In the Laboratory
The Synthesis and Analysis of Ammine Complexes of Copper and Silver Sulfate
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An Undergraduate Laboratory Project Steven S. Clareen, Shireen R. Marshall, Kristin E. Price, Margaret B. Royall, Claude H. Yoder, and Richard W. Schaeffer* Department of Chemistry, Franklin and Marshall College, Lancaster, PA 17604; *
[email protected] Transition metal complexes comprise a large and interesting group because of their diversity in structure, bonding, reactivity, and properties (1, 2). In the first-year laboratory, metal ammine complexes are easily introduced because of the ease of obtaining and using aqueous ammonia as a ligand source and the mild conditions under which at least some of the complexes can made and handled. Moreover, complexes with more than one coordination number can be readily synthesized. This provides the student with the experimental challenge of determining the formula of the product, as well as the conceptual challenge of rationalizing the accompanying differences in structure, geometry, and bonding. Ammonia forms complexes in aqueous solution with both copper and silver cations. We report the synthesis of both diamminesilver(I) sulfate and tetraamminecopper(II) sulfate by reacting the simple sulfates with aqueous ammonia (3–5) and cooling with the addition of ethanol to reduce the solubility of the product:
titration is complete, the same solutions are rendered basic by the addition of two pellets of NaOH (approximately 0.2 g). A pale blue precipitate of copper hydroxide forms, which is then heated to near boiling to produce copper oxide for gravimetric analysis. Triplicate determinations of the same product yielded an average ammonia-to-copper ratio of 4.1 with a standard deviation of 0.3 (7.3% RSD). We believe that the project provides a convenient preparation of two “complex” compounds whose identities and formulas will not be obvious to the student. The analytical procedures illustrate the fundamentals of gravimetric and volumetric analysis and some basic characteristics of simple coordination compounds. The analytical data allow the student to determine the identity of the product by determining its empirical formula.
Ag2SO4(s) + 2NH3(aq) → [Ag(NH3)2]2SO4(aq) → [Ag(NH3)2]2SO4(s)
Supplemental material for this article is available in this issue of JCE Online.
CuSO4(s) + 4NH3(aq) → Cu(NH3)4SO4(aq) → Cu(NH3)4SO4(s)
The analysis of the silver complex is accomplished by dissolving a sample in a known amount of dilute standardized (ca. 0.2 M) nitric acid. The acid remaining after neutralizing the ammonia from the complex is then titrated against standardized NaOH to a methyl red end point. After the back titration is complete, the same solution is rendered slightly acidic by the addition of a few drops of dilute nitric acid. A slight excess of an aqueous NaCl solution is added to precipitate the silver for gravimetric analysis as AgCl (6 ). Triplicate determinations of the same product yielded an average ammonia-to-silver ratio of 2.01 with a standard deviation of 0.05 (2.5% RSD). The analysis of the copper complex is accomplished by dissolving a sample in a known amount of dilute standardized (ca. 0.2 M) nitric acid. The acid remaining after neutralizing the ammonia from the complex is then titrated against standardized NaOH to a methyl red end point. After the back
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Supplemental Material
Literature Cited 1. Slabaugh, W. H. J. Chem. Educ. 1965, 42, 470. 2. Winter, M. J. In d-Block Chemistry; Evans, J., Ed.; Oxford Chemistry Primers; Oxford University Press: New York, 1996; pp 1–76. 3. Meyer, H. J. Chem. Educ. 1992, 69, 499. 4. Schlessinger, G. G. Inorganic Laboratory Preparations; Chemical Publishing: New York, 1962; pp 158, 165. 5. Cannon, R. D.; Bochmann, M. In Inorganic Experiments; Woolins, J. D., Ed.; VCH: New York, 1994; pp 7–13. Nathan, L. C. A Laboratory Project in Modern Coordination Chemistry; Brooks/Cole: Monterey, GA, 1981; pp 1–91. These references give examples of the synthesis of a related ammine complex. 6. Skoog, D. A.; West, D. M.; Holler, F. J. Fundamentals of Analytical Chemistry, 7th ed.; Saunders: New York, 1996; pp 814– 815.
Journal of Chemical Education • Vol. 77 No. 7 July 2000 • JChemEd.chem.wisc.edu
