chromel is an alloy composed of nickel, iron, and chromium. A 0.6392-g sample was dissolved and diluted to 250.0 mL. When a 50.00-mL aliquot of 0.05173 M EDTA was mixed with an equal volume of the diluted sample, all three ions were chelated, and a 5.15-mL back-titration with 0.06139 M copper(II) was required. The chromium in a second 50.0-mL aliquot was masked through the addition of hexamethylenetetramine; titration of the Fe and Ni required 34.27 mL of 0.05173 M EDTA. Iron and chromium were masked with pyrophosphate in a third 50.0-mL aliquot, and the nickel was titrated with 24.31 mL of the EDTA solution. Calculate the percentages of nickel, chromium, and iron in the alloy. Percentage of nickel = % Percentage of iron = Percentage of chromium = % 10
Chromel is an alloy composed of nickel, iron and chromium. A 0.6553-g sample was dissolved and diluted to 250.0 mL. When a 50.00-mL aliquot of 0.05173 M EDTA was mixed with an equal volume of the diluted sample, all three ions were chelated, and a 5.34-mL back titration with 0.06139 M copper (II) was required.The chromium in a second 50.0-mL aliquot was masked through the addition of hexamethylenetetramine; titration of the Fe and Ni required 36.98 mL of 0.05173M EDTA. Iron and chromium were masked with pyrophosphate in a third 50.00-mL aliquot, and the nickel was titrated with 24.53 mL of the EDTA solution. Calculate the percentage of Cr in the alloy. Express your answer in 2 decimal places.
A 0.9352g sample of ore containing Fe³+, Al³+ and Sr²+ was dissolved and made up to 500.00 mL. The analysis of metals was performed using complexation volumetry. Initially, an aliquot of 50.00 mL had its pH adjusted to 1.0 and titrated with a standard 0.03145 mol/L EDTA solution, requiring 6.95 mL to reach the end point. Subsequently, another 25.00 mL aliquot was buffered at pH=5 and titrated with the same EDTA solution, requiring 6.24 mL to reach the end point. Finally, a third aliquot of 25.00 mL was titrated at pH=11, requiring 11.10 mL of the same EDTA solution to complete the titration. Given the molar masses: Fe=55.845 g/mol; Al-26.982 g/mol and Sr-87.620 g/mol. a) Determine the percentage of each of the metals in the sample. b) Explain why the change in pH allows the determination of the three ions in this sample.
Calculate the amount of manganese (54.94 g/mol) from a processed ore using the following data. Standardization data: 2.000 mL KMnO4 = 0.02015 g Na2C2O4 (134 g/mol) Sample analysis data: Weight of sample = 0.1012 g Na2C2O4 used(in excess)= 0.3200 g KMnO4 used for back-titration = 9.93 mL Rxn: 2MnO4- + 5C2O42- + 16H+ → 2Mn2+ + 10CO2 + 8H2O
show solutions 1. 10.000 grams of Clay was analyze for Iron content. Its moisture content is 2.00%. The sample was digested with oxidizing acids to convert all Iron into Fe3+. An excess of NH4OH was added and yielded a gelatinous precipitate of Fe(OH)3. The sample was then ignited in a furnace and yielded 0.1212 grams of residue as Fe2O3. Calculate the percentage of Iron. 2. A 0.3000 gram sample contains only KCl and CaCl2. The sample was dissolved in water and yielded 0.5000 grams of AgCl upon addition of excess AgNO3 reagent. Calculate the percentage of KCl and MgCl2.
An alloy containing Ni, Fe and Cr was analyzed by a complexation titration using EDTA as titrant. A 0.7176 g sample of the alloy was dissolved in HNO3 and diluted to 250 mL in a flask. A 50.00 mL aliquot of the sample, treated with pyrophosphate to mask Fe and Cr, required 26.14 mL of 0.05831 M EDTA to reach the murexide endpoint. A second 50.00 mL aliquot was treated with hexamethylenetetramine to mask Cr and titration with 0.05831 M EDTA required 35.43 mL to reach the murexide endpoint. Finally, a third 50.00 mL aliquot was treated with 50.00 mL of 0.05831 M EDTA and titrated back to the murexide endpoint with 6.21 mL of 0.06316 M Cu(II). the weight percentages of Ni, Fe and Cr in the alloy.
To analyze the amount of iron (Fe; Mw = 55.85 g/mol) contained in an ore sample, the sample was digested with acid and diluted to 50 mL with water. This solution was then treated with 25.00 mL of 0.2922 M EDTA. The excess EDTA was back titrated with 6.47 mL of 0.0843 M Zn2+ to reach the equivalence point. How many grams of Fe contained in the ore sample?