Suitable treatment of a 2.566 g soil sample converts all arsenic to AsO43-. 50.00 mL of 0.082 M Ag+ was added to form Ag3AsO4 precipitate. The excess Ag+ was back-titrated with 21.8 mL of 0.024 M SCN- to reach the equivalence point Ag+ + SCN- → AgSCN(s) Solve for the % As (MW = 74.92 g/mol) in the sample.

Suitable treatment of a 2.566 g soil sample converts all arsenic to AsO43-. 50.00 mL of 0.082 M Ag+ was added to form Ag3AsO4 precipitate. The excess Ag+ was back-titrated with 21.8 mL of 0.024 M SCN- to reach the equivalence point Ag+ + SCN- → AgSCN(s) Solve for the % As (MW = 74.92 g/mol) in the sample.

Principles of Instrumental Analysis

7th Edition

ISBN:9781305577213

Author:Douglas A. Skoog, F. James Holler, Stanley R. Crouch

Publisher:Douglas A. Skoog, F. James Holler, Stanley R. Crouch

Chapter24: Coulometry

Section: Chapter Questions

Problem 24.12QAP

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Sulfide ion (S2- ) is formed in wastewater by the action of an aerobic bacteria on organic matter. Sulfide can be readily protonated to form volatile, toxic H2S. In addition to the toxicity and noxious odor, sulfide and H2S cause corrosion problems because they can be easily converted to sulfuric acid when conditions change to aerobic. One common method to determine sulfide is by coulometric titration with generated silver ion.At the generator electrode, the reaction is Ag Ag+ + e-. The titration reaction is S2- + 2Ag+ Ag2S(s). (a) A digital chloridometer was used to determine the mass of sulfide in a wastewater sample. The chloridometer reads out directly in ng Cl-.In chloride determinations, the same generator reaction is used,but the titration reaction is Cl- + Ag+ AgCI(s). Derive an equation that relates the desired quantity, mass S2- (ng), to the chloridometer readout in mass Cl- (ng). (b) A particular wastewater standard gave a reading of 1689.6 ng Cl-. What total charge in coulombs was required to generate the Ag+ needed to precipitate the sulfide in this standard? (c) The following results were obtained on 20.00-mL samples containing known amounts of sulfide.17 Each standard was analyzed in triplicate and the mass of chloride recorded. Convert each of the chloride results to mass S2- (ng). (d) Determine the average mass of S2- (ng), the standard deviation, and the %RSD) of each standard. (e) Prepare a plot ofthe average mass of S2- determined (ng) versus the actual mass (ng). Determine theslope, the intercept, the standard error, and the R2 value. Comment on the fit of the data to a linear model. (f) Determine the detection limit (ng) and in parts per million using a k factor of 2 (see Equation 1-12). (g) An unknown wastewater sample gave an average reading of 893.2 ng Cl. What is the mass of sulfide (ng)? If 20.00 mL of the wastewater sample was introduced into the titration vessel, what is the concentration of S2- n parts per million?
As part of a soil analysis on a plot of land, a scientist wants to determine the ammonium content using gravimetric analysis with sodium tetraphenylborate, Na+B(C6H5)4−. Unfortunately, the amount of potassium, which also precipitates with sodium tetraphenylborate, is non‑negligible and must be accounted for in the analysis. Assume that all potassium in the soil is present as K2CO3 and all ammonium is present as NH4Cl. A 5.095 g soil sample was dissolved to give 0.500 L of solution. A 150.0 mL aliquot was acidified and excess sodium tetraphenylborate was added to precipitate both K+ and NH4+ ions completely. B(C6H5)4-+K+⟶KB(C6H5)4(s) B(C6H5)4-+NH4+⟶NH4B(C6H5)4(s) The resulting precipitate amounted to 0.269 g. A new 300.0 mL aliquot of the original solution was made alkaline and heated to remove all of the NH4+ as NH3. The resulting solution was then acidified, and excess sodium tetraphenylborate was added to give 0.129 g of precipitate. Find the mass percentages of NH4Cl and…
The amount of copper in a wire was determined by a redox titration using KMnO4 as the titrant. A 0.4185-g sample was dissolved in acid and the liberated Cu2+ quantitatively reduced to Cu+, using a reductor column. Titrating with 0.0250 M KMnO4 requires 41.27 mL to reach the endpoint. Determine the % w/w CuO in the sample of meteorite. Answer: % CuO =
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The sulfate in 266.5 mg sample was precipitated as BaSO4 by addition of 27.00 mL of 0.0340 M BaCl2. The precipitate was removed by filtration and the remaining BaCl2 consumed 34.2 mL of 0.0200 M EDTA for titration to the end point. (All 1:1 ratio) Calculate the % SO3 in the sample. (MW of SO3 is 80.06 g/mol)
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