Analytical Chem istry - DePauw University

400 Analytical Chemistry 2.0nese, and other metals was dissolved in acid and treated with appropriatemasking agents to prevent an interference from other metals. Theiron and manganese were precipitated and isolated as Fe(C 9 H 6 NO) 3and Mn(C 9 H 6 NO) 2 , yielding a total mass of 867.8 mg. The amountof 8-hydroxyquinolate in the mixed precipitate was determined to be5.276 mmol. Calculate the %w/w Fe and %w/w Mn in the alloy.20. A 0.8612-g sample of a mixture of NaBr, NaI, and NaNO 3 was analyzedby adding AgNO 3 and precipitating a 1.0186-g mixture of AgBrand AgI. The precipitate was then heated in a stream of Cl 2 , convertingit to 0.7125 g of AgCl. Calculate the %w/w NaNO 3 in the sample.A B C D EA NP Y NP WB Y W WC NP NPDWFigure 8.16 Results of the binary mixingof solutions A–E for Problem 8.22.20. The earliest determinations of elemental atomic weights were accomplishedgravimetrically. In determining the atomic weight of manganese,a carefully purified sample of MnBr 2 weighing 7.16539 g wasdissolved and the Br – precipitated as AgBr, yielding 12.53112 g. Whatis the atomic weight for Mn if the atomic weights for Ag and Br aretaken to be 107.868 and 79.904, respectively?22. While working as a laboratory assistant you prepared 0.4 M solutionsof AgNO 3 , Pb(NO 3 ) 2 , BaCl 2 , KI and Na 2 SO 4 . Unfortunately, youbecame distracted and forgot to label the solutions before leaving thelaboratory. Realizing your error, you label the solutions A–E and performall possible binary mixings of the five solutions, obtaining theresults shown in Figure 8.16 (key: NP means no precipitate formed,W means a white precipitate formed, and Y means a yellow precipitateformed). Identify solutions A–E.23. A solid sample has approximately equal amounts of two or more of thefollowing soluble salts: AgNO 3 , ZnCl 2 , K 2 CO 3 , MgSO 4 , Ba(C 2 H 3 O 2 ) 2 ,and NH 4 NO 3 . A sample of the solid, sufficient to give at least 0.04moles of any single salt, was added to 100 mL of water, yielding awhite precipitate and a clear solution. The precipitate was collectedand rinsed with water. When a portion of the precipitate was placedin dilute HNO 3 it completely dissolved, leaving a colorless solution.A second portion of the precipitate was placed in dilute HCl, yieldinga precipitate and a clear solution. Finally, the filtrate from the originalprecipitate was treated with excess NH 3 , yielding a white precipitate.Identify the salts that must be present in the sample, the salts that mustbe absent and the salts for which there is insufficient information tomake this determination. 1324. Two methods have been proposed for the analysis of sulfur in impuresamples of pyrite, FeS 2 . Sulfur can be determined in a direct analysis by13 Adapted from Sorum, C. H.; Lagowski, J. J. Introduction to Semimicro Qualitative Analysis,Prentice-Hall: Englewood Cliffs, N. J., 5th Ed., 1977, p. 285.